BPF verifier rotating log
Subsystems (5)
Andrii Nakryiko
maintainerv3 cover BPF verifier rotating log
This patch set changes BPF verifier log behavior to behave as a rotating log, by default. If user-supplied log buffer is big enough to contain entire verifier log output, there is no effective difference. But where previously user supplied too small log buffer and would get -ENOSPC error result and the beginning part of the verifier log, now there will be no error and user will get ending part of verifier log filling up user-supplied log buffer. Which is, in absolute majority of cases, is exactly what's useful, relevant, and what users want and need, as the ending of the verifier log is containing details of verifier failure and relevant state that got us to that failure. So this rotating mode is made default, but for some niche advanced debugging scenarios it's possible to request old behavior by specifying additional BPF_LOG_FIXED (8) flag.
This patch set adjusts libbpf to allow specifying flags beyond 1 | 2 | 4. We also add --log-size and --log-fixed options to veristat to be able to both test this functionality manually, but also to be used in various debugging scenarios. We also add selftests that tries many variants of log buffer size to stress-test correctness of internal verifier log bookkeeping code.
Further, this patch set is merged with log_size_actual v1 patchset ([0]), which adds ability to get required log buffer size to fit entire verifier log output.
This addresses a long-standing limitation, which causes users and BPF loader library writers to guess and pre-size log buffer, often allocating unnecessary extra memory for this or doing extra program verifications just to size logs better, ultimately wasting resources. This was requested most recently by Go BPF library maintainers ([1]).
See respective patches for details. A bunch of them some drive-by fixes detecting during working with the code. Some other further refactor and compratmentalize verifier log handling code into kernel/bpf/log.c, which should also make it simpler to integrate such verbose log for other complicated bpf() syscall commands, if necessary. The rest are actual logic to calculate maximum log buffer size needed and return it to user-space. Few patches wire this on libbpf side, and the rest add selftests to test proper log truncation and log_buf==NULL handling.
This turned into a pretty sizable patch set with lots of arithmetics, but hopefully the set of features added to verifier log in this patch set are both useful for BPF users and are self-contained and isolated enough to not cause troubles going forward.
v2->v3:
- typos and comment improvement (Lorenz);
- merged with log_size_actual v1 ([0]) patch set (Alexei);
- added log_buf==NULL condition allowed (Lorenz);
- added BPF_BTF_LOAD logs tests (Lorenz);
- more clean up and refactoring of internal verifier log API;v1->v2:
- return -ENOSPC even in rotating log mode for preserving backwards
compatibility (Lorenz);
[0] https://patchwork.kernel.org/project/netdevbpf/list/?series=735213&state=*
[1] https://lore.kernel.org/bpf/CAN+4W8iNoEbQzQVbB_o1W0MWBDV4xCJAq7K3f6psVE-kkCfMqg@mail.gmail.com/
Andrii Nakryiko (19):
bpf: split off basic BPF verifier log into separate file
bpf: remove minimum size restrictions on verifier log buffer
bpf: switch BPF verifier log to be a rotating log by default
libbpf: don't enforce unnecessary verifier log restrictions on libbpf
side
veristat: add more veristat control over verifier log options selftests/bpf: add fixed vs rotating verifier log tests
bpf: ignore verifier log reset in BPF_LOG_KERNEL mode
bpf: fix missing -EFAULT return on user log buf error in btf_parse()
bpf: avoid incorrect -EFAULT error in BPF_LOG_KERNEL mode
bpf: simplify logging-related error conditions handling
bpf: keep track of total log content size in both fixed and rolling
modes
bpf: add log_size_actual output field to return log contents size
bpf: simplify internal verifier log interface
bpf: relax log_buf NULL conditions when log_level>0 is requested
libbpf: wire through log_size_actual returned from kernel for
BPF_PROG_LOAD
libbpf: wire through log_size_actual for bpf_btf_load() API selftests/bpf: add tests to validate log_size_actual feature selftests/bpf: add testing of log_buf==NULL condition for
BPF_PROG_LOAD
selftests/bpf: add verifier log tests for BPF_BTF_LOAD command
include/linux/bpf.h | 2 +- include/linux/bpf_verifier.h | 41 +- include/linux/btf.h | 2 +- include/uapi/linux/bpf.h | 10 + kernel/bpf/Makefile | 3 +- kernel/bpf/btf.c | 74 +-- kernel/bpf/log.c | 332 +++++++++++++ kernel/bpf/syscall.c | 16 +- kernel/bpf/verifier.c | 125 ++--- tools/include/uapi/linux/bpf.h | 12 +- tools/lib/bpf/bpf.c | 17 +- tools/lib/bpf/bpf.h | 22 +- .../selftests/bpf/prog_tests/log_fixup.c | 1 + .../selftests/bpf/prog_tests/verifier_log.c | 437 ++++++++++++++++++ tools/testing/selftests/bpf/veristat.c | 44 +- 15 files changed, 954 insertions(+), 184 deletions(-) create mode 100644 kernel/bpf/log.c create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier_log.c
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 1/19 bpf: split off basic BPF verifier log into separate file
kernel/bpf/verifier.c file is large and growing larger all the time. So it's good to start splitting off more or less self-contained parts into separate files to keep source code size (somewhat) somewhat under control.
This patch is a one step in this direction, moving some of BPF verifier log routines into a separate kernel/bpf/log.c. Right now it's most low-level and isolated routines to append data to log, reset log to previous position, etc. Eventually we could probably move verifier state printing logic here as well, but this patch doesn't attempt to do that yet.
Subsequent patches will add more logic to verifier log management, so having basics in a separate file will make sure verifier.c doesn't grow more with new changes.
--- include/linux/bpf_verifier.h | 19 +++----- kernel/bpf/Makefile | 3 +- kernel/bpf/log.c | 85 ++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 69 ----------------------------- 4 files changed, 94 insertions(+), 82 deletions(-) create mode 100644 kernel/bpf/log.c
include/linux/bpf_verifier.h +7 -12
@@ -498,11 +498,6 @@ struct bpf_verifier_log {u32 len_total; }; -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) -{ -return log->len_used >= log->len_total -1 ; -} -#define BPF_LOG_LEVEL1 1#define BPF_LOG_LEVEL2 2#define BPF_LOG_STATS 4
@@ -512,6 +507,11 @@ static inline bool bpf_verifier_log_full(const struct bpf_verifier_log *log)#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U +static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) +{ +return log->len_used >= log->len_total -1 ; +} +static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) { return log &&
@@ -519,13 +519,6 @@ static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log) log->level == BPF_LOG_KERNEL); } -static inline bool -bpf_verifier_log_attr_valid (const struct bpf_verifier_log *log) -{ -return log->len_total >=128 && log->len_total <=UINT_MAX >>2 && - log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); -} -#define BPF_MAX_SUBPROGS 256struct bpf_subprog_info {
@@ -608,12 +601,14 @@ struct bpf_verifier_env {char type_str_buf[TYPE_STR_BUF_LEN ]; }; +bool bpf_verifier_log_attr_valid (const struct bpf_verifier_log *log); __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,const char *fmt,va_list args); __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,const char *fmt, ...); __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,const char *fmt, ...); +void bpf_vlog_reset (struct bpf_verifier_log *log,u32 new_pos);static inline struct bpf_func_state *cur_func (struct bpf_verifier_env *env) {
kernel/bpf/Makefile +2 -1
@@ -6,7 +6,8 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse endif CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy) -obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o +obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o log.o +obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
kernel/bpf/log.c new file +85 -0
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kernel/bpf/verifier.c +0 -69
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Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 2/19 bpf: remove minimum size restrictions on verifier log buffer
In reply to Andrii NakryikoIt's not clear why we have 128 as minimum size, but it makes testing harder and seems unnecessary, as we carefully handle truncation scenarios and use proper snprintf variants. So remove this limitation and just enforce positive length for log buffer.
--- kernel/bpf/log.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/bpf/log.c +1 -1
@@ -11,7 +11,7 @@bool bpf_verifier_log_attr_valid (const struct bpf_verifier_log *log) { -return log->len_total >=128 && log->len_total <=UINT_MAX >>2 && +return log->len_total >0 && log->len_total <=UINT_MAX >>2 && log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); }
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 3/19 bpf: switch BPF verifier log to be a rotating log by default
In reply to Andrii NakryikoCurrently, if user-supplied log buffer to collect BPF verifier log turns out to be too small to contain full log, bpf() syscall returns -ENOSPC, fails BPF program verification/load, and preserves first N-1 bytes of the verifier log (where N is the size of user-supplied buffer).
This is problematic in a bunch of common scenarios, especially when working with real-world BPF programs that tend to be pretty complex as far as verification goes and require big log buffers. Typically, it's when debugging tricky cases at log level 2 (verbose). Also, when BPF program is successfully validated, log level 2 is the only way to actually see verifier state progression and all the important details.
Even with log level 1, it's possible to get -ENOSPC even if the final verifier log fits in log buffer, if there is a code path that's deep enough to fill up entire log, even if normally it would be reset later on (there is a logic to chop off successfully validated portions of BPF verifier log).
In short, it's not always possible to pre-size log buffer. Also, what's worse, in practice, the end of the log most often is way more important than the beginning, but verifier stops emitting log as soon as initial log buffer is filled up.
This patch switches BPF verifier log behavior to effectively behave as rotating log. That is, if user-supplied log buffer turns out to be too short, verifier will keep overwriting previously written log, effectively treating user's log buffer as a ring buffer. -ENOSPC is still going to be returned at the end, to notify user that log contents was truncated, but the important last N bytes of the log would be returned, which might be all that user really needs. This consistent -ENOSPC behavior, regardless of rotating or fixed log behavior, allows to prevent backwards compatibility breakage. The only user-visible change is which portion of verifier log user ends up seeing *if buffer is too small*. Given contents of verifier log itself is not an ABI, there is no breakage due to this behavior change. Specialized tools that rely on specific contents of verifier log in -ENOSPC scenario are expected to be easily adapted to accommodate old and new behaviors.
Importantly, though, to preserve good user experience and not require every user-space application to adopt to this new behavior, before exiting to user-space verifier will rotate log (in place) to make it start at the very beginning of user buffer as a continuous zero-terminated string. The contents will be a chopped off N-1 last bytes of full verifier log, of course.
Given beginning of log is sometimes important as well, we add BPF_LOG_FIXED (which equals 8) flag to force old behavior, which allows tools like veristat to request first part of verifier log, if necessary. BPF_LOG_FIXED flag is also a simple and straightforward way to check if BPF verifier supports rotating behavior.
On the implementation side, conceptually, it's all simple. We maintain 64-bit logical start and end positions. If we need to truncate the log, start position will be adjusted accordingly to lag end position by N bytes. We then use those logical positions to calculate their matching actual positions in user buffer and handle wrap around the end of the buffer properly. Finally, right before returning from bpf_check(), we rotate user log buffer contents in-place as necessary, to make log contents contiguous. See comments in relevant functions for details.
--- include/linux/bpf_verifier.h | 33 ++- kernel/bpf/btf.c | 3 +- kernel/bpf/log.c | 196 +++++++++++++++++- kernel/bpf/verifier.c | 19 +- .../selftests/bpf/prog_tests/log_fixup.c | 1 + 5 files changed, 226 insertions(+), 26 deletions(-)
include/linux/bpf_verifier.h +26 -7
@@ -491,25 +491,42 @@ struct bpf_insn_aux_data {#define BPF_VERIFIER_TMP_LOG_SIZE 1024struct bpf_verifier_log { -u32 level; -char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; +/* Logical start and end positions of a "log window" of the verifier log. +* start_pos == 0 means we haven't truncated anything. +* Once truncation starts to happen, start_pos + len_total == end_pos, +* except during log reset situations, in which (end_pos - start_pos) +* might get smaller than len_total (see bpf_vlog_reset()). +* Generally, (end_pos - start_pos) gives number of useful data in +* user log buffer. +*/ +u64 start_pos; +u64 end_pos;char __user *ubuf; -u32 len_used; +u32 level;u32 len_total; +char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; };#define BPF_LOG_LEVEL1 1#define BPF_LOG_LEVEL2 2#define BPF_LOG_STATS 4 +#define BPF_LOG_FIXED 8#define BPF_LOG_LEVEL (BPF_LOG_LEVEL1 | BPF_LOG_LEVEL2) -#define BPF_LOG_MASK (BPF_LOG_LEVEL | BPF_LOG_STATS) +#define BPF_LOG_MASK (BPF_LOG_LEVEL | BPF_LOG_STATS | BPF_LOG_FIXED)#define BPF_LOG_KERNEL (BPF_LOG_MASK + 1)/* kernel internal flag */ #define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U +static inline u32 bpf_log_used (const struct bpf_verifier_log *log) +{ +return log->end_pos - log->start_pos; +} +static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) { -return log->len_used >= log->len_total -1 ; +if (log->level &BPF_LOG_FIXED ) +return bpf_log_used (log) >= log->len_total -1 ; +return false; }static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log)
@@ -596,7 +613,7 @@ struct bpf_verifier_env {u32 scratched_regs;/* Same as scratched_regs but for stack slots */ u64 scratched_stack_slots; -u32 prev_log_len, prev_insn_print_len; +u64 prev_log_pos, prev_insn_print_pos;/* buffer used in reg_type_str() to generate reg_type string */ char type_str_buf[TYPE_STR_BUF_LEN ]; };
@@ -608,7 +625,9 @@ __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env, const char *fmt, ...); __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,const char *fmt, ...); -void bpf_vlog_reset (struct bpf_verifier_log *log,u32 new_pos); +void bpf_vlog_reset (struct bpf_verifier_log *log,u64 new_pos); +void bpf_vlog_finalize (struct bpf_verifier_log *log); +bool bpf_vlog_truncated (const struct bpf_verifier_log *log);static inline struct bpf_func_state *cur_func (struct bpf_verifier_env *env) {
kernel/bpf/btf.c +2 -1
@@ -5593,7 +5593,8 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, } } -if (log->level &&bpf_verifier_log_full (log)) { +bpf_vlog_finalize (log); +if (log->level &&bpf_vlog_truncated (log)) { err = -ENOSPC ; goto errout_meta; }
kernel/bpf/log.c +187 -9
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kernel/bpf/verifier.c +10 -9
@@ -1439,10 +1439,10 @@ static inline u32 vlog_alignment(u32 pos)static void print_insn_state (struct bpf_verifier_env *env,const struct bpf_func_state *state) { -if (env->prev_log_len && env->prev_log_len == env->log.len_used) { +if (env->prev_log_pos && env->prev_log_pos == env->log.end_pos) {/* remove new line character */ -bpf_vlog_reset (&env->log, env->prev_log_len -1 ); -verbose (env,"%*c;" ,vlog_alignment (env->prev_insn_print_len),' ' ); +bpf_vlog_reset (&env->log, env->prev_log_pos -1 ); +verbose (env,"%*c;" ,vlog_alignment (env->prev_insn_print_pos),' ' ); }else {verbose (env,"%d:" , env->insn_idx); }
@@ -1750,7 +1750,7 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env, elem->insn_idx = insn_idx; elem->prev_insn_idx = prev_insn_idx; elem->next = env->head; - elem->log_pos = env->log.len_used; + elem->log_pos = env->log.end_pos; env->head = elem; env->stack_size++; err =copy_verifier_state (&elem->st, cur);
@@ -2286,7 +2286,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env, elem->insn_idx = insn_idx; elem->prev_insn_idx = prev_insn_idx; elem->next = env->head; - elem->log_pos = env->log.len_used; + elem->log_pos = env->log.end_pos; env->head = elem; env->stack_size++;if (env->stack_size >BPF_COMPLEXITY_LIMIT_JMP_SEQ ) {
@@ -15569,11 +15569,11 @@ static int do_check(struct bpf_verifier_env *env)print_insn_state (env, state->frame[state->curframe]);verbose_linfo (env, env->insn_idx,"; " ); - env->prev_log_len = env->log.len_used; + env->prev_log_pos = env->log.end_pos;verbose (env,"%d: " , env->insn_idx);print_bpf_insn (&cbs, insn, env->allow_ptr_leaks); - env->prev_insn_print_len = env->log.len_used - env->prev_log_len; - env->prev_log_len = env->log.len_used; + env->prev_insn_print_pos = env->log.end_pos - env->prev_log_pos; + env->prev_log_pos = env->log.end_pos; }if (bpf_prog_is_offloaded (env->prog->aux)) {
@@ -18791,7 +18791,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr)print_verification_stats (env); env->prog->aux->verified_insns = env->insn_processed; -if (log->level &&bpf_verifier_log_full (log)) +bpf_vlog_finalize (log); +if (log->level &&bpf_vlog_truncated (log)) ret = -ENOSPC ;if (log->level && !log->ubuf) { ret = -EFAULT ;
tools/testing/selftests/bpf/prog_tests/log_fixup.c +1 -0
@@ -24,6 +24,7 @@ static void bad_core_relo(size_t log_buf_size, enum trunc_type trunc_type)bpf_program__set_autoload (skel->progs.bad_relo, true);memset (log_buf,0 ,sizeof (log_buf));bpf_program__set_log_buf (skel->progs.bad_relo, log_buf, log_buf_size ?:sizeof (log_buf)); +bpf_program__set_log_level (skel->progs.bad_relo,1 |8 );/* BPF_LOG_FIXED to force truncation */ err =test_log_fixup__load (skel);if (!ASSERT_ERR (err,"load_fail" ))
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 4/19 libbpf: don't enforce unnecessary verifier log restrictions on libbpf side
In reply to Andrii NakryikoThis basically prevents any forward compatibility. And we either way just return -EINVAL, which would otherwise be returned from bpf() syscall anyways.
Similarly, drop enforcement of non-NULL log_buf when log_level > 0. This won't be true anymore soon.
--- tools/lib/bpf/bpf.c | 4 ---- 1 file changed, 4 deletions(-)
tools/lib/bpf/bpf.c +0 -4
@@ -290,10 +290,6 @@ int bpf_prog_load(enum bpf_prog_type prog_type,if (!!log_buf != !!log_size)return libbpf_err (-EINVAL ); -if (log_level > (4 |2 |1 )) -return libbpf_err (-EINVAL ); -if (log_level && !log_buf) -return libbpf_err (-EINVAL ); func_info_rec_size =OPTS_GET (opts, func_info_rec_size,0 ); func_info =OPTS_GET (opts, func_info,NULL );
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 5/19 veristat: add more veristat control over verifier log options
In reply to Andrii NakryikoAdd --log-size to be able to customize log buffer sent to bpf() syscall for BPF program verification logging.
