lib/Kconfig.kasan

   1 # SPDX-License-Identifier: GPL-2.0-only
   2 # This config refers to the generic KASAN mode.
   3 config HAVE_ARCH_KASAN
   4         bool
   5
   6 config HAVE_ARCH_KASAN_SW_TAGS
   7         bool
   8
   9 config  HAVE_ARCH_KASAN_VMALLOC
  10         bool
  11
  12 config CC_HAS_KASAN_GENERIC
  13         def_bool $(cc-option, -fsanitize=kernel-address)
  14
  15 config CC_HAS_KASAN_SW_TAGS
  16         def_bool $(cc-option, -fsanitize=kernel-hwaddress)
  17
  18 config CC_HAS_WORKING_NOSANITIZE_ADDRESS
  19         def_bool !CC_IS_GCC || GCC_VERSION >= 80300
  20
  21 menuconfig KASAN
  22         bool "KASAN: runtime memory debugger"
  23         depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
  24                    (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
  25         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  26         depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
  27         help
  28           Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
  29           designed to find out-of-bounds accesses and use-after-free bugs.
  30           See Documentation/dev-tools/kasan.rst for details.
  31
  32 if KASAN
  33
  34 choice
  35         prompt "KASAN mode"
  36         default KASAN_GENERIC
  37         help
  38           KASAN has two modes: generic KASAN (similar to userspace ASan,
  39           x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
  40           software tag-based KASAN (a version based on software memory
  41           tagging, arm64 only, similar to userspace HWASan, enabled with
  42           CONFIG_KASAN_SW_TAGS).
  43
  44           Both generic and tag-based KASAN are strictly debugging features.
  45
  46 config KASAN_GENERIC
  47         bool "Generic mode"
  48         depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
  49         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  50         select SLUB_DEBUG if SLUB
  51         select CONSTRUCTORS
  52         select STACKDEPOT
  53         help
  54           Enables generic KASAN mode.
  55
  56           This mode is supported in both GCC and Clang. With GCC it requires
  57           version 8.3.0 or later. Any supported Clang version is compatible,
  58           but detection of out-of-bounds accesses for global variables is
  59           supported only since Clang 11.
  60
  61           This mode consumes about 1/8th of available memory at kernel start
  62           and introduces an overhead of ~x1.5 for the rest of the allocations.
  63           The performance slowdown is ~x3.
  64
  65           For better error detection enable CONFIG_STACKTRACE.
  66
  67           Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
  68           (the resulting kernel does not boot).
  69
  70 config KASAN_SW_TAGS
  71         bool "Software tag-based mode"
  72         depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
  73         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  74         select SLUB_DEBUG if SLUB
  75         select CONSTRUCTORS
  76         select STACKDEPOT
  77         help
  78           Enables software tag-based KASAN mode.
  79
  80           This mode requires Top Byte Ignore support by the CPU and therefore
  81           is only supported for arm64. This mode requires Clang.
  82
  83           This mode consumes about 1/16th of available memory at kernel start
  84           and introduces an overhead of ~20% for the rest of the allocations.
  85           This mode may potentially introduce problems relating to pointer
  86           casting and comparison, as it embeds tags into the top byte of each
  87           pointer.
  88
  89           For better error detection enable CONFIG_STACKTRACE.
  90
  91           Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
  92           (the resulting kernel does not boot).
  93
  94 endchoice
  95
  96 choice
  97         prompt "Instrumentation type"
  98         default KASAN_OUTLINE
  99
 100 config KASAN_OUTLINE
 101         bool "Outline instrumentation"
 102         help
 103           Before every memory access compiler insert function call
 104           __asan_load*/__asan_store*. These functions performs check
 105           of shadow memory. This is slower than inline instrumentation,
 106           however it doesn't bloat size of kernel's .text section so
 107           much as inline does.
 108
 109 config KASAN_INLINE
 110         bool "Inline instrumentation"
 111         help
 112           Compiler directly inserts code checking shadow memory before
 113           memory accesses. This is faster than outline (in some workloads
 114           it gives about x2 boost over outline instrumentation), but
 115           make kernel's .text size much bigger.
 116
 117 endchoice
 118
 119 config KASAN_STACK_ENABLE
 120         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 121         help
 122           The LLVM stack address sanitizer has a know problem that
 123           causes excessive stack usage in a lot of functions, see
 124           https://bugs.llvm.org/show_bug.cgi?id=38809
 125           Disabling asan-stack makes it safe to run kernels build
 126           with clang-8 with KASAN enabled, though it loses some of
 127           the functionality.
 128           This feature is always disabled when compile-testing with clang
 129           to avoid cluttering the output in stack overflow warnings,
 130           but clang users can still enable it for builds without
 131           CONFIG_COMPILE_TEST.  On gcc it is assumed to always be safe
 132           to use and enabled by default.
 133
 134 config KASAN_STACK
 135         int
 136         default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
 137         default 0
 138
 139 config KASAN_S390_4_LEVEL_PAGING
 140         bool "KASan: use 4-level paging"
 141         depends on S390
 142         help
 143           Compiling the kernel with KASan disables automatic 3-level vs
 144           4-level paging selection. 3-level paging is used by default (up
 145           to 3TB of RAM with KASan enabled). This options allows to force
 146           4-level paging instead.
 147
 148 config KASAN_SW_TAGS_IDENTIFY
 149         bool "Enable memory corruption identification"
 150         depends on KASAN_SW_TAGS
 151         help
 152           This option enables best-effort identification of bug type
 153           (use-after-free or out-of-bounds) at the cost of increased
 154           memory consumption.
 155
 156 config KASAN_VMALLOC
 157         bool "Back mappings in vmalloc space with real shadow memory"
 158         depends on HAVE_ARCH_KASAN_VMALLOC
 159         help
 160           By default, the shadow region for vmalloc space is the read-only
 161           zero page. This means that KASAN cannot detect errors involving
 162           vmalloc space.
 163
 164           Enabling this option will hook in to vmap/vmalloc and back those
 165           mappings with real shadow memory allocated on demand. This allows
 166           for KASAN to detect more sorts of errors (and to support vmapped
 167           stacks), but at the cost of higher memory usage.
 168
 169 config KASAN_KUNIT_TEST
 170         tristate "KUnit-compatible tests of KASAN bug detection capabilities" if !KUNIT_ALL_TESTS
 171         depends on KASAN && KUNIT
 172         default KUNIT_ALL_TESTS
 173         help
 174           This is a KUnit test suite doing various nasty things like
 175           out of bounds and use after free accesses. It is useful for testing
 176           kernel debugging features like KASAN.
 177
 178           For more information on KUnit and unit tests in general, please refer
 179           to the KUnit documentation in Documentation/dev-tools/kunit
 180
 181 config TEST_KASAN_MODULE
 182         tristate "KUnit-incompatible tests of KASAN bug detection capabilities"
 183         depends on m && KASAN
 184         help
 185           This is a part of the KASAN test suite that is incompatible with
 186           KUnit. Currently includes tests that do bad copy_from/to_user
 187           accesses.
 188
 189 endif # KASAN