Add k/uprobe & fentry & error_injection supported

From: Guo Ren <[email protected]>

This the 5th round of riscv k/uprobe support patchset, it's based on linux-5.10 and you can test it with the repo:

https://github.com/c-sky/csky-linux/tree/linux-5.10-probe-dev

The important fixup is about the trampoline call site, we change the prologue of the function call site from:

    <funca>:
        nop -> addi sp, sp, -SZREG
        nop -> REG_S ra, (sp)
        nop -> auipc ra, 0x?
        nop -> jalr ?(ra)
        nop -> REG_L ra, (sp)
        nop -> addi sp, sp, -SZREG
        ...

to:

    <funca>:
        nop -> REG_S ra, -SZREG(sp)
        nop -> auipc ra, 0x?
        nop -> jalr ?(ra)
        nop -> REG_L ra, -SZREG(sp)
        ...

It's wrong to change the sp in callsite, because when you change the value of ra then the sp is broken and the same with HAVE_OPTPROBES.

The patchset includes kprobe/uprobe support and some related fixups. Patrick provides HAVE_REGS_AND_STACK_ACCESS_API support and some kprobe's code. The framework of k/uprobe is from csky but also refers to other arches'. kprobes on ftrace is also supported in the patchset. Modify dynamic ftrace mechanism from mcount to fentry.

There is no single step exception in riscv ISA, only single-step facility for jtag. See riscv-Privileged spec:

Interrupt Exception Code-Description
1 0 Reserved
1 1 Supervisor software interrupt
1 2–4 Reserved
1 5 Supervisor timer interrupt
1 6–8 Reserved
1 9 Supervisor external interrupt
1 10–15 Reserved
1 ≥16 Available for platform use
0 0 Instruction address misaligned
0 1 Instruction access fault
0 2 Illegal instruction
0 3 Breakpoint
0 4 Load address misaligned
0 5 Load access fault
0 6 Store/AMO address misaligned
0 7 Store/AMO access fault
0 8 Environment call from U-mode
0 9 Environment call from S-mode
0 10–11 Reserved
0 12 Instruction page fault
0 13 Load page fault
0 14 Reserved
0 15 Store/AMO page fault
0 16–23 Reserved
0 24–31 Available for custom use
0 32–47 Reserved
0 48–63 Available for custom use
0 ≥64 Reserved

No single step!

Other arches use hardware single-step exception for k/uprobe, eg:
- powerpc: regs->msr |= MSR_SINGLESTEP
- arm/arm64: PSTATE.D for enabling software step exceptions
- s390: Set PER control regs, turns on single step for the given address
- x86: regs->flags |= X86_EFLAGS_TF
- csky: of course use hw single step :)

All the above arches use a hardware single-step exception mechanism to execute the instruction that was replaced with a probe breakpoint. So utilize ebreak to simulate.

Some pc related instructions couldn't be executed out of line and some system/fence instructions couldn't be a trace site at all. So we give out a reject list and simulate list in decode-insn.c.

You could use uprobe to test simulate code like this:

echo 'p:enter_current_state_one /hello:0x6e4 a0=%a0 a1=%a1' >> /sys/kernel/debug/tracing/uprobe_events echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable
/hello
^C
cat /sys/kernel/debug/tracing/trace
tracer: nop

entries-in-buffer/entries-written: 1/1 #P:1

                              _-----=> irqs-off
                             / _----=> need-resched
                            | / _---=> hardirq/softirq
                            || / _--=> preempt-depth
                            ||| /     delay
           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
              | |       |   ||||       |         |
          hello-94    [000] d...    55.404242: enter_current_state_one: (0x106e4) a0=0x1 a1=0x3fffa8ada8

Be care /hello:0x6e4 is the file offset in elf and it relate to 0x106e4 in memory and hello is your target elf program.

Try kprobe like this:

echo 'p:myprobe sys_clone a0=%a0 a1=%a1 a2=%a2 a3=%a3 stach_val=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events echo 'r:myretprobe sys_clone $retval' >> /sys/kernel/debug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
cat /sys/kernel/debug/tracing/trace
tracer: nop

entries-in-buffer/entries-written: 2/2 #P:1

                                _-----=> irqs-off
                               / _----=> need-resched
                              | / _---=> hardirq/softirq
                              || / _--=> preempt-depth
                              ||| /     delay
           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
              | |         |   ||||      |         |
              sh-92      [000] .n..  8506.435857: myprobe: (sys_clone+0x0/0x28) a0=0x1200011 a1=0x0 a2=0x0 a3=0x0 stach_val=0x2044ecffffffe0
              sh-92      [000] d...  8506.445620: myretprobe: (ret_from_syscall+0x0/0x2 <- sys_clone) arg1=0x64

Changlog v5:
- Fixup fentry modified sp cause fail_inject error
- Fixup function_graph broken
- Update to linux-5.10
- Fixup checkpatch.pl issues

Changlog v4:
- Revert fixup kprobes handler couldn't change pc
- Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
- rebase on linux-tree:
commit 071a0578b0ce0b0e543d1e38ee6926b9cc21c198
Merge: fad7011 be4df0c
Author: Linus Torvalds <[email protected]>
Date: Fri Oct 16 15:29:46 2020 -0700

