From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan: don't emit builtin calls when sanitization is off With KASAN enabled the kernel has two different memset() functions, one with KASAN checks (memset) and one without (__memset). KASAN uses some macro tricks to use the proper version where required. For example memset() calls in mm/slub.c are without KASAN checks, since they operate on poisoned slab object metadata. The issue is that clang emits memset() calls even when there is no memset() in the source code. They get linked with improper memset() implementation and the kernel fails to boot due to a huge amount of KASAN reports during early boot stages. The solution is to add -fno-builtin flag for files with KASAN_SANITIZE := n marker. Link: http://lkml.kernel.org/r/8ffecfffe04088c52c42b92739c2bd8a0bcb3f5e.1516384594.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> Cc: Michal Marek <michal.lkml@xxxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Makefile | 3 ++- scripts/Makefile.kasan | 3 +++ scripts/Makefile.lib | 2 +- 3 files changed, 6 insertions(+), 2 deletions(-) diff -puN Makefile~kasan-dont-emit-builtin-calls-when-sanitization-is-off Makefile --- a/Makefile~kasan-dont-emit-builtin-calls-when-sanitization-is-off +++ a/Makefile @@ -434,7 +434,8 @@ export MAKE LEX YACC AWK GENKSYMS INSTAL export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS -export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_KASAN CFLAGS_UBSAN +export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL diff -puN scripts/Makefile.kasan~kasan-dont-emit-builtin-calls-when-sanitization-is-off scripts/Makefile.kasan --- a/scripts/Makefile.kasan~kasan-dont-emit-builtin-calls-when-sanitization-is-off +++ a/scripts/Makefile.kasan @@ -31,4 +31,7 @@ else endif CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope) + +CFLAGS_KASAN_NOSANITIZE := -fno-builtin + endif diff -puN scripts/Makefile.lib~kasan-dont-emit-builtin-calls-when-sanitization-is-off scripts/Makefile.lib --- a/scripts/Makefile.lib~kasan-dont-emit-builtin-calls-when-sanitization-is-off +++ a/scripts/Makefile.lib @@ -121,7 +121,7 @@ endif ifeq ($(CONFIG_KASAN),y) _c_flags += $(if $(patsubst n%,, \ $(KASAN_SANITIZE_$(basetarget).o)$(KASAN_SANITIZE)y), \ - $(CFLAGS_KASAN)) + $(CFLAGS_KASAN), $(CFLAGS_KASAN_NOSANITIZE)) endif ifeq ($(CONFIG_UBSAN),y) _