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kasan: don't emit builtin calls when sanitization is off
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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 <[email protected]>
Acked-by: Nick Desaulniers <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@xairy @torvalds
xairy authored and torvalds committed Feb 7, 2018
1 parent e237f98 commit 0e410e1
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Showing 3 changed files with 6 additions and 2 deletions.
3 changes: 2 additions & 1 deletion Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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3 changes: 3 additions & 0 deletions scripts/Makefile.kasan
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Original file line number Diff line number Diff line change
Expand Up @@ -31,4 +31,7 @@ else
endif

CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)

CFLAGS_KASAN_NOSANITIZE := -fno-builtin

endif
2 changes: 1 addition & 1 deletion scripts/Makefile.lib
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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