Merge tag 'ovl-update-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Changlog v3:
- Add upport for function error injection
- Fixup kprobes handler couldn't change pc

Changlog v2:
- Add Reviewed-by, Tested-by, Acked-by, thx for all of you
- Add kprobes on ftrace feature
- Use __always_inline as same as fix_to_virt for fixup BUILD_BUG_ON
- Use const "const unsigned int" for 2th param for fixup BUILD_BUG_ON

Guo Ren (8):
riscv: Fixup compile error BUILD_BUG_ON failed
riscv: Fixup wrong ftrace remove cflag
riscv: Fixup patch_text panic in ftrace
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
riscv: Add kprobes supported
riscv: Add KPROBES_ON_FTRACE supported
riscv: Add uprobes supported
riscv: Add support for function error injection

Patrick Stählin (1):
RISC-V: Implement ptrace regs and stack API

 arch/riscv/Kconfig                            |   8 +
 arch/riscv/Makefile                           |   2 +
 arch/riscv/include/asm/kprobes.h              |  40 +++
 arch/riscv/include/asm/probes.h               |  24 ++
 arch/riscv/include/asm/processor.h            |   1 +
 arch/riscv/include/asm/ptrace.h               |  35 +++
 arch/riscv/include/asm/thread_info.h          |   4 +-
 arch/riscv/include/asm/uprobes.h              |  40 +++
 arch/riscv/kernel/Makefile                    |   6 +-
 arch/riscv/kernel/ftrace.c                    |  95 +++---
 arch/riscv/kernel/mcount-dyn.S                | 342 ++++++++++------------
 arch/riscv/kernel/patch.c                     |   8 +-
 arch/riscv/kernel/probes/Makefile             |   6 +
 arch/riscv/kernel/probes/decode-insn.c        |  48 ++++
 arch/riscv/kernel/probes/decode-insn.h        |  18 ++
 arch/riscv/kernel/probes/ftrace.c             |  53 ++++
 arch/riscv/kernel/probes/kprobes.c            | 398 ++++++++++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  93 ++++++
 arch/riscv/kernel/probes/simulate-insn.c      |  85 ++++++
 arch/riscv/kernel/probes/simulate-insn.h      |  47 +++
 arch/riscv/kernel/probes/uprobes.c            | 186 ++++++++++++
 arch/riscv/kernel/ptrace.c                    |  99 +++++++
 arch/riscv/kernel/signal.c                    |   3 +
 arch/riscv/kernel/traps.c                     |  19 ++
 arch/riscv/lib/Makefile                       |   2 +
 arch/riscv/lib/error-inject.c                 |  10 +
 arch/riscv/mm/Makefile                        |   3 +-
 arch/riscv/mm/fault.c                         |  10 +
 28 files changed, 1444 insertions(+), 241 deletions(-)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/include/asm/uprobes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/ftrace.c
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
 create mode 100644 arch/riscv/kernel/probes/uprobes.c
 create mode 100644 arch/riscv/lib/error-inject.c

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From: Patrick Stählin <[email protected]>

Needed for kprobes support. Copied and adapted from arm64 code.

Guo Ren fixup pt_regs type for linux-5.8-rc1.

---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h | 29 ++++++++++++
 arch/riscv/kernel/ptrace.c      | 99 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 129 insertions(+)

index 44377fd..62a4958 100644
@@ -72,6 +72,7 @@ config RISCV
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN

index ee49f80..23372bb 100644
@@ -8,6 +8,7 @@
 
 #include <uapi/asm/ptrace.h>
 #include <asm/csr.h>
+#include <linux/compiler.h>
 
 #ifndef __ASSEMBLY__
 

@@ -60,6 +61,7 @@ struct pt_regs {
 
 #define user_mode(regs) (((regs)->status & SR_PP) == 0)
 
+#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
 
 /* Helpers for working with the instruction pointer */
 static inline unsigned long instruction_pointer(struct pt_regs *regs)

@@ -85,6 +87,12 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->sp =  val;
 }
 
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->sp;
+}
+
 /* Helpers for working with the frame pointer */
 static inline unsigned long frame_pointer(struct pt_regs *regs)
 {

@@ -101,6 +109,27 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 	return regs->a0;
 }
 
+extern int regs_query_register_offset(const char *name);
+extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+					       unsigned int n);
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	pt_regs from which register value is gotten
+ * @offset:	offset of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+					      unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PTRACE_H */

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From: Guo Ren <[email protected]>

Unfortunately, the current code couldn't be compiled:

CC arch/riscv/kernel/patch.o
In file included from ./include/linux/kernel.h:11,

                 from ./include/linux/list.h:9,
                 from ./include/linux/preempt.h:11,
                 from ./include/linux/spinlock.h:51,
                 from arch/riscv/kernel/patch.c:6:

In function ‘fix_to_virt’,
inlined from ‘patch_map’ at arch/riscv/kernel/patch.c:37:17:
./include/linux/compiler.h:392:38: error: call to ‘__compiletime_assert_205’ declared with attribute error: BUILD_BUG_ON failed: idx >= __end_of_fixed_addresses
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

                                      ^
./include/linux/compiler.h:373:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~

./include/linux/compiler.h:392:2: note: in expansion of macro ‘_compiletime_assert’
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’

 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~

./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) ^~~~~~~~~~~~~~~~
./include/asm-generic/fixmap.h:32:2: note: in expansion of macro ‘BUILD_BUG_ON’
BUILD_BUG_ON(idx >= __end_of_fixed_addresses);
^~~~~~~~~~~~

Because fix_to_virt(, idx) needs a const value, not a dynamic variable of reg-a0 or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".

