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kernel_optimize_test/lib/Kconfig.kasan
Arnd Bergmann 6baec880d7 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/20190222222950.3997333-1-arnd@arndb.de
Link: https://bugs.llvm.org/show_bug.cgi?id=38809
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Qian Cai <cai@lca.pw>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-01 09:02:33 -08:00

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# This config refers to the generic KASAN mode.
config HAVE_ARCH_KASAN
bool
config HAVE_ARCH_KASAN_SW_TAGS
bool
config CC_HAS_KASAN_GENERIC
def_bool $(cc-option, -fsanitize=kernel-address)
config CC_HAS_KASAN_SW_TAGS
def_bool $(cc-option, -fsanitize=kernel-hwaddress)
config KASAN
bool "KASAN: runtime memory debugger"
depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
(HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
help
Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
designed to find out-of-bounds accesses and use-after-free bugs.
See Documentation/dev-tools/kasan.rst for details.
choice
prompt "KASAN mode"
depends on KASAN
default KASAN_GENERIC
help
KASAN has two modes: generic KASAN (similar to userspace ASan,
x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
software tag-based KASAN (a version based on software memory
tagging, arm64 only, similar to userspace HWASan, enabled with
CONFIG_KASAN_SW_TAGS).
Both generic and tag-based KASAN are strictly debugging features.
config KASAN_GENERIC
bool "Generic mode"
depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
select STACKDEPOT
help
Enables generic KASAN mode.
Supported in both GCC and Clang. With GCC it requires version 4.9.2
or later for basic support and version 5.0 or later for detection of
out-of-bounds accesses for stack and global variables and for inline
instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
version 3.7.0 or later and it doesn't support detection of
out-of-bounds accesses for global variables yet.
This mode consumes about 1/8th of available memory at kernel start
and introduces an overhead of ~x1.5 for the rest of the allocations.
The performance slowdown is ~x3.
For better error detection enable CONFIG_STACKTRACE.
Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
config KASAN_SW_TAGS
bool "Software tag-based mode"
depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
select STACKDEPOT
help
Enables software tag-based KASAN mode.
This mode requires Top Byte Ignore support by the CPU and therefore
is only supported for arm64.
This mode requires Clang version 7.0.0 or later.
This mode consumes about 1/16th of available memory at kernel start
and introduces an overhead of ~20% for the rest of the allocations.
This mode may potentially introduce problems relating to pointer
casting and comparison, as it embeds tags into the top byte of each
pointer.
For better error detection enable CONFIG_STACKTRACE.
Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
endchoice
config KASAN_EXTRA
bool "KASAN: extra checks"
depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST
help
This enables further checks in generic KASAN, 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.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715
choice
prompt "Instrumentation type"
depends on KASAN
default KASAN_OUTLINE
config KASAN_OUTLINE
bool "Outline instrumentation"
help
Before every memory access compiler insert function call
__asan_load*/__asan_store*. These functions performs check
of shadow memory. This is slower than inline instrumentation,
however it doesn't bloat size of kernel's .text section so
much as inline does.
config KASAN_INLINE
bool "Inline instrumentation"
help
Compiler directly inserts code checking shadow memory before
memory accesses. This is faster than outline (in some workloads
it gives about x2 boost over outline instrumentation), but
make kernel's .text size much bigger.
For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
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
help
Compiling the kernel with KASan disables automatic 3-level vs
4-level paging selection. 3-level paging is used by default (up
to 3TB of RAM with KASan enabled). This options allows to force
4-level paging instead.
config TEST_KASAN
tristate "Module for testing KASAN for bug detection"
depends on m && KASAN
help
This is a test module doing various nasty things like
out of bounds accesses, use after free. It is useful for testing
kernel debugging features like KASAN.
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