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Subject: Re: [PATCH v12 4/5] LoongArch: Mark some assembler symbols as
 non-kprobe-able
To:     Huacai Chen <chenhuacai@kernel.org>
References: <1674007261-9198-1-git-send-email-yangtiezhu@loongson.cn>
 <1674007261-9198-5-git-send-email-yangtiezhu@loongson.cn>
 <CAAhV-H7Dt5MhaMU1=D9HxPFR+xjjoQG6RguaYMydy=v_jvrtiA@mail.gmail.com>
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
From:   Tiezhu Yang <yangtiezhu@loongson.cn>
Message-ID: <48f0508f-3908-c6ca-c8ba-7c12dd6b3f11@loongson.cn>
Date:   Wed, 18 Jan 2023 12:23:23 +0800
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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@kernel.org/

Thanks,
Tiezhu

>
> Huacai
>
> On Wed, Jan 18, 2023 at 10:01 AM Tiezhu Yang <yangtiezhu@loongson.cn> 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@kernel.org/
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
>> ---
>>  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
>>