---
 arch/riscv/kernel/patch.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index 3fe7a52..0b55287 100644
@@ -20,7 +20,12 @@ struct patch_insn {
 };
 
 #ifdef CONFIG_MMU
-static void *patch_map(void *addr, int fixmap)
+/*
+ * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
+ * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
+ * So use '__always_inline' and 'const unsigned int fixmap' here.
+ */
+static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
 {
 	uintptr_t uintaddr = (uintptr_t) addr;
 	struct page *page;

@@ -37,7 +42,6 @@ static void *patch_map(void *addr, int fixmap)
 	return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
 					 (uintaddr & ~PAGE_MASK));
 }
-NOKPROBE_SYMBOL(patch_map);
 
 static void patch_unmap(int fixmap)
 {

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From: Guo Ren <[email protected]>

We must use $(CC_FLAGS_FTRACE) instead of directly using -pg. It will cause -fpatchable-function-entry error.

---
 arch/riscv/kernel/Makefile | 4 ++--
 arch/riscv/mm/Makefile     | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

index fa896c5..27f10eb 100644
@@ -4,8 +4,8 @@
 #
 
 ifdef CONFIG_FTRACE
-CFLAGS_REMOVE_ftrace.o	= -pg
-CFLAGS_REMOVE_patch.o	= -pg
+CFLAGS_REMOVE_ftrace.o	= $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_patch.o	= $(CC_FLAGS_FTRACE)
 endif
 
 extra-y += head.o

index c0185e5..6b4b7ec 100644
@@ -2,7 +2,7 @@
 
 CFLAGS_init.o := -mcmodel=medany
 ifdef CONFIG_FTRACE
-CFLAGS_REMOVE_init.o = -pg
+CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
 endif
 
 KCOV_INSTRUMENT_init.o := n

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From: Guo Ren <[email protected]>

Just like arm64, we can't trace the function in the patch_text path.

Here is the bug log:

[   45.234334] Unable to handle kernel paging request at virtual address ffffffd38ae80900
[   45.242313] Oops [#1]
[   45.244600] Modules linked in:
[   45.247678] CPU: 0 PID: 11 Comm: migration/0 Not tainted 5.9.0-00025-g9b7db83-dirty #215
[   45.255797] epc: ffffffe00021689a ra : ffffffe00021718e sp : ffffffe01afabb58
[   45.262955]  gp : ffffffe00136afa0 tp : ffffffe01af94d00 t0 : 0000000000000002
[   45.270200]  t1 : 0000000000000000 t2 : 0000000000000001 s0 : ffffffe01afabc08
[   45.277443]  s1 : ffffffe0013718a8 a0 : 0000000000000000 a1 : ffffffe01afabba8
[   45.284686]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : c4c16ad38ae80900
[   45.291929]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43
[   45.299173]  s2 : 0000000000000001 s3 : ffffffe000206a60 s4 : ffffffe000206a60
[   45.306415]  s5 : 00000000000009ec s6 : ffffffe0013718a8 s7 : c4c16ad38ae80900
[   45.313658]  s8 : 0000000000000004 s9 : 0000000000000001 s10: 0000000000000001
[   45.320902]  s11: 0000000000000003 t3 : 0000000000000001 t4 : ffffffffd192fe79
[   45.328144]  t5 : ffffffffb8f80000 t6 : 0000000000040000
[   45.333472] status: 0000000200000100 badaddr: ffffffd38ae80900 cause: 000000000000000f
[   45.341514] ---[ end trace d95102172248fdcf ]---
[   45.346176] note: migration/0[11] exited with preempt_count 1

(gdb) x /2i $pc
=> 0xffffffe00021689a <__do_proc_dointvec+196>: sd zero,0(s7)
0xffffffe00021689e <__do_proc_dointvec+200>: li s11,0

