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.

Reviewed-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20250307041914.937329-2-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

Author: kees

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)

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		\