This Linux kernel change "kasan: turn off asan-stack for clang-8 and earlier" is included in the Linux 5.0 release. This change is authored by Arnd Bergmann <arnd [at] arndb.de> on Thu Feb 28 16:21:58 2019 -0800. The commit for this change in Linux stable tree is 6baec88 (patch).
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: http://lkml.kernel.org/r/[email protected] Link: https://bugs.llvm.org/show_bug.cgi?id=38809 Signed-off-by: Arnd Bergmann <[email protected]> Reviewed-by: Qian Cai <[email protected]> Reviewed-by: Mark Brown <[email protected]> Acked-by: Andrey Ryabinin <[email protected]> Cc: Dmitry Vyukov <[email protected]> Cc: Nick Desaulniers <[email protected]> Cc: Kostya Serebryany <[email protected]> Cc: Andrey Konovalov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
There are 24 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.
lib/Kconfig.kasan | 22 ++++++++++++++++++++++ scripts/Makefile.kasan | 2 +- 2 files changed, 23 insertions(+), 1 deletion(-) diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan index d8c474b6..9737059 100644 --- a/lib/Kconfig.kasan +++ b/lib/Kconfig.kasan @@ -113,6 +113,28 @@ config KASAN_INLINE endchoice +config KASAN_STACK_ENABLE + bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST + default !(CLANG_VERSION < 90000) + depends on KASAN + help + The LLVM stack address sanitizer has a know problem that + causes excessive stack usage in a lot of functions, see + https://bugs.llvm.org/show_bug.cgi?id=38809 + 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. + +config KASAN_STACK + int + default 1 if KASAN_STACK_ENABLE || CC_IS_GCC + default 0 + config KASAN_S390_4_LEVEL_PAGING bool "KASan: use 4-level paging" depends on KASAN && S390 diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan index 25c259d..6deabed 100644 --- a/scripts/Makefile.kasan +++ b/scripts/Makefile.kasan @@ -26,7 +26,7 @@ else CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \ $(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) endif