(gdb) bt
0 __do_proc_dointvec (tbl_data=0x0, table=0xffffffe01afabba8, write=0, buffer=0x0, lenp=0x7bf897061f9a0800, ppos=0x4, conv=0x0, data=0x52464e43) at kernel/sysctl.c:581
1 0xffffffe00021718e in do_proc_dointvec (data=<optimized out>, conv=<optimized out>, ppos=<optimized out>, lenp=<optimized out>, buffer=<optimized out>, write=<optimized out>, table=<optimized out>) at kernel/sysctl.c:964
2 proc_dointvec_minmax (ppos=<optimized out>, lenp=<optimized out>, buffer=<optimized out>, write=<optimized out>, table=<optimized out>) at kernel/sysctl.c:964
3 proc_do_static_key (table=<optimized out>, write=1, buffer=0x0, lenp=0x0, ppos=0x7bf897061f9a0800) at kernel/sysctl.c:1643
4 0xffffffe000206792 in ftrace_make_call (rec=<optimized out>, addr=<optimized out>) at arch/riscv/kernel/ftrace.c:109
5 0xffffffe0002c9c04 in __ftrace_replace_code (rec=0xffffffe01ae40c30, enable=3) at kernel/trace/ftrace.c:2503
6 0xffffffe0002ca0b2 in ftrace_replace_code (mod_flags=<optimized out>) at kernel/trace/ftrace.c:2530
7 0xffffffe0002ca26a in ftrace_modify_all_code (command=5) at kernel/trace/ftrace.c:2677
8 0xffffffe0002ca30e in __ftrace_modify_code (data=<optimized out>) at kernel/trace/ftrace.c:2703
9 0xffffffe0002c13b0 in multi_cpu_stop (data=0x0) at kernel/stop_machine.c:224 10 0xffffffe0002c0fde in cpu_stopper_thread (cpu=<optimized out>) at kernel/stop_machine.c:491
11 0xffffffe0002343de in smpboot_thread_fn (data=0x0) at kernel/smpboot.c:165 12 0xffffffe00022f8b4 in kthread (_create=0xffffffe01af0c040) at kernel/kthread.c:292
13 0xffffffe000201fac in handle_exception () at arch/riscv/kernel/entry.S:236

   0xffffffe00020678a <+114>:   auipc   ra,0xffffe
   0xffffffe00020678e <+118>:   jalr    -118(ra) # 0xffffffe000204714 <patch_text_nosync>
   0xffffffe000206792 <+122>:   snez    a0,a0

(gdb) disassemble patch_text_nosync
Dump of assembler code for function patch_text_nosync:

   0xffffffe000204714 <+0>:     addi    sp,sp,-32
   0xffffffe000204716 <+2>:     sd      s0,16(sp)
   0xffffffe000204718 <+4>:     sd      ra,24(sp)
   0xffffffe00020471a <+6>:     addi    s0,sp,32
   0xffffffe00020471c <+8>:     auipc   ra,0x0
   0xffffffe000204720 <+12>:    jalr    -384(ra) # 0xffffffe00020459c <patch_insn_write>
   0xffffffe000204724 <+16>:    beqz    a0,0xffffffe00020472e <patch_text_nosync+26>
   0xffffffe000204726 <+18>:    ld      ra,24(sp)
   0xffffffe000204728 <+20>:    ld      s0,16(sp)
   0xffffffe00020472a <+22>:    addi    sp,sp,32
   0xffffffe00020472c <+24>:    ret
   0xffffffe00020472e <+26>:    sd      a0,-24(s0)
   0xffffffe000204732 <+30>:    auipc   ra,0x4
   0xffffffe000204736 <+34>:    jalr    -1464(ra) # 0xffffffe00020817a <flush_icache_all>
   0xffffffe00020473a <+38>:    ld      a0,-24(s0)
   0xffffffe00020473e <+42>:    ld      ra,24(sp)
   0xffffffe000204740 <+44>:    ld      s0,16(sp)
   0xffffffe000204742 <+46>:    addi    sp,sp,32
   0xffffffe000204744 <+48>:    ret

(gdb) disassemble flush_icache_all-4
Dump of assembler code for function flush_icache_all:

   0xffffffe00020817a <+0>:     addi    sp,sp,-8
   0xffffffe00020817c <+2>:     sd      ra,0(sp)
   0xffffffe00020817e <+4>:     auipc   ra,0xfffff
   0xffffffe000208182 <+8>:     jalr    -1822(ra) # 0xffffffe000206a60 <ftrace_caller>
   0xffffffe000208186 <+12>:    ld      ra,0(sp)
   0xffffffe000208188 <+14>:    addi    sp,sp,8
   0xffffffe00020818a <+0>:     addi    sp,sp,-16
   0xffffffe00020818c <+2>:     sd      s0,0(sp)
   0xffffffe00020818e <+4>:     sd      ra,8(sp)
   0xffffffe000208190 <+6>:     addi    s0,sp,16
   0xffffffe000208192 <+8>:     li      a0,0
   0xffffffe000208194 <+10>:    auipc   ra,0xfffff
   0xffffffe000208198 <+14>:    jalr    -410(ra) # 0xffffffe000206ffa <sbi_remote_fence_i>
   0xffffffe00020819c <+18>:    ld      s0,0(sp)
   0xffffffe00020819e <+20>:    ld      ra,8(sp)
   0xffffffe0002081a0 <+22>:    addi    sp,sp,16
   0xffffffe0002081a2 <+24>:    ret

(gdb) frame 5
(rec=0xffffffe01ae40c30, enable=3) at kernel/trace/ftrace.c:2503
2503 return ftrace_make_call(rec, ftrace_addr);
(gdb) p /x rec->ip
$2 = 0xffffffe00020817a -> flush_icache_all !