Add --log-fixed to enforce BPF_LOG_FIXED behavior for BPF verifier log. This is useful in unlikely event that beginning of truncated verifier log is more important than the end of it (which with rotating verifier log behavior is the default now).
--- tools/testing/selftests/bpf/veristat.c | 44 ++++++++++++++++++++------ 1 file changed, 35 insertions(+), 9 deletions(-)
tools/testing/selftests/bpf/veristat.c +35 -9
@@ -141,12 +141,15 @@ static struct env {bool verbose;bool debug;bool quiet; -int log_level;enum resfmt out_fmt;bool show_version;bool comparison_mode;bool replay_mode; +int log_level; +int log_size; +bool log_fixed; +struct verif_stats *prog_stats;int prog_stat_cnt;
@@ -193,12 +196,19 @@ const char argp_program_doc[] =" OR: veristat -C <baseline.csv> <comparison.csv>\n" " OR: veristat -R <results.csv>\n" ; +enum { +OPT_LOG_FIXED =1000 , +OPT_LOG_SIZE =1001 , +}; +static const struct argp_option opts[] = { {NULL ,'h' ,NULL ,OPTION_HIDDEN ,"Show the full help" }, {"version" ,'V' ,NULL ,0 ,"Print version" }, {"verbose" ,'v' ,NULL ,0 ,"Verbose mode" }, - {"log-level" ,'l' ,"LEVEL" ,0 ,"Verifier log level (default 0 for normal mode, 1 for verbose mode)" }, {"debug" ,'d' ,NULL ,0 ,"Debug mode (turns on libbpf debug logging)" }, + {"log-level" ,'l' ,"LEVEL" ,0 ,"Verifier log level (default 0 for normal mode, 1 for verbose mode)" }, + {"log-fixed" ,OPT_LOG_FIXED ,NULL ,0 ,"Disable verifier log rotation" }, + {"log-size" ,OPT_LOG_SIZE ,"BYTES" ,0 ,"Customize verifier log size (default to 16MB)" }, {"quiet" ,'q' ,NULL ,0 ,"Quiet mode" }, {"emit" ,'e' ,"SPEC" ,0 ,"Specify stats to be emitted" }, {"sort" ,'s' ,"SPEC" ,0 ,"Specify sort order" },
@@ -263,6 +273,17 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state)argp_usage (state); }break ; +case OPT_LOG_FIXED : + env.log_fixed = true; +break ; +case OPT_LOG_SIZE : + errno =0 ; + env.log_size =strtol (arg,NULL ,10 ); +if (errno) { +fprintf (stderr,"invalid log size: %s\n" , arg); +argp_usage (state); + } +break ;case 'C' : env.comparison_mode = true;break ;
@@ -929,8 +950,8 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf {const char *prog_name =bpf_program__name (prog);const char *base_filename =basename (filename); -size_t buf_sz =sizeof (verif_log_buf); -char *buf = verif_log_buf; +char *buf; +int buf_sz, log_level;struct verif_stats *stats;int err =0 ;void *tmp;
@@ -948,18 +969,23 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpfmemset (stats,0 ,sizeof (*stats));if (env.verbose) { - buf_sz =16 *1024 *1024 ; + buf_sz = env.log_size ? env.log_size :16 *1024 *1024 ; buf =malloc (buf_sz);if (!buf)return -ENOMEM ; -bpf_program__set_log_buf (prog, buf, buf_sz); -bpf_program__set_log_level (prog, env.log_level |4 );/* stats + log */ +/* ensure we always request stats */ + log_level = env.log_level |4 | (env.log_fixed ?8 :0 ); }else { -bpf_program__set_log_buf (prog, buf, buf_sz); -bpf_program__set_log_level (prog,4 );/* only verifier stats */ + buf = verif_log_buf; + buf_sz =sizeof (verif_log_buf); +/* request only verifier stats */ + log_level =4 | (env.log_fixed ?8 :0 ); } verif_log_buf[0 ] ='\0' ; +bpf_program__set_log_buf (prog, buf, buf_sz); +bpf_program__set_log_level (prog, log_level); +/* increase chances of successful BPF object loading */ fixup_obj (obj, prog, base_filename);
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 6/19 selftests/bpf: add fixed vs rotating verifier log tests
In reply to Andrii NakryikoAdd selftests validating BPF_LOG_FIXED behavior, which used to be the only behavior, and now default rotating BPF verifier log, which returns just up to last N bytes of full verifier log, instead of returning -ENOSPC.
To stress test correctness of in-kernel verifier log logic, we force it to truncate program's verifier log to all lengths from 1 all the way to its full size (about 450 bytes today). This was a useful stress test while developing the feature.
For both fixed and rotating log modes we expect -ENOSPC if log contents doesn't fit in user-supplied log buffer.
--- .../selftests/bpf/prog_tests/verifier_log.c | 164 ++++++++++++++++++ 1 file changed, 164 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier_log.c
tools/testing/selftests/bpf/prog_tests/verifier_log.c new file +164 -0
@@ -0,0 +1,164 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */ + +#include <test_progs.h> +#include <bpf/btf.h> + +#include "test_log_buf.skel.h" + + +static bool check_prog_load (int prog_fd,bool expect_err,const char *tag) +{ +if (expect_err) { +if (!ASSERT_LT (prog_fd,0 , tag)) { +close (prog_fd); +return false; + } + }else /* !expect_err */ { +if (!ASSERT_GT (prog_fd,0 , tag)) +return false; + } +return true; +} + +static void verif_log_subtest (const char *name,bool expect_load_error,int log_level) +{ +LIBBPF_OPTS (bpf_prog_load_opts, opts); +struct { +/* strategically placed before others to avoid accidental modification by kernel */ +char filler[1024 ]; +char buf[1024 ]; +/* strategically placed after buf[] to catch more accidental corruptions */ +char reference[1024 ]; + } logs; +char *exp_log, prog_name[16 ], op_name[32 ]; +struct test_log_buf *skel; +struct bpf_program *prog; +const struct bpf_insn *insns; +size_t insn_cnt, fixed_log_sz; +int i, err, prog_fd; + + skel =test_log_buf__open (); +if (!ASSERT_OK_PTR (skel,"skel_open" )) +return ; + +bpf_object__for_each_program (prog, skel->obj) { +if (strcmp (bpf_program__name (prog), name) ==0 ) +bpf_program__set_autoload (prog, true); +else +bpf_program__set_autoload (prog, false); + } + + err =test_log_buf__load (skel); +if (!expect_load_error && !ASSERT_OK (err,"unexpected_load_failure" )) + goto cleanup; +if (expect_load_error && !ASSERT_ERR (err,"unexpected_load_success" )) + goto cleanup; + + insns =bpf_program__insns (skel->progs.good_prog); + insn_cnt =bpf_program__insn_cnt (skel->progs.good_prog); + + opts.log_buf = logs.reference; + opts.log_size =sizeof (logs.reference); + opts.log_level = log_level |8 /* BPF_LOG_FIXED */ ; + prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_fixed" , +"GPL" , insns, insn_cnt, &opts); +if (!check_prog_load (prog_fd, expect_load_error,"fixed_buf_prog_load" )) + goto cleanup; +close (prog_fd); + + fixed_log_sz =strlen (logs.reference) +1 ; +if (!ASSERT_GT (fixed_log_sz,50 ,"fixed_log_sz" )) + goto cleanup; +memset (logs.reference + fixed_log_sz,0 ,sizeof (logs.reference) - fixed_log_sz); + +/* validate BPF_LOG_FIXED works as verifier log used to work, that is: +* we get -ENOSPC and beginning of the full verifier log. This only +* works for log_level 2 and log_level 1 + failed program. For log +* level 2 we don't reset log at all. For log_level 1 + failed program +* we don't get to verification stats output. With log level 1 +* for successful program final result will be just verifier stats. +* But if provided too short log buf, kernel will NULL-out log->ubuf +* and will stop emitting further log. This means we'll never see +* predictable verifier stats. +* Long story short, we do the following -ENOSPC test only for +* predictable combinations. +*/ +if (log_level >=2 || expect_load_error) { + opts.log_buf = logs.buf; + opts.log_level = log_level |8 ;/* fixed-length log */ + opts.log_size =25 ; + + prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_fixed50" , +"GPL" , insns, insn_cnt, &opts); +if (!ASSERT_EQ (prog_fd, -ENOSPC ,"unexpected_log_fixed_prog_load_result" )) { +if (prog_fd >=0 ) +close (prog_fd); + goto cleanup; + } +if (!ASSERT_EQ (strlen (logs.buf),24 ,"log_fixed_25" )) + goto cleanup; +if (!ASSERT_STRNEQ (logs.buf, logs.reference,24 , op_name)) + goto cleanup; + } + +/* validate rolling verifier log logic: try all variations of log buf +* length to force various truncation scenarios +*/ + opts.log_buf = logs.buf; + opts.log_level = log_level;/* rolling log */ + +/* prefill logs.buf with 'A's to detect any write beyond allowed length */ +memset (logs.filler,'A' ,sizeof (logs.filler)); + logs.filler[sizeof (logs.filler) -1 ] ='\0' ; +memset (logs.buf,'A' ,sizeof (logs.buf)); + logs.buf[sizeof (logs.buf) -1 ] ='\0' ; + +for (i =1 ; i < fixed_log_sz; i++) { + opts.log_size = i; + +snprintf (prog_name,sizeof (prog_name),"log_roll_%d" , i); + prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT , prog_name, +"GPL" , insns, insn_cnt, &opts); + +snprintf (op_name,sizeof (op_name),"log_roll_prog_load_%d" , i); +if (!ASSERT_EQ (prog_fd, -ENOSPC , op_name)) { +if (prog_fd >=0 ) +close (prog_fd); + goto cleanup; + } + + exp_log = logs.reference + fixed_log_sz - i; +snprintf (op_name,sizeof (op_name),"log_roll_contents_%d" , i); +if (!ASSERT_STREQ (logs.buf, exp_log, op_name)) { +printf ("CMP:%d\nS1:'%s'\nS2:'%s'\n" , +strcmp (logs.buf, exp_log), + logs.buf, exp_log); + goto cleanup; + } + +/* check that unused portions of logs.buf is not overwritten */ +snprintf (op_name,sizeof (op_name),"log_roll_unused_tail_%d" , i); +if (!ASSERT_STREQ (logs.buf + i, logs.filler + i, op_name)) { +printf ("CMP:%d\nS1:'%s'\nS2:'%s'\n" , +strcmp (logs.buf + i, logs.filler + i), + logs.buf + i, logs.filler + i); + goto cleanup; + } + } + +cleanup: +test_log_buf__destroy (skel); +} + +void test_verifier_log (void ) +{ +if (test__start_subtest ("good_prog-level1" )) +verif_log_subtest ("good_prog" , false,1 ); +if (test__start_subtest ("good_prog-level2" )) +verif_log_subtest ("good_prog" , false,2 ); +if (test__start_subtest ("bad_prog-level1" )) +verif_log_subtest ("bad_prog" , true,1 ); +if (test__start_subtest ("bad_prog-level2" )) +verif_log_subtest ("bad_prog" , true,2 ); +}
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 7/19 bpf: ignore verifier log reset in BPF_LOG_KERNEL mode
In reply to Andrii NakryikoVerifier log position reset is meaningless in BPF_LOG_KERNEL mode, so just exit early in bpf_vlog_reset() if log->level is BPF_LOG_KERNEL.
This avoid meaningless put_user() into NULL log->ubuf.
--- kernel/bpf/log.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/bpf/log.c +1 -1
@@ -104,7 +104,7 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos)char zero =0 ;u32 pos; -if (!bpf_verifier_log_needed (log)) +if (!bpf_verifier_log_needed (log) || log->level ==BPF_LOG_KERNEL )return ;/* if position to which we reset is beyond current log window,
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 07/19] bpf: ignore verifier log reset in BPF_LOG_KERNEL mode
Quoted 7 lines · Andrii Nakryiko
Verifier log position reset is meaningless in
BPF_LOG_KERNELmode, so just exit early inbpf_vlog_reset()iflog->levelisBPF_LOG_KERNEL.This avoid meaningless
put_user()into NULLlog->ubuf.Signed-off-by Andrii Nakryiko <[email protected]>
Andrii Nakryiko
maintainerPATCH v3 8/19 bpf: fix missing -EFAULT return on user log buf error in btf_parse()
In reply to Andrii Nakryikobtf_parse() is missing -EFAULT error return if log->ubuf was NULL-ed out due to error while copying data into user-provided buffer. Add it, but handle a special case of BPF_LOG_KERNEL in which log->ubuf is always NULL.
--- kernel/bpf/btf.c | 4 ++++ 1 file changed, 4 insertions(+)
kernel/bpf/btf.c +4 -0
@@ -5598,6 +5598,10 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, err = -ENOSPC ; goto errout_meta; } +if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf) { + err = -EFAULT ; + goto errout_meta; + }btf_verifier_env_free (env);refcount_set (&btf->refcnt,1 );
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 08/19] bpf: fix missing -EFAULT return on user log buf error in btf_parse()
Quoted 6 lines · Andrii Nakryiko
btf_parse()is missing-EFAULTerror return iflog->ubufwas NULL-ed out due to error while copying data into user-provided buffer. Add it, but handle a special case ofBPF_LOG_KERNELin whichlog->ubufis always NULL.Signed-off-by Andrii Nakryiko <[email protected]>
Andrii Nakryiko
maintainerPATCH v3 9/19 bpf: avoid incorrect -EFAULT error in BPF_LOG_KERNEL mode
In reply to Andrii NakryikoIf verifier log is in BPF_LOG_KERNEL mode, no log->ubuf is expected and it stays NULL throughout entire verification process. Don't erroneously return -EFAULT in such case.
--- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/bpf/verifier.c +1 -1
@@ -18794,7 +18794,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr)bpf_vlog_finalize (log);if (log->level &&bpf_vlog_truncated (log)) ret = -ENOSPC ; -if (log->level && !log->ubuf) { +if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf) { ret = -EFAULT ; goto err_release_maps; }
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 09/19] bpf: avoid incorrect -EFAULT error in BPF_LOG_KERNEL mode
Quoted 6 lines · Andrii Nakryiko
If verifier log is in
BPF_LOG_KERNELmode, nolog->ubufis expected and it stays NULL throughout entire verification process. Don't erroneously return-EFAULTin such case.Signed-off-by Andrii Nakryiko <[email protected]>
Andrii Nakryiko
maintainerPATCH v3 10/19 bpf: simplify logging-related error conditions handling
In reply to Andrii NakryikoMove log->level == 0 check into bpf_vlog_truncated() instead of doing it explicitly. Also remove unnecessary goto in kernel/bpf/verifier.c.
--- kernel/bpf/btf.c | 2 +- kernel/bpf/log.c | 4 +++- kernel/bpf/verifier.c | 6 ++---- 3 files changed, 6 insertions(+), 6 deletions(-)
kernel/bpf/btf.c +1 -1
@@ -5594,7 +5594,7 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, }bpf_vlog_finalize (log); -if (log->level &&bpf_vlog_truncated (log)) { +if (bpf_vlog_truncated (log)) { err = -ENOSPC ; goto errout_meta; }
kernel/bpf/log.c +3 -1
@@ -167,7 +167,9 @@ static int bpf_vlog_reverse_ubuf(struct bpf_verifier_log *log, int start, int enbool bpf_vlog_truncated (const struct bpf_verifier_log *log) { -if (log->level &BPF_LOG_FIXED ) +if (!log->level) +return false; +else if (log->level &BPF_LOG_FIXED )return bpf_log_used (log) >= log->len_total -1 ;else return log->start_pos >0 ;
kernel/bpf/verifier.c +2 -4
@@ -18792,12 +18792,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr) env->prog->aux->verified_insns = env->insn_processed;bpf_vlog_finalize (log); -if (log->level &&bpf_vlog_truncated (log)) +if (bpf_vlog_truncated (log)) ret = -ENOSPC ; -if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf) { +if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf) ret = -EFAULT ; - goto err_release_maps; - }if (ret) goto err_release_maps;
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 10/19] bpf: simplify logging-related error conditions handling
Quoted 5 lines · Andrii Nakryiko
Move
log->level== 0 check intobpf_vlog_truncated()instead of doing it explicitly. Also remove unnecessary goto inkernel/bpf/verifier.c.Signed-off-by Andrii Nakryiko <[email protected]>
Andrii Nakryiko
maintainerPATCH v3 11/19 bpf: keep track of total log content size in both fixed and rolling modes
In reply to Andrii NakryikoChange how we do accounting in BPF_LOG_FIXED mode and adopt log->end_pos as *logical* log position. This means that we can go beyond physical log buffer size now and be able to tell what log buffer size should be to fit entire log contents without -ENOSPC.
To do this for BPF_LOG_FIXED mode, we need to remove a short-circuiting logic of not vsnprintf()'ing further log content once we filled up user-provided buffer, which is done by bpf_verifier_log_needed() checks. We modify these checks to always keep going if log->level is non-zero (i.e., log is requested), even if log->ubuf was NULL'ed out due to copying data to user-space, or if entire log buffer is physically full. We adopt bpf_verifier_vlog() routine to work correctly with log->ubuf == NULL condition, performing log formatting into temporary kernel buffer, doing all the necessary accounting, but just avoiding copying data out if buffer is full or NULL'ed out.
With these changes, it's now possible to do this sort of determination of log contents size in both BPF_LOG_FIXED and default rolling log mode. We need to keep in mind bpf_vlog_reset(), though, which shrinks log contents after successful verification of a particular code path. This log reset means that log->end_pos isn't always increasing, so to return back to users what should be the log buffer size to fit all log content without causing -ENOSPC even in the presenec of log resetting, we need to keep maximum over "lifetime" of logging. We do this accounting in bpf_vlog_update_len_max() helper.
A related and subtle aspect is that with this logical log->end_pos even in BPF_LOG_FIXED mode we could temporary "overflow" buffer, but then reset it back with bpf_vlog_reset() to a position inside user-supplied log_buf. In such situation we still want to properly maintain terminating zero. We will eventually return -ENOSPC even if final log buffer is small (we detect this through log->len_max check). This behavior is simpler to reason about and is consistent with current behavior of verifier log. Handling of this required a small addition to bpf_vlog_reset() logic to avoid doing put_user() beyond physical log buffer dimensions.
Another issue to keep in mind is that we limit log buffer size to 32-bit value and keep such log length as u32, but theoretically verifier could produce huge log stretching beyond 4GB. Instead of keeping (and later returning) 64-bit log length, we cap it at UINT_MAX. Current UAPI makes it impossible to specify log buffer size bigger than 4GB anyways, so we don't really loose anything here and keep everything consistently 32-bit in UAPI. This property will be utilized in next patch.
