Commit 6baec880 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Linus Torvalds

kasan: turn off asan-stack for clang-8 and earlier

Building an arm64 allmodconfig kernel with clang results in over 140
warnings about overly large stack frames, the worst ones being:

  drivers/gpu/drm/panel/panel-sitronix-st7789v.c:196:12: error: stack frame size of 20224 bytes in function 'st7789v_prepare'
  drivers/video/fbdev/omap2/omapfb/displays/panel-tpo-td028ttec1.c:196:12: error: stack frame size of 13120 bytes in function 'td028ttec1_panel_enable'
  drivers/usb/host/max3421-hcd.c:1395:1: error: stack frame size of 10048 bytes in function 'max3421_spi_thread'
  drivers/net/wan/slic_ds26522.c:209:12: error: stack frame size of 9664 bytes in function 'slic_ds26522_probe'
  drivers/crypto/ccp/ccp-ops.c:2434:5: error: stack frame size of 8832 bytes in function 'ccp_run_cmd'
  drivers/media/dvb-frontends/stv0367.c:1005:12: error: stack frame size of 7840 bytes in function 'stv0367ter_algo'

None of these happen with gcc today, and almost all of these are the
result of a single known issue in llvm.  Hopefully it will eventually
get fixed with the clang-9 release.

In the meantime, the best idea I have is to turn off asan-stack for
clang-8 and earlier, so we can produce a kernel that is safe to run.

I have posted three patches that address the frame overflow warnings
that are not addressed by turning off asan-stack, so in combination with
this change, we get much closer to a clean allmodconfig build, which in
turn is necessary to do meaningful build regression testing.

It is still possible to turn on the CONFIG_ASAN_STACK option on all
versions of clang, and it's always enabled for gcc, but when
CONFIG_COMPILE_TEST is set, the option remains invisible, so
allmodconfig and randconfig builds (which are normally done with a
forced CONFIG_COMPILE_TEST) will still result in a mostly clean build.

Link: default avatarArnd Bergmann <>
Reviewed-by: default avatarQian Cai <>
Reviewed-by: default avatarMark Brown <>
Acked-by: default avatarAndrey Ryabinin <>
Cc: Dmitry Vyukov <>
Cc: Nick Desaulniers <>
Cc: Kostya Serebryany <>
Cc: Andrey Konovalov <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7d762d69
......@@ -113,6 +113,28 @@ config KASAN_INLINE
bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
default !(CLANG_VERSION < 90000)
depends on KASAN
The LLVM stack address sanitizer has a know problem that
causes excessive stack usage in a lot of functions, see
Disabling asan-stack makes it safe to run kernels build
with clang-8 with KASAN enabled, though it loses some of
the functionality.
This feature is always disabled when compile-testing with clang-8
or earlier to avoid cluttering the output in stack overflow
warnings, but clang-8 users can still enable it for builds without
CONFIG_COMPILE_TEST. On gcc and later clang versions it is
assumed to always be safe to use and enabled by default.
default 0
bool "KASan: use 4-level paging"
depends on KASAN && S390
......@@ -26,7 +26,7 @@ else
$(call cc-param,asan-globals=1) \
$(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
$(call cc-param,asan-stack=1) \
$(call cc-param,asan-stack=$(CONFIG_KASAN_STACK)) \
$(call cc-param,asan-use-after-scope=1) \
$(call cc-param,asan-instrument-allocas=1)
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