ubsan: introduce CONFIG_UBSAN_LOCAL_BOUNDS for Clang

When the kernel is compiled with Clang, -fsanitize=bounds expands to
-fsanitize=array-bounds and -fsanitize=local-bounds.

Enabling -fsanitize=local-bounds with Clang has the unfortunate
side-effect of inserting traps; this goes back to its original intent,
which was as a hardening and not a debugging feature [1].  The same
feature made its way into -fsanitize=bounds, but the traps remained.  For
that reason, -fsanitize=bounds was split into 'array-bounds' and
'local-bounds' [2].

Since 'local-bounds' doesn't behave like a normal sanitizer, enable it
with Clang only if trapping behaviour was requested by

Add the UBSAN_BOUNDS_LOCAL config to Kconfig.ubsan to enable the
'local-bounds' option by default when UBSAN_TRAP is enabled.


Suggested-by: Marco Elver <>
Signed-off-by: George Popescu <>
Signed-off-by: Andrew Morton <>
Reviewed-by: David Brazdil <>
Reviewed-by: Marco Elver <>
Cc: Masahiro Yamada <>
Cc: Michal Marek <>
Cc: Nathan Chancellor <>
Cc: Nick Desaulniers <>
Cc: Kees Cook <>
Cc: Dmitry Vyukov <>
Cc: Arnd Bergmann <>
Cc: Peter Zijlstra <>
Signed-off-by: Linus Torvalds <>
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 774315d..58f8d03 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -47,6 +47,20 @@
 	  to the {str,mem}*cpy() family of functions (that is addressed
+	bool "Perform array local bounds checking"
+	depends on UBSAN_TRAP
+	depends on CC_IS_CLANG
+	depends on !UBSAN_KCOV_BROKEN
+	help
+	  This option enables -fsanitize=local-bounds which traps when an
+	  exception/error is detected. Therefore, it should be enabled only
+	  if trapping is expected.
+	  Enabling this option detects errors due to accesses through a
+	  pointer that is derived from an object of a statically-known size,
+	  where an added offset (which may not be known statically) is
+	  out-of-bounds.
 config UBSAN_MISC
 	bool "Enable all other Undefined Behavior sanity checks"
 	default UBSAN
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 2734802..4e3fff0 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -4,7 +4,15 @@
-      CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
+      ifdef CONFIG_CC_IS_CLANG
+            CFLAGS_UBSAN += -fsanitize=array-bounds
+      else
+            CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
+      endif
+      CFLAGS_UBSAN += -fsanitize=local-bounds