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

[Jinyang He]

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.

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