Doing the same determination of maximum log buffer for rolling mode is trivial, as log->end_pos and log->start_pos are already logical positions, so there is nothing new there.
These changes do incidentally fix one small issue with previous logging logic. Previously, if use provided log buffer of size N, and actual log output was exactly N-1 bytes + terminating \0, kernel logic coun't distinguish this condition from log truncation scenario which would end up with truncated log contents of N-1 bytes + terminating \0 as well.
But now with log->end_pos being logical position that could go beyond actual log buffer size, we can distinguish these two conditions, which we do in this patch. This plays nicely with returning log_size_actual (implemented in UAPI in the next patch), as we can now guarantee that if user takes such log_size_actual and provides log buffer of that exact size, they will not get -ENOSPC in return.
All in all, all these changes do conceptually unify fixed and rolling log modes much better, and allow a nice feature requested by users:
knowing what should be the size of the buffer to avoid -ENOSPC.
We'll plumb this through the UAPI and the code in the next patch.
--- include/linux/bpf_verifier.h | 12 ++----- kernel/bpf/log.c | 68 +++++++++++++++++++++++++----------- 2 files changed, 50 insertions(+), 30 deletions(-)
include/linux/bpf_verifier.h +3 -9
@@ -504,6 +504,7 @@ struct bpf_verifier_log {char __user *ubuf;u32 level;u32 len_total; +u32 len_max;char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; };
@@ -517,23 +518,16 @@ struct bpf_verifier_log {#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U -static inline u32 bpf_log_used (const struct bpf_verifier_log *log) -{ -return log->end_pos - log->start_pos; -} -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) {if (log->level &BPF_LOG_FIXED ) -return bpf_log_used (log) >= log->len_total -1 ; +return log->end_pos >= log->len_total;return false; }static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) { -return log && - ((log->level && log->ubuf && !bpf_verifier_log_full (log)) || - log->level ==BPF_LOG_KERNEL ); +return log && log->level; }#define BPF_MAX_SUBPROGS 256
kernel/bpf/log.c +47 -21
113 lines not on this page · raw message
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 11/19] bpf: keep track of total log content size in both fixed and rolling modes
Quoted 8 lines · Andrii Nakryiko
With these changes, it's now possible to do this sort of determination of log contents size in both
BPF_LOG_FIXEDand default rolling log mode. We need to keep in mindbpf_vlog_reset(), though, which shrinks log contents after successful verification of a particular code path. This log reset means thatlog->end_posisn't always increasing, so to return back to users what should be the log buffer size to fit all log content without causing-ENOSPCeven in the presenec of log resetting, we need
Just for you :) Nit: presence
Quoted 2 lines
to keep maximum over "lifetime" of logging. We do this accounting in
bpf_vlog_update_len_max()helper.
Ah, this is interesting! The way I conceived of this working is that the kernel gives me the buffer size required to avoid truncation at the final copy out _given the same flags_. From a user space POV I don't care about the intermediate log that was truncated away, since I in a way asked the kernel to not give me this information. Can we drop the len_max logic and simply use end_pos?
Quoted 103 lines
Another issue to keep in mind is that we limit log buffer size to 32-bit value and keep such log length as u32, but theoretically verifier could produce huge log stretching beyond 4GB. Instead of keeping (and later returning) 64-bit log length, we cap it at
UINT_MAX. Current UAPI makes it impossible to specify log buffer size bigger than 4GB anyways, so we don't really loose anything here and keep everything consistently 32-bit in UAPI. This property will be utilized in next patch.
These changes do incidentally fix one small issue with previous logging logic. Previously, if use provided log buffer of size N, and actual log output was exactly N-1 bytes + terminating \0, kernel logic coun't distinguish this condition from log truncation scenario which would end up with truncated log contents of N-1 bytes + terminating \0 as well.But now with
log->end_posbeing logical position that could go beyond actual log buffer size, we can distinguish these two conditions, which we do in this patch. This plays nicely with returninglog_size_actual(implemented in UAPI in the next patch), as we can now guarantee that if user takes suchlog_size_actualand provides log buffer of that exact size, they will not get-ENOSPCin return.All in all, all these changes do conceptually unify fixed and rolling log modes much better, and allow a nice feature requested by users:
knowing what should be the size of the buffer to avoid-ENOSPC.We'll plumb this through the UAPI and the code in the next patch.
Signed-off-by Andrii Nakryiko <[email protected]>--- include/linux/bpf_verifier.h | 12 ++----- kernel/bpf/log.c | 68 +++++++++++++++++++++++++----------- 2 files changed, 50 insertions(+), 30 deletions(-)include/linux/bpf_verifier.h +3
-9@@ -504,6 +504,7 @@ struct bpf_verifier_log {char __user *ubuf;u32 level;u32 len_total; +u32 len_max;char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; };@@ -517,23 +518,16 @@ struct bpf_verifier_log {#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U -static inline u32 bpf_log_used (const struct bpf_verifier_log *log) -{ -return log->end_pos - log->start_pos; -} -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) {if (log->level &BPF_LOG_FIXED ) -return bpf_log_used (log) >= log->len_total -1 ; +return log->end_pos >= log->len_total;return false; }static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) { -return log && - ((log->level && log->ubuf && !bpf_verifier_log_full (log)) || - log->level ==BPF_LOG_KERNEL ); +return log && log->level; }#define BPF_MAX_SUBPROGS 256kernel/bpf/log.c +17
-1@@ -16,10 +16,26 @@ bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log) log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); } +static void bpf_vlog_update_len_max (struct bpf_verifier_log *log,u32 add_len) +{ +/* add_len includes terminal \0, so no need for +1. */ +u64 len = log->end_pos + add_len; + +/* log->len_max could be larger than our current len due to +* bpf_vlog_reset() calls, so we maintain the max of any length at any +* previous point +*/ +if (len >UINT_MAX ) + log->len_max =UINT_MAX ; +else if (len > log->len_max) + log->len_max = len; +} +void bpf_verifier_vlog (struct bpf_verifier_log *log,const char *fmt,va_list args) { -unsigned int n; +u64 cur_pos; +u32 new_n, n; n =vscnprintf (log->kbuf,BPF_VERIFIER_TMP_LOG_SIZE , fmt, args);
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, · line 52
Quoted 4 lines
kernel/bpf/log.c +1
-0@@ -33,21 +49,28 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,return ; } + n +=1 ;/* include terminating zero */
So above we WARN_ONCE if n >= BPF_VERIFIER_TMP_LOG_SIZE - 1, but here we add 1 anyways. Doesn't that mean we may read 1 byte past the end of kbuf?
Quoted 89 lines
kernel/bpf/log.c +29
-21if (log->level &BPF_LOG_FIXED ) { - n =min (log->len_total -bpf_log_used (log) -1 , n); - log->kbuf[n] ='\0' ; - n +=1 ; - -if (copy_to_user (log->ubuf + log->end_pos, log->kbuf, n)) - goto fail; +/* check if we have at least something to put into user buf */ + new_n =0 ; +if (log->end_pos < log->len_total -1 ) { + new_n =min_t (u32, log->len_total - log->end_pos, n); + log->kbuf[new_n -1 ] ='\0' ; + } +bpf_vlog_update_len_max (log, n); + cur_pos = log->end_pos; log->end_pos += n -1 ;/* don't count terminating '\0' */ + +if (log->ubuf && new_n && +copy_to_user (log->ubuf + cur_pos, log->kbuf, new_n)) + goto fail; }else { -u64 new_end, new_start, cur_pos; +u64 new_end, new_start;u32 buf_start, buf_end, new_n; - log->kbuf[n] ='\0' ; - n +=1 ; + log->kbuf[n -1 ] ='\0' ; +bpf_vlog_update_len_max (log, n); new_end = log->end_pos + n;if (new_end - log->start_pos >= log->len_total)@@ -66,6 +89,12 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,if (buf_end ==0 ) buf_end = log->len_total; + log->start_pos = new_start; + log->end_pos = new_end -1 ;/* don't count terminating '\0' */ + +if (!log->ubuf) +return ; +/* if buf_start > buf_end, we wrapped around; * if buf_start == buf_end, then we fill ubuf completely; we * can't have buf_start == buf_end to mean that there is @@ -89,9 +118,6 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, buf_end)) goto fail; } - - log->start_pos = new_start; - log->end_pos = new_end -1 ;/* don't count terminating '\0' */ }return ;@@ -114,8 +140,13 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos) log->end_pos = new_pos;if (log->end_pos < log->start_pos) log->start_pos = log->end_pos; -div_u64_rem (new_pos, log->len_total, &pos); -if (put_user (zero, log->ubuf + pos)) + +if (log->level &BPF_LOG_FIXED ) + pos = log->end_pos +1 ; +else +div_u64_rem (new_pos, log->len_total, &pos); + +if (log->ubuf && pos < log->len_total &&put_user (zero, log->ubuf + pos)) log->ubuf =NULL ; }@@ -167,12 +198,7 @@ static int bpf_vlog_reverse_ubuf(struct bpf_verifier_log *log, int start, int enbool bpf_vlog_truncated (const struct bpf_verifier_log *log) { -if (!log->level) -return false; -else if (log->level &BPF_LOG_FIXED ) -return bpf_log_used (log) >= log->len_total -1 ; -else -return log->start_pos >0 ; +return log->len_max > log->len_total; }void bpf_vlog_finalize (struct bpf_verifier_log *log) --2.34.1
Re: [PATCH v3 bpf-next 11/19] bpf: keep track of total log content size in both fixed and rolling modes
Quoted 16 lines · Lorenz Bauer
Quoted 8 lines · Andrii Nakryiko
With these changes, it's now possible to do this sort of determination of log contents size in both
BPF_LOG_FIXEDand default rolling log mode. We need to keep in mindbpf_vlog_reset(), though, which shrinks log contents after successful verification of a particular code path. This log reset means thatlog->end_posisn't always increasing, so to return back to users what should be the log buffer size to fit all log content without causing-ENOSPCeven in the presenec of log resetting, we needJust for you :) Nit: presence
Quoted 2 lines
to keep maximum over "lifetime" of logging. We do this accounting in
bpf_vlog_update_len_max()helper.
Quoted 6 lines
Ah, this is interesting! The way I conceived of this working is that the kernel gives me the buffer size required to avoid truncation at the final copy out
_giventhe sameflags_. From a user space POV I don't care about the intermediate log that was truncated away, since I in a way asked the kernel to not give me this information. Can we drop thelen_maxlogic and simply useend_pos?
No, we can't, because if we don't take into account this max, then you'll get -ENOSPC. This has all to do with verifier position resetting. In log_level=1 log can grow while we process some code path branch, and as soon as we get to EXIT successfully, verifier will "forget" relevant parts of the log to go back to parent state. This was done a while ago to only leave verifier history from beginning to failure, without all the successfully verified (and thus irrelevant for debugging) information. This was a huge usability boost and I don't think we want to go back.
But it does mean that even if final log content is small, required log buffer size at some point might have been much bigger. And it's pretty much always the case for successfully verified programs. They end up having a small verifier stats summary and no log of what verifier did for state verification.
So, no, we can't just use final end_pos, otherwise we get a useless feature.
Quoted 107 lines
Quoted 107 lines
Another issue to keep in mind is that we limit log buffer size to 32-bit value and keep such log length as u32, but theoretically verifier could produce huge log stretching beyond 4GB. Instead of keeping (and later returning) 64-bit log length, we cap it at
UINT_MAX. Current UAPI makes it impossible to specify log buffer size bigger than 4GB anyways, so we don't really loose anything here and keep everything consistently 32-bit in UAPI. This property will be utilized in next patch.
These changes do incidentally fix one small issue with previous logging logic. Previously, if use provided log buffer of size N, and actual log output was exactly N-1 bytes + terminating \0, kernel logic coun't distinguish this condition from log truncation scenario which would end up with truncated log contents of N-1 bytes + terminating \0 as well.But now with
log->end_posbeing logical position that could go beyond actual log buffer size, we can distinguish these two conditions, which we do in this patch. This plays nicely with returninglog_size_actual(implemented in UAPI in the next patch), as we can now guarantee that if user takes suchlog_size_actualand provides log buffer of that exact size, they will not get-ENOSPCin return.All in all, all these changes do conceptually unify fixed and rolling log modes much better, and allow a nice feature requested by users:
knowing what should be the size of the buffer to avoid-ENOSPC.We'll plumb this through the UAPI and the code in the next patch.
Signed-off-by Andrii Nakryiko <[email protected]>--- include/linux/bpf_verifier.h | 12 ++----- kernel/bpf/log.c | 68 +++++++++++++++++++++++++----------- 2 files changed, 50 insertions(+), 30 deletions(-)include/linux/bpf_verifier.h +3
-9@@ -504,6 +504,7 @@ struct bpf_verifier_log {char __user *ubuf;u32 level;u32 len_total; +u32 len_max;char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; };@@ -517,23 +518,16 @@ struct bpf_verifier_log {#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U -static inline u32 bpf_log_used (const struct bpf_verifier_log *log) -{ -return log->end_pos - log->start_pos; -} -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) {if (log->level &BPF_LOG_FIXED ) -return bpf_log_used (log) >= log->len_total -1 ; +return log->end_pos >= log->len_total;return false; }static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) { -return log && - ((log->level && log->ubuf && !bpf_verifier_log_full (log)) || - log->level ==BPF_LOG_KERNEL ); +return log && log->level; }#define BPF_MAX_SUBPROGS 256kernel/bpf/log.c +17
-1@@ -16,10 +16,26 @@ bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log) log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); } +static void bpf_vlog_update_len_max (struct bpf_verifier_log *log,u32 add_len) +{ +/* add_len includes terminal \0, so no need for +1. */ +u64 len = log->end_pos + add_len; + +/* log->len_max could be larger than our current len due to +* bpf_vlog_reset() calls, so we maintain the max of any length at any +* previous point +*/ +if (len >UINT_MAX ) + log->len_max =UINT_MAX ; +else if (len > log->len_max) + log->len_max = len; +} +void bpf_verifier_vlog (struct bpf_verifier_log *log,const char *fmt,va_list args) { -unsigned int n; +u64 cur_pos; +u32 new_n, n; n =vscnprintf (log->kbuf,BPF_VERIFIER_TMP_LOG_SIZE , fmt, args);@@ -33,21 +49,28 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,return ; }
Quoted 5 lines
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, · line 52
Quoted 1 line
kernel/bpf/log.c +1
-0+ n +=1 ;/* include terminating zero */ So above we
WARN_ONCEif n >=BPF_VERIFIER_TMP_LOG_SIZE- 1, but here we add 1 anyways. Doesn't that mean we may read 1 byte past the end of kbuf?
Nice catch! I guess I have to do `n = min(n, BPF_VERIFIER_TMP_LOG_SIZE
- 1)` before that, will fix it, thanks!
Quoted 23 lines
Quoted 23 lines
kernel/bpf/log.c +12
-6if (log->level &BPF_LOG_FIXED ) { - n =min (log->len_total -bpf_log_used (log) -1 , n); - log->kbuf[n] ='\0' ; - n +=1 ; - -if (copy_to_user (log->ubuf + log->end_pos, log->kbuf, n)) - goto fail; +/* check if we have at least something to put into user buf */ + new_n =0 ; +if (log->end_pos < log->len_total -1 ) { + new_n =min_t (u32, log->len_total - log->end_pos, n); + log->kbuf[new_n -1 ] ='\0' ; + } +bpf_vlog_update_len_max (log, n); + cur_pos = log->end_pos; log->end_pos += n -1 ;/* don't count terminating '\0' */ + +if (log->ubuf && new_n && +copy_to_user (log->ubuf + cur_pos, log->kbuf, new_n)) + goto fail;
[...]
Re: [PATCH v3 bpf-next 11/19] bpf: keep track of total log content size in both fixed and rolling modes
Quoted 150 lines · Andrii Nakryiko
Quoted 16 lines · Lorenz Bauer
Quoted 8 lines · Andrii Nakryiko
With these changes, it's now possible to do this sort of determination of log contents size in both
BPF_LOG_FIXEDand default rolling log mode. We need to keep in mindbpf_vlog_reset(), though, which shrinks log contents after successful verification of a particular code path. This log reset means thatlog->end_posisn't always increasing, so to return back to users what should be the log buffer size to fit all log content without causing-ENOSPCeven in the presenec of log resetting, we needJust for you :) Nit: presence
Quoted 2 lines
to keep maximum over "lifetime" of logging. We do this accounting in
bpf_vlog_update_len_max()helper.Quoted 6 lines
Ah, this is interesting! The way I conceived of this working is that the kernel gives me the buffer size required to avoid truncation at the final copy out
_giventhe sameflags_. From a user space POV I don't care about the intermediate log that was truncated away, since I in a way asked the kernel to not give me this information. Can we drop thelen_maxlogic and simply useend_pos?No, we can't, because if we don't take into account this max, then you'll get
-ENOSPC. This has all to do with verifier position resetting. In log_level=1 log can grow while we process some code path branch, and as soon as we get to EXIT successfully, verifier will "forget" relevant parts of the log to go back to parent state. This was done a while ago to only leave verifier history from beginning to failure, without all the successfully verified (and thus irrelevant for debugging) information. This was a huge usability boost and I don't think we want to go back.But it does mean that even if final log content is small, required log buffer size at some point might have been much bigger. And it's pretty much always the case for successfully verified programs. They end up having a small verifier stats summary and no log of what verifier did for state verification.
So, no, we can't just use final
end_pos, otherwise we get a useless feature.Quoted 107 lines
Quoted 107 lines
Another issue to keep in mind is that we limit log buffer size to 32-bit value and keep such log length as u32, but theoretically verifier could produce huge log stretching beyond 4GB. Instead of keeping (and later returning) 64-bit log length, we cap it at
UINT_MAX. Current UAPI makes it impossible to specify log buffer size bigger than 4GB anyways, so we don't really loose anything here and keep everything consistently 32-bit in UAPI. This property will be utilized in next patch.
These changes do incidentally fix one small issue with previous logging logic. Previously, if use provided log buffer of size N, and actual log output was exactly N-1 bytes + terminating \0, kernel logic coun't distinguish this condition from log truncation scenario which would end up with truncated log contents of N-1 bytes + terminating \0 as well.But now with
log->end_posbeing logical position that could go beyond actual log buffer size, we can distinguish these two conditions, which we do in this patch. This plays nicely with returninglog_size_actual(implemented in UAPI in the next patch), as we can now guarantee that if user takes suchlog_size_actualand provides log buffer of that exact size, they will not get-ENOSPCin return.All in all, all these changes do conceptually unify fixed and rolling log modes much better, and allow a nice feature requested by users:
knowing what should be the size of the buffer to avoid-ENOSPC.We'll plumb this through the UAPI and the code in the next patch.
