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

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Message-ID: <6879b948-2d61-8e09-a9d4-bc2ede31c52b@loongson.cn>
Date:   Wed, 18 Jan 2023 14:24:46 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Jinyang He <hejinyang@...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 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"

>
> 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
>>>>
>>