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bpf, libbpf: introduce bpf_object__probe_caps to test BPF capabilities

PATCH In review Stanislav Fomichev 2 participants 4 messages Nov 21, 2018 – Nov 22, 2018

Subsystems (4)
Networking Network drivers BPF libbpf
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Stanislav Fomichev

author
#0 lore raw

PATCH v3 1/3 bpf, libbpf: introduce bpf_object__probe_caps to test BPF capabilities

It currently only checks whether kernel supports map/prog names. This capability check will be used in the next two commits to skip setting prog/map names.

Suggested-by Daniel Borkmann <[email protected]>
Signed-off-by Stanislav Fomichev <[email protected]>
---
 tools/lib/bpf/libbpf.c | 58 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
tools/lib/bpf/libbpf.c +58 -0
index cb6565d79603..3f7f476d8751 100644
@@ -24,6 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/bpf.h>
 #include <linux/btf.h>
+#include <linux/filter.h>
 #include <linux/list.h>
 #include <linux/limits.h>
 #include <linux/perf_event.h>

@@ -114,6 +115,11 @@ void libbpf_set_print(libbpf_print_fn_t warn,
 # define LIBBPF_ELF_C_READ_MMAP ELF_C_READ
 #endif
 
+struct bpf_capabilities {
+	/* v4.14: kernel support for program & map names. */
+	__u32 name:1;
+};
+
 /*
  * bpf_prog should be a better name but it has been used in
  * linux/filter.h.

@@ -160,6 +166,8 @@ struct bpf_program {
 	void *func_info;
 	__u32 func_info_rec_size;
 	__u32 func_info_len;
+
+	struct bpf_capabilities *caps;
 };
 
 struct bpf_map {

@@ -221,6 +229,8 @@ struct bpf_object {
 	void *priv;
 	bpf_object_clear_priv_t clear_priv;
 
+	struct bpf_capabilities caps;
+
 	char path[];
 };
 #define obj_elf_valid(o)	((o)->efile.elf)

@@ -342,6 +352,7 @@ bpf_object__add_program(struct bpf_object *obj, void *data, size_t size,
 	if (err)
 		return err;
 
+	prog.caps = &obj->caps;
 	progs = obj->programs;
 	nr_progs = obj->nr_programs;
 

@@ -1135,6 +1146,52 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 	return -errno;
 }
 
+static int
+bpf_object__probe_name(struct bpf_object *obj)
+{
+	struct bpf_load_program_attr attr;
+	char *cp, errmsg[STRERR_BUFSIZE];
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int ret;
+
+	/* make sure basic loading works */
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+	attr.insns = insns;
+	attr.insns_cnt = ARRAY_SIZE(insns);
+	attr.license = "GPL";
+
+	ret = bpf_load_program_xattr(&attr, NULL, 0);
+	if (ret < 0) {
+		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		pr_warning("Error in %s():%s(%d). Couldn't load basic 'r0 = 0' BPF program.\n",
+			   __func__, cp, errno);
+		return -errno;
+	}
+	close(ret);
+
+	/* now try the same program, but with the name */
+
+	attr.name = "test";
+	ret = bpf_load_program_xattr(&attr, NULL, 0);
+	if (ret >= 0) {
+		obj->caps.name = 1;
+		close(ret);
+	}
+
+	return 0;
+}
+
+static int
+bpf_object__probe_caps(struct bpf_object *obj)
+{
+	return bpf_object__probe_name(obj);
+}
+
 static int
 bpf_object__create_maps(struct bpf_object *obj)
 {

@@ -1708,6 +1765,7 @@ int bpf_object__load(struct bpf_object *obj)
 
 	obj->loaded = true;
 
+	CHECK_ERR(bpf_object__probe_caps(obj), err, out);
 	CHECK_ERR(bpf_object__create_maps(obj), err, out);
 	CHECK_ERR(bpf_object__relocate(obj), err, out);
 	CHECK_ERR(bpf_object__load_progs(obj), err, out);
Signature · 1 line
2.19.1.1215.g8438c0b245-goog
author
#1 lore raw

PATCH v3 2/3 bpf: libbpf: remove map name retry from bpf_create_map_xattr

Instead, check for a newly created caps.name bpf_object capability. If kernel doesn't support names, don't specify the attribute.

See commit 23499442c319 ("bpf: libbpf: retry map creation without the name") for rationale.

Signed-off-by Stanislav Fomichev <[email protected]>
---
 tools/lib/bpf/bpf.c    | 11 +----------
 tools/lib/bpf/libbpf.c |  3 ++-
 2 files changed, 3 insertions(+), 11 deletions(-)
tools/lib/bpf/bpf.c +1 -10
index 836447bb4f14..ce1822194590 100644
@@ -69,7 +69,6 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 {
 	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
 	union bpf_attr attr;
-	int ret;
 
 	memset(&attr, '\0', sizeof(attr));
 

@@ -87,15 +86,7 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 	attr.map_ifindex = create_attr->map_ifindex;
 	attr.inner_map_fd = create_attr->inner_map_fd;
 
-	ret = sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
-	if (ret < 0 && errno == EINVAL && create_attr->name) {
-		/* Retry the same syscall, but without the name.
-		 * Pre v4.14 kernels don't support map names.
-		 */
-		memset(attr.map_name, 0, sizeof(attr.map_name));
-		return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
-	}
-	return ret;
+	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
 }
 
 int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
tools/lib/bpf/libbpf.c +2 -1
index 3f7f476d8751..bf45f285d0a0 100644
@@ -1211,7 +1211,8 @@ bpf_object__create_maps(struct bpf_object *obj)
 			continue;
 		}
 
-		create_attr.name = map->name;
+		if (obj->caps.name)
+			create_attr.name = map->name;
 		create_attr.map_ifindex = map->map_ifindex;
 		create_attr.map_type = def->type;
 		create_attr.map_flags = def->map_flags;
Signature · 1 line
2.19.1.1215.g8438c0b245-goog
author
#2 lore raw

PATCH v3 3/3 bpf: libbpf: don't specify prog name if kernel doesn't support it

In reply to Stanislav Fomichev

Use recently added capability check.

See commit 23499442c319 ("bpf: libbpf: retry map creation without the name") for rationale.

Signed-off-by Stanislav Fomichev <[email protected]>
---
 tools/lib/bpf/libbpf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
tools/lib/bpf/libbpf.c +2 -1
index bf45f285d0a0..a080aeff7e2e 100644
@@ -1439,7 +1439,8 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 	memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
 	load_attr.prog_type = prog->type;
 	load_attr.expected_attach_type = prog->expected_attach_type;
-	load_attr.name = prog->name;
+	if (prog->caps->name)
+		load_attr.name = prog->name;
 	load_attr.insns = insns;
 	load_attr.insns_cnt = insns_cnt;
 	load_attr.license = license;
Signature · 1 line
2.19.1.1215.g8438c0b245-goog