# SPDX-License-Identifier: GPL-2.0-only
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# This config refers to the generic KASAN mode.
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config HAVE_ARCH_KASAN
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bool
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config HAVE_ARCH_KASAN_SW_TAGS
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bool
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config HAVE_ARCH_KASAN_HW_TAGS
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bool
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config HAVE_ARCH_KASAN_VMALLOC
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bool
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config CC_HAS_KASAN_GENERIC
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def_bool $(cc-option, -fsanitize=kernel-address)
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config CC_HAS_KASAN_SW_TAGS
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def_bool $(cc-option, -fsanitize=kernel-hwaddress)
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# This option is only required for software KASAN modes.
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# Old GCC versions don't have proper support for no_sanitize_address.
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# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89124 for details.
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config CC_HAS_WORKING_NOSANITIZE_ADDRESS
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def_bool !CC_IS_GCC || GCC_VERSION >= 80300
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menuconfig KASAN
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bool "KASAN: runtime memory debugger"
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depends on (((HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
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(HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
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CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
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HAVE_ARCH_KASAN_HW_TAGS
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depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
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select STACKDEPOT
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help
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Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
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designed to find out-of-bounds accesses and use-after-free bugs.
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See Documentation/dev-tools/kasan.rst for details.
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if KASAN
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choice
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prompt "KASAN mode"
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default KASAN_GENERIC
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help
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KASAN has three modes:
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1. generic KASAN (similar to userspace ASan,
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x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC),
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2. software tag-based KASAN (arm64 only, based on software
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memory tagging (similar to userspace HWASan), enabled with
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CONFIG_KASAN_SW_TAGS), and
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3. hardware tag-based KASAN (arm64 only, based on hardware
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memory tagging, enabled with CONFIG_KASAN_HW_TAGS).
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All KASAN modes are strictly debugging features.
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For better error reports enable CONFIG_STACKTRACE.
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config KASAN_GENERIC
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bool "Generic mode"
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depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
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depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
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select SLUB_DEBUG if SLUB
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select CONSTRUCTORS
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help
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Enables generic KASAN mode.
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This mode is supported in both GCC and Clang. With GCC it requires
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version 8.3.0 or later. Any supported Clang version is compatible,
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but detection of out-of-bounds accesses for global variables is
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supported only since Clang 11.
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This mode consumes about 1/8th of available memory at kernel start
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and introduces an overhead of ~x1.5 for the rest of the allocations.
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The performance slowdown is ~x3.
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Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
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(the resulting kernel does not boot).
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config KASAN_SW_TAGS
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bool "Software tag-based mode"
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depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
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depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
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select SLUB_DEBUG if SLUB
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select CONSTRUCTORS
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help
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Enables software tag-based KASAN mode.
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This mode require software memory tagging support in the form of
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HWASan-like compiler instrumentation.
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Currently this mode is only implemented for arm64 CPUs and relies on
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Top Byte Ignore. This mode requires Clang.
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This mode consumes about 1/16th of available memory at kernel start
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and introduces an overhead of ~20% for the rest of the allocations.
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This mode may potentially introduce problems relating to pointer
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casting and comparison, as it embeds tags into the top byte of each
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pointer.
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Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
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(the resulting kernel does not boot).
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config KASAN_HW_TAGS
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bool "Hardware tag-based mode"
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depends on HAVE_ARCH_KASAN_HW_TAGS
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depends on SLUB
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help
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Enables hardware tag-based KASAN mode.
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This mode requires hardware memory tagging support, and can be used
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by any architecture that provides it.
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Currently this mode is only implemented for arm64 CPUs starting from
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ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore.
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endchoice
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choice
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prompt "Instrumentation type"
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depends on KASAN_GENERIC || KASAN_SW_TAGS
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default KASAN_OUTLINE
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config KASAN_OUTLINE
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bool "Outline instrumentation"
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help
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Before every memory access compiler insert function call
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__asan_load*/__asan_store*. These functions performs check
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of shadow memory. This is slower than inline instrumentation,
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however it doesn't bloat size of kernel's .text section so
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much as inline does.
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config KASAN_INLINE
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bool "Inline instrumentation"
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help
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Compiler directly inserts code checking shadow memory before
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memory accesses. This is faster than outline (in some workloads
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it gives about x2 boost over outline instrumentation), but
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make kernel's .text size much bigger.
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endchoice
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config KASAN_STACK
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bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
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depends on KASAN_GENERIC || KASAN_SW_TAGS
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default y if CC_IS_GCC
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help
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The LLVM stack address sanitizer has a know problem that
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causes excessive stack usage in a lot of functions, see
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https://bugs.llvm.org/show_bug.cgi?id=38809
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Disabling asan-stack makes it safe to run kernels build
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with clang-8 with KASAN enabled, though it loses some of
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the functionality.
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This feature is always disabled when compile-testing with clang
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to avoid cluttering the output in stack overflow warnings,
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but clang users can still enable it for builds without
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CONFIG_COMPILE_TEST. On gcc it is assumed to always be safe
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to use and enabled by default.
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config KASAN_S390_4_LEVEL_PAGING
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bool "KASan: use 4-level paging"
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depends on S390
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help
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Compiling the kernel with KASan disables automatic 3-level vs
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4-level paging selection. 3-level paging is used by default (up
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to 3TB of RAM with KASan enabled). This options allows to force
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4-level paging instead.
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config KASAN_SW_TAGS_IDENTIFY
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bool "Enable memory corruption identification"
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depends on KASAN_SW_TAGS
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help
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This option enables best-effort identification of bug type
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(use-after-free or out-of-bounds) at the cost of increased
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memory consumption.
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config KASAN_VMALLOC
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bool "Back mappings in vmalloc space with real shadow memory"
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depends on KASAN_GENERIC && HAVE_ARCH_KASAN_VMALLOC
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help
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By default, the shadow region for vmalloc space is the read-only
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zero page. This means that KASAN cannot detect errors involving
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vmalloc space.
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Enabling this option will hook in to vmap/vmalloc and back those
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mappings with real shadow memory allocated on demand. This allows
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for KASAN to detect more sorts of errors (and to support vmapped
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stacks), but at the cost of higher memory usage.
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config KASAN_KUNIT_TEST
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tristate "KUnit-compatible tests of KASAN bug detection capabilities" if !KUNIT_ALL_TESTS
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depends on KASAN && KUNIT
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default KUNIT_ALL_TESTS
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help
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This is a KUnit test suite doing various nasty things like
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out of bounds and use after free accesses. It is useful for testing
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kernel debugging features like KASAN.
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For more information on KUnit and unit tests in general, please refer
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to the KUnit documentation in Documentation/dev-tools/kunit.
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config KASAN_MODULE_TEST
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tristate "KUnit-incompatible tests of KASAN bug detection capabilities"
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depends on m && KASAN && !KASAN_HW_TAGS
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help
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This is a part of the KASAN test suite that is incompatible with
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KUnit. Currently includes tests that do bad copy_from/to_user
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accesses.
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endif # KASAN
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