Re: [PATCH] KMSAN: fix memset() when using fortify-source, again

[Kees Cook <kees@kernel.org>]

On Thu, Jun 18, 2026 at 04:29:43PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Both kmsan and fortify-source replace the memset function. When both
> are enabled at the same time, the kmsan version gets used, which triggers
> a warning about fortify-source being nonfunctional:
> 
> warning: unsafe memset() usage lacked '__write_overflow' symbol in /home/arnd/arm-soc/lib/test_fortify/write_overflow-memset.c
> warning: unsafe memset() usage lacked '__write_overflow_field' symbol in /home/arnd/arm-soc/lib/test_fortify/write_overflow_field-memset.c
> 
> Commit 78a498c3a227 already tried to address this, but this seems
> to only have worked for memcpy() and memmove() but not memset(),
> which is still lacking the macro definition when KMSAN is enabled.
> 
> Remove the incorrect #ifndef check around the memset() macro.

Ah, nice find.

> 
> Fixes: ff901d80fff6 ("x86: kmsan: use __msan_ string functions where possible.")
> Fixes: 78a498c3a227 ("x86: fortify: kmsan: fix KMSAN fortify builds")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> The patch passes randconfig builds on x86/arm/arm64/s390 for me,
> but please double-check all the corner cases, as it's still
> possible that the #ifndef is required to work around a runtime
> issue that I did not test.

How about I drop this into -next right after -rc2 and we can see what
falls out of it?

-Kees

-- 
Kees Cook