When we modified flush_icache_all's patchable-entry with ftrace_caller:
- Insert ftrace_caller at flush_icache_all prologue.
- Call flush_icache_all to sync I/Dcache, but flush_icache_all is
just we modified by half.

---
 arch/riscv/kernel/Makefile | 1 +
 arch/riscv/mm/Makefile     | 1 +
 2 files changed, 2 insertions(+)

index 27f10eb..62de075 100644
@@ -6,6 +6,7 @@
 ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_ftrace.o	= $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_patch.o	= $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sbi.o	= $(CC_FLAGS_FTRACE)
 endif
 
 extra-y += head.o

index 6b4b7ec..7ebaef1 100644
@@ -3,6 +3,7 @@
 CFLAGS_init.o := -mcmodel=medany
 ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
 endif
 
 KCOV_INSTRUMENT_init.o := n

2.7.4


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From: Guo Ren <[email protected]>

This patch changes the current detour mechanism of dynamic ftrace which has been discussed during LPC 2020 RISCV-MC [1].

Before the patch, we used mcount for detour:
<funca>:

	addi sp,sp,-16
	sd   ra,8(sp)
	sd   s0,0(sp)
	addi s0,sp,16
	mv   a5,ra
	mv   a0,a5
	auipc ra,0x0 -> nop
	jalr  -296(ra) <_mcount@plt> ->nop
	...

After the patch, we use nop call site area for detour:
<funca>:

	nop -> REG_S ra, -SZREG(sp)
	nop -> auipc ra, 0x?
	nop -> jalr ?(ra)
	nop -> REG_L ra, -SZREG(sp)
	...

The mcount mechanism is mixed with gcc function prologue which is not very clear. The patchable function entry just put 16 bytes nop before the front of the function prologue which could be filled with a separated detour mechanism.

[1] https://www.linuxplumbersconf.org/event/7/contributions/807/

---
 arch/riscv/Makefile            |   2 +
 arch/riscv/kernel/ftrace.c     |  95 ++++++------
 arch/riscv/kernel/mcount-dyn.S | 342 ++++++++++++++++++-----------------------
 3 files changed, 204 insertions(+), 235 deletions(-)

index 0289a97..b6eb946 100644
@@ -12,6 +12,8 @@ OBJCOPYFLAGS    := -O binary
 LDFLAGS_vmlinux :=
 ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
 	LDFLAGS_vmlinux := --no-relax
+	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
+	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
 endif
 
 ifeq ($(CONFIG_64BIT)$(CONFIG_CMODEL_MEDLOW),yy)

2.7.4


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From: Guo Ren <[email protected]>

This patch enables "kprobe & kretprobe" to work with ftrace interface. It utilized software breakpoint as single-step mechanism.

Some instructions which can't be single-step executed must be simulated in kernel execution slot, such as: branch, jal, auipc, la ...

Some instructions should be rejected for probing and we use a blacklist to filter, such as: ecall, ebreak, ...

We use ebreak & c.ebreak to replace origin instruction and the kprobe handler prepares an executable memory slot for out-of-line execution with a copy of the original instruction being probed. In execution slot we add ebreak behind original instruction to simulate a single-setp mechanism.

The patch is based on packi's work [1] and csky's work [2].
- The kprobes_trampoline.S is all from packi's patch
- The single-step mechanism is new designed for riscv without hw single-step trap
- The simulation codes are from csky
- Frankly, all codes refer to other archs' implementation

[1] https://lore.kernel.org/linux-riscv/[email protected]/
[2] https://lore.kernel.org/linux-csky/[email protected]/

---
 arch/riscv/Kconfig                            |   2 +
 arch/riscv/include/asm/kprobes.h              |  40 +++
 arch/riscv/include/asm/probes.h               |  24 ++
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/probes/Makefile             |   4 +
 arch/riscv/kernel/probes/decode-insn.c        |  48 ++++
 arch/riscv/kernel/probes/decode-insn.h        |  18 ++
 arch/riscv/kernel/probes/kprobes.c            | 398 ++++++++++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  93 ++++++
 arch/riscv/kernel/probes/simulate-insn.c      |  85 ++++++
 arch/riscv/kernel/probes/simulate-insn.h      |  47 +++
 arch/riscv/kernel/traps.c                     |   9 +
 arch/riscv/mm/fault.c                         |   4 +
 13 files changed, 773 insertions(+)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h

index 62a4958..9a920ed 100644
@@ -68,6 +68,8 @@ config RISCV
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
 	select HAVE_GENERIC_VDSO if MMU && 64BIT
+	select HAVE_KPROBES
+	select HAVE_KRETPROBES
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS

