Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for noinstr

[Mark Rutland]

On Sat, Oct 01, 2022 at 09:24:44PM -0400, guoren@xxxxxxxxxx wrote:
> From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> 
> And it will be extended for C entry code.
> 
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> ---
>  include/linux/compiler_types.h | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 4f2a819fd60a..e9ce11ea4d8b 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -227,9 +227,11 @@ struct ftrace_likely_data {
>  #endif
>  
>  /* Section for code which can't be instrumented at all */
> -#define noinstr								\
> -	noinline notrace __attribute((__section__(".noinstr.text")))	\
> -	__no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
> +#define __noinstr_section(section)				\
> +	noinline notrace __section(section) __no_profile	\
> +	__no_kcsan __no_sanitize_address __no_sanitize_coverage
> +
> +#define noinstr __noinstr_section(".noinstr.text")

One thing proably worth noting here is that while KPROBES will avoid
instrumenting `.noinstr.text`, that won't happen automatically for other
__noinstr_section() sections, and that will need to be inhibited through other
means (e.g. the kprobes blacklist, explicit NOKPROBE_SYMBOL() annotation, or
otherwise).

Thanks,
Mark.