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

[Nathan Chancellor]

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 <l...@intel.com>
Closes: https://lore.kernel.org/r/202510220236...@intel.com/
Signed-off-by: Nathan Chancellor <nat...@kernel.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 <nat...@kernel.org>

[Nicolas Schier]

Thanks!

Acked-by: Nicolas Schier <n...@kernel.org>


--
Nicolas

[Nathan Chancellor]

On Thu, 23 Oct 2025 21:01:29 +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:
>

> [...]

Applied, thanks!

[1/1] KMSAN: Restore dynamic check for '-fsanitize=kernel-memory'
https://git.kernel.org/kbuild/c/a16758f0142ab

[Nathan Chancellor]

Whoops, sent the applied message for the wrong change... This is going
to be in kbuild-fixes as https://git.kernel.org/kbuild/c/3423b2866797c
for -next testing but I will adjust it for any tags I receive in the
next few days.

Cheers,
Nathan