xref: /openbmc/linux/lib/Kconfig.kasan (revision a13f2ef1) 
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 CC_HAS_WORKING_NOSANITIZE_ADDRESS
19	def_bool !CC_IS_GCC || GCC_VERSION >= 80300
20
21config 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
32choice
33	prompt "KASAN mode"
34	depends on KASAN
35	default KASAN_GENERIC
36	help
37	  KASAN has two modes: generic KASAN (similar to userspace ASan,
38	  x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
39	  software tag-based KASAN (a version based on software memory
40	  tagging, arm64 only, similar to userspace HWASan, enabled with
41	  CONFIG_KASAN_SW_TAGS).
42	  Both generic and tag-based KASAN are strictly debugging features.
43
44config KASAN_GENERIC
45	bool "Generic mode"
46	depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
47	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
48	select SLUB_DEBUG if SLUB
49	select CONSTRUCTORS
50	select STACKDEPOT
51	help
52	  Enables generic KASAN mode.
53	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
54	  or later for basic support and version 5.0 or later for detection of
55	  out-of-bounds accesses for stack and global variables and for inline
56	  instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
57	  version 3.7.0 or later and it doesn't support detection of
58	  out-of-bounds accesses for global variables yet.
59	  This mode consumes about 1/8th of available memory at kernel start
60	  and introduces an overhead of ~x1.5 for the rest of the allocations.
61	  The performance slowdown is ~x3.
62	  For better error detection enable CONFIG_STACKTRACE.
63	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
64	  (the resulting kernel does not boot).
65
66config KASAN_SW_TAGS
67	bool "Software tag-based mode"
68	depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
69	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
70	select SLUB_DEBUG if SLUB
71	select CONSTRUCTORS
72	select STACKDEPOT
73	help
74	  Enables software tag-based KASAN mode.
75	  This mode requires Top Byte Ignore support by the CPU and therefore
76	  is only supported for arm64.
77	  This mode requires Clang version 7.0.0 or later.
78	  This mode consumes about 1/16th of available memory at kernel start
79	  and introduces an overhead of ~20% for the rest of the allocations.
80	  This mode may potentially introduce problems relating to pointer
81	  casting and comparison, as it embeds tags into the top byte of each
82	  pointer.
83	  For better error detection enable CONFIG_STACKTRACE.
84	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
85	  (the resulting kernel does not boot).
86
87endchoice
88
89choice
90	prompt "Instrumentation type"
91	depends on KASAN
92	default KASAN_OUTLINE
93
94config KASAN_OUTLINE
95	bool "Outline instrumentation"
96	help
97	  Before every memory access compiler insert function call
98	  __asan_load*/__asan_store*. These functions performs check
99	  of shadow memory. This is slower than inline instrumentation,
100	  however it doesn't bloat size of kernel's .text section so
101	  much as inline does.
102
103config KASAN_INLINE
104	bool "Inline instrumentation"
105	help
106	  Compiler directly inserts code checking shadow memory before
107	  memory accesses. This is faster than outline (in some workloads
108	  it gives about x2 boost over outline instrumentation), but
109	  make kernel's .text size much bigger.
110	  For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
111
112endchoice
113
114config KASAN_STACK_ENABLE
115	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
116	depends on KASAN
117	help
118	  The LLVM stack address sanitizer has a know problem that
119	  causes excessive stack usage in a lot of functions, see
120	  https://bugs.llvm.org/show_bug.cgi?id=38809
121	  Disabling asan-stack makes it safe to run kernels build
122	  with clang-8 with KASAN enabled, though it loses some of
123	  the functionality.
124	  This feature is always disabled when compile-testing with clang
125	  to avoid cluttering the output in stack overflow warnings,
126	  but clang users can still enable it for builds without
127	  CONFIG_COMPILE_TEST.	On gcc it is assumed to always be safe
128	  to use and enabled by default.
129
130config KASAN_STACK
131	int
132	default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
133	default 0
134
135config KASAN_S390_4_LEVEL_PAGING
136	bool "KASan: use 4-level paging"
137	depends on KASAN && S390
138	help
139	  Compiling the kernel with KASan disables automatic 3-level vs
140	  4-level paging selection. 3-level paging is used by default (up
141	  to 3TB of RAM with KASan enabled). This options allows to force
142	  4-level paging instead.
143
144config KASAN_SW_TAGS_IDENTIFY
145	bool "Enable memory corruption identification"
146	depends on KASAN_SW_TAGS
147	help
148	  This option enables best-effort identification of bug type
149	  (use-after-free or out-of-bounds) at the cost of increased
150	  memory consumption.
151
152config KASAN_VMALLOC
153	bool "Back mappings in vmalloc space with real shadow memory"
154	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
155	help
156	  By default, the shadow region for vmalloc space is the read-only
157	  zero page. This means that KASAN cannot detect errors involving
158	  vmalloc space.
159
160	  Enabling this option will hook in to vmap/vmalloc and back those
161	  mappings with real shadow memory allocated on demand. This allows
162	  for KASAN to detect more sorts of errors (and to support vmapped
163	  stacks), but at the cost of higher memory usage.
164
165config TEST_KASAN
166	tristate "Module for testing KASAN for bug detection"
167	depends on m && KASAN
168	help
169	  This is a test module doing various nasty things like
170	  out of bounds accesses, use after free. It is useful for testing
171	  kernel debugging features like KASAN.
172