linux-kernel - Re: [PATCH] KMSAN: Restore dynamic check for '-fsanitize=kernel-memory'

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Message-ID: <aPqHCrC0JPwQynWd@levanger>
Date: Thu, 23 Oct 2025 21:50:34 +0200
From: Nicolas Schier <nsc@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, Kees Cook <kees@...nel.org>,
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] KMSAN: Restore dynamic check for
 '-fsanitize=kernel-memory'

On Thu, Oct 23, 2025 at 09:01:29PM +0200, Nathan Chancellor wrote:
> Commit 5ff8c11775c7 ("KMSAN: Remove tautological checks") changed
> CONFIG_HAVE_KMSAN_COMPILER from a dynamic check for
> '-fsanitize=kernel-memory' to just being true for CONFIG_CC_IS_CLANG.
> This missed the fact that not all architectures supported
> '-fsanitize=kernel-memory' at the same time. For example, SystemZ / s390
> gained support for KMSAN in clang-18 [1], so builds with clang-15
> through clang-17 can select KMSAN but they error with:
> 
>   clang-16: error: unsupported option '-fsanitize=kernel-memory' for target 's390x-unknown-linux-gnu'
> 
> Restore the cc-option check for '-fsanitize=kernel-memory' to make sure
> the compiler target properly supports '-fsanitize=kernel-memory'. The
> check for '-msan-disable-checks=1' does not need to be restored because
> all supported clang versions for building the kernel support it.
> 
> Fixes: 5ff8c11775c7 ("KMSAN: Remove tautological checks")
> Link: https://github.com/llvm/llvm-project/commit/a3e56a8792ffaf3a3d3538736e1042b8db45ab89 [1]
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/r/202510220236.AVuXXCYy-lkp@intel.com/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> I plan to take this via kbuild-fixes for 6.18-rc3 or -rc4.
> ---
>  lib/Kconfig.kmsan | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> index 7251b6b59e69..cae1ddcc18e1 100644
> --- a/lib/Kconfig.kmsan
> +++ b/lib/Kconfig.kmsan
> @@ -3,7 +3,7 @@ config HAVE_ARCH_KMSAN
>  	bool
>  
>  config HAVE_KMSAN_COMPILER
> -	def_bool CC_IS_CLANG
> +	def_bool $(cc-option,-fsanitize=kernel-memory)
>  
>  config KMSAN
>  	bool "KMSAN: detector of uninitialized values use"
> 
> ---
> base-commit: 211ddde0823f1442e4ad052a2f30f050145ccada
> change-id: 20251023-fix-kmsan-check-s390-clang-190d37bbcff3
> 
> Best regards,
> --  
> Nathan Chancellor <nathan@...nel.org>
> 

Thanks!

Acked-by: Nicolas Schier <nsc@...nel.org>


-- 
Nicolas