Re: [PATCH] riscv: blacklist assembly symbols for kprobe

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Oct 04, 2023 at 03:10:09PM +0200, Clément Léger wrote:
> Adding kprobes on some assembly functions (mainly exception handling)
> will result in crashes (either recursive trap or panic). To avoid such
> errors, add ASM_NOKPROBE() macro which allow adding specific symbols
> into the __kprobe_blacklist section and use to blacklist the following
> symbols that showed to be problematic:
> - handle_exception()
> - ret_from_exception()
> - handle_kernel_stack_overflow()
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---
>  arch/riscv/include/asm/asm.h | 10 ++++++++++
>  arch/riscv/kernel/entry.S    |  3 +++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
> index 114bbadaef41..9194e334de15 100644
> --- a/arch/riscv/include/asm/asm.h
> +++ b/arch/riscv/include/asm/asm.h
> @@ -142,6 +142,16 @@
>  	REG_L x31, PT_T6(sp)
>  	.endm
>  
> +/* Annotate a function as being unsuitable for kprobes. */
> +#ifdef CONFIG_KPROBES
> +#define ASM_NOKPROBE(name)				\
> +	.pushsection "_kprobe_blacklist", "aw";		\
> +	RISCV_PTR name;					\
> +	.popsection
> +#else
> +#define ASM_NOKPROBE(name)
> +#endif
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_RISCV_ASM_H */
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 143a2bb3e697..f24bc4eeedde 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -101,6 +101,7 @@ _save_context:
>  1:
>  	tail do_trap_unknown
>  SYM_CODE_END(handle_exception)
> +ASM_NOKPROBE(handle_exception)
>  
>  /*
>   * The ret_from_exception must be called with interrupt disabled. Here is the
> @@ -167,6 +168,7 @@ SYM_CODE_START_NOALIGN(ret_from_exception)
>  	sret
>  #endif
>  SYM_CODE_END(ret_from_exception)
> +ASM_NOKPROBE(ret_from_exception)
>  
>  #ifdef CONFIG_VMAP_STACK
>  SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
> @@ -254,6 +256,7 @@ restore_caller_reg:
>  	move a0, sp
>  	tail handle_bad_stack
>  SYM_CODE_END(handle_kernel_stack_overflow)
> +ASM_NOKPROBE(handle_kernel_stack_overflow)
>  #endif
>  
>  SYM_CODE_START(ret_from_fork)
> -- 
> 2.42.0
> 
> 
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Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

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