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. With Clang it requires version 7.0.0 or
  58           later, but detection of out-of-bounds accesses for global variables
  59           is 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 version 7.0.0
  82           or later.
  83
  84           This mode consumes about 1/16th of available memory at kernel start
  85           and introduces an overhead of ~20% for the rest of the allocations.
  86           This mode may potentially introduce problems relating to pointer
  87           casting and comparison, as it embeds tags into the top byte of each
  88           pointer.
  89
  90           For better error detection enable CONFIG_STACKTRACE.
  91
  92           Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
  93           (the resulting kernel does not boot).
  94
  95 endchoice
  96
  97 choice
  98         prompt "Instrumentation type"
  99         default KASAN_OUTLINE
 100
 101 config KASAN_OUTLINE
 102         bool "Outline instrumentation"
 103         help
 104           Before every memory access compiler insert function call
 105           __asan_load*/__asan_store*. These functions performs check
 106           of shadow memory. This is slower than inline instrumentation,
 107           however it doesn't bloat size of kernel's .text section so
 108           much as inline does.
 109
 110 config KASAN_INLINE
 111         bool "Inline instrumentation"
 112         help
 113           Compiler directly inserts code checking shadow memory before
 114           memory accesses. This is faster than outline (in some workloads
 115           it gives about x2 boost over outline instrumentation), but
 116           make kernel's .text size much bigger.
 117
 118 endchoice
 119
 120 config KASAN_STACK_ENABLE
 121         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 122         help
 123           The LLVM stack address sanitizer has a know problem that
 124           causes excessive stack usage in a lot of functions, see
 125           https://bugs.llvm.org/show_bug.cgi?id=38809
 126           Disabling asan-stack makes it safe to run kernels build
 127           with clang-8 with KASAN enabled, though it loses some of
 128           the functionality.
 129           This feature is always disabled when compile-testing with clang
 130           to avoid cluttering the output in stack overflow warnings,
 131           but clang users can still enable it for builds without
 132           CONFIG_COMPILE_TEST.  On gcc it is assumed to always be safe
 133           to use and enabled by default.
 134
 135 config KASAN_STACK
 136         int
 137         default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
 138         default 0
 139
 140 config KASAN_S390_4_LEVEL_PAGING
 141         bool "KASan: use 4-level paging"
 142         depends on S390
 143         help
 144           Compiling the kernel with KASan disables automatic 3-level vs
 145           4-level paging selection. 3-level paging is used by default (up
 146           to 3TB of RAM with KASan enabled). This options allows to force
 147           4-level paging instead.
 148
 149 config KASAN_SW_TAGS_IDENTIFY
 150         bool "Enable memory corruption identification"
 151         depends on KASAN_SW_TAGS
 152         help
 153           This option enables best-effort identification of bug type
 154           (use-after-free or out-of-bounds) at the cost of increased
 155           memory consumption.
 156
 157 config KASAN_VMALLOC
 158         bool "Back mappings in vmalloc space with real shadow memory"
 159         depends on HAVE_ARCH_KASAN_VMALLOC
 160         help
 161           By default, the shadow region for vmalloc space is the read-only
 162           zero page. This means that KASAN cannot detect errors involving
 163           vmalloc space.
 164
 165           Enabling this option will hook in to vmap/vmalloc and back those
 166           mappings with real shadow memory allocated on demand. This allows
 167           for KASAN to detect more sorts of errors (and to support vmapped
 168           stacks), but at the cost of higher memory usage.
 169
 170 config TEST_KASAN
 171         tristate "Module for testing KASAN for bug detection"
 172         depends on m
 173         help
 174           This is a test module doing various nasty things like
 175           out of bounds accesses, use after free. It is useful for testing
 176           kernel debugging features like KASAN.
 177
 178 endif # KASAN