linux-kernel - [PATCH] kasan: fix GCC mem-intrinsic prefix with sw tags

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Message-ID: <20250821120735.156244-1-ada.coupriediaz@arm.com>
Date: Thu, 21 Aug 2025 13:07:35 +0100
From: Ada Couprie Diaz <ada.coupriediaz@....com>
To: kasan-dev@...glegroups.com
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Marco Elver <elver@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Mark Rutland <mark.rutland@....com>,
	Yeoreum Yun <yeoreum.yun@....com>,
	Ada Couprie Diaz <ada.coupriediaz@....com>
Subject: [PATCH] kasan: fix GCC mem-intrinsic prefix with sw tags

GCC doesn't support "hwasan-kernel-mem-intrinsic-prefix", only
"asan-kernel-mem-intrinsic-prefix"[0], while LLVM supports both.
This is already taken into account when checking
"CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX", but not in the KASAN Makefile
adding those parameters when "CONFIG_KASAN_SW_TAGS" is enabled.

Replace the version check with "CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX",
which already validates that mem-intrinsic prefix parameter can be used,
and choose the correct name depending on compiler.

GCC 13 and above trigger "CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX" which
prevents `mem{cpy,move,set}()` being redefined in "mm/kasan/shadow.c"
since commit 36be5cba99f6 ("kasan: treat meminstrinsic as builtins
in uninstrumented files"), as we expect the compiler to prefix
those calls with `__(hw)asan_` instead.
But as the option passed to GCC has been incorrect, the compiler has
not been emitting those prefixes, effectively never calling
the instrumented versions of `mem{cpy,move,set}()`
with "CONFIG_KASAN_SW_TAGS" enabled.

If "CONFIG_FORTIFY_SOURCES" is enabled, this issue would be mitigated
as it redefines `mem{cpy,move,set}()` and properly aliases the
`__underlying_mem*()` that will be called to the instrumented versions.

[0]: https://gcc.gnu.org/onlinedocs/gcc-13.4.0/gcc/Optimize-Options.html

Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@....com>
Fixes: 36be5cba99f6 ("kasan: treat meminstrinsic as builtins in uninstrumented files")
---
 scripts/Makefile.kasan | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 693dbbebebba..0ba2aac3b8dc 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -86,10 +86,14 @@ kasan_params += hwasan-instrument-stack=$(stack_enable) \
 		hwasan-use-short-granules=0 \
 		hwasan-inline-all-checks=0

-# Instrument memcpy/memset/memmove calls by using instrumented __hwasan_mem*().
-ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
-	kasan_params += hwasan-kernel-mem-intrinsic-prefix=1
-endif
+# Instrument memcpy/memset/memmove calls by using instrumented __(hw)asan_mem*().
+ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	ifdef CONFIG_CC_IS_GCC
+		kasan_params += asan-kernel-mem-intrinsic-prefix=1
+	else
+		kasan_params += hwasan-kernel-mem-intrinsic-prefix=1
+	endif
+endif # CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX

 endif # CONFIG_KASAN_SW_TAGS

base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
-- 
2.43.0