xref: /linux/lib/Kconfig.kasan (revision 9a6b55ac) 
1# SPDX-License-Identifier: GPL-2.0-only
2# This config refers to the generic KASAN mode.
3config HAVE_ARCH_KASAN
4	bool
5
6config HAVE_ARCH_KASAN_SW_TAGS
7	bool
8
9config	HAVE_ARCH_KASAN_VMALLOC
10	bool
11
12config CC_HAS_KASAN_GENERIC
13	def_bool $(cc-option, -fsanitize=kernel-address)
14
15config CC_HAS_KASAN_SW_TAGS
16	def_bool $(cc-option, -fsanitize=kernel-hwaddress)
17
18config KASAN
19	bool "KASAN: runtime memory debugger"
20	depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
21		   (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
22	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
23	help
24	  Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
25	  designed to find out-of-bounds accesses and use-after-free bugs.
26	  See Documentation/dev-tools/kasan.rst for details.
27
28choice
29	prompt "KASAN mode"
30	depends on KASAN
31	default KASAN_GENERIC
32	help
33	  KASAN has two modes: generic KASAN (similar to userspace ASan,
34	  x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
35	  software tag-based KASAN (a version based on software memory
36	  tagging, arm64 only, similar to userspace HWASan, enabled with
37	  CONFIG_KASAN_SW_TAGS).
38	  Both generic and tag-based KASAN are strictly debugging features.
39
40config KASAN_GENERIC
41	bool "Generic mode"
42	depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
43	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
44	select SLUB_DEBUG if SLUB
45	select CONSTRUCTORS
46	select STACKDEPOT
47	help
48	  Enables generic KASAN mode.
49	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
50	  or later for basic support and version 5.0 or later for detection of
51	  out-of-bounds accesses for stack and global variables and for inline
52	  instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
53	  version 3.7.0 or later and it doesn't support detection of
54	  out-of-bounds accesses for global variables yet.
55	  This mode consumes about 1/8th of available memory at kernel start
56	  and introduces an overhead of ~x1.5 for the rest of the allocations.
57	  The performance slowdown is ~x3.
58	  For better error detection enable CONFIG_STACKTRACE.
59	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
60	  (the resulting kernel does not boot).
61
62config KASAN_SW_TAGS
63	bool "Software tag-based mode"
64	depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
65	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
66	select SLUB_DEBUG if SLUB
67	select CONSTRUCTORS
68	select STACKDEPOT
69	help
70	  Enables software tag-based KASAN mode.
71	  This mode requires Top Byte Ignore support by the CPU and therefore
72	  is only supported for arm64.
73	  This mode requires Clang version 7.0.0 or later.
74	  This mode consumes about 1/16th of available memory at kernel start
75	  and introduces an overhead of ~20% for the rest of the allocations.
76	  This mode may potentially introduce problems relating to pointer
77	  casting and comparison, as it embeds tags into the top byte of each
78	  pointer.
79	  For better error detection enable CONFIG_STACKTRACE.
80	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
81	  (the resulting kernel does not boot).
82
83endchoice
84
85choice
86	prompt "Instrumentation type"
87	depends on KASAN
88	default KASAN_OUTLINE
89
90config KASAN_OUTLINE
91	bool "Outline instrumentation"
92	help
93	  Before every memory access compiler insert function call
94	  __asan_load*/__asan_store*. These functions performs check
95	  of shadow memory. This is slower than inline instrumentation,
96	  however it doesn't bloat size of kernel's .text section so
97	  much as inline does.
98
99config KASAN_INLINE
100	bool "Inline instrumentation"
101	help
102	  Compiler directly inserts code checking shadow memory before
103	  memory accesses. This is faster than outline (in some workloads
104	  it gives about x2 boost over outline instrumentation), but
105	  make kernel's .text size much bigger.
106	  For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
107
108endchoice
109
110config KASAN_STACK_ENABLE
111	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
112	depends on KASAN
113	help
114	  The LLVM stack address sanitizer has a know problem that
115	  causes excessive stack usage in a lot of functions, see
116	  https://bugs.llvm.org/show_bug.cgi?id=38809
117	  Disabling asan-stack makes it safe to run kernels build
118	  with clang-8 with KASAN enabled, though it loses some of
119	  the functionality.
120	  This feature is always disabled when compile-testing with clang
121	  to avoid cluttering the output in stack overflow warnings,
122	  but clang users can still enable it for builds without
123	  CONFIG_COMPILE_TEST.	On gcc it is assumed to always be safe
124	  to use and enabled by default.
125
126config KASAN_STACK
127	int
128	default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
129	default 0
130
131config KASAN_S390_4_LEVEL_PAGING
132	bool "KASan: use 4-level paging"
133	depends on KASAN && S390
134	help
135	  Compiling the kernel with KASan disables automatic 3-level vs
136	  4-level paging selection. 3-level paging is used by default (up
137	  to 3TB of RAM with KASan enabled). This options allows to force
138	  4-level paging instead.
139
140config KASAN_SW_TAGS_IDENTIFY
141	bool "Enable memory corruption identification"
142	depends on KASAN_SW_TAGS
143	help
144	  This option enables best-effort identification of bug type
145	  (use-after-free or out-of-bounds) at the cost of increased
146	  memory consumption.
147
148config KASAN_VMALLOC
149	bool "Back mappings in vmalloc space with real shadow memory"
150	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
151	help
152	  By default, the shadow region for vmalloc space is the read-only
153	  zero page. This means that KASAN cannot detect errors involving
154	  vmalloc space.
155
156	  Enabling this option will hook in to vmap/vmalloc and back those
157	  mappings with real shadow memory allocated on demand. This allows
158	  for KASAN to detect more sorts of errors (and to support vmapped
159	  stacks), but at the cost of higher memory usage.
160
161config TEST_KASAN
162	tristate "Module for testing KASAN for bug detection"
163	depends on m && KASAN
164	help
165	  This is a test module doing various nasty things like
166	  out of bounds accesses, use after free. It is useful for testing
167	  kernel debugging features like KASAN.
168