linux-kernel - [PATCH 2/3] ubsan/overflow: Enable pattern exclusions

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Message-Id: <20250307041914.937329-2-kees@kernel.org>
Date: Thu,  6 Mar 2025 20:19:10 -0800
From: Kees Cook <kees@...nel.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	linux-kbuild@...r.kernel.org,
	kasan-dev@...glegroups.com,
	linux-hardening@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.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: [PATCH 2/3] ubsan/overflow: Enable pattern exclusions

To make integer wrap-around mitigation actually useful, the associated
sanitizers must not instrument cases where the wrap-around is explicitly
defined (e.g. "-2UL"), being tested for (e.g. "if (a + b < a)"), or
where it has no impact on code flow (e.g. "while (var--)"). Enable
pattern exclusions for the integer wrap sanitizers.

Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nicolas Schier <nicolas@...sle.eu>
Cc: Marco Elver <elver@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...il.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: linux-kbuild@...r.kernel.org
Cc: kasan-dev@...glegroups.com
Cc: linux-hardening@...r.kernel.org
---
 lib/Kconfig.ubsan      | 1 +
 scripts/Makefile.ubsan | 1 +
 2 files changed, 2 insertions(+)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 63e5622010e0..888c2e72c586 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -120,6 +120,7 @@ config UBSAN_INTEGER_WRAP
 	bool "Perform checking for integer arithmetic wrap-around"
 	default UBSAN
 	depends on !COMPILE_TEST
+	depends on $(cc-option,-fsanitize-undefined-ignore-overflow-pattern=all)
 	depends on $(cc-option,-fsanitize=signed-integer-overflow)
 	depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
 	depends on $(cc-option,-fsanitize=implicit-signed-integer-truncation)
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 4fad9afed24c..233379c193a7 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -15,6 +15,7 @@ ubsan-cflags-$(CONFIG_UBSAN_TRAP)		+= $(call cc-option,-fsanitize-trap=undefined
 export CFLAGS_UBSAN := $(ubsan-cflags-y)
 
 ubsan-integer-wrap-cflags-$(CONFIG_UBSAN_INTEGER_WRAP)     +=	\
+	-fsanitize-undefined-ignore-overflow-pattern=all	\
 	-fsanitize=signed-integer-overflow			\
 	-fsanitize=unsigned-integer-overflow			\
 	-fsanitize=implicit-signed-integer-truncation		\
-- 
2.34.1