Signed-off-by Andrii Nakryiko <[email protected]>--- include/linux/bpf_verifier.h | 12 ++----- kernel/bpf/log.c | 68 +++++++++++++++++++++++++----------- 2 files changed, 50 insertions(+), 30 deletions(-)include/linux/bpf_verifier.h +3
-9@@ -504,6 +504,7 @@ struct bpf_verifier_log {char __user *ubuf;u32 level;u32 len_total; +u32 len_max;char kbuf[BPF_VERIFIER_TMP_LOG_SIZE ]; };@@ -517,23 +518,16 @@ struct bpf_verifier_log {#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U -static inline u32 bpf_log_used (const struct bpf_verifier_log *log) -{ -return log->end_pos - log->start_pos; -} -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) {if (log->level &BPF_LOG_FIXED ) -return bpf_log_used (log) >= log->len_total -1 ; +return log->end_pos >= log->len_total;return false; }static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) { -return log && - ((log->level && log->ubuf && !bpf_verifier_log_full (log)) || - log->level ==BPF_LOG_KERNEL ); +return log && log->level; }#define BPF_MAX_SUBPROGS 256kernel/bpf/log.c +17
-1@@ -16,10 +16,26 @@ bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log) log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); } +static void bpf_vlog_update_len_max (struct bpf_verifier_log *log,u32 add_len) +{ +/* add_len includes terminal \0, so no need for +1. */ +u64 len = log->end_pos + add_len; + +/* log->len_max could be larger than our current len due to +* bpf_vlog_reset() calls, so we maintain the max of any length at any +* previous point +*/ +if (len >UINT_MAX ) + log->len_max =UINT_MAX ; +else if (len > log->len_max) + log->len_max = len; +} +void bpf_verifier_vlog (struct bpf_verifier_log *log,const char *fmt,va_list args) { -unsigned int n; +u64 cur_pos; +u32 new_n, n; n =vscnprintf (log->kbuf,BPF_VERIFIER_TMP_LOG_SIZE , fmt, args);@@ -33,21 +49,28 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,return ; }
Quoted 9 lines
Quoted 5 lines
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, · line 52
Quoted 1 line
kernel/bpf/log.c +1
-0+ n +=1 ;/* include terminating zero */ So above we
WARN_ONCEif n >=BPF_VERIFIER_TMP_LOG_SIZE- 1, but here we add 1 anyways. Doesn't that mean we may read 1 byte past the end of kbuf?Nice catch! I guess I have to do `n = min(n,
BPF_VERIFIER_TMP_LOG_SIZE
- 1)` before that, will fix it, thanks!
Ok, so looking at your comment about vscnprintf and checking the source code, no, we don't have a problem here. vscnprintf() will at most return buf size - 1, and will still put zero into the last byte. So we can never read past buffer end.
Quoted 25 lines
Quoted 23 lines
Quoted 23 lines
kernel/bpf/log.c +12
-6if (log->level &BPF_LOG_FIXED ) { - n =min (log->len_total -bpf_log_used (log) -1 , n); - log->kbuf[n] ='\0' ; - n +=1 ; - -if (copy_to_user (log->ubuf + log->end_pos, log->kbuf, n)) - goto fail; +/* check if we have at least something to put into user buf */ + new_n =0 ; +if (log->end_pos < log->len_total -1 ) { + new_n =min_t (u32, log->len_total - log->end_pos, n); + log->kbuf[new_n -1 ] ='\0' ; + } +bpf_vlog_update_len_max (log, n); + cur_pos = log->end_pos; log->end_pos += n -1 ;/* don't count terminating '\0' */ + +if (log->ubuf && new_n && +copy_to_user (log->ubuf + cur_pos, log->kbuf, new_n)) + goto fail;[...]
Andrii Nakryiko
maintainerPATCH v3 12/19 bpf: add log_size_actual output field to return log contents size
In reply to Andrii NakryikoAdd output-only log_size_actual/btf_log_size_actual field to BPF_PROG_LOAD and BPF_BTF_LOAD commands, respectively. It will return the size of log buffer necessary to fit in all the log contents at specified log_level. This is very useful for BPF loader libraries like libbpf to be able to size log buffer correctly, but could be used by users directly, if necessary, as well.
This patch plumbs all this through the code, taking into account actual bpf_attr size provided by user to determine if these new fields are expected by users. And if they are, set them from kernel on return.
We refactory btf_parse() function to accommodate this, moving attr and uattr handling inside it. The rest is very straightforward code, which is split from the logging accounting changes in the previous patch to make it simpler to review logic vs UAPI changes.
--- include/linux/bpf.h | 2 +- include/linux/btf.h | 2 +- include/uapi/linux/bpf.h | 10 ++++++++++ kernel/bpf/btf.c | 32 ++++++++++++++++++-------------- kernel/bpf/syscall.c | 16 ++++++++-------- kernel/bpf/verifier.c | 8 +++++++- tools/include/uapi/linux/bpf.h | 12 +++++++++++- 7 files changed, 56 insertions(+), 26 deletions(-)
include/linux/bpf.h +1 -1
@@ -2176,7 +2176,7 @@ int bpf_check_uarg_tail_zero(bpfptr_t uaddr, size_t expected_size, size_t actual_size);/* verify correctness of eBPF program */ -int bpf_check (struct bpf_prog **fp,union bpf_attr *attr,bpfptr_t uattr); +int bpf_check (struct bpf_prog **fp,union bpf_attr *attr,bpfptr_t uattr,u32 uattr_size);#ifndef CONFIG_BPF_JIT_ALWAYS_ON void bpf_patch_call_args (struct bpf_insn *insn,u32 stack_depth);
include/linux/btf.h +1 -1
@@ -125,7 +125,7 @@ extern const struct file_operations btf_fops;void btf_get (struct btf *btf);void btf_put (struct btf *btf); -int btf_new_fd (const union bpf_attr *attr,bpfptr_t uattr); +int btf_new_fd (const union bpf_attr *attr,bpfptr_t uattr,u32 uattr_sz);struct btf *btf_get_by_fd (int fd); int btf_get_info_by_fd(const struct btf *btf, const union bpf_attr *attr,
include/uapi/linux/bpf.h +10 -0
@@ -1407,6 +1407,11 @@ union bpf_attr {__aligned_u64 fd_array;/* array of FDs */ __aligned_u64 core_relos;__u32 core_relo_rec_size;/* sizeof(struct bpf_core_relo) */ +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 log_size_actual; };struct {/* anonymous struct used by BPF_OBJ_* commands */
@@ -1492,6 +1497,11 @@ union bpf_attr {__u32 btf_size;__u32 btf_log_size;__u32 btf_log_level; +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 btf_log_size_actual; };struct {
kernel/bpf/btf.c +18 -14
@@ -5504,9 +5504,10 @@ static int btf_check_type_tags(struct btf_verifier_env *env,return 0 ; } -static struct btf *btf_parse (bpfptr_t btf_data,u32 btf_data_size, -u32 log_level,char __user *log_ubuf,u32 log_size) +static struct btf *btf_parse (const union bpf_attr *attr,bpfptr_t uattr,u32 uattr_size) { +bpfptr_t btf_data =make_bpfptr (attr->btf, uattr.is_kernel); +char __user *log_ubuf =u64_to_user_ptr (attr->btf_log_buf);struct btf_struct_metas *struct_meta_tab;struct btf_verifier_env *env =NULL ;struct bpf_verifier_log *log;
@@ -5514,7 +5515,7 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,u8 *data;int err; -if (btf_data_size >BTF_MAX_SIZE ) +if (attr->btf_size >BTF_MAX_SIZE )return ERR_PTR (-E2BIG ); env =kzalloc (sizeof (*env),GFP_KERNEL | __GFP_NOWARN);
@@ -5522,13 +5523,13 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,return ERR_PTR (-ENOMEM ); log = &env->log; -if (log_level || log_ubuf || log_size) { +if (attr->btf_log_level || log_ubuf || attr->btf_log_size) {/* user requested verbose verifier output * and supplied buffer to store the verification trace */ - log->level = log_level; + log->level = attr->btf_log_level; log->ubuf = log_ubuf; - log->len_total = log_size; + log->len_total = attr->btf_log_size;/* log attributes have to be sane */ if (!bpf_verifier_log_attr_valid (log)) {
@@ -5544,16 +5545,16 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, } env->btf = btf; - data =kvmalloc (btf_data_size,GFP_KERNEL | __GFP_NOWARN); + data =kvmalloc (attr->btf_size,GFP_KERNEL | __GFP_NOWARN);if (!data) { err = -ENOMEM ; goto errout; } btf->data = data; - btf->data_size = btf_data_size; + btf->data_size = attr->btf_size; -if (copy_from_bpfptr (data, btf_data, btf_data_size)) { +if (copy_from_bpfptr (data, btf_data, attr->btf_size)) { err = -EFAULT ; goto errout; }
@@ -5594,6 +5595,12 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, }bpf_vlog_finalize (log); + if (uattr_size >= offsetofend(union bpf_attr, btf_log_size_actual) && +copy_to_bpfptr_offset (uattr, offsetof(union bpf_attr , btf_log_size_actual), + &log->len_max,sizeof (log->len_max))) { + err = -EFAULT ; + goto errout_meta; + }if (bpf_vlog_truncated (log)) { err = -ENOSPC ; goto errout_meta;
@@ -7214,15 +7221,12 @@ static int __btf_new_fd(struct btf *btf)return anon_inode_getfd ("btf" , &btf_fops, btf,O_RDONLY |O_CLOEXEC ); } -int btf_new_fd (const union bpf_attr *attr,bpfptr_t uattr) +int btf_new_fd (const union bpf_attr *attr,bpfptr_t uattr,u32 uattr_size) {struct btf *btf;int ret; - btf =btf_parse (make_bpfptr (attr->btf, uattr.is_kernel), - attr->btf_size, attr->btf_log_level, -u64_to_user_ptr (attr->btf_log_buf), - attr->btf_log_size); + btf =btf_parse (attr, uattr, uattr_size);if (IS_ERR (btf))return PTR_ERR (btf);
kernel/bpf/syscall.c +8 -8
@@ -2501,9 +2501,9 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type) }/* last field in 'union bpf_attr' used by this command */ -#define BPF_PROG_LOAD_LAST_FIELD core_relo_rec_size +#define BPF_PROG_LOAD_LAST_FIELD log_size_actual -static int bpf_prog_load (union bpf_attr *attr,bpfptr_t uattr) +static int bpf_prog_load (union bpf_attr *attr,bpfptr_t uattr,u32 uattr_size) {enum bpf_prog_type type = attr->prog_type;struct bpf_prog *prog, *dst_prog =NULL ;
@@ -2653,7 +2653,7 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr) goto free_prog_sec;/* run eBPF verifier */ - err =bpf_check (&prog, attr, uattr); + err =bpf_check (&prog, attr, uattr, uattr_size);if (err <0 ) goto free_used_maps;
@@ -4371,9 +4371,9 @@ static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,return err; } -#define BPF_BTF_LOAD_LAST_FIELD btf_log_level +#define BPF_BTF_LOAD_LAST_FIELD btf_log_size_actual -static int bpf_btf_load (const union bpf_attr *attr,bpfptr_t uattr) +static int bpf_btf_load (const union bpf_attr *attr,bpfptr_t uattr,__u32 uattr_size) {if (CHECK_ATTR (BPF_BTF_LOAD ))return -EINVAL ;
@@ -4381,7 +4381,7 @@ static int bpf_btf_load(const union bpf_attr *attr, bpfptr_t uattr)if (!bpf_capable ())return -EPERM ; -return btf_new_fd (attr, uattr); +return btf_new_fd (attr, uattr, uattr_size); }#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD btf_id
@@ -5059,7 +5059,7 @@ static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size) err =map_freeze (&attr);break ;case BPF_PROG_LOAD : - err =bpf_prog_load (&attr, uattr); + err =bpf_prog_load (&attr, uattr, size);break ;case BPF_OBJ_PIN : err =bpf_obj_pin (&attr);
@@ -5104,7 +5104,7 @@ static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size) err =bpf_raw_tracepoint_open (&attr);break ;case BPF_BTF_LOAD : - err =bpf_btf_load (&attr, uattr); + err =bpf_btf_load (&attr, uattr, size);break ;case BPF_BTF_GET_FD_BY_ID : err =bpf_btf_get_fd_by_id (&attr);
kernel/bpf/verifier.c +7 -1
@@ -18625,7 +18625,7 @@ struct btf *bpf_get_btf_vmlinux(void)return btf_vmlinux; } -int bpf_check (struct bpf_prog **prog,union bpf_attr *attr,bpfptr_t uattr) +int bpf_check (struct bpf_prog **prog,union bpf_attr *attr,bpfptr_t uattr,__u32 uattr_size) {u64 start_time =ktime_get_ns ();struct bpf_verifier_env *env;
@@ -18792,6 +18792,12 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr) env->prog->aux->verified_insns = env->insn_processed;bpf_vlog_finalize (log); + if (uattr_size >= offsetofend(union bpf_attr, log_size_actual) && +copy_to_bpfptr_offset (uattr, offsetof(union bpf_attr , log_size_actual), + &log->len_max,sizeof (log->len_max))) { + ret = -EFAULT ; + goto err_release_maps; + }if (bpf_vlog_truncated (log)) ret = -ENOSPC ;if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf)
tools/include/uapi/linux/bpf.h +11 -1
@@ -1407,6 +1407,11 @@ union bpf_attr {__aligned_u64 fd_array;/* array of FDs */ __aligned_u64 core_relos;__u32 core_relo_rec_size;/* sizeof(struct bpf_core_relo) */ +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 log_size_actual; };struct {/* anonymous struct used by BPF_OBJ_* commands */
@@ -1492,6 +1497,11 @@ union bpf_attr {__u32 btf_size;__u32 btf_log_size;__u32 btf_log_level; +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 btf_log_size_actual; };struct {
@@ -1513,7 +1523,7 @@ union bpf_attr {struct {/* struct used by BPF_LINK_CREATE command */ union {__u32 prog_fd;/* eBPF program to attach */ -__u32 map_fd;/* eBPF struct_ops to attach */ +__u32 map_fd;/* struct_ops to attach */ };union {__u32 target_fd;/* object to attach to */
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
include/uapi/linux/bpf.h union bpf_attr { · line 1414
Quoted 9 lines · Andrii Nakryiko
include/uapi/linux/bpf.h +5
-0@@ -1407,6 +1407,11 @@ union bpf_attr {__aligned_u64 fd_array;/* array of FDs */ __aligned_u64 core_relos;__u32 core_relo_rec_size;/* sizeof(struct bpf_core_relo) */ +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 log_size_actual;
Naming nit..
In the networking subsystem there is skb->truesize.
The concept is exposed to user space through tracepoints and well understood in networking. May be call this field 'log_truesize' ?
With or without underscore.
Other than this the rest looks good and I believe it addresses Lorenz and Timo concerns. Would be good to hear from them.
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
Quoted 17 lines · Alexei Starovoitov
include/uapi/linux/bpf.h union bpf_attr { · line 1414
Quoted 9 lines · Andrii Nakryiko
include/uapi/linux/bpf.h +5
-0@@ -1407,6 +1407,11 @@ union bpf_attr {__aligned_u64 fd_array;/* array of FDs */ __aligned_u64 core_relos;__u32 core_relo_rec_size;/* sizeof(struct bpf_core_relo) */ +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +*/ +__u32 log_size_actual;Naming nit..
In the networking subsystem there isskb->truesize.
The concept is exposed to user space through tracepoints and well understood in networking. May be call this field 'log_truesize' ?
With or without underscore.
Sounds good, naming pretty much the only part I wasn't sure about. log_size_true or log_true_size, any preference? Latter reads more naturally, so I'm guessing you'll prefer that one? Unless naming "regularity" of log_size_true is preferred?
Quoted 3 lines
Other than this the rest looks good and I believe it addresses Lorenz and Timo concerns. Would be good to hear from them.
+1, yep. I'll wait a bit more before resubmitting.
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
In reply to Andrii NakryikoQuoted 11 lines · Andrii Nakryiko
Add output-only log_size_actual/btf_log_size_actual field to
BPF_PROG_LOADandBPF_BTF_LOADcommands, respectively. It will return the size of log buffer necessary to fit in all the log contents at specifiedlog_level. This is very useful for BPF loader libraries like libbpf to be able to size log buffer correctly, but could be used by users directly, if necessary, as well.This patch plumbs all this through the code, taking into account actual
bpf_attrsize provided by user to determine if these new fields are expected by users. And if they are, set them from kernel on return.
Can we check that both fields are zero when entering the syscall?
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
Quoted 10 lines · Lorenz Bauer
Quoted 8 lines · Andrii Nakryiko
Add output-only log_size_actual/btf_log_size_actual field to
BPF_PROG_LOADandBPF_BTF_LOADcommands, respectively. It will return the size of log buffer necessary to fit in all the log contents at specifiedlog_level. This is very useful for BPF loader libraries like libbpf to be able to size log buffer correctly, but could be used by users directly, if necessary, as well.
Quoted 5 lines
Quoted 3 lines
This patch plumbs all this through the code, taking into account actual
bpf_attrsize provided by user to determine if these new fields are expected by users. And if they are, set them from kernel on return.Can we check that both fields are zero when entering the syscall?
Yep, it already happens and is done by genericbpf_check_uarg_tail_zero() check in __sys_bpf.
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
Quoted 4 lines · Andrii Nakryiko
Quoted 1 line
Can we check that both fields are zero when entering the syscall?
Yep, it already happens and is done by generic
bpf_check_uarg_tail_zero()check in__sys_bpf.
I thought that check only happens if expected_size > actual_size? I'm thinking of the actual_size == expected_size case, what prevents user space from setting log_size_actual to a non-zero value?
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
Quoted 11 lines · Lorenz Bauer
Quoted 4 lines · Andrii Nakryiko
Quoted 1 line
Can we check that both fields are zero when entering the syscall?
Yep, it already happens and is done by generic
bpf_check_uarg_tail_zero()check in__sys_bpf.I thought that check only happens if
expected_size>actual_size? I'm thinking of theactual_size==expected_sizecase, what prevents user space from settinglog_size_actualto a non-zero value?
ah, in that sense... What's the reasoning for this enforcement? I'm just afraid that it will complicate applications that don't care and are not aware of this field and do retries with the same attribute. On first try, the kernel fills out log_true_size, application retries and doesn't clear log_true_size (because it was written a while ago, but compiled against latest kernel UAPI, so passes sizeof(union bpf_attr) that includes new field). And that suddenly starts failing with -EINVAL.
