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

[Jinyang He]

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@xxxxxxxxxx/ 
> >
> > 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@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