index 56a98ea3..4647d38 100644
@@ -11,4 +11,44 @@
 
 #include <asm-generic/kprobes.h>
 
+#ifdef CONFIG_KPROBES
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define __ARCH_WANT_KPROBES_INSN_SLOT
+#define MAX_INSN_SIZE			2
+
+#define flush_insn_slot(p)		do { } while (0)
+#define kretprobe_blacklist_size	0
+
+#include <asm/probes.h>
+
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned int status;
+};
+
+/* Single step context for kprobe */
+struct kprobe_step_ctx {
+	unsigned long ss_pending;
+	unsigned long match_addr;
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned int kprobe_status;
+	unsigned long saved_status;
+	struct prev_kprobe prev_kprobe;
+	struct kprobe_step_ctx ss_ctx;
+};
+
+void arch_remove_kprobe(struct kprobe *p);
+int kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr);
+bool kprobe_breakpoint_handler(struct pt_regs *regs);
+bool kprobe_single_step_handler(struct pt_regs *regs);
+void kretprobe_trampoline(void);
+void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
+
+#endif /* CONFIG_KPROBES */
 #endif /* _ASM_RISCV_KPROBES_H */

new file mode 100644
index 00000000..a787e6d
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_RISCV_PROBES_H
+#define _ASM_RISCV_PROBES_H
+
+typedef u32 probe_opcode_t;
+typedef bool (probes_handler_t) (u32 opcode, unsigned long addr, struct pt_regs *);
+
+/* architecture specific copy of original instruction */
+struct arch_probe_insn {
+	probe_opcode_t *insn;
+	probes_handler_t *handler;
+	/* restore address after simulation */
+	unsigned long restore;
+};
+
+#ifdef CONFIG_KPROBES
+typedef u32 kprobe_opcode_t;
+struct arch_specific_insn {
+	struct arch_probe_insn api;
+};
+#endif
+
+#endif /* _ASM_RISCV_PROBES_H */

index 62de075..76c7975 100644
@@ -30,6 +30,7 @@ obj-y	+= riscv_ksyms.o
 obj-y	+= stacktrace.o
 obj-y	+= cacheinfo.o
 obj-y	+= patch.o
+obj-y	+= probes/
 obj-$(CONFIG_MMU) += vdso.o vdso/
 
 obj-$(CONFIG_RISCV_M_MODE)	+= traps_misaligned.o

new file mode 100644
index 00000000..8a39507
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o
+obj-$(CONFIG_KPROBES)		+= kprobes_trampoline.o
+CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)

new file mode 100644
index 00000000..42269a7
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+
+#include <asm/sections.h>
+#include <asm/kprobes.h>
+
+enum probe_insn {
+	INSN_REJECTED,
+	INSN_GOOD_NO_SLOT,
+	INSN_GOOD,
+};
+
+enum probe_insn __kprobes
+riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *asi);
+
+#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */

index ad14f44..19a788a 100644
@@ -12,6 +12,7 @@
 #include <linux/signal.h>
 #include <linux/kdebug.h>
 #include <linux/uaccess.h>
+#include <linux/kprobes.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/irq.h>

@@ -145,6 +146,14 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
 
 asmlinkage __visible void do_trap_break(struct pt_regs *regs)
 {
+#ifdef CONFIG_KPROBES
+	if (kprobe_single_step_handler(regs))
+		return;
+
+	if (kprobe_breakpoint_handler(regs))
+		return;
+#endif
+
 	if (user_mode(regs))
 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
 #ifdef CONFIG_KGDB

index 3c8b9e4..602f125 100644
@@ -13,6 +13,7 @@
 #include <linux/perf_event.h>
 #include <linux/signal.h>
 #include <linux/uaccess.h>
+#include <linux/kprobes.h>
 
 #include <asm/ptrace.h>
 #include <asm/tlbflush.h>

@@ -202,6 +203,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	tsk = current;
 	mm = tsk->mm;
 
+	if (kprobe_page_fault(regs, cause))
+		return;
+
 	/*
 	 * Fault-in kernel-space virtual memory on-demand.
 	 * The 'reference' page table is init_mm.pgd.

2.7.4


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From: Guo Ren <[email protected]>

This patch adds support for kprobes on ftrace call sites to avoids much of the overhead with regular kprobes. Try it with simple steps:

echo 'p:myprobe sys_clone a0=%a0 a1=%a1 stack_val=+4($stack)' > /sys/kernel/de
bug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
cat /sys/kernel/debug/tracing/trace
tracer: nop

entries-in-buffer/entries-written: 1/1 #P:1

                                _-----=> irqs-off
                               / _----=> need-resched
                              | / _---=> hardirq/softirq
                              || / _--=> preempt-depth
                              ||| /     delay
           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
              | |         |   ||||      |         |
              sh-92      [000] ....   369.899962: myprobe: (sys_clone+0x0/0x28) a0=0x1200011 a1=0x0 stack_val=0x201c20ffffffe0
 cat /sys/kernel/debug/kprobes/list
ffffffe00020b584  k  sys_clone+0x0    [FTRACE]
                                       ^^^^^^

---
 arch/riscv/Kconfig                |  1 +
 arch/riscv/kernel/probes/Makefile |  1 +
 arch/riscv/kernel/probes/ftrace.c | 53 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 arch/riscv/kernel/probes/ftrace.c

index 9a920ed..f58b234 100644
@@ -69,6 +69,7 @@ config RISCV
 	select HAVE_GCC_PLUGINS
 	select HAVE_GENERIC_VDSO if MMU && 64BIT
 	select HAVE_KPROBES
+	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS

index 8a39507..abbd131 100644
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o
 obj-$(CONFIG_KPROBES)		+= kprobes_trampoline.o
+obj-$(CONFIG_KPROBES_ON_FTRACE)	+= ftrace.o
 CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)

2.7.4


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From: Guo Ren <[email protected]>

This patch adds support for uprobes on riscv architecture.

