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From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Wed, 18 Jan 2023 15:17:00 +0800
Message-ID: <CAAhV-H7KJTtZPC9=OZEZfQvMjd6Gw37Q3kZODk=wk9pt6VZuAQ@mail.gmail.com>
Subject: Re: [PATCH v12 4/5] LoongArch: Mark some assembler symbols as non-kprobe-able
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Jinyang He <hejinyang@loongson.cn>,
        WANG Xuerui <kernel@xen0n.name>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
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On Wed, Jan 18, 2023 at 2:24 PM Tiezhu Yang <yangtiezhu@loongson.cn> 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"
Then, why is handle_syscall different from other exception handlers?

Huacai
>
> >
> > 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@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
> >>>>
> >>
>
>