lib/Kconfig.kasan

# 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 ARCH_DISABLE_KASAN_INLINE
	bool
	help
	  Disables both inline and stack instrumentation. Selected by
	  architectures that do not support these instrumentation types.

config ARCH_NEEDS_DEFER_KASAN
	bool

config ARCH_DEFER_KASAN
	def_bool y
	depends on KASAN && ARCH_NEEDS_DEFER_KASAN
	help
	  Architectures should select this if they need to defer KASAN
	  initialization until shadow memory is properly set up. This
	  enables runtime control via static keys. Otherwise, KASAN uses
	  compile-time constants for better performance.

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 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: 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) || \
		   HAVE_ARCH_KASAN_HW_TAGS
	depends on SYSFS && !SLUB_TINY
	select STACKDEPOT_ALWAYS_INIT
	help
	  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

config CC_HAS_KASAN_MEMINTRINSIC_PREFIX
	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address -mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param asan-kernel-mem-intrinsic-prefix=1))
	# Don't define it if we don't need it: compilation of the test uses
	# this variable to decide how the compiler should treat builtins.
	depends on !KASAN_HW_TAGS
	help
	  The compiler is able to prefix memintrinsics with __asan or __hwasan.

choice
	prompt "KASAN mode"
	default KASAN_GENERIC
	help
	  KASAN has three modes:

	  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).

	  See Documentation/dev-tools/kasan.rst for details about each mode.

config KASAN_GENERIC
	bool "Generic KASAN"
	depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
	depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
	select SLUB_DEBUG
	select CONSTRUCTORS
	help
	  Enables Generic KASAN.

	  Requires GCC 8.3.0+ or Clang.

	  Consumes about 1/8th of available memory at kernel start and adds an
	  overhead of ~50% for dynamic allocations.
	  The performance slowdown is ~x3.

config KASAN_SW_TAGS
	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
	select CONSTRUCTORS
	help
	  Enables Software Tag-Based KASAN.

	  Requires GCC 11+ or Clang.

	  Supported only on arm64 CPUs and relies on Top Byte Ignore.

	  Consumes about 1/16th of available memory at kernel start and
	  add an overhead of ~20% for dynamic allocations.

	  May potentially introduce problems related to pointer casting and
	  comparison, as it embeds a tag into the top byte of each pointer.

config KASAN_HW_TAGS
	bool "Hardware Tag-Based KASAN"
	depends on HAVE_ARCH_KASAN_HW_TAGS
	help
	  Enables Hardware Tag-Based KASAN.

	  Requires GCC 10+ or Clang 12+.

	  Supported only on 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

choice
	prompt "Instrumentation type"
	depends on KASAN_GENERIC || KASAN_SW_TAGS
	default KASAN_INLINE if !ARCH_DISABLE_KASAN_INLINE

config KASAN_OUTLINE
	bool "Outline instrumentation"
	help
	  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
	  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 "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
	  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://llvm.org/pr38809. 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_VMALLOC
	bool "Check accesses to vmalloc allocations"
	depends on HAVE_ARCH_KASAN_VMALLOC
	help
	  Makes KASAN check the validity of accesses to vmalloc allocations.

	  With software KASAN modes, all types vmalloc allocations are
	  checked. Enabling this option leads to higher 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 && TRACEPOINTS
	default KUNIT_ALL_TESTS
	help
	  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/.

config KASAN_EXTRA_INFO
	bool "Record and report more information"
	depends on KASAN
	help
	  Record and report more information to help us find the cause of the
	  bug and to help us correlate the error with other system events.

	  Currently, the CPU number and timestamp are additionally
	  recorded for each heap block at allocation and free time, and
	  8 bytes will be added to each metadata structure that records
	  allocation or free information.

	  In Generic KASAN, each kmalloc-8 and kmalloc-16 object will add
	  16 bytes of additional memory consumption, and each kmalloc-32
	  object will add 8 bytes of additional memory consumption, not
	  affecting other larger objects.

	  In SW_TAGS KASAN and HW_TAGS KASAN, depending on the stack_ring_size
	  boot parameter, it will add 8 * stack_ring_size bytes of additional
	  memory consumption.

endif # KASAN