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

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Message-ID: <upvdnfozcexlpb2x4auimec347adozkl2al4hu2yp3kfagdeyp@dqs2ft6wdmog>
Date: Fri, 7 Mar 2025 15:33:01 -0800
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <kees@...nel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
	Marco Elver <elver@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Andrey Ryabinin <ryabinin.a.a@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, kasan-dev@...glegroups.com, linux-hardening@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, Bill Wendling <morbo@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Tony Ambardar <tony.ambardar@...il.com>, 
	Alexander Potapenko <glider@...gle.com>, Jan Hendrik Farr <kernel@...rr.cc>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 3/3] ubsan/overflow: Enable ignorelist parsing and add
 type filter

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@...nel.org>
> ---
> Cc: Justin Stitt <justinstitt@...gle.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: Marco Elver <elver@...gle.com>
> Cc: Andrey Konovalov <andreyknvl@...il.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Nicolas Schier <nicolas@...sle.eu>
> Cc: kasan-dev@...glegroups.com
> Cc: linux-hardening@...r.kernel.org
> Cc: linux-kbuild@...r.kernel.org
> ---
>  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@...gle.com>

[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