Seems like an unfortunate side effect, no? What's the harm in not validating this field, if it's an output-only parameter?
Re: [PATCH v3 bpf-next 12/19] bpf: add log_size_actual output field to return log contents size
Quoted 10 lines · Andrii Nakryiko
ah, in that sense... What's the reasoning for this enforcement? I'm just afraid that it will complicate applications that don't care and are not aware of this field and do retries with the same attribute. On first try, the kernel fills out
log_true_size, application retries and doesn't clearlog_true_size(because it was written a while ago, but compiled against latest kernel UAPI, so passessizeof(union bpf_attr)that includes new field). And that suddenly starts failing with-EINVAL.
Quoted 2 lines
Seems like an unfortunate side effect, no? What's the harm in not validating this field, if it's an output-only parameter?
Hmm good point. Just abundance of caution, but in this case it doesn't make sense.
Andrii Nakryiko
maintainerPATCH v3 13/19 bpf: simplify internal verifier log interface
In reply to Andrii NakryikoSimplify internal verifier log API down to bpf_vlog_init() and bpf_vlog_finalize(). The former handles input arguments validation in one place and makes it easier to change it. The latter subsumes -ENOSPC (truncation) and -EFAULT handling and simplifies both caller's code (bpf_check() and btf_parse()).
For btf_parse(), this patch also makes sure that verifier log finalization happens even if there is some error condition during BTF verification process prior to normal finalization step.
--- include/linux/bpf_verifier.h | 13 ++------ kernel/bpf/btf.c | 65 ++++++++++++++++++------------------ kernel/bpf/log.c | 48 +++++++++++++++++++++----- kernel/bpf/verifier.c | 39 +++++++++------------- 4 files changed, 90 insertions(+), 75 deletions(-)
include/linux/bpf_verifier.h +3 -10
@@ -518,13 +518,6 @@ struct bpf_verifier_log {#define BPF_LOG_MIN_ALIGNMENT 8U#define BPF_LOG_ALIGNMENT 40U -static inline bool bpf_verifier_log_full (const struct bpf_verifier_log *log) -{ -if (log->level &BPF_LOG_FIXED ) -return log->end_pos >= log->len_total; -return false; -} -static inline bool bpf_verifier_log_needed (const struct bpf_verifier_log *log) {return log && log->level;
@@ -612,16 +605,16 @@ struct bpf_verifier_env {char type_str_buf[TYPE_STR_BUF_LEN ]; }; -bool bpf_verifier_log_attr_valid (const struct bpf_verifier_log *log); __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,const char *fmt,va_list args); __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,const char *fmt, ...); __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,const char *fmt, ...); +int bpf_vlog_init (struct bpf_verifier_log *log,u32 log_level, +char __user *log_buf,u32 log_size);void bpf_vlog_reset (struct bpf_verifier_log *log,u64 new_pos); -void bpf_vlog_finalize (struct bpf_verifier_log *log); -bool bpf_vlog_truncated (const struct bpf_verifier_log *log); +int bpf_vlog_finalize (struct bpf_verifier_log *log,u32 *log_size_actual);static inline struct bpf_func_state *cur_func (struct bpf_verifier_env *env) {
kernel/bpf/btf.c +32 -33
103 lines not on this page · raw message
kernel/bpf/log.c +39 -9
81 lines not on this page · raw message
kernel/bpf/verifier.c +16 -23
@@ -18629,8 +18629,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3 {u64 start_time =ktime_get_ns ();struct bpf_verifier_env *env; -struct bpf_verifier_log *log; -int i, len, ret = -EINVAL ; +int i, len, ret = -EINVAL , err; +u32 log_size_actual;bool is_priv;/* no program is valid */
@@ -18643,7 +18643,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3 env =kzalloc (sizeof (struct bpf_verifier_env ),GFP_KERNEL );if (!env)return -ENOMEM ; - log = &env->log; len = (*prog)->len; env->insn_aux_data =
@@ -18664,20 +18663,14 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3if (!is_priv)mutex_lock (&bpf_verifier_lock); -if (attr->log_level || attr->log_buf || attr->log_size) { -/* user requested verbose verifier output -* and supplied buffer to store the verification trace -*/ - log->level = attr->log_level; - log->ubuf = (char __user *) (unsigned long ) attr->log_buf; - log->len_total = attr->log_size; - -/* log attributes have to be sane */ -if (!bpf_verifier_log_attr_valid (log)) { - ret = -EINVAL ; - goto err_unlock; - } - } +/* user could have requested verbose verifier output +* and supplied buffer to store the verification trace +*/ + ret =bpf_vlog_init (&env->log, attr->log_level, + (char __user *) (unsigned long ) attr->log_buf, + attr->log_size); +if (ret) + goto err_unlock;mark_verifier_state_clean (env);
@@ -18791,17 +18784,17 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3print_verification_stats (env); env->prog->aux->verified_insns = env->insn_processed; -bpf_vlog_finalize (log); +/* preserve original error even if log finalization is successful */ + err =bpf_vlog_finalize (&env->log, &log_size_actual); +if (err) + ret = err; + if (uattr_size >= offsetofend(union bpf_attr, log_size_actual) &©_to_bpfptr_offset (uattr, offsetof(union bpf_attr , log_size_actual), - &log->len_max,sizeof (log->len_max))) { + &log_size_actual,sizeof (log_size_actual))) { ret = -EFAULT ; goto err_release_maps; } -if (bpf_vlog_truncated (log)) - ret = -ENOSPC ; -if (log->level && log->level !=BPF_LOG_KERNEL && !log->ubuf) - ret = -EFAULT ;if (ret) goto err_release_maps;
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 13/19] bpf: simplify internal verifier log interface
Quoted 7 lines · Andrii Nakryiko
Simplify internal verifier log API down to
bpf_vlog_init()andbpf_vlog_finalize(). The former handles input arguments validation in one place and makes it easier to change it. The latter subsumes-ENOSPC(truncation) and-EFAULThandling and simplifies both caller's code (bpf_check()andbtf_parse()).
Quoted 5 lines
For
btf_parse(), this patch also makes sure that verifier log finalization happens even if there is some error condition during BTF verification process prior to normal finalization step.Signed-off-by Andrii Nakryiko <[email protected]>
Quoted 8 lines
kernel/bpf/btf.c +0
-0@@ -5504,16 +5504,30 @@ static int btf_check_type_tags(struct btf_verifier_env *env,return 0 ; }
kernel/bpf/btf.c static int btf_check_type_tags(struct btf_verifier_env *env, · line 5516
Quoted 10 lines
kernel/bpf/btf.c +10
-0+static int finalize_log (struct bpf_verifier_log *log,bpfptr_t uattr,u32 uattr_size) +{ +u32 log_size_actual; +int err; + + err =bpf_vlog_finalize (log, &log_size_actual); + + if (uattr_size >= offsetofend(union bpf_attr, btf_log_size_actual) && +copy_to_bpfptr_offset (uattr, offsetof(union bpf_attr , btf_log_size_actual), + &log_size_actual,sizeof (log_size_actual)))
Why not share this with the verifier as well?
Re: [PATCH v3 bpf-next 13/19] bpf: simplify internal verifier log interface
Quoted 25 lines · Lorenz Bauer
Quoted 7 lines · Andrii Nakryiko
Simplify internal verifier log API down to
bpf_vlog_init()andbpf_vlog_finalize(). The former handles input arguments validation in one place and makes it easier to change it. The latter subsumes-ENOSPC(truncation) and-EFAULThandling and simplifies both caller's code (bpf_check()andbtf_parse()).Quoted 5 lines
For
btf_parse(), this patch also makes sure that verifier log finalization happens even if there is some error condition during BTF verification process prior to normal finalization step.Signed-off-by Andrii Nakryiko <[email protected]>Acked-by Lorenz Bauer <[email protected]>Quoted 8 lines
kernel/bpf/btf.c +0
-0@@ -5504,16 +5504,30 @@ static int btf_check_type_tags(struct btf_verifier_env *env,return 0 ; }
Quoted 12 lines
kernel/bpf/btf.c static int btf_check_type_tags(struct btf_verifier_env *env, · line 5516
Quoted 10 lines
kernel/bpf/btf.c +10
-0+static int finalize_log (struct bpf_verifier_log *log,bpfptr_t uattr,u32 uattr_size) +{ +u32 log_size_actual; +int err; + + err =bpf_vlog_finalize (log, &log_size_actual); + + if (uattr_size >= offsetofend(union bpf_attr, btf_log_size_actual) && +copy_to_bpfptr_offset (uattr, offsetof(union bpf_attr , btf_log_size_actual), + &log_size_actual,sizeof (log_size_actual)))Why not share this with the verifier as well?
it's different field names (right now, log_size_actual for BPF_PROG_LOAD and btf_log_size_actual for BPF_BTF_LOAD), so different offsets as well. We could pass offsets, but that seems ugly and I don't think it would save us much in terms of complexity.
Andrii Nakryiko
maintainerPATCH v3 14/19 bpf: relax log_buf NULL conditions when log_level>0 is requested
In reply to Andrii NakryikoDrop the log_size>0 and log_buf!=NULL condition when log_level>0. This
allows users to request log_size_actual of a full log without providing
actual (even if small) log buffer. Verifier log handling code was mostly ready to handle NULL log->ubuf, so only few small changes were necessary to prevent NULL log->ubuf from causing problems.
Note, that user is basically guaranteed to receive -ENOSPC when providing log_level>0 and log_buf==NULL. We also still enforce that either (log_buf==NULL && log_size==0) or (log_buf!=NULL && log_size>0).
--- kernel/bpf/log.c | 39 +++++++++++++++++++++++++-------------- 1 file changed, 25 insertions(+), 14 deletions(-)
kernel/bpf/log.c +25 -14
@@ -12,8 +12,17 @@static bool bpf_verifier_log_attr_valid (const struct bpf_verifier_log *log) { -return log->len_total >0 && log->len_total <=UINT_MAX >>2 && - log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK ); +/* ubuf and len_total should both be specified (or not) together */ +if (!!log->ubuf != !!log->len_total) +return false; +/* log buf without log_level is meaningless */ +if (log->ubuf && log->level ==0 ) +return false; +if (log->level & ~BPF_LOG_MASK ) +return false; +if (log->len_total >UINT_MAX >>2 ) +return false; +return true; } int bpf_vlog_init(struct bpf_verifier_log *log, u32 log_level,
@@ -64,15 +73,15 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, } n +=1 ;/* include terminating zero */ +bpf_vlog_update_len_max (log, n); +if (log->level &BPF_LOG_FIXED ) {/* check if we have at least something to put into user buf */ new_n =0 ; -if (log->end_pos < log->len_total -1 ) { +if (log->end_pos +1 < log->len_total) { new_n =min_t (u32, log->len_total - log->end_pos, n); log->kbuf[new_n -1 ] ='\0' ; } - -bpf_vlog_update_len_max (log, n); cur_pos = log->end_pos; log->end_pos += n -1 ;/* don't count terminating '\0' */
@@ -84,16 +93,21 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,u32 buf_start, buf_end, new_n; log->kbuf[n -1 ] ='\0' ; -bpf_vlog_update_len_max (log, n); new_end = log->end_pos + n;if (new_end - log->start_pos >= log->len_total) new_start = new_end - log->len_total;else new_start = log->start_pos; + + log->start_pos = new_start; + log->end_pos = new_end -1 ;/* don't count terminating '\0' */ + +if (!log->ubuf) +return ; + new_n =min (n, log->len_total); cur_pos = new_end - new_n; -div_u64_rem (cur_pos, log->len_total, &buf_start);div_u64_rem (new_end, log->len_total, &buf_end);/* new_end and buf_end are exclusive indices, so if buf_end is
@@ -103,12 +117,6 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,if (buf_end ==0 ) buf_end = log->len_total; - log->start_pos = new_start; - log->end_pos = new_end -1 ;/* don't count terminating '\0' */ - -if (!log->ubuf) -return ; -/* if buf_start > buf_end, we wrapped around; * if buf_start == buf_end, then we fill ubuf completely; we * can't have buf_start == buf_end to mean that there is
@@ -155,12 +163,15 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos)if (log->end_pos < log->start_pos) log->start_pos = log->end_pos; +if (!log->ubuf) +return ; +if (log->level &BPF_LOG_FIXED ) pos = log->end_pos +1 ;else div_u64_rem (new_pos, log->len_total, &pos); -if (log->ubuf && pos < log->len_total &&put_user (zero, log->ubuf + pos)) +if (pos < log->len_total &&put_user (zero, log->ubuf + pos)) log->ubuf =NULL ; }
Signature · 1 line
2.34.1
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
Quoted 8 lines · Andrii Nakryiko
Drop the log_size>0 and log_buf!=NULL condition when log_level>0. This
allows users to requestlog_size_actualof a full log without providing
actual (even if small) log buffer. Verifier log handling code was mostly ready to handle NULLlog->ubuf, so only few small changes were necessary to prevent NULLlog->ubuffrom causing problems.Note, that user is basically guaranteed to receive
-ENOSPCwhen providing log_level>0 and log_buf==NULL. We also still enforce that either (log_buf==NULL && log_size==0) or (log_buf!=NULL && log_size>0).
Is it possible to change it so that log_buf == NULL && log_size == 0 && log_level > 0 only fills in log_size_actual and doesn't return ENOSPC? Otherwise we can't do oneshot loading.
if PROG_LOAD(buf=NULL, size=0, level=1) >= 0:
return fd
else
retry PROG_LOAD(buf!=NULL, size=log_size_actual, level=1)
If the first PROG_LOAD returned ENOSPC we'd have to re-run it without the log enabled to see whether ENOSPC is masking a real verification error. With the current semantics we can work around this with three syscalls, but that seems wasteful?
if PROG_LOAD(buf=NULL, size=0, level=0) >= 0:
return fd
PROG_LOAD(buf=NULL, size=0, level=1) == ENOSPC PROG_LOAD(buf!=NULL, size=log_size_actual, level=1)
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
Quoted 25 lines · Lorenz Bauer
Quoted 8 lines · Andrii Nakryiko
Drop the log_size>0 and log_buf!=NULL condition when log_level>0. This
allows users to requestlog_size_actualof a full log without providing
actual (even if small) log buffer. Verifier log handling code was mostly ready to handle NULLlog->ubuf, so only few small changes were necessary to prevent NULLlog->ubuffrom causing problems.Note, that user is basically guaranteed to receive
-ENOSPCwhen providing log_level>0 and log_buf==NULL. We also still enforce that either (log_buf==NULL && log_size==0) or (log_buf!=NULL && log_size>0).Is it possible to change it so that
log_buf== NULL &&log_size== 0 &&log_level> 0 only fills inlog_size_actualand doesn't return ENOSPC? Otherwise we can't do oneshot loading.if
PROG_LOAD(buf=NULL, size=0, level=1)>= 0:
return fd
elseretry PROG_LOAD(buf!=NULL, size=log_size_actual, level=1)If the first
PROG_LOADreturned ENOSPC we'd have to re-run it without the log enabled to see whether ENOSPC is masking a real verification error. With the current semantics we can work around this with three syscalls, but that seems wasteful?
Quoted 5 lines
if
PROG_LOAD(buf=NULL, size=0, level=0)>= 0:
return fd
PROG_LOAD(buf=NULL, size=0, level=1)== ENOSPCPROG_LOAD(buf!=NULL, size=log_size_actual, level=1)
We could and I thought about this, but verifier logging is quite an expensive operation due to all the extra formatting and reporting, so it's not advised to have log_level=1 permanently enabled for production BPF program loading. So I didn't want to encourage this pattern. Note that even if log_buf==NULL when log_level>0 we'd be doing printf()-ing everything, which is the expensive part. So do you really want to add all this extra overhead *constantly* to all production BPF programs?
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
On Wed, Apr 5, 2023 at 6:44 PM Andrii Nakryiko
<[email protected]> wrote:>
Quoted 4 lines
We could and I thought about this, but verifier logging is quite an expensive operation due to all the extra formatting and reporting, so it's not advised to have log_level=1 permanently enabled for production BPF program loading.
Any idea how expensive this is?
Quoted 4 lines
Note that even if log_buf==NULL when log_level>0 we'd be doing printf()-ing everything, which is the expensive part. So do you really want to add all this extra overhead *constantly* to all production BPF programs?
No, I'm just going off of what UAPI I would like to use. Keeping semantics as they are is fine if it's too slow. We could always use a small-ish buffer for the first retry and hope things fit.
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
Quoted 10 lines · Lorenz Bauer
On Wed, Apr 5, 2023 at 6:44 PM Andrii Nakryiko
<[email protected]> wrote:>Quoted 4 lines
We could and I thought about this, but verifier logging is quite an expensive operation due to all the extra formatting and reporting, so it's not advised to have log_level=1 permanently enabled for production BPF program loading.
Any idea how expensive this is?
It will depend on the specific program, of course. But just to estimate, here's pyperf100 selftests with log_level=1 and log_level=4 (just stats, basically free).
[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o -v >/dev/null
real 0m1.761s user 0m0.008s sys 0m1.743s
[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o >/dev/null
real 0m0.869s user 0m0.009s sys 0m0.846s
2x difference. So I'd definitely not recommend running with log_level=1 by default.
Quoted 8 lines
Quoted 4 lines
Note that even if log_buf==NULL when log_level>0 we'd be doing printf()-ing everything, which is the expensive part. So do you really want to add all this extra overhead *constantly* to all production BPF programs?
No, I'm just going off of what UAPI I would like to use. Keeping semantics as they are is fine if it's too slow. We could always use a small-ish buffer for the first retry and hope things fit.
It's easy for me to implement it either way, Alexei and Daniel, any thoughts on this?
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
Quoted 36 lines · Andrii Nakryiko
Quoted 10 lines · Lorenz Bauer
On Wed, Apr 5, 2023 at 6:44 PM Andrii Nakryiko
<[email protected]> wrote:>Quoted 4 lines
We could and I thought about this, but verifier logging is quite an expensive operation due to all the extra formatting and reporting, so it's not advised to have log_level=1 permanently enabled for production BPF program loading.
Any idea how expensive this is?
It will depend on the specific program, of course. But just to estimate, here's pyperf100 selftests with log_level=1 and log_level=4 (just stats, basically free).
[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o -v >/dev/null
real 0m1.761s user 0m0.008s sys 0m1.743s[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o >/dev/null
real 0m0.869s user 0m0.009s sys 0m0.846s2x difference. So I'd definitely not recommend running with log_level=1 by default.
