ubsan/overflow: Enable ignorelist parsing and add type filter

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.

Reviewed-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20250307041914.937329-3-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

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,

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)

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