The patch titled
Subject: kasan: rework Kconfig settings
has been added to the -mm tree. Its filename is
kasan-rework-kconfig-settings.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kasan-rework-kconfig-settings.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kasan-rework-kconfig-settings.patch
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From: Arnd Bergmann <arnd@xxxxxxxx>
Subject: kasan: rework Kconfig settings
We get a lot of very large stack frames using gcc-7.0.1 with the default
-fsanitize-address-use-after-scope --param asan-stack=1 options, which can
easily cause an overflow of the kernel stack, e.g.
drivers/gpu/drm/i915/gvt/handlers.c:2434:1: warning: the frame size of 46176 bytes is larger than 3072 bytes
drivers/net/wireless/ralink/rt2x00/rt2800lib.c:5650:1: warning: the frame size of 23632 bytes is larger than 3072 bytes
lib/atomic64_test.c:250:1: warning: the frame size of 11200 bytes is larger than 3072 bytes
drivers/gpu/drm/i915/gvt/handlers.c:2621:1: warning: the frame size of 9208 bytes is larger than 3072 bytes
drivers/media/dvb-frontends/stv090x.c:3431:1: warning: the frame size of 6816 bytes is larger than 3072 bytes
fs/fscache/stats.c:287:1: warning: the frame size of 6536 bytes is larger than 3072 bytes
To reduce this risk, -fsanitize-address-use-after-scope is now split out
into a separate CONFIG_KASAN_EXTRA Kconfig option, leading to stack frames
that are smaller than 2 kilobytes most of the time on x86_64. An earlier
version of this patch also prevented combining KASAN_EXTRA with
KASAN_INLINE, but that is no longer necessary with gcc-7.0.1.
All patches to get the frame size below 2048 bytes with CONFIG_KASAN=y and
CONFIG_KASAN_EXTRA=n have been merged by maintainers now, so we can bring
back that default now. KASAN_EXTRA=y still causes lots of warnings but
now defaults to !COMPILE_TEST to disable it in allmodconfig, and it
remains disabled in all other defconfigs since it is a new option. I
arbitrarily raise the warning limit for KASAN_EXTRA to 3072 to reduce the
noise, but an allmodconfig kernel still has around 50 warnings on gcc-7.
I experimented a bit more with smaller stack frames and have another
follow-up series that reduces the warning limit for 64-bit architectures
to 1280 bytes (without CONFIG_KASAN).
With earlier versions of this patch series, I also had patches to address
the warnings we get with KASAN and/or KASAN_EXTRA, using a
"noinline_if_stackbloat" annotation. That annotation now got replaced
with a gcc-8 bugfix (see
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715) and a workaround for
older compilers, which means that KASAN_EXTRA is now just as bad as before
and will lead to an instant stack overflow in a few extreme cases.
This reverts parts of commit commit 3f181b4 ("lib/Kconfig.debug: disable
-Wframe-larger-than warnings with KASAN=y"). Two patches in linux-next
should be merged first to avoid introducing warnings in an allmodconfig
build:
3cd890dbe2a4 ("media: dvb-frontends: fix i2c access helpers for KASAN")
16c3ada89cff ("media: r820t: fix r820t_write_reg for KASAN")
Link: http://lkml.kernel.org/r/20171221134744.2295529-1-arnd@xxxxxxxx
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
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>
---
lib/Kconfig.debug | 2 +-
lib/Kconfig.kasan | 11 +++++++++++
scripts/Makefile.kasan | 3 +++
3 files changed, 15 insertions(+), 1 deletion(-)
diff -puN lib/Kconfig.debug~kasan-rework-kconfig-settings lib/Kconfig.debug
--- a/lib/Kconfig.debug~kasan-rework-kconfig-settings
+++ a/lib/Kconfig.debug
@@ -217,7 +217,7 @@ config ENABLE_MUST_CHECK
config FRAME_WARN
int "Warn for stack frames larger than (needs gcc 4.4)"
range 0 8192
- default 0 if KASAN
+ default 3072 if KASAN_EXTRA
default 2048 if GCC_PLUGIN_LATENT_ENTROPY
default 1280 if (!64BIT && PARISC)
default 1024 if (!64BIT && !PARISC)
diff -puN lib/Kconfig.kasan~kasan-rework-kconfig-settings lib/Kconfig.kasan
--- a/lib/Kconfig.kasan~kasan-rework-kconfig-settings
+++ a/lib/Kconfig.kasan
@@ -20,6 +20,17 @@ config KASAN
Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
+config KASAN_EXTRA
+ bool "KAsan: extra checks"
+ depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST
+ help
+ This enables further checks in the kernel address sanitizer, for now
+ it only includes the address-use-after-scope check that can lead
+ to excessive kernel stack usage, frame size warnings and longer
+ compile time.
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more
+
+
choice
prompt "Instrumentation type"
depends on KASAN
diff -puN scripts/Makefile.kasan~kasan-rework-kconfig-settings scripts/Makefile.kasan
--- a/scripts/Makefile.kasan~kasan-rework-kconfig-settings
+++ a/scripts/Makefile.kasan
@@ -38,5 +38,8 @@ else
endif
+ifdef CONFIG_KASAN_EXTRA
CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
endif
+
+endif
_
Patches currently in -mm which might be from arnd@xxxxxxxx are
mm-thp-use-down_read_trylock-in-khugepaged-to-avoid-long-block-fix-2.patch
bugh-work-around-gcc-pr82365-in-bug.patch
kasan-rework-kconfig-settings.patch