Quoted 5 lines
Quoted 4 lines
Note that even if log_buf==NULL when log_level>0 we'd be doing printf()-ing everything, which is the expensive part. So do you really want to add all this extra overhead *constantly* to all production BPF programs?
Quoted 6 lines
Quoted 3 lines
No, I'm just going off of what UAPI I would like to use. Keeping semantics as they are is fine if it's too slow. We could always use a small-ish buffer for the first retry and hope things fit.
It's easy for me to implement it either way, Alexei and Daniel, any thoughts on this?
I like this part of the idea:
Quoted 7 lines
Is it possible to change it so that
log_buf== NULL &&log_size== 0 &&log_level> 0 only fills inlog_size_actualand doesn't return ENOSPC? Otherwise we can't do oneshot loading.
ifPROG_LOAD(buf=NULL, size=0, level=1)>= 0:
return fd
else
retryPROG_LOAD(buf!=NULL, size=log_size_actual, level=1)
libbpf shouldn't be doing it by default, since load time matters, but it could be useful in other scenarios.
Like central bpf loading daemon can use (buf=NULL, size=0, level=(1 | 4)) every 100th prog_load as part of stats collection.
veristat can do it by default.
log_true_size should more or less align with verified_insns uapi number, but still interesting to see and track over time.
Re: [PATCH v3 bpf-next 14/19] bpf: relax log_buf NULL conditions when log_level>0 is requested
Quoted 56 lines · Alexei Starovoitov
Quoted 36 lines · Andrii Nakryiko
Quoted 10 lines · Lorenz Bauer
On Wed, Apr 5, 2023 at 6:44 PM Andrii Nakryiko
<[email protected]> wrote:>Quoted 4 lines
We could and I thought about this, but verifier logging is quite an expensive operation due to all the extra formatting and reporting, so it's not advised to have log_level=1 permanently enabled for production BPF program loading.
Any idea how expensive this is?
It will depend on the specific program, of course. But just to estimate, here's pyperf100 selftests with log_level=1 and log_level=4 (just stats, basically free).
[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o -v >/dev/null
real 0m1.761s user 0m0.008s sys 0m1.743s[vmuser@archvm bpf]$ time sudo ./veristat pyperf100.bpf.o >/dev/null
real 0m0.869s user 0m0.009s sys 0m0.846s2x difference. So I'd definitely not recommend running with log_level=1 by default.
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Note that even if log_buf==NULL when log_level>0 we'd be doing printf()-ing everything, which is the expensive part. So do you really want to add all this extra overhead *constantly* to all production BPF programs?
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No, I'm just going off of what UAPI I would like to use. Keeping semantics as they are is fine if it's too slow. We could always use a small-ish buffer for the first retry and hope things fit.
It's easy for me to implement it either way, Alexei and Daniel, any thoughts on this?
I like this part of the idea:
Quoted 7 lines
Is it possible to change it so that
log_buf== NULL &&log_size== 0 &&log_level> 0 only fills inlog_size_actualand doesn't return ENOSPC? Otherwise we can't do oneshot loading.
ifPROG_LOAD(buf=NULL, size=0, level=1)>= 0:
return fd
else
retryPROG_LOAD(buf!=NULL, size=log_size_actual, level=1)
Quoted 5 lines
libbpf shouldn't be doing it by default, since load time matters, but it could be useful in other scenarios.
Like central bpf loading daemon can use (buf=NULL, size=0, level=(1 | 4)) every 100thprog_loadas part of stats collection.
veristat can do it by default.
makes sense, then no -ENOSPC for log_buf==NULL, will do in next version
Quoted 3 lines
log_true_sizeshould more or less align withverified_insnsuapi number, but still interesting to see and track over time.
Andrii Nakryiko
maintainerPATCH v3 15/19 libbpf: wire through log_size_actual returned from kernel for BPF_PROG_LOAD
In reply to Andrii NakryikoAdd output-only log_size_actual field to bpf_prog_load_opts to return bpf_attr->log_size_actual value back from bpf() syscall.
Note, that we have to drop const modifier from opts in bpf_prog_load(). This could potentially cause compilation error for some users. But the usual practice is to define bpf_prog_load_ops
as a local variable next to bpf_prog_load() call and pass pointer to it, so const vs non-const makes no difference and won't even come up in most (if not all) cases.
There are no runtime and ABI backwards/forward compatibility issues at all. If user provides old struct bpf_prog_load_opts, libbpf won't set new fields. If old libbpf is provided new bpf_prog_load_opts, nothing will happen either as old libbpf doesn't yet know about this new field.
Adding a new variant of bpf_prog_load() just for this seems like a big and unnecessary overkill. As a corroborating evidence is the fact that entire selftests/bpf code base required not adjustment whatsoever.
--- tools/lib/bpf/bpf.c | 7 +++++-- tools/lib/bpf/bpf.h | 11 +++++++++-- 2 files changed, 14 insertions(+), 4 deletions(-)
tools/lib/bpf/bpf.c +5 -2
@@ -230,9 +230,9 @@ alloc_zero_tailing_info(const void *orecord, __u32 cnt,int bpf_prog_load (enum bpf_prog_type prog_type,const char *prog_name,const char *license,const struct bpf_insn *insns,size_t insn_cnt, -const struct bpf_prog_load_opts *opts) +struct bpf_prog_load_opts *opts) { - const size_t attr_sz = offsetofend(union bpf_attr, fd_array); + const size_t attr_sz = offsetofend(union bpf_attr, log_size_actual);void *finfo =NULL , *linfo =NULL ;const char *func_info, *line_info;__u32 log_size, log_level, attach_prog_fd, attach_btf_obj_fd;
@@ -312,6 +312,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, } fd =sys_bpf_prog_load (&attr, attr_sz, attempts); +OPTS_SET (opts, log_size_actual, attr.log_size_actual);if (fd >=0 )return fd;
@@ -352,6 +353,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, } fd =sys_bpf_prog_load (&attr, attr_sz, attempts); +OPTS_SET (opts, log_size_actual, attr.log_size_actual);if (fd >=0 ) goto done; }
@@ -366,6 +368,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, attr.log_level =1 ; fd =sys_bpf_prog_load (&attr, attr_sz, attempts); +OPTS_SET (opts, log_size_actual, attr.log_size_actual); } done:/* free() doesn't affect errno, so we don't need to restore it */
tools/lib/bpf/bpf.h +9 -2
@@ -96,13 +96,20 @@ struct bpf_prog_load_opts {__u32 log_level;__u32 log_size;char *log_buf; +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +* If kernel doesn't support this feature, log_size is left unchanged. +*/ +__u32 log_size_actual; + size_t :0; }; -#define bpf_prog_load_opts__last_field log_buf +#define bpf_prog_load_opts__last_field log_size_actual LIBBPF_API int bpf_prog_load(enum bpf_prog_type prog_type,const char *prog_name,const char *license,const struct bpf_insn *insns,size_t insn_cnt, -const struct bpf_prog_load_opts *opts); +struct bpf_prog_load_opts *opts);/* Flags to direct loading requirements */ #define MAPS_RELAX_COMPAT 0x01
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 16/19 libbpf: wire through log_size_actual for bpf_btf_load() API
In reply to Andrii NakryikoSimilar to what we did for bpf_prog_load() in previous patch, wire returning of log_size_actual value from kernel back to the user through OPTS out field.
--- tools/lib/bpf/bpf.c | 6 ++++-- tools/lib/bpf/bpf.h | 11 +++++++++-- 2 files changed, 13 insertions(+), 4 deletions(-)
tools/lib/bpf/bpf.c +4 -2
@@ -1083,9 +1083,9 @@ int bpf_raw_tracepoint_open(const char *name, int prog_fd)return libbpf_err_errno (fd); } -int bpf_btf_load (const void *btf_data,size_t btf_size,const struct bpf_btf_load_opts *opts) +int bpf_btf_load (const void *btf_data,size_t btf_size,struct bpf_btf_load_opts *opts) { - const size_t attr_sz = offsetofend(union bpf_attr, btf_log_level); + const size_t attr_sz = offsetofend(union bpf_attr, btf_log_size_actual);union bpf_attr attr;char *log_buf;size_t log_size;
@@ -1128,6 +1128,8 @@ int bpf_btf_load(const void *btf_data, size_t btf_size, const struct bpf_btf_loa attr.btf_log_level =1 ; fd =sys_bpf_fd (BPF_BTF_LOAD , &attr, attr_sz); } + +OPTS_SET (opts, log_size_actual, attr.btf_log_size_actual);return libbpf_err_errno (fd); }
tools/lib/bpf/bpf.h +9 -2
@@ -124,11 +124,18 @@ struct bpf_btf_load_opts {char *log_buf;__u32 log_level;__u32 log_size; +/* output: actual total log contents size (including termintaing zero). +* It could be both larger than original log_size (if log was +* truncated), or smaller (if log buffer wasn't filled completely). +* If kernel doesn't support this feature, log_size is left unchanged. +*/ +__u32 log_size_actual; + size_t :0; }; -#define bpf_btf_load_opts__last_field log_size +#define bpf_btf_load_opts__last_field log_size_actual LIBBPF_API int bpf_btf_load(const void *btf_data, size_t btf_size, -const struct bpf_btf_load_opts *opts); +struct bpf_btf_load_opts *opts); LIBBPF_API int bpf_map_update_elem(int fd, const void *key, const void *value,__u64 flags);
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 17/19 selftests/bpf: add tests to validate log_size_actual feature
In reply to Andrii NakryikoAdd additional test cases validating that log_size_actual is consistent between fixed and rotating log modes, and that log_size_actual can be used *exactly* without causing -ENOSPC, while using just 1 byte shorter log buffer would cause -ENOSPC.
--- .../selftests/bpf/prog_tests/verifier_log.c | 92 +++++++++++++++---- 1 file changed, 76 insertions(+), 16 deletions(-)
tools/testing/selftests/bpf/prog_tests/verifier_log.c +76 -16
@@ -18,25 +18,41 @@ static bool check_prog_load(int prog_fd, bool expect_err, const char *tag)if (!ASSERT_GT (prog_fd,0 , tag))return false; } +if (prog_fd >=0 ) +close (prog_fd);return true; } +static struct { +/* strategically placed before others to avoid accidental modification by kernel */ +char filler[1024 ]; +char buf[1024 ]; +/* strategically placed after buf[] to catch more accidental corruptions */ +char reference[1024 ]; +} logs; +static const struct bpf_insn *insns; +static size_t insn_cnt; + +static int load_prog (struct bpf_prog_load_opts *opts,bool expect_load_error) +{ +int prog_fd; + + prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_prog" , +"GPL" , insns, insn_cnt, opts); +check_prog_load (prog_fd, expect_load_error,"prog_load" ); + +return prog_fd; +} +static void verif_log_subtest (const char *name,bool expect_load_error,int log_level) {LIBBPF_OPTS (bpf_prog_load_opts, opts); -struct { -/* strategically placed before others to avoid accidental modification by kernel */ -char filler[1024 ]; -char buf[1024 ]; -/* strategically placed after buf[] to catch more accidental corruptions */ -char reference[1024 ]; - } logs;char *exp_log, prog_name[16 ], op_name[32 ];struct test_log_buf *skel;struct bpf_program *prog; -const struct bpf_insn *insns; -size_t insn_cnt, fixed_log_sz; -int i, err, prog_fd; +size_t fixed_log_sz; +__u32 log_sz_actual_fixed, log_sz_actual_rolling; +int i, err, prog_fd, res; skel =test_log_buf__open ();if (!ASSERT_OK_PTR (skel,"skel_open" ))
@@ -61,11 +77,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ opts.log_buf = logs.reference; opts.log_size =sizeof (logs.reference); opts.log_level = log_level |8 /* BPF_LOG_FIXED */ ; - prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_fixed" , -"GPL" , insns, insn_cnt, &opts); -if (!check_prog_load (prog_fd, expect_load_error,"fixed_buf_prog_load" )) - goto cleanup; -close (prog_fd); +load_prog (&opts, expect_load_error); fixed_log_sz =strlen (logs.reference) +1 ;if (!ASSERT_GT (fixed_log_sz,50 ,"fixed_log_sz" ))
@@ -89,7 +101,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ opts.log_level = log_level |8 ;/* fixed-length log */ opts.log_size =25 ; - prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_fixed50" , + prog_fd =bpf_prog_load (BPF_PROG_TYPE_RAW_TRACEPOINT ,"log_fixed25" ,"GPL" , insns, insn_cnt, &opts);if (!ASSERT_EQ (prog_fd, -ENOSPC ,"unexpected_log_fixed_prog_load_result" )) {if (prog_fd >=0 )
@@ -147,6 +159,54 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ } } +/* (FIXED) get actual log size */ + opts.log_buf = logs.buf; + opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ + opts.log_size =sizeof (logs.buf); + res =load_prog (&opts, expect_load_error); +ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_fixed" ); + + log_sz_actual_fixed = opts.log_size_actual; +ASSERT_GT (log_sz_actual_fixed,0 ,"log_sz_actual_fixed" ); + +/* (ROLLING) get actual log size */ + opts.log_buf = logs.buf; + opts.log_level = log_level; + opts.log_size =sizeof (logs.buf); + res =load_prog (&opts, expect_load_error); +ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_rolling" ); + + log_sz_actual_rolling = opts.log_size_actual; +ASSERT_EQ (log_sz_actual_rolling, log_sz_actual_fixed,"log_sz_actual_eq" ); + +/* (FIXED) expect -ENOSPC for one byte short log */ + opts.log_buf = logs.buf; + opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ + opts.log_size = log_sz_actual_fixed -1 ; + res =load_prog (&opts, true/* should fail */ ); +ASSERT_EQ (res, -ENOSPC ,"prog_load_res_too_short_fixed" ); + +/* (FIXED) expect *not* -ENOSPC with exact log_size_actual buffer */ + opts.log_buf = logs.buf; + opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ + opts.log_size = log_sz_actual_fixed; + res =load_prog (&opts, expect_load_error); +ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_just_right_fixed" ); + +/* (ROLLING) expect -ENOSPC for one byte short log */ + opts.log_buf = logs.buf; + opts.log_level = log_level; + opts.log_size = log_sz_actual_rolling -1 ; + res =load_prog (&opts, true/* should fail */ ); +ASSERT_EQ (res, -ENOSPC ,"prog_load_res_too_short_rolling" ); + +/* (ROLLING) expect *not* -ENOSPC with exact log_size_actual buffer */ + opts.log_buf = logs.buf; + opts.log_level = log_level; + opts.log_size = log_sz_actual_rolling; + res =load_prog (&opts, expect_load_error); +ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_just_right_rolling" ); + cleanup:test_log_buf__destroy (skel); }
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 18/19 selftests/bpf: add testing of log_buf==NULL condition for BPF_PROG_LOAD
In reply to Andrii NakryikoAdd few extra test conditions to validate that it's ok to pass log_buf==NULL and log_size==0 to BPF_PROG_LOAD command with the intent to get log_size_actual without providing a buffer.
--- .../selftests/bpf/prog_tests/verifier_log.c | 25 +++++++++++++++++++ 1 file changed, 25 insertions(+)
tools/testing/selftests/bpf/prog_tests/verifier_log.c +25 -0
@@ -163,26 +163,49 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ opts.log_buf = logs.buf; opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ opts.log_size =sizeof (logs.buf); + opts.log_size_actual =0 ; res =load_prog (&opts, expect_load_error);ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_fixed" ); log_sz_actual_fixed = opts.log_size_actual;ASSERT_GT (log_sz_actual_fixed,0 ,"log_sz_actual_fixed" ); +/* (FIXED, NULL) get actual log size */ + opts.log_buf =NULL ; + opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ + opts.log_size =0 ; + opts.log_size_actual =0 ; + res =load_prog (&opts, true/* should fail */ ); +ASSERT_EQ (res, -ENOSPC ,"prog_load_res_fixed_null" ); +ASSERT_EQ (opts.log_size_actual, log_sz_actual_fixed,"log_sz_fixed_null_eq" ); +printf ("FIXED ACTUAL %u\n" , opts.log_size_actual); +/* (ROLLING) get actual log size */ opts.log_buf = logs.buf; opts.log_level = log_level; opts.log_size =sizeof (logs.buf); + opts.log_size_actual =0 ; res =load_prog (&opts, expect_load_error);ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_rolling" ); log_sz_actual_rolling = opts.log_size_actual;ASSERT_EQ (log_sz_actual_rolling, log_sz_actual_fixed,"log_sz_actual_eq" ); +/* (ROLLING, NULL) get actual log size */ + opts.log_buf =NULL ; + opts.log_level = log_level; + opts.log_size =0 ; + opts.log_size_actual =0 ; + res =load_prog (&opts, true/* should fail */ ); +ASSERT_EQ (res, -ENOSPC ,"prog_load_res_rolling_null" ); +ASSERT_EQ (opts.log_size_actual, log_sz_actual_rolling,"log_sz_actual_null_eq" ); +printf ("ROLLING ACTUAL %u\n" , opts.log_size_actual); +/* (FIXED) expect -ENOSPC for one byte short log */ opts.log_buf = logs.buf; opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ opts.log_size = log_sz_actual_fixed -1 ; + opts.log_size_actual =0 ; res =load_prog (&opts, true/* should fail */ );ASSERT_EQ (res, -ENOSPC ,"prog_load_res_too_short_fixed" );
@@ -190,6 +213,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ opts.log_buf = logs.buf; opts.log_level = log_level |8 ;/* BPF_LOG_FIXED */ opts.log_size = log_sz_actual_fixed; + opts.log_size_actual =0 ; res =load_prog (&opts, expect_load_error);ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_just_right_fixed" );
@@ -204,6 +228,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_ opts.log_buf = logs.buf; opts.log_level = log_level; opts.log_size = log_sz_actual_rolling; + opts.log_size_actual =0 ; res =load_prog (&opts, expect_load_error);ASSERT_NEQ (res, -ENOSPC ,"prog_load_res_just_right_rolling" );
Signature · 1 line
2.34.1
Andrii Nakryiko
maintainerPATCH v3 19/19 selftests/bpf: add verifier log tests for BPF_BTF_LOAD command
In reply to Andrii NakryikoAdd verifier log tests for BPF_BTF_LOAD command, which are very similar, conceptually, to BPF_PROG_LOAD tests. These are two separate commands dealing with verbose verifier log, so should be both tested separately.
