Patch "kasan: don't emit builtin calls when sanitization is off" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kasan-don-t-emit-builtin-calls-when-sanitization-is-off.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrey Konovalov <[email protected]>
Date: Tue, 6 Feb 2018 15:36:00 -0800
Subject: kasan: don't emit builtin calls when sanitization is off

From: Andrey Konovalov <[email protected]>

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.

---
 Makefile               |    3 ++-
 scripts/Makefile.kasan |    3 +++
 scripts/Makefile.lib   |    2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

@@ -432,7 +432,8 @@ export MAKE AWK GENKSYMS INSTALLKERNEL P
 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

@@ -31,4 +31,7 @@ else
 endif
 
 CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
+
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+
 endif

@@ -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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/kasan-rework-kconfig-settings.patch queue-4.15/media-hdpvr-fix-an-error-handling-path-in-hdpvr_probe.patch queue-4.15/media-dvb-usb-v2-lmedm04-move-ts2020-attach-to-dm04_lme2510_tuner.patch queue-4.15/kasan-don-t-emit-builtin-calls-when-sanitization-is-off.patch queue-4.15/media-dvb-usb-v2-lmedm04-improve-logic-checking-of-warm-start.patch