On 12/21/2017 04:46 PM, Arnd Bergmann wrote: > 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") > > Cc: stable@xxxxxxxxxxxxxxx > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: kasan-dev@xxxxxxxxxxxxxxxx > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