--- .../selftests/bpf/prog_tests/verifier_log.c | 188 ++++++++++++++++++ 1 file changed, 188 insertions(+)
tools/testing/selftests/bpf/prog_tests/verifier_log.c +188 -0
@@ -236,6 +236,190 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_test_log_buf__destroy (skel); } +static const void *btf_data; +static u32 btf_data_sz; + +static int load_btf (struct bpf_btf_load_opts *opts,bool expect_err) +{ +int fd; + + fd =bpf_btf_load (btf_data, btf_data_sz, opts); +if (fd >=0 ) +close (fd); +if (expect_err) +ASSERT_LT (fd,0 ,"btf_load_failure" ); +else /* !expect_err */ +ASSERT_GT (fd,0 ,"btf_load_success" ); +return fd; +} + +static void verif_btf_log_subtest (bool bad_btf) +{ +LIBBPF_OPTS (bpf_btf_load_opts, opts); +struct btf *btf; +struct btf_type *t; +char *exp_log, op_name[32 ]; +size_t fixed_log_sz; +__u32 log_sz_actual_fixed, log_sz_actual_rolling; +int i, res; + +/* prepare simple BTF contents */ + btf =btf__new_empty (); +if (!ASSERT_OK_PTR (btf,"btf_new_empty" )) +return ; + res =btf__add_int (btf,"whatever" ,4 ,0 ); +if (!ASSERT_GT (res,0 ,"btf_add_int_id" )) + goto cleanup; +if (bad_btf) { +/* btf__add_int() doesn't allow bad value of size, so we'll just +* force-cast btf_type pointer and manually override size to invalid +* 3 if we need to simulate failure +*/ + t = (void *)btf__type_by_id (btf, res); +if (!ASSERT_OK_PTR (t,"int_btf_type" )) + goto cleanup; + t->size =3 ; + } + + btf_data =btf__raw_data (btf, &btf_data_sz); +if (!ASSERT_OK_PTR (btf_data,"btf_data" )) + goto cleanup; + +load_btf (&opts, bad_btf); + + opts.log_buf = logs.reference; + opts.log_size =sizeof (logs.reference); + opts.log_level =1 |8 /* BPF_LOG_FIXED */ ; +load_btf (&opts, bad_btf); + + fixed_log_sz =strlen (logs.reference) +1 ; +if (!ASSERT_GT (fixed_log_sz,50 ,"fixed_log_sz" )) + goto cleanup; +memset (logs.reference + fixed_log_sz,0 ,sizeof (logs.reference) - fixed_log_sz); + +/* validate BPF_LOG_FIXED truncation works as verifier log used to work */ + opts.log_buf = logs.buf; + opts.log_level =1 |8 ;/* fixed-length log */ + opts.log_size =25 ; + res =load_btf (&opts, true); +ASSERT_EQ (res, -ENOSPC ,"half_log_fd" ); +ASSERT_EQ (strlen (logs.buf),24 ,"log_fixed_25" ); +ASSERT_STRNEQ (logs.buf, logs.reference,24 , op_name); + +/* validate rolling verifier log logic: try all variations of log buf +* length to force various truncation scenarios +*/ + opts.log_buf = logs.buf; + opts.log_level =1 ;/* rolling log */ + +/* prefill logs.buf with 'A's to detect any write beyond allowed length */ +memset (logs.filler,'A' ,sizeof (logs.filler)); + logs.filler[sizeof (logs.filler) -1 ] ='\0' ; +memset (logs.buf,'A' ,sizeof (logs.buf)); + logs.buf[sizeof (logs.buf) -1 ] ='\0' ; + +for (i =1 ; i < fixed_log_sz; i++) { + opts.log_size = i; + +snprintf (op_name,sizeof (op_name),"log_roll_btf_load_%d" , i); + res =load_btf (&opts, true); +if (!ASSERT_EQ (res, -ENOSPC , op_name)) + goto cleanup; + + exp_log = logs.reference + fixed_log_sz - i; +snprintf (op_name,sizeof (op_name),"log_roll_contents_%d" , i); +if (!ASSERT_STREQ (logs.buf, exp_log, op_name)) { +printf ("CMP:%d\nS1:'%s'\nS2:'%s'\n" , +strcmp (logs.buf, exp_log), + logs.buf, exp_log); + goto cleanup; + } + +/* check that unused portions of logs.buf are not overwritten */ +snprintf (op_name,sizeof (op_name),"log_roll_unused_tail_%d" , i); +if (!ASSERT_STREQ (logs.buf + i, logs.filler + i, op_name)) { +printf ("CMP:%d\nS1:'%s'\nS2:'%s'\n" , +strcmp (logs.buf + i, logs.filler + i), + logs.buf + i, logs.filler + i); + goto cleanup; + } + } + +/* (FIXED) get actual log size */ + opts.log_buf = logs.buf; + opts.log_level =1 |8 ;/* BPF_LOG_FIXED */ + opts.log_size =sizeof (logs.buf); + opts.log_size_actual =0 ; + res =load_btf (&opts, bad_btf); +ASSERT_NEQ (res, -ENOSPC ,"btf_load_res_fixed" ); + + log_sz_actual_fixed = opts.log_size_actual; +ASSERT_GT (log_sz_actual_fixed,0 ,"log_sz_actual_fixed" ); + +/* (FIXED, NULL) get actual log size */ + opts.log_buf =NULL ; + opts.log_level =1 |8 ;/* BPF_LOG_FIXED */ + opts.log_size =0 ; + opts.log_size_actual =0 ; + res =load_btf (&opts, true); +ASSERT_EQ (res, -ENOSPC ,"btf_load_res_fixed_null" ); +ASSERT_EQ (opts.log_size_actual, log_sz_actual_fixed,"log_sz_fixed_null_eq" ); + +/* (ROLLING) get actual log size */ + opts.log_buf = logs.buf; + opts.log_level =1 ; + opts.log_size =sizeof (logs.buf); + opts.log_size_actual =0 ; + res =load_btf (&opts, bad_btf); +ASSERT_NEQ (res, -ENOSPC ,"btf_load_res_rolling" ); + + log_sz_actual_rolling = opts.log_size_actual; +ASSERT_EQ (log_sz_actual_rolling, log_sz_actual_fixed,"log_sz_actual_eq" ); + +/* (ROLLING, NULL) get actual log size */ + opts.log_buf =NULL ; + opts.log_level =1 ; + opts.log_size =0 ; + opts.log_size_actual =0 ; + res =load_btf (&opts, true); +ASSERT_EQ (res, -ENOSPC ,"btf_load_res_rolling_null" ); +ASSERT_EQ (opts.log_size_actual, log_sz_actual_rolling,"log_sz_actual_null_eq" ); + +/* (FIXED) expect -ENOSPC for one byte short log */ + opts.log_buf = logs.buf; + opts.log_level =1 |8 ;/* BPF_LOG_FIXED */ + opts.log_size = log_sz_actual_fixed -1 ; + opts.log_size_actual =0 ; + res =load_btf (&opts, true); +ASSERT_EQ (res, -ENOSPC ,"btf_load_res_too_short_fixed" ); + +/* (FIXED) expect *not* -ENOSPC with exact log_size_actual buffer */ + opts.log_buf = logs.buf; + opts.log_level =1 |8 ;/* BPF_LOG_FIXED */ + opts.log_size = log_sz_actual_fixed; + opts.log_size_actual =0 ; + res =load_btf (&opts, bad_btf); +ASSERT_NEQ (res, -ENOSPC ,"btf_load_res_just_right_fixed" ); + +/* (ROLLING) expect -ENOSPC for one byte short log */ + opts.log_buf = logs.buf; + opts.log_level =1 ; + opts.log_size = log_sz_actual_rolling -1 ; + res =load_btf (&opts, true); +ASSERT_EQ (res, -ENOSPC ,"btf_load_res_too_short_rolling" ); + +/* (ROLLING) expect *not* -ENOSPC with exact log_size_actual buffer */ + opts.log_buf = logs.buf; + opts.log_level =1 ; + opts.log_size = log_sz_actual_rolling; + opts.log_size_actual =0 ; + res =load_btf (&opts, bad_btf); +ASSERT_NEQ (res, -ENOSPC ,"btf_load_res_just_right_rolling" ); + +cleanup: +btf__free (btf); +} +void test_verifier_log (void ) {if (test__start_subtest ("good_prog-level1" ))
@@ -246,4 +430,8 @@ void test_verifier_log(void)verif_log_subtest ("bad_prog" , true,1 );if (test__start_subtest ("bad_prog-level2" ))verif_log_subtest ("bad_prog" , true,2 ); +if (test__start_subtest ("bad_btf" )) +verif_btf_log_subtest (true/* bad btf */ ); +if (test__start_subtest ("good_btf" )) +verif_btf_log_subtest (false/* !bad btf */ ); }
Signature · 1 line
2.34.1
Quoted 5 lines · Andrii Nakryiko
This turned into a pretty sizable patch set with lots of arithmetics, but hopefully the set of features added to verifier log in this patch set are both useful for BPF users and are self-contained and isolated enough to not cause troubles going forward.
Hi Andrii,
Thanks for pushing this forward, this will make all of the log handling so much nicer. Sorry it took a while to review, but it's quite a chunky series as you point out yourself :) Maybe it makes sense to pull out some of the acked bits (moving code around, etc.) into a separate patch set?
I'll send out individual reviews shortly, but wanted to put my my main proposal here. It's only compile tested, but it's hopefully clearer than my words. Note that I didn't fix up whitespace to make the diff smaller. It should apply on top of your branch.
From 162afa86d109954a4951d052513580849bd5cc54 Mon Sep 17 00:00:00 2001
From: Lorenz Bauer <[email protected]>
Date: Wed, 5 Apr 2023 18:24:42 +0100
Subject: [PATCH] bpf: simplify log nul termination and FIXED mode
--- kernel/bpf/log.c | 105 ++++++++++++++++++++++------------------------- 1 file changed, 50 insertions(+), 55 deletions(-)
kernel/bpf/log.c +0 -0
@@ -54,45 +54,13 @@ static void bpf_vlog_update_len_max(struct
bpf_verifier_log *log, u32 add_len)
log->len_max = len;
}
-void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,
- va_list args)
+static void bpf_vlog_emit(struct bpf_verifier_log *log, const char *kbuf, u32 n)
{
u64 cur_pos;- u32 new_n, n;
-
- n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
-
- WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
- "verifier log line truncated - local buffer too short\n");
-
- if (log->level == BPF_LOG_KERNEL) {
- bool newline = n > 0 && log->kbuf[n - 1] == '\n';
-
- pr_err("BPF: %s%s", log->kbuf, newline ? "" : "\n");
- return;
- }
-
- n += 1; /* include terminating zero */
- bpf_vlog_update_len_max(log, n);
-
- if (log->level & BPF_LOG_FIXED) {
- /* check if we have at least something to put into user buf */
- new_n = 0;
- if (log->end_pos + 1 < log->len_total) {
- new_n = min_t(u32, log->len_total - log->end_pos, n);
- log->kbuf[new_n - 1] = '\0';
- }
- cur_pos = log->end_pos;
- log->end_pos += n - 1; /* don't count terminating '\0' */-
- if (log->ubuf && new_n &&
- copy_to_user(log->ubuf + cur_pos, log->kbuf, new_n))
- goto fail;
- } else {
u64 new_end, new_start;
u32 buf_start, buf_end, new_n;- log->kbuf[n - 1] = '\0';
+ bpf_vlog_update_len_max(log, n);
new_end = log->end_pos + n;
if (new_end - log->start_pos >= log->len_total)
@@ -101,7 +69,7 @@ void bpf_verifier_vlog(struct bpf_verifier_log
*log, const char *fmt,
new_start = log->start_pos;
log->start_pos = new_start;- log->end_pos = new_end - 1; /* don't count terminating '\0' */
+ log->end_pos = new_end;
if (!log->ubuf)
return;
@@ -126,35 +94,60 @@ void bpf_verifier_vlog(struct bpf_verifier_log
*log, const char *fmt,
if (buf_start < buf_end) {
/* message fits within contiguous chunk of ubuf */
if (copy_to_user(log->ubuf + buf_start,
- log->kbuf + n - new_n,
+ kbuf + n - new_n,
buf_end - buf_start))
goto fail;
} else {
/* message wraps around the end of ubuf, copy in two chunks */
if (copy_to_user(log->ubuf + buf_start,
- log->kbuf + n - new_n,
+ kbuf + n - new_n,
log->len_total - buf_start))
goto fail;
if (copy_to_user(log->ubuf,
- log->kbuf + n - buf_end,
+ kbuf + n - buf_end,
buf_end))
goto fail;
}
- }
-
return;
fail:
log->ubuf = NULL;}
-void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos) +static u32 bpf_vlog_available(const struct bpf_verifier_log *log)
{
- char zero = 0; - u32 pos; + return log->len_total - (log->end_pos - log->start_pos);
+}
+
+void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,
+ va_list args)
+{
+ /* NB: contrary to vsnprintf n can't be larger than sizeof(log->kbuf) */
+ u32 n = vscnprintf(log->kbuf, sizeof(log->kbuf), fmt, args);
+
+ if (log->level == BPF_LOG_KERNEL) {
+ bool newline = n > 0 && log->kbuf[n - 1] == '\n';
+
+ pr_err("BPF: %s%s", log->kbuf, newline ? "" : "\n");
+ return;
+ }
+ if (log->level & BPF_LOG_FIXED) {
+ bpf_vlog_update_len_max(log, n); + /* avoid rotation by never emitting more than what's unused */ + n = min_t(u32, n, bpf_vlog_available(log));
+ }
+
+ bpf_vlog_emit(log, log->kbuf, n);
+}
+
+void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos)
+{
if (!bpf_verifier_log_needed(log) || log->level == BPF_LOG_KERNEL)
return;+ if (WARN_ON_ONCE(new_pos > log->end_pos))
+ return;
+
/* if position to which we reset is beyond current log window,
* then we didn't preserve any useful content and should adjust
* start_pos to end up with an empty log (start_pos == end_pos)
@@ -162,17 +155,6 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos)
log->end_pos = new_pos;
if (log->end_pos < log->start_pos)
log->start_pos = log->end_pos;-
- if (!log->ubuf)
- return;
-
- if (log->level & BPF_LOG_FIXED)
- pos = log->end_pos + 1;
- else
- div_u64_rem(new_pos, log->len_total, &pos);
-
- if (pos < log->len_total && put_user(zero, log->ubuf + pos))
- log->ubuf = NULL;
}
static void bpf_vlog_reverse_kbuf(char *buf, int len)
@@ -228,6 +210,7 @@ static bool bpf_vlog_truncated(const struct bpf_verifier_log *log)
int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) {
+ char zero = 0;
u32 sublen;
int err;@@ -237,8 +220,20 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual)
if (!log->ubuf)
goto skip_log_rotate;+
+ if (log->level & BPF_LOG_FIXED) {
+ bpf_vlog_update_len_max(log, 1);
+
+ /* terminate by (potentially) overwriting the last byte */
+ if (put_user(zero, log->ubuf + min_t(u32, log->end_pos,
log->len_total-1))
+ return -EFAULT;
+ } else {
+ /* terminate by (potentially) rotating out the first byte */
+ bpf_vlog_emit(log, &zero, 1);
+ }
+
/* If we never truncated log, there is nothing to move around. */
- if ((log->level & BPF_LOG_FIXED) || log->start_pos == 0)
+ if (log->start_pos == 0)
goto skip_log_rotate;
/* Otherwise we need to rotate log contents to make it start from theSignature · 1 line
2.39.2
Quoted 26 lines · Lorenz Bauer
Quoted 5 lines · Andrii Nakryiko
This turned into a pretty sizable patch set with lots of arithmetics, but hopefully the set of features added to verifier log in this patch set are both useful for BPF users and are self-contained and isolated enough to not cause troubles going forward.
Hi Andrii,
Thanks for pushing this forward, this will make all of the log handling so much nicer. Sorry it took a while to review, but it's quite a chunky series as you point out yourself :) Maybe it makes sense to pull out some of the acked bits (moving code around, etc.) into a separate patch set?
I'll send out individual reviews shortly, but wanted to put my my main proposal here. It's only compile tested, but it's hopefully clearer than my words. Note that I didn't fix up whitespace to make the diff smaller. It should apply on top of your branch.
From
162afa86d109954a4951d052513580849bd5cc54Mon Sep 17 00:00:00 2001
From: Lorenz Bauer <[email protected]>
Date: Wed, 5 Apr 2023 18:24:42 +0100
Subject: [PATCH] bpf: simplify log nul termination and FIXED mode
Quoted 4 lines
Signed-off-by Lorenz Bauer <[email protected]>--- kernel/bpf/log.c | 105 ++++++++++++++++++++++------------------------- 1 file changed, 50 insertions(+), 55 deletions(-)
Thanks for the code, I do understand your idea much better now. Basically, you are saying to tread FIXED as a partial case of rotating by adjusting N to never go beyond the end of the buffer. While I do find explicit FIXED code path in bpf_verifier_log() a bit easier to reason about, I can see this as a conceptual simplification, yep. The finalization/zero termination is still special-cased for fixed vs rotating.
I still fail to see how zero termination every single time is complicating everything, and even with your implementation we can support this easily with no more code (just kbuf[n - 1] = 0; before we delegate to bpf_vlog_emit()).
So all in all, looking at stats, I don't really see a big simplification. On the other hand, I spent a considerable time thinking, debugging, and testing my existing implementation thoroughly. Then there is also interaction with log_buf==NULL && log_size==0 case, I'd need to re-analyze everything again.
How strong do you feel the need for me to redo this tricky part to save a few lines of C code (and lose easy debuggability at least of kbuf contents)? I'm a bit on the fence. I noted a few things I would add (or remove) even to existing code and I'll apply that. But unless someone comes out and says "let's do it this way", I'd rather not waste half a day on debugging some random off-by-one error again.
