Re: [PATCH 3/3] ubsan/overflow: Enable ignorelist parsing and add type filter

[Justin Stitt]

Hi,

On Thu, Mar 06, 2025 at 08:19:11PM -0800, Kees Cook wrote:
> Limit integer wrap-around mitigation to only the "size_t" type (for
> now). Notably this covers all special functions/builtins that return
> "size_t", like sizeof(). This remains an experimental feature and is
> likely to be replaced with type annotations.

For future travelers, track the progress of type annotations over at
[1]. There's still discussion on how these will be implemented in Clang.

> 
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> ---
> Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Nicolas Schier <nicolas@xxxxxxxxx>
> Cc: kasan-dev@xxxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Cc: linux-kbuild@xxxxxxxxxxxxxxx
> ---
>  lib/Kconfig.ubsan               | 1 +
>  scripts/Makefile.ubsan          | 3 ++-
>  scripts/integer-wrap-ignore.scl | 3 +++
>  3 files changed, 6 insertions(+), 1 deletion(-)
>  create mode 100644 scripts/integer-wrap-ignore.scl
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 888c2e72c586..4216b3a4ff21 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -125,6 +125,7 @@ config UBSAN_INTEGER_WRAP
>  	depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
>  	depends on $(cc-option,-fsanitize=implicit-signed-integer-truncation)
>  	depends on $(cc-option,-fsanitize=implicit-unsigned-integer-truncation)
> +	depends on $(cc-option,-fsanitize-ignorelist=/dev/null)
>  	help
>  	  This option enables all of the sanitizers involved in integer overflow
>  	  (wrap-around) mitigation: signed-integer-overflow, unsigned-integer-overflow,
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 233379c193a7..9e35198edbf0 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -19,5 +19,6 @@ ubsan-integer-wrap-cflags-$(CONFIG_UBSAN_INTEGER_WRAP)     +=	\
>  	-fsanitize=signed-integer-overflow			\
>  	-fsanitize=unsigned-integer-overflow			\
>  	-fsanitize=implicit-signed-integer-truncation		\
> -	-fsanitize=implicit-unsigned-integer-truncation
> +	-fsanitize=implicit-unsigned-integer-truncation		\
> +	-fsanitize-ignorelist=$(srctree)/scripts/integer-wrap-ignore.scl
>  export CFLAGS_UBSAN_INTEGER_WRAP := $(ubsan-integer-wrap-cflags-y)
> diff --git a/scripts/integer-wrap-ignore.scl b/scripts/integer-wrap-ignore.scl
> new file mode 100644
> index 000000000000..431c3053a4a2
> --- /dev/null
> +++ b/scripts/integer-wrap-ignore.scl
> @@ -0,0 +1,3 @@
> +[{unsigned-integer-overflow,signed-integer-overflow,implicit-signed-integer-truncation,implicit-unsigned-integer-truncation}]
> +type:*
> +type:size_t=sanitize

Hi again future travelers, sanitizer special case list support for
overflow/truncation sanitizers as well as the "=sanitize" comes from a
new Clang 20 feature allowing SCL's to specify sanitize categories, see [2].

> -- 
> 2.34.1
> 
>

The plumbing looks correct,

Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx>

[1]: https://discourse.llvm.org/t/rfc-clang-canonical-wrapping-and-non-wrapping-types/84356
[2]: https://github.com/llvm/llvm-project/pull/107332

Thanks
Justin