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@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Makefile b/Makefile
index 11aff0f9e105f19f45f6f4861c22c25fe65b86d6..0d49ff4022fb532ab8db9da7bb03dbfa672e88fb 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -434,7 +434,8 @@ export MAKE LEX YACC AWK GENKSYMS INSTALLKERNEL PERL PYTHON UTS_MACHINE
 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 --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 1ce7115aa499b756abb9e713f41adb99b0fb4997..94c9e65cc83adb7be3464c77d83aec3ce835226e 100644 (file)
--- a/scripts/Makefile.kasan
+++ b/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 --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 5fdc1a19b02c02e8ad5c6353585b6deb09101c14..5589bae34af6299ca26bc0ae7760dc1586949430 100644 (file)
--- a/scripts/Makefile.lib
+++ b/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)