linux-kernel - Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr

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Date:   Mon, 3 Oct 2022 12:38:59 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     guoren@...nel.org
Cc:     arnd@...db.de, palmer@...osinc.com, tglx@...utronix.de,
        peterz@...radead.org, luto@...nel.org, conor.dooley@...rochip.com,
        heiko@...ech.de, jszhang@...nel.org, lazyparser@...il.com,
        falcon@...ylab.org, chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, zouyipeng@...wei.com,
        bigeasy@...utronix.de, David.Laight@...lab.com,
        chenzhongjin@...wei.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Borislav Petkov <bp@...en8.de>,
        Miguel Ojeda <ojeda@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for
 noinstr

On Sat, Oct 01, 2022 at 09:24:44PM -0400, guoren@...nel.org wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> And it will be extended for C entry code.
> 
> Cc: Borislav Petkov <bp@...en8.de>
> Reviewed-by: Miguel Ojeda <ojeda@...nel.org>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> ---
>  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.