# 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 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 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.