Re: [PATCH] ubsan: integer-overflow: depend on BROKEN to keep this out of CI

[Nathan Chancellor <nathan@kernel.org>]

On Wed, May 28, 2025 at 11:26:22AM -0700, Kees Cook wrote:
> Depending on !COMPILE_TEST isn't sufficient to keep this feature out of
> CI because we can't stop it from being included in randconfig builds.
> This feature is still highly experimental, and is developed in lock-step
> with Clang's Overflow Behavior Types[1]. Depend on BROKEN to keep it
> from being enabled by anyone not expecting it.
> 
> Link: https://discourse.llvm.org/t/rfc-v2-clang-introduce-overflowbehaviortypes-for-wrapping-and-non-wrapping-arithmetic/86507 [1]
> Signed-off-by: Kees Cook <kees@kernel.org>

Should this have a 'Cc: stable@vger.kernel.org' on it? There might not
be much randconfig testing on stable but it is still very much possible
for some random user to turn this on and report problems.

Regardless of that though, I think this is a good idea with how much of
this feature is still being ironed out.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Once this lands, I plan to mark all issues in the CBL issue tracker that
came about from UBSAN_INTEGER_WRAP as 'have a workaround applied' since
it will not be possible for regular users to hit them but you may
consider notating them in case they need to be addressed before the
feature can be reenabled.

> ---
> Cc: Justin Stitt <justinstitt@google.com>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Jann Horn <jannh@google.com>
> Cc: Marco Elver <elver@google.com>
> Cc: llvm@lists.linux.dev
> Cc: <linux-hardening@vger.kernel.org>
> ---
>  lib/Kconfig.ubsan | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index f6ea0c5b5da3..96cd89668467 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -118,6 +118,8 @@ config UBSAN_UNREACHABLE
>  
>  config UBSAN_INTEGER_WRAP
>  	bool "Perform checking for integer arithmetic wrap-around"
> +	# This is very experimental so drop the next line if you really want it
> +	depends on BROKEN
>  	depends on !COMPILE_TEST
>  	depends on $(cc-option,-fsanitize-undefined-ignore-overflow-pattern=all)
>  	depends on $(cc-option,-fsanitize=signed-integer-overflow)
> -- 
> 2.34.1
> 
>