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

[Huacai Chen]

If memcpy should be blacklisted, then what about memset and memmove?

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
>