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

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Message-ID: <14547aca-5649-c442-e062-a2e81052164b@loongson.cn>
Date:   Wed, 18 Jan 2023 15:20:38 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 4/5] LoongArch: Mark some assembler symbols as
 non-kprobe-able


On 2023-01-18 14:24, Tiezhu Yang wrote:
>
>
> On 01/18/2023 02:05 PM, Jinyang He wrote:
>>
>> 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@kernel.org/ 
>>>
>>>
>>
>> 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.
>
> Please remove the related "_ASM_NOKPROBE(memcpy)" code in
> arch/loongarch/lib/memcpy.S, and then compile and update kernel,
> execute the following cmd after reboot, I can reproduce the hang
> problem easily (it will take a few minutes).
>
> modprobe kprobe_example symbol="memcpy"

Okay, I can reproduce the hang, but sometimes quickly while
sometimes slowly. I do not know why it happend. Can you
explain how recursion happens? I means, can you explain why

no need mark {vprintk_store, vprintk, ... } as it may also cause recursion.


>
>>
>> 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@...ngson.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@...ngson.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
>>>>>
>>>