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 CC_HAS_KASAN_GENERIC
  10         def_bool $(cc-option, -fsanitize=kernel-address)
  11
  12 config CC_HAS_KASAN_SW_TAGS
  13         def_bool $(cc-option, -fsanitize=kernel-hwaddress)
  14
  15 config KASAN
  16         bool "KASAN: runtime memory debugger"
  17         depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
  18                    (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
  19         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  20         help
  21           Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
  22           designed to find out-of-bounds accesses and use-after-free bugs.
  23           See Documentation/dev-tools/kasan.rst for details.
  24
  25 choice
  26         prompt "KASAN mode"
  27         depends on KASAN
  28         default KASAN_GENERIC
  29         help
  30           KASAN has two modes: generic KASAN (similar to userspace ASan,
  31           x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
  32           software tag-based KASAN (a version based on software memory
  33           tagging, arm64 only, similar to userspace HWASan, enabled with
  34           CONFIG_KASAN_SW_TAGS).
  35           Both generic and tag-based KASAN are strictly debugging features.
  36
  37 config KASAN_GENERIC
  38         bool "Generic mode"
  39         depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
  40         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  41         select SLUB_DEBUG if SLUB
  42         select CONSTRUCTORS
  43         select STACKDEPOT
  44         help
  45           Enables generic KASAN mode.
  46           Supported in both GCC and Clang. With GCC it requires version 4.9.2
  47           or later for basic support and version 5.0 or later for detection of
  48           out-of-bounds accesses for stack and global variables and for inline
  49           instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
  50           version 3.7.0 or later and it doesn't support detection of
  51           out-of-bounds accesses for global variables yet.
  52           This mode consumes about 1/8th of available memory at kernel start
  53           and introduces an overhead of ~x1.5 for the rest of the allocations.
  54           The performance slowdown is ~x3.
  55           For better error detection enable CONFIG_STACKTRACE.
  56           Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
  57           (the resulting kernel does not boot).
  58
  59 config KASAN_SW_TAGS
  60         bool "Software tag-based mode"
  61         depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
  62         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
  63         select SLUB_DEBUG if SLUB
  64         select CONSTRUCTORS
  65         select STACKDEPOT
  66         help
  67           Enables software tag-based KASAN mode.
  68           This mode requires Top Byte Ignore support by the CPU and therefore
  69           is only supported for arm64.
  70           This mode requires Clang version 7.0.0 or later.
  71           This mode consumes about 1/16th of available memory at kernel start
  72           and introduces an overhead of ~20% for the rest of the allocations.
  73           This mode may potentially introduce problems relating to pointer
  74           casting and comparison, as it embeds tags into the top byte of each
  75           pointer.
  76           For better error detection enable CONFIG_STACKTRACE.
  77           Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
  78           (the resulting kernel does not boot).
  79
  80 endchoice
  81
  82 choice
  83         prompt "Instrumentation type"
  84         depends on KASAN
  85         default KASAN_OUTLINE
  86
  87 config KASAN_OUTLINE
  88         bool "Outline instrumentation"
  89         help
  90           Before every memory access compiler insert function call
  91           __asan_load*/__asan_store*. These functions performs check
  92           of shadow memory. This is slower than inline instrumentation,
  93           however it doesn't bloat size of kernel's .text section so
  94           much as inline does.
  95
  96 config KASAN_INLINE
  97         bool "Inline instrumentation"
  98         help
  99           Compiler directly inserts code checking shadow memory before
 100           memory accesses. This is faster than outline (in some workloads
 101           it gives about x2 boost over outline instrumentation), but
 102           make kernel's .text size much bigger.
 103           For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
 104
 105 endchoice
 106
 107 config KASAN_STACK_ENABLE
 108         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 109         default !(CLANG_VERSION < 90000)
 110         depends on KASAN
 111         help
 112           The LLVM stack address sanitizer has a know problem that
 113           causes excessive stack usage in a lot of functions, see
 114           https://bugs.llvm.org/show_bug.cgi?id=38809
 115           Disabling asan-stack makes it safe to run kernels build
 116           with clang-8 with KASAN enabled, though it loses some of
 117           the functionality.
 118           This feature is always disabled when compile-testing with clang-8
 119           or earlier to avoid cluttering the output in stack overflow
 120           warnings, but clang-8 users can still enable it for builds without
 121           CONFIG_COMPILE_TEST.  On gcc and later clang versions it is
 122           assumed to always be safe to use and enabled by default.
 123
 124 config KASAN_STACK
 125         int
 126         default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
 127         default 0
 128
 129 config KASAN_S390_4_LEVEL_PAGING
 130         bool "KASan: use 4-level paging"
 131         depends on KASAN && S390
 132         help
 133           Compiling the kernel with KASan disables automatic 3-level vs
 134           4-level paging selection. 3-level paging is used by default (up
 135           to 3TB of RAM with KASan enabled). This options allows to force
 136           4-level paging instead.
 137
 138 config TEST_KASAN
 139         tristate "Module for testing KASAN for bug detection"
 140         depends on m && KASAN
 141         help
 142           This is a test module doing various nasty things like
 143           out of bounds accesses, use after free. It is useful for testing
 144           kernel debugging features like KASAN.