kasan: don't emit builtin calls when sanitization is off

commit 0e410e158e5baa1300bdf678cea4f4e0cf9d8b94 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Makefile b/Makefile
index 76a0b13..a7160d6 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -416,7 +416,8 @@ export MAKE 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 1ce7115..94c9e65 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 04b5633..0b46136 100644 (file)
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -128,7 +128,7 @@ 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)