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

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Message-Id: <20251023-fix-kmsan-check-s390-clang-v1-1-4e6df477a4cc@kernel.org>
Date: Thu, 23 Oct 2025 21:01:29 +0200
From: Nathan Chancellor <nathan@...nel.org>
To: Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, 
 Dmitry Vyukov <dvyukov@...gle.com>
Cc: Nicolas Schier <nsc@...nel.org>, Kees Cook <kees@...nel.org>, 
 kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>, 
 Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] KMSAN: Restore dynamic check for
 '-fsanitize=kernel-memory'

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>