Just like kprobe, it support single-step and simulate instructions.

---
 arch/riscv/Kconfig                   |   3 +
 arch/riscv/include/asm/processor.h   |   1 +
 arch/riscv/include/asm/thread_info.h |   4 +-
 arch/riscv/include/asm/uprobes.h     |  40 ++++++++
 arch/riscv/kernel/probes/Makefile    |   1 +
 arch/riscv/kernel/probes/uprobes.c   | 186 +++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/signal.c           |   3 +
 arch/riscv/kernel/traps.c            |  10 ++
 arch/riscv/mm/fault.c                |   6 ++
 9 files changed, 253 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/uprobes.h
 create mode 100644 arch/riscv/kernel/probes/uprobes.c

index f58b234..af0ec36 100644
@@ -160,6 +160,9 @@ config ARCH_WANT_GENERAL_HUGETLB
 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	def_bool y
 
+config ARCH_SUPPORTS_UPROBES
+	def_bool y
+
 config SYS_SUPPORTS_HUGETLBFS
 	depends on MMU
 	def_bool y

index bdddcd5..3a24003 100644
@@ -34,6 +34,7 @@ struct thread_struct {
 	unsigned long sp;	/* Kernel mode stack */
 	unsigned long s[12];	/* s[0]: frame pointer */
 	struct __riscv_d_ext_state fstate;
+	unsigned long bad_cause;
 };
 
 #define INIT_THREAD {					\

index a390711..bdb5928 100644
@@ -74,6 +74,7 @@ struct thread_info {
 #define TIF_SYSCALL_TRACEPOINT  6       /* syscall tracepoint instrumentation */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing */
 #define TIF_SECCOMP		8	/* syscall secure computing */
+#define TIF_UPROBE		9	/* uprobe breakpoint or singlestep */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)

@@ -82,9 +83,10 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
+#define _TIF_UPROBE		(1 << TIF_UPROBE)
 
 #define _TIF_WORK_MASK \
-	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED)
+	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED | _TIF_UPROBE)
 
 #define _TIF_SYSCALL_WORK \
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT | \

new file mode 100644
index 00000000..f2183e0
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _ASM_RISCV_UPROBES_H
+#define _ASM_RISCV_UPROBES_H
+
+#include <asm/probes.h>
+#include <asm/patch.h>
+#include <asm/bug.h>
+
+#define MAX_UINSN_BYTES		8
+
+#ifdef CONFIG_RISCV_ISA_C
+#define UPROBE_SWBP_INSN	__BUG_INSN_16
+#define UPROBE_SWBP_INSN_SIZE	2
+#else
+#define UPROBE_SWBP_INSN	__BUG_INSN_32
+#define UPROBE_SWBP_INSN_SIZE	4
+#endif
+#define UPROBE_XOL_SLOT_BYTES	MAX_UINSN_BYTES
+
+typedef u32 uprobe_opcode_t;
+
+struct arch_uprobe_task {
+	unsigned long   saved_cause;
+};
+
+struct arch_uprobe {
+	union {
+		u8 insn[MAX_UINSN_BYTES];
+		u8 ixol[MAX_UINSN_BYTES];
+	};
+	struct arch_probe_insn api;
+	unsigned long insn_size;
+	bool simulate;
+};
+
+bool uprobe_breakpoint_handler(struct pt_regs *regs);
+bool uprobe_single_step_handler(struct pt_regs *regs);
+
+#endif /* _ASM_RISCV_UPROBES_H */

index abbd131..7f0840d 100644
@@ -2,4 +2,5 @@
 obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o
 obj-$(CONFIG_KPROBES)		+= kprobes_trampoline.o
 obj-$(CONFIG_KPROBES_ON_FTRACE)	+= ftrace.o
+obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o simulate-insn.o
 CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)

index bc68418..18fd97a 100644
@@ -309,6 +309,9 @@ static void do_signal(struct pt_regs *regs)
 asmlinkage __visible void do_notify_resume(struct pt_regs *regs,
 					   unsigned long thread_info_flags)
 {
+	if (thread_info_flags & _TIF_UPROBE)
+		uprobe_notify_resume(regs);
+
 	/* Handle pending signal delivery */
 	if (thread_info_flags & _TIF_SIGPENDING)
 		do_signal(regs);

index 19a788a..2bca2fa 100644
@@ -76,6 +76,8 @@ void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
 static void do_trap_error(struct pt_regs *regs, int signo, int code,
 	unsigned long addr, const char *str)
 {
+	current->thread.bad_cause = regs->cause;
+
 	if (user_mode(regs)) {
 		do_trap(regs, signo, code, addr);
 	} else {

