Messages in this thread | | | From | Huacai Chen <> | Date | Fri, 20 Jan 2023 21:23:18 +0800 | Subject | Re: [PATCH v12 4/5] LoongArch: Mark some assembler symbols as non-kprobe-able |
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On Thu, Jan 19, 2023 at 11:32 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > On Wed, 18 Jan 2023 15:17:00 +0800 > Huacai Chen <chenhuacai@kernel.org> wrote: > > > 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? > > I need to check the loongarch implementation of handle_syscall() but > I guess in that handler the register set is not completely set as > kernel one. In that case, the software breakpoint handler may not > possible to handle it correctly. So it is better to avoid probing such > "border" function by kprobes. Seems reasonable, handle_syscall() indeed doesn't save all registers. But for memcpy(), I still think memmove() and memset() may have the same problem.
Huacai > > Thank you, > > > > > 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 > > > >>>> > > > >> > > > > > > > > > -- > Masami Hiramatsu (Google) <mhiramat@kernel.org>
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