linux-hardening - Re: [PATCH 1/5] compiler_types.h: Move _

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Message-ID: <20250827194657.GA3572128@ax162>
Date: Wed, 27 Aug 2025 12:46:57 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...flux.net>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Puranjay Mohan <puranjay@...nel.org>,
	Jonathan Corbet <corbet@....net>, x86@...nel.org,
	linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, llvm@...ts.linux.dev,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/5] compiler_types.h: Move __nocfi out of
 compiler-specific header

On Mon, Aug 25, 2025 at 07:25:48AM -0700, Kees Cook wrote:
> From: Kees Cook <kees@...flux.net>
> 
> Prepare for GCC KCFI support and move the __nocfi attribute from
> compiler-clang.h to compiler_types.h. This was already effectively gated
> by CONFIG_CFI_CLANG, so this remains safe for non-KCFI GCC builds.
> 
> Signed-off-by: Kees Cook <kees@...flux.net>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  include/linux/compiler-clang.h | 5 -----
>  include/linux/compiler_types.h | 4 +++-
>  2 files changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index fa4ffe037bc7..7a4568e421dc 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -96,11 +96,6 @@
>  # define __noscs	__attribute__((__no_sanitize__("shadow-call-stack")))
>  #endif
>  
> -#if __has_feature(kcfi)
> -/* Disable CFI checking inside a function. */
> -#define __nocfi		__attribute__((__no_sanitize__("kcfi")))
> -#endif
> -
>  /*
>   * Turn individual warnings and errors on and off locally, depending
>   * on version.
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 16755431fc11..a910f9fa5341 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -432,7 +432,9 @@ struct ftrace_likely_data {
>  # define __noscs
>  #endif
>  
> -#ifndef __nocfi
> +#if defined(CONFIG_CFI_CLANG)

I tend to prefer '#ifdef' for single symbols.

> +# define __nocfi		__attribute__((__no_sanitize__("kcfi")))
> +#else
>  # define __nocfi
>  #endif
>  
> -- 
> 2.34.1
>