Re: [PATCH v12 4/5] LoongArch: Mark some assembler symbols as non-kprobe-able

From: Jinyang He
Date: Wed Jan 18 2023 - 01:22:14 EST



On 2023-01-18 12:23, Tiezhu Yang wrote:


On 01/18/2023 12:14 PM, Huacai Chen wrote:
If memcpy should be blacklisted, then what about memset and memmove?

According to the test results, there are no problems to probe
memset and memmove, so no need to blacklist them for now,
blacklist memcpy is because it may cause recursive exceptions,
there is a detailed discussion in the following link:

https://lore.kernel.org/lkml/20230114143859.7ccc45c1c5d9ce302113ab0a@xxxxxxxxxx/

Hi, Tiezhu,

I cannot reproduce the results when kprobe memcpy. Could you please give
some details. Emm, I just replace "kernel_clone" with "memcpy" in
kprobe_example.c.

And for your call trace,

 handler_pre()
   pr_info()
     printk()
      _printk()
        vprintk()
          vprintk_store()
            memcpy()

I think when we should skip this time kprobe which triggered in
handler_{pre, post}. That means this time kprobe will not call
handler_{pre, post} agian, and not cause recursion. I remember
your codes had done this skip action. So, that's so strange if
recursion in handler_{pre, post}.


Thanks,

Jinyang



Thanks,
Tiezhu


Huacai

On Wed, Jan 18, 2023 at 10:01 AM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:

Some assembler symbols are not kprobe safe, such as handle_syscall
(used as syscall exception handler), *memcpy* (may cause recursive
exceptions), they can not be instrumented, just blacklist them for
kprobing.

Here is a related problem and discussion:
Link: https://lore.kernel.org/lkml/20230114143859.7ccc45c1c5d9ce302113ab0a@xxxxxxxxxx/

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 arch/loongarch/include/asm/asm.h | 10 ++++++++++
 arch/loongarch/kernel/entry.S    |  1 +
 arch/loongarch/lib/memcpy.S      |  3 +++
 3 files changed, 14 insertions(+)

diff --git a/arch/loongarch/include/asm/asm.h b/arch/loongarch/include/asm/asm.h
index 40eea6a..f591b32 100644
--- a/arch/loongarch/include/asm/asm.h
+++ b/arch/loongarch/include/asm/asm.h
@@ -188,4 +188,14 @@
 #define PTRLOG         3
 #endif

+/* Annotate a function as being unsuitable for kprobes. */
+#ifdef CONFIG_KPROBES
+#define _ASM_NOKPROBE(name)                            \
+       .pushsection "_kprobe_blacklist", "aw";         \
+       .quad   name;                                   \
+       .popsection
+#else
+#define _ASM_NOKPROBE(name)
+#endif
+
 #endif /* __ASM_ASM_H */
diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
index d53b631..55e23b1 100644
--- a/arch/loongarch/kernel/entry.S
+++ b/arch/loongarch/kernel/entry.S
@@ -67,6 +67,7 @@ SYM_FUNC_START(handle_syscall)

        RESTORE_ALL_AND_RET
 SYM_FUNC_END(handle_syscall)
+_ASM_NOKPROBE(handle_syscall)

 SYM_CODE_START(ret_from_fork)
        bl      schedule_tail           # a0 = struct task_struct *prev
diff --git a/arch/loongarch/lib/memcpy.S b/arch/loongarch/lib/memcpy.S
index 7c07d59..3b7e1de 100644
--- a/arch/loongarch/lib/memcpy.S
+++ b/arch/loongarch/lib/memcpy.S
@@ -17,6 +17,7 @@ SYM_FUNC_START(memcpy)
        ALTERNATIVE     "b __memcpy_generic", \
                        "b __memcpy_fast", CPU_FEATURE_UAL
 SYM_FUNC_END(memcpy)
+_ASM_NOKPROBE(memcpy)

 EXPORT_SYMBOL(memcpy)

@@ -41,6 +42,7 @@ SYM_FUNC_START(__memcpy_generic)
 2:     move    a0, a3
        jr      ra
 SYM_FUNC_END(__memcpy_generic)
+_ASM_NOKPROBE(__memcpy_generic)

 /*
  * void *__memcpy_fast(void *dst, const void *src, size_t n)
@@ -93,3 +95,4 @@ SYM_FUNC_START(__memcpy_fast)
 3:     move    a0, a3
        jr      ra
 SYM_FUNC_END(__memcpy_fast)
+_ASM_NOKPROBE(__memcpy_fast)
--
2.1.0