Quoted 29 lines
kernel/bpf/log.c +1
-15@@ -54,45 +54,13 @@ static void bpf_vlog_update_len_max(struct bpf_verifier_log *log, u32 add_len) log->len_max = len; } -void bpf_verifier_vlog (struct bpf_verifier_log *log,const char *fmt, - va_list args) +static void bpf_vlog_emit (struct bpf_verifier_log *log,const char *kbuf,u32 n) {u64 cur_pos; -u32 new_n, n; - - n =vscnprintf (log->kbuf,BPF_VERIFIER_TMP_LOG_SIZE , fmt, args); - -WARN_ONCE (n >=BPF_VERIFIER_TMP_LOG_SIZE -1 , -"verifier log line truncated - local buffer too short\n" ); - -if (log->level ==BPF_LOG_KERNEL ) { -bool newline = n >0 && log->kbuf[n -1 ] =='\n' ; - -pr_err ("BPF: %s%s" , log->kbuf, newline ?"" :"\n" ); -return ; - }
kernel/bpf/log.c static void bpf_vlog_update_len_max(struct · line 85
Quoted 10 lines
kernel/bpf/log.c +0
-10- - n +=1 ;/* include terminating zero */ -bpf_vlog_update_len_max (log, n); - -if (log->level &BPF_LOG_FIXED ) { -/* check if we have at least something to put into user buf */ - new_n =0 ; -if (log->end_pos +1 < log->len_total) { - new_n =min_t (u32, log->len_total - log->end_pos, n); - log->kbuf[new_n -1 ] ='\0' ;
without this part I can't debug what kernel is actually emitting into user-space with a simple printk()...
kernel/bpf/log.c static void bpf_vlog_update_len_max(struct · line 97
Quoted 12 lines
kernel/bpf/log.c +0
-9- } - cur_pos = log->end_pos; - log->end_pos += n -1 ;/* don't count terminating '\0' */ - -if (log->ubuf && new_n && -copy_to_user (log->ubuf + cur_pos, log->kbuf, new_n)) - goto fail; - }else {u64 new_end, new_start;u32 buf_start, buf_end, new_n; - log->kbuf[n -1 ] ='\0' ;
realized we don't really need this zero-termination for rotating case, will drop it
Quoted 45 lines
kernel/bpf/log.c +1
-0+bpf_vlog_update_len_max (log, n);new_end = log->end_pos + n; if (new_end - log->start_pos >= log->len_total)kernel/bpf/log.c +1
-1@@ -101,7 +69,7 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, new_start = log->start_pos; log->start_pos = new_start; - log->end_pos = new_end -1 ;/* don't count terminating '\0' */ + log->end_pos = new_end;if (!log->ubuf)return;kernel/bpf/log.c +4
-6@@ -126,35 +94,60 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, if (buf_start < buf_end) {/* message fits within contiguous chunk of ubuf */ if (copy_to_user (log->ubuf + buf_start, - log->kbuf + n - new_n, + kbuf + n - new_n, buf_end - buf_start)) goto fail; } else {/* message wraps around the end of ubuf, copy in two chunks */ if (copy_to_user (log->ubuf + buf_start, - log->kbuf + n - new_n, + kbuf + n - new_n, log->len_total - buf_start)) goto fail;if (copy_to_user (log->ubuf, - log->kbuf + n - buf_end, + kbuf + n - buf_end, buf_end)) goto fail; } - } -return ; fail: log->ubuf =NULL ; } -void bpf_vlog_reset (struct bpf_verifier_log *log,u64 new_pos) +static u32 bpf_vlog_available (const struct bpf_verifier_log *log)
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log · line 125
Quoted 10 lines
kernel/bpf/log.c +7
-2{ -char zero =0 ; -u32 pos; +return log->len_total - (log->end_pos - log->start_pos); +} + +void bpf_verifier_vlog (struct bpf_verifier_log *log,const char *fmt, +va_list args) +{ +/* NB: contrary to vsnprintf n can't be larger than sizeof(log->kbuf) */
it can't be even equal to sizeof(log->kbuf)
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log · line 136
Quoted 11 lines
kernel/bpf/log.c +10
-0+u32 n =vscnprintf (log->kbuf,sizeof (log->kbuf), fmt, args); + +if (log->level ==BPF_LOG_KERNEL ) { +bool newline = n >0 && log->kbuf[n -1 ] =='\n' ; + +pr_err ("BPF: %s%s" , log->kbuf, newline ?"" :"\n" ); +return ; + } +if (log->level &BPF_LOG_FIXED ) { +bpf_vlog_update_len_max (log, n);
this made me pause for a second to prove we are not double-accounting something. We don't, but I find the argument of a simplification a bit weaker due to this :)
Quoted 4 lines
kernel/bpf/log.c +4
-0+/* avoid rotation by never emitting more than what's unused */ + n =min_t (u32, n,bpf_vlog_available (log)); + } +
kernel/bpf/log.c void bpf_verifier_vlog(struct bpf_verifier_log · line 150
Quoted 10 lines
kernel/bpf/log.c +7
-0+bpf_vlog_emit (log, log->kbuf, n); +} + +void bpf_vlog_reset (struct bpf_verifier_log *log,u64 new_pos) +{if (!bpf_verifier_log_needed (log) || log->level ==BPF_LOG_KERNEL )return ; +if (WARN_ON_ONCE (new_pos > log->end_pos)) +return ;
will add this warn, good point
Quoted 10 lines
kernel/bpf/log.c +1
-0+/* if position to which we reset is beyond current log window, * then we didn't preserve any useful content and should adjust *
start_posto end up with an empty log (start_pos==end_pos)kernel/bpf/log.c +0
-1@@ -162,17 +155,6 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos) log->end_pos = new_pos;if (log->end_pos < log->start_pos) log->start_pos = log->end_pos; -
kernel/bpf/log.c void bpf_vlog_reset(struct bpf_verifier_log *log, · line 176
Quoted 10 lines
kernel/bpf/log.c +0
-10-if (!log->ubuf) -return ; - -if (log->level &BPF_LOG_FIXED ) - pos = log->end_pos +1 ; -else -div_u64_rem (new_pos, log->len_total, &pos); - -if (pos < log->len_total &&put_user (zero, log->ubuf + pos)) - log->ubuf =NULL ;
equivalent to what you do in vlog_finalize, right?
Quoted 19 lines
kernel/bpf/log.c +0
-0}static void
bpf_vlog_reverse_kbuf(char *buf, int len)kernel/bpf/log.c +3
-0@@ -228,6 +210,7 @@ static bool bpf_vlog_truncated(const struct bpf_verifier_log *log)int bpf_vlog_finalize (struct bpf_verifier_log *log,u32 *log_size_actual) { +char zero =0 ;u32 sublen;int err;@@ -237,8 +220,20 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual)if (!log->ubuf) goto skip_log_rotate; + +if (log->level &BPF_LOG_FIXED ) {
kernel/bpf/log.c int bpf_vlog_finalize(struct bpf_verifier_log · line 235
Quoted 10 lines
kernel/bpf/log.c +9
-0+bpf_vlog_update_len_max (log,1 ); + +/* terminate by (potentially) overwriting the last byte */ +if (put_user (zero, log->ubuf +min_t (u32, log->end_pos, log->len_total-1)) +return -EFAULT ; + }else { +/* terminate by (potentially) rotating out the first byte */ +bpf_vlog_emit (log, &zero,1 ); + }
not a big fan of this part where we still do two separate handlings for two modes
kernel/bpf/log.c int bpf_vlog_finalize(struct bpf_verifier_log · line 238
Quoted 4 lines
kernel/bpf/log.c +2
-1+/* If we never truncated log, there is nothing to move around. */ -if ((log->level &BPF_LOG_FIXED ) || log->start_pos ==0 ) +if (log->start_pos ==0 )
yep, BPF_LOG_FIXED implied start_pos == 0, unnecessary check
Quoted 5 lines
kernel/bpf/log.c +0
-0goto skip_log_rotate;/* Otherwise we need to rotate log contents to make it start from the--
2.39.2
Quoted 6 lines · Andrii Nakryiko
So all in all, looking at stats, I don't really see a big simplification. On the other hand, I spent a considerable time thinking, debugging, and testing my existing implementation thoroughly. Then there is also interaction with log_buf==NULL && log_size==0 case, I'd need to re-analyze everything again.
Quoted 6 lines
How strong do you feel the need for me to redo this tricky part to save a few lines of C code (and lose easy debuggability at least of kbuf contents)? I'm a bit on the fence. I noted a few things I would add (or remove) even to existing code and I'll apply that. But unless someone comes out and says "let's do it this way", I'd rather not waste half a day on debugging some random off-by-one error again.
Well, what are you optimising for? Is it getting the code in or is it ease of understanding for future readers (including you in a year or so?)
Feel free to submit it as it is, maybe I can trim down my solution some more to get rid of some more special cases ;)
Quoted 5 lines
Review
Quoted 2 lines
(quoted diff) +0
-2- new_n = min_t(u32, log->len_total - log->end_pos, n); - log->kbuf[new_n - 1] = '\0';without this part I can't debug what kernel is actually emitting into user-space with a simple
printk()...
As I just learned, vscnprintf always null terminates so log->kbuf can always be printed?
Quoted 6 lines
Review
Quoted 4 lines
(quoted diff) +4
-0+void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, + va_list args) +{ + /* NB: contrary to vsnprintf n can't be larger than sizeof(log->kbuf) */it can't be even equal to
sizeof(log->kbuf)
Yes... C string functions are the worst.
Quoted 10 lines
Quoted 10 lines
(quoted diff) +8
-0+ u32 n = vscnprintf(log->kbuf, sizeof(log->kbuf), fmt, args); + + if (log->level == BPF_LOG_KERNEL) { + bool newline = n > 0 && log->kbuf[n - 1] == '\n'; + + pr_err("BPF: %s%s", log->kbuf, newline ? "" : "\n"); + return; + }
Quoted 6 lines
Review
Quoted 2 lines
(quoted diff) +2
-0+ if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, n);this made me pause for a second to prove we are not double-accounting something. We don't, but I find the argument of a simplification a bit weaker due to this :)
Yeah. I found a way to get rid of this, I might submit that as a follow up.
Quoted 9 lines
Review
Quoted 7 lines
(quoted diff) +0
-7- if (log->level & BPF_LOG_FIXED) - pos = log->end_pos + 1; - else - div_u64_rem(new_pos, log->len_total, &pos); - - if (pos < log->len_total && put_user(zero, log->ubuf + pos)) - log->ubuf = NULL;equivalent to what you do in
vlog_finalize, right?
Yep
Quoted 12 lines
Quoted 12 lines
(quoted diff) +6
-0@@ -237,8 +220,20 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) if (!log->ubuf) goto skip_log_rotate; + + if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, 1); + + /* terminate by (potentially) overwriting the last byte */ + if (put_user(zero, log->ubuf + min_t(u32, log->end_pos, log->len_total-1))
Quoted 8 lines
Review int bpf_vlog_finalize(struct bpf_verifier_log · line 235
Quoted 5 lines
(quoted diff) +5
-0+ return -EFAULT; + } else { + /* terminate by (potentially) rotating out the first byte */ + bpf_vlog_emit(log, &zero, 1); + }not a big fan of this part where we still do two separate handlings for two modes
Agreed, but I'm not sure it can be avoided at all since we need to clamp different parts of the buffer depending on which mode we are in.
Quoted 17 lines · Lorenz Bauer
Quoted 6 lines · Andrii Nakryiko
So all in all, looking at stats, I don't really see a big simplification. On the other hand, I spent a considerable time thinking, debugging, and testing my existing implementation thoroughly. Then there is also interaction with log_buf==NULL && log_size==0 case, I'd need to re-analyze everything again.
Quoted 6 lines
How strong do you feel the need for me to redo this tricky part to save a few lines of C code (and lose easy debuggability at least of kbuf contents)? I'm a bit on the fence. I noted a few things I would add (or remove) even to existing code and I'll apply that. But unless someone comes out and says "let's do it this way", I'd rather not waste half a day on debugging some random off-by-one error again.
Quoted 3 lines
Well, what are you optimising for? Is it getting the code in or is it ease of understanding for future readers (including you in a year or so?)
I'm just saying that ease of understanding is subjective. So given I'm not convinced that your approach is simpler, I'd avoid unnecessary extra changes to the code that I've spent a lot of time testing and debugging and am pretty confident about.
The point of code review is not to satisfy every nit, but to see if there are problems with the proposed solution and if something can be done better. Not *different*, but *better*.
One of the things I wanted to hear feedback on was if the overall UAPI behavior makes sense. You had concerns about enabling rotating log mode by default, which I believe are addressed by returning -ENOSPC. Can you please confirm that this approach is acceptable now? Thanks!
Quoted 4 lines
Feel free to submit it as it is, maybe I can trim down my solution some more to get rid of some more special cases ;)
Quoted 8 lines
Quoted 5 lines
Review
Quoted 2 lines
(quoted diff) +0
-2- new_n = min_t(u32, log->len_total - log->end_pos, n); - log->kbuf[new_n - 1] = '\0';without this part I can't debug what kernel is actually emitting into user-space with a simple
printk()...As I just learned, vscnprintf always null terminates so
log->kbufcan always be printed?
aren't we adjusting n in this branch and would need to zero-terminate anew? Yes we can safely print it, it just won't be the contents we are putting into the user buffer.
Quoted 64 lines
Quoted 7 lines
Review
Quoted 5 lines
(quoted diff) +4
-0+void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, + va_list args) +{ + /* NB: contrary to vsnprintf n can't be larger than sizeof(log->kbuf) */it can't be even equal to
sizeof(log->kbuf)Yes... C string functions are the worst.
Quoted 10 lines
Quoted 10 lines
(quoted diff) +8
-0+ u32 n = vscnprintf(log->kbuf, sizeof(log->kbuf), fmt, args); + + if (log->level == BPF_LOG_KERNEL) { + bool newline = n > 0 && log->kbuf[n - 1] == '\n'; + + pr_err("BPF: %s%s", log->kbuf, newline ? "" : "\n"); + return; + }Quoted 6 lines
Review
Quoted 2 lines
(quoted diff) +2
-0+ if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, n);this made me pause for a second to prove we are not double-accounting something. We don't, but I find the argument of a simplification a bit weaker due to this :)
Yeah. I found a way to get rid of this, I might submit that as a follow up.
Quoted 9 lines
Review
Quoted 7 lines
(quoted diff) +0
-7- if (log->level & BPF_LOG_FIXED) - pos = log->end_pos + 1; - else - div_u64_rem(new_pos, log->len_total, &pos); - - if (pos < log->len_total && put_user(zero, log->ubuf + pos)) - log->ubuf = NULL;equivalent to what you do in
vlog_finalize, right?Yep
Quoted 12 lines
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(quoted diff) +6
-0@@ -237,8 +220,20 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) if (!log->ubuf) goto skip_log_rotate; + + if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, 1); + + /* terminate by (potentially) overwriting the last byte */ + if (put_user(zero, log->ubuf + min_t(u32, log->end_pos, log->len_total-1))Quoted 8 lines
Review int bpf_vlog_finalize(struct bpf_verifier_log · line 235
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-0+ return -EFAULT; + } else { + /* terminate by (potentially) rotating out the first byte */ + bpf_vlog_emit(log, &zero, 1); + }not a big fan of this part where we still do two separate handlings for two modes
Agreed, but I'm not sure it can be avoided at all since we need to clamp different parts of the buffer depending on which mode we are in.
Quoted 23 lines · Andrii Nakryiko
Quoted 17 lines · Lorenz Bauer
Quoted 6 lines · Andrii Nakryiko
So all in all, looking at stats, I don't really see a big simplification. On the other hand, I spent a considerable time thinking, debugging, and testing my existing implementation thoroughly. Then there is also interaction with log_buf==NULL && log_size==0 case, I'd need to re-analyze everything again.
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How strong do you feel the need for me to redo this tricky part to save a few lines of C code (and lose easy debuggability at least of kbuf contents)? I'm a bit on the fence. I noted a few things I would add (or remove) even to existing code and I'll apply that. But unless someone comes out and says "let's do it this way", I'd rather not waste half a day on debugging some random off-by-one error again.
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Well, what are you optimising for? Is it getting the code in or is it ease of understanding for future readers (including you in a year or so?)
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I'm just saying that ease of understanding is subjective. So given I'm not convinced that your approach is simpler, I'd avoid unnecessary extra changes to the code that I've spent a lot of time testing and debugging and am pretty confident about.
The point of code review is not to satisfy every nit, but to see if there are problems with the proposed solution and if something can be done better. Not *different*, but *better*.
So, I did an honest attempt to implement the idea of BPF_LOG_FIXED being just a partial case of rotating mode by just adjusting N. And this breaks down once we start calculating len_max and using log->end_pos as logical position that can go beyond log->len_total. I had to abandon this idea, sorry. As I mentioned before, interactions with log_size==0 are not obvious and straightforward.
I did more testing, though, verifying fixed mode truncation. That actually caught a corner case when len_total = 1, in which case buffer wasn't zero-terminated. So at least that's the payoff. :)
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One of the things I wanted to hear feedback on was if the overall UAPI behavior makes sense. You had concerns about enabling rotating log mode by default, which I believe are addressed by returning
-ENOSPC. Can you please confirm that this approach is acceptable now? Thanks!Quoted 4 lines
Feel free to submit it as it is, maybe I can trim down my solution some more to get rid of some more special cases ;)
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-2- new_n = min_t(u32, log->len_total - log->end_pos, n); - log->kbuf[new_n - 1] = '\0';without this part I can't debug what kernel is actually emitting into user-space with a simple
printk()...As I just learned, vscnprintf always null terminates so
log->kbufcan always be printed?aren't we adjusting n in this branch and would need to zero-terminate anew? Yes we can safely print it, it just won't be the contents we are putting into the user buffer.
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-0+void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, + va_list args) +{ + /* NB: contrary to vsnprintf n can't be larger than sizeof(log->kbuf) */it can't be even equal to
sizeof(log->kbuf)Yes... C string functions are the worst.
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-0+ u32 n = vscnprintf(log->kbuf, sizeof(log->kbuf), fmt, args); + + if (log->level == BPF_LOG_KERNEL) { + bool newline = n > 0 && log->kbuf[n - 1] == '\n'; + + pr_err("BPF: %s%s", log->kbuf, newline ? "" : "\n"); + return; + }Quoted 6 lines
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-0+ if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, n);this made me pause for a second to prove we are not double-accounting something. We don't, but I find the argument of a simplification a bit weaker due to this :)
Yeah. I found a way to get rid of this, I might submit that as a follow up.
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-7- if (log->level & BPF_LOG_FIXED) - pos = log->end_pos + 1; - else - div_u64_rem(new_pos, log->len_total, &pos); - - if (pos < log->len_total && put_user(zero, log->ubuf + pos)) - log->ubuf = NULL;equivalent to what you do in
vlog_finalize, right?Yep
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-0@@ -237,8 +220,20 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) if (!log->ubuf) goto skip_log_rotate; + + if (log->level & BPF_LOG_FIXED) { + bpf_vlog_update_len_max(log, 1); + + /* terminate by (potentially) overwriting the last byte */ + if (put_user(zero, log->ubuf + min_t(u32, log->end_pos, log->len_total-1))Quoted 8 lines
Review int bpf_vlog_finalize(struct bpf_verifier_log · line 235
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-0+ return -EFAULT; + } else { + /* terminate by (potentially) rotating out the first byte */ + bpf_vlog_emit(log, &zero, 1); + }not a big fan of this part where we still do two separate handlings for two modes
Agreed, but I'm not sure it can be avoided at all since we need to clamp different parts of the buffer depending on which mode we are in.