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Commit fe30ddca authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Andrew Morton
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kasan: clean-up kconfig options descriptions 

Various readability clean-ups of KASAN Kconfig options.

No functional changes.

Link: https://lkml.kernel.org/r/c160840dd9e4b1ad5529ecfdb0bba35d9a14d826.1652203271.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/47afaecec29221347bee49f58c258ac1ced3b429.1652123204.git.andreyknvl@google.comSigned-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: default avatarMarco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ca89f2a2
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Showing with 82 additions and 86 deletions
lib/Kconfig.kasan
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# SPDX-License-Identifier: GPL-2.0-only
# This config refers to the generic KASAN mode.
config HAVE_ARCH_KASAN
bool
......@@ -15,9 +16,8 @@ config HAVE_ARCH_KASAN_VMALLOC
config ARCH_DISABLE_KASAN_INLINE
bool
help
An architecture might not support inline instrumentation.
When this option is selected, inline and stack instrumentation are
disabled.
Disables both inline and stack instrumentation. Selected by
architectures that do not support these instrumentation types.
config CC_HAS_KASAN_GENERIC
def_bool $(cc-option, -fsanitize=kernel-address)
......@@ -26,13 +26,13 @@ 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.
# Old GCC versions do not 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"
bool "KASAN: dynamic memory safety error detector"
depends on (((HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
(HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
......@@ -40,10 +40,13 @@ menuconfig KASAN
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
select STACKDEPOT_ALWAYS_INIT
help
Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
designed to find out-of-bounds accesses and use-after-free bugs.
Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
error detector designed to find out-of-bounds and use-after-free bugs.
See Documentation/dev-tools/kasan.rst for details.
For better error reports, also enable CONFIG_STACKTRACE.
if KASAN
choice
......@@ -51,75 +54,71 @@ choice
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.
1. Generic KASAN (supported by many architectures, enabled with
CONFIG_KASAN_GENERIC, similar to userspace ASan),
2. Software Tag-Based KASAN (arm64 only, based on software memory
tagging, enabled with CONFIG_KASAN_SW_TAGS, similar to userspace
HWASan), and
3. Hardware Tag-Based KASAN (arm64 only, based on hardware memory
tagging, enabled with CONFIG_KASAN_HW_TAGS).
For better error reports enable CONFIG_STACKTRACE.
See Documentation/dev-tools/kasan.rst for details about each mode.
config KASAN_GENERIC
bool "Generic mode"
bool "Generic KASAN"
depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
help
Enables generic KASAN mode.
Enables Generic KASAN.
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.
Requires GCC 8.3.0+ or Clang.
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.
Consumes about 1/8th of available memory at kernel start and adds an
overhead of ~50% for dynamic allocations.
The performance slowdown is ~x3.
Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
(Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
config KASAN_SW_TAGS
bool "Software tag-based mode"
bool "Software Tag-Based KASAN"
depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
help
Enables software tag-based KASAN mode.
Enables Software Tag-Based KASAN.
This mode require software memory tagging support in the form of
HWASan-like compiler instrumentation.
Requires GCC 11+ or Clang.
Currently this mode is only implemented for arm64 CPUs and relies on
Top Byte Ignore. This mode requires Clang.
Supported only on arm64 CPUs and relies on Top Byte Ignore.
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.
Consumes about 1/16th of available memory at kernel start and
add an overhead of ~20% for dynamic allocations.
Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
May potentially introduce problems related to pointer casting and
comparison, as it embeds a tag into the top byte of each pointer.
(Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
config KASAN_HW_TAGS
bool "Hardware tag-based mode"
bool "Hardware Tag-Based KASAN"
depends on HAVE_ARCH_KASAN_HW_TAGS
depends on SLUB
help
Enables hardware tag-based KASAN mode.
Enables Hardware Tag-Based KASAN.
Requires GCC 10+ or Clang 12+.
This mode requires hardware memory tagging support, and can be used
by any architecture that provides it.
Supported only on arm64 CPUs starting from ARMv8.5 and relies on
Memory Tagging Extension and Top Byte Ignore.
Currently this mode is only implemented for arm64 CPUs starting from
ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore.
Consumes about 1/32nd of available memory.
May potentially introduce problems related to pointer casting and
comparison, as it embeds a tag into the top byte of each pointer.
endchoice
......@@ -131,83 +130,80 @@ choice
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.
Makes the compiler insert function calls that check whether the memory
is accessible before each memory access. Slower than KASAN_INLINE, but
does not bloat the size of the kernel's .text section so much.
config KASAN_INLINE
bool "Inline instrumentation"
depends on !ARCH_DISABLE_KASAN_INLINE
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.
Makes the compiler directly insert memory accessibility checks before
each memory access. Faster than KASAN_OUTLINE (gives ~x2 boost for
some workloads), but makes the kernel's .text size much bigger.
endchoice
config KASAN_STACK
bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
bool "Stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
depends on KASAN_GENERIC || KASAN_SW_TAGS
depends on !ARCH_DISABLE_KASAN_INLINE
default y if CC_IS_GCC
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.
If the architecture disables inline instrumentation, stack
instrumentation is also disabled as it adds inline-style
instrumentation that is run unconditionally.
Disables stack instrumentation and thus KASAN's ability to detect
out-of-bounds bugs in stack variables.
With Clang, stack instrumentation has a problem that causes excessive
stack usage, see https://bugs.llvm.org/show_bug.cgi?id=38809. Thus,
with Clang, this option is deemed unsafe.
This option is always disabled when compile-testing with Clang to
avoid cluttering the log with stack overflow warnings.
With GCC, enabling stack instrumentation is assumed to be safe.
If the architecture disables inline instrumentation via
ARCH_DISABLE_KASAN_INLINE, stack instrumentation gets disabled
as well, as it adds inline-style instrumentation that is run
unconditionally.
config KASAN_TAGS_IDENTIFY
bool "Enable memory corruption identification"
bool "Memory corruption type identification"
depends on KASAN_SW_TAGS || KASAN_HW_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.
Enables best-effort identification of the bug types (use-after-free
or out-of-bounds) at the cost of increased memory consumption.
Only applicable for the tag-based KASAN modes.
config KASAN_VMALLOC
bool "Check accesses to vmalloc allocations"
depends on HAVE_ARCH_KASAN_VMALLOC
help
This mode makes KASAN check accesses to vmalloc allocations for
validity.
Makes KASAN check the validity of accesses to vmalloc allocations.
With software KASAN modes, checking is done for all types of vmalloc
allocations. Enabling this option leads to higher memory usage.
With software KASAN modes, all types vmalloc allocations are
checked. Enabling this option leads to higher memory usage.
With hardware tag-based KASAN, only VM_ALLOC mappings are checked.
There is no additional memory usage.
With Hardware Tag-Based KASAN, only non-executable VM_ALLOC mappings
are checked. There is no additional 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.
A KUnit-based KASAN test suite. Triggers different kinds of
out-of-bounds and use-after-free accesses. Useful for testing whether
KASAN can detect certain bug types.
For more information on KUnit and unit tests in general, please refer
to the KUnit documentation in Documentation/dev-tools/kunit.
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.
A part of the KASAN test suite that is not integrated with KUnit.
Incompatible with Hardware Tag-Based KASAN.
endif # KASAN
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