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linux/lib/Kconfig.kasan
Andrey Konovalov d9b571c885 kasan: fix KASAN_STACK dependency for HW_TAGS 
There's a runtime failure when running HW_TAGS-enabled kernel built with
GCC on hardware that doesn't support MTE.  GCC-built kernels always have
CONFIG_KASAN_STACK enabled, even though stack instrumentation isn't
supported by HW_TAGS.  Having that config enabled causes KASAN to issue
MTE-only instructions to unpoison kernel stacks, which causes the failure.

Fix the issue by disallowing CONFIG_KASAN_STACK when HW_TAGS is used.

(The commit that introduced CONFIG_KASAN_HW_TAGS specified proper
 dependency for CONFIG_KASAN_STACK_ENABLE but not for CONFIG_KASAN_STACK.)

Link: https://lkml.kernel.org/r/59e75426241dbb5611277758c8d4d6f5f9298dac.1615215441.git.andreyknvl@google.com
Fixes: 6a63a63ff1 ("kasan: introduce CONFIG_KASAN_HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: <stable@vger.kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-03-13 11:27:31 -08:00

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# SPDX-License-Identifier: GPL-2.0-only
# This config refers to the generic KASAN mode.
config HAVE_ARCH_KASAN
bool
config HAVE_ARCH_KASAN_SW_TAGS
bool
config HAVE_ARCH_KASAN_HW_TAGS
bool
config HAVE_ARCH_KASAN_VMALLOC
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)
# This option is only required for software KASAN modes.
# Old GCC versions don't have proper support for no_sanitize_address.
# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89124 for details.
config CC_HAS_WORKING_NOSANITIZE_ADDRESS
def_bool !CC_IS_GCC || GCC_VERSION >= 80300
menuconfig 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)) && \
CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
HAVE_ARCH_KASAN_HW_TAGS
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
select STACKDEPOT
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.
if KASAN
choice
prompt "KASAN mode"
default KASAN_GENERIC
help
KASAN has three modes:
1. generic KASAN (similar to userspace ASan,
x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC),
2. software tag-based KASAN (arm64 only, based on software
memory tagging (similar to userspace HWASan), enabled with
CONFIG_KASAN_SW_TAGS), and
3. hardware tag-based KASAN (arm64 only, based on hardware
memory tagging, enabled with CONFIG_KASAN_HW_TAGS).
All KASAN modes are strictly debugging features.
For better error reports enable CONFIG_STACKTRACE.
config KASAN_GENERIC
bool "Generic mode"
depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
help
Enables generic KASAN mode.
This mode is supported in both GCC and Clang. With GCC it requires
version 8.3.0 or later. Any supported Clang version is compatible,
but detection of out-of-bounds accesses for global variables is
supported only since Clang 11.
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.
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
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
help
Enables software tag-based KASAN mode.
This mode require software memory tagging support in the form of
HWASan-like compiler instrumentation.
Currently this mode is only implemented for arm64 CPUs and relies on
Top Byte Ignore. This mode requires Clang.
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.
Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
config KASAN_HW_TAGS
bool "Hardware tag-based mode"
depends on HAVE_ARCH_KASAN_HW_TAGS
depends on SLUB
help
Enables hardware tag-based KASAN mode.
This mode requires hardware memory tagging support, and can be used
by any architecture that provides it.
Currently this mode is only implemented for arm64 CPUs starting from
ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore.
endchoice
choice
prompt "Instrumentation type"
depends on KASAN_GENERIC || KASAN_SW_TAGS
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.
endchoice
config KASAN_STACK_ENABLE
bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
depends on KASAN_GENERIC || KASAN_SW_TAGS
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
to avoid cluttering the output in stack overflow warnings,
but clang users can still enable it for builds without
CONFIG_COMPILE_TEST. On gcc it is assumed to always be safe
to use and enabled by default.
config KASAN_STACK
int
depends on KASAN_GENERIC || KASAN_SW_TAGS
default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
default 0
config KASAN_SW_TAGS_IDENTIFY
bool "Enable memory corruption identification"
depends on KASAN_SW_TAGS
help
This option enables best-effort identification of bug type
(use-after-free or out-of-bounds) at the cost of increased
memory consumption.
config KASAN_VMALLOC
bool "Back mappings in vmalloc space with real shadow memory"
depends on KASAN_GENERIC && HAVE_ARCH_KASAN_VMALLOC
help
By default, the shadow region for vmalloc space is the read-only
zero page. This means that KASAN cannot detect errors involving
vmalloc space.
Enabling this option will hook in to vmap/vmalloc and back those
mappings with real shadow memory allocated on demand. This allows
for KASAN to detect more sorts of errors (and to support vmapped
stacks), but at the cost of higher memory usage.
config KASAN_KUNIT_TEST
tristate "KUnit-compatible tests of KASAN bug detection capabilities" if !KUNIT_ALL_TESTS
depends on KASAN && KUNIT
default KUNIT_ALL_TESTS
help
This is a KUnit test suite doing various nasty things like
out of bounds and use after free accesses. It is useful for testing
kernel debugging features like KASAN.
For more information on KUnit and unit tests in general, please refer
to the KUnit documentation in Documentation/dev-tools/kunit.
config KASAN_MODULE_TEST
tristate "KUnit-incompatible tests of KASAN bug detection capabilities"
depends on m && KASAN && !KASAN_HW_TAGS
help
This is a part of the KASAN test suite that is incompatible with
KUnit. Currently includes tests that do bad copy_from/to_user
accesses.
endif # KASAN
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