kasan: turn off asan-stack for clang-8 and earlier [Linux 5.0]

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 d8c474b..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

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