@@ -153,6 +155,14 @@ asmlinkage __visible void do_trap_break(struct pt_regs *regs)
 	if (kprobe_breakpoint_handler(regs))
 		return;
 #endif
+#ifdef CONFIG_UPROBES
+	if (uprobe_single_step_handler(regs))
+		return;
+
+	if (uprobe_breakpoint_handler(regs))
+		return;
+#endif
+	current->thread.bad_cause = regs->cause;
 
 	if (user_mode(regs))
 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);

index 602f125..0c98db9 100644
@@ -229,6 +229,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	 * in an atomic region, then we must not take the fault.
 	 */
 	if (unlikely(faulthandler_disabled() || !mm)) {
+		tsk->thread.bad_cause = cause;
 		no_context(regs, addr);
 		return;
 	}

@@ -246,16 +247,19 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	mmap_read_lock(mm);
 	vma = find_vma(mm, addr);
 	if (unlikely(!vma)) {
+		tsk->thread.bad_cause = cause;
 		bad_area(regs, mm, code, addr);
 		return;
 	}
 	if (likely(vma->vm_start <= addr))
 		goto good_area;
 	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
+		tsk->thread.bad_cause = cause;
 		bad_area(regs, mm, code, addr);
 		return;
 	}
 	if (unlikely(expand_stack(vma, addr))) {
+		tsk->thread.bad_cause = cause;
 		bad_area(regs, mm, code, addr);
 		return;
 	}

@@ -268,6 +272,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	code = SEGV_ACCERR;
 
 	if (unlikely(access_error(cause, vma))) {
+		tsk->thread.bad_cause = cause;
 		bad_area(regs, mm, code, addr);
 		return;
 	}

@@ -301,6 +306,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	mmap_read_unlock(mm);
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
+		tsk->thread.bad_cause = cause;
 		mm_fault_error(regs, addr, fault);
 		return;
 	}

2.7.4


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From: Guo Ren <[email protected]>

Inspired by the commit 42d038c4fb00 ("arm64: Add support for function error injection"), this patch supports function error injection for riscv.

This patch mainly support two functions: one is regs_set_return_value() which is used to overwrite the return value; the another function is override_function_with_return() which is to override the probed function returning and jump to its caller.

Test log:
cd /sys/kernel/debug/fail_function
echo sys_clone > inject
echo 100 > probability
echo 1 > interval
ls /

[  313.176875] FAULT_INJECTION: forcing a failure.
[  313.176875] name fail_function, interval 1, probability 100, space 0, times 1
[  313.184357] CPU: 0 PID: 87 Comm: sh Not tainted 5.8.0-rc5-00007-g6a758cc #117
[  313.187616] Call Trace:
[  313.189100] [<ffffffe0002036b6>] walk_stackframe+0x0/0xc2
[  313.191626] [<ffffffe00020395c>] show_stack+0x40/0x4c
[  313.193927] [<ffffffe000556c60>] dump_stack+0x7c/0x96
[  313.194795] [<ffffffe0005522e8>] should_fail+0x140/0x142
[  313.195923] [<ffffffe000299ffc>] fei_kprobe_handler+0x2c/0x5a
[  313.197687] [<ffffffe0009e2ec4>] kprobe_breakpoint_handler+0xb4/0x18a
[  313.200054] [<ffffffe00020357e>] do_trap_break+0x36/0xca
[  313.202147] [<ffffffe000201bca>] ret_from_exception+0x0/0xc
[  313.204556] [<ffffffe000201bbc>] ret_from_syscall+0x0/0x2

-sh: can't fork: Invalid argument

---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h |  6 ++++++
 arch/riscv/lib/Makefile         |  2 ++
 arch/riscv/lib/error-inject.c   | 10 ++++++++++
 4 files changed, 19 insertions(+)
 create mode 100644 arch/riscv/lib/error-inject.c

index af0ec36..a627ae2 100644
@@ -67,6 +67,7 @@ config RISCV
 	select HAVE_EBPF_JIT if MMU
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
+	select HAVE_FUNCTION_ERROR_INJECTION
 	select HAVE_GENERIC_VDSO if MMU && 64BIT
 	select HAVE_KPROBES
 	select HAVE_KPROBES_ON_FTRACE

index 23372bb..cb4abb6 100644
@@ -109,6 +109,12 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 	return regs->a0;
 }
 
+static inline void regs_set_return_value(struct pt_regs *regs,
+					 unsigned long val)
+{
+	regs->a0 = val;
+}
+
 extern int regs_query_register_offset(const char *name);
 extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
 					       unsigned int n);

index 47e7a82..699ed20 100644
@@ -4,3 +4,5 @@ lib-y			+= memcpy.o
 lib-y			+= memset.o
 lib-$(CONFIG_MMU)	+= uaccess.o
 lib-$(CONFIG_64BIT)	+= tishift.o
+
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o

new file mode 100644
index 00000000..d667ade
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/error-injection.h>
+#include <linux/kprobes.h>
+
+void override_function_with_return(struct pt_regs *regs)
+{
+	instruction_pointer_set(regs, regs->ra);
+}
+NOKPROBE_SYMBOL(override_function_with_return);

2.7.4


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Thanks, these are on for-next. I've fixed up a few things, LMK if there were any issues.

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