xref: /openbmc/linux/lib/Kconfig.kcsan (revision c4f7ac64)
1# SPDX-License-Identifier: GPL-2.0-only
2
3config HAVE_ARCH_KCSAN
4	bool
5
6config HAVE_KCSAN_COMPILER
7	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)) || \
8		 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1))
9	help
10	  For the list of compilers that support KCSAN, please see
11	  <file:Documentation/dev-tools/kcsan.rst>.
12
13config KCSAN_KCOV_BROKEN
14	def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
15	depends on CC_IS_CLANG
16	depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)
17	help
18	  Some versions of clang support either KCSAN and KCOV but not the
19	  combination of the two.
20	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
21	  in newer releases.
22
23menuconfig KCSAN
24	bool "KCSAN: dynamic data race detector"
25	depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
26	depends on DEBUG_KERNEL && !KASAN
27	depends on !KCSAN_KCOV_BROKEN
28	select STACKTRACE
29	help
30	  The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
31	  data-race detector that relies on compile-time instrumentation.
32	  KCSAN uses a watchpoint-based sampling approach to detect races.
33
34	  While KCSAN's primary purpose is to detect data races, it
35	  also provides assertions to check data access constraints.
36	  These assertions can expose bugs that do not manifest as
37	  data races.
38
39	  See <file:Documentation/dev-tools/kcsan.rst> for more details.
40
41if KCSAN
42
43# Compiler capabilities that should not fail the test if they are unavailable.
44config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
45	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
46		 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
47
48config KCSAN_VERBOSE
49	bool "Show verbose reports with more information about system state"
50	depends on PROVE_LOCKING
51	help
52	  If enabled, reports show more information about the system state that
53	  may help better analyze and debug races. This includes held locks and
54	  IRQ trace events.
55
56	  While this option should generally be benign, we call into more
57	  external functions on report generation; if a race report is
58	  generated from any one of them, system stability may suffer due to
59	  deadlocks or recursion.  If in doubt, say N.
60
61config KCSAN_DEBUG
62	bool "Debugging of KCSAN internals"
63
64config KCSAN_SELFTEST
65	bool "Perform short selftests on boot"
66	default y
67	help
68	  Run KCSAN selftests on boot. On test failure, causes the kernel to
69	  panic. Recommended to be enabled, ensuring critical functionality
70	  works as intended.
71
72config KCSAN_KUNIT_TEST
73	tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
74	default KUNIT_ALL_TESTS
75	depends on TRACEPOINTS && KUNIT
76	select TORTURE_TEST
77	help
78	  KCSAN test focusing on behaviour of the integrated runtime. Tests
79	  various race scenarios, and verifies the reports generated to
80	  console. Makes use of KUnit for test organization, and the Torture
81	  framework for test thread control.
82
83	  Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
84	  milliseconds. Test run duration may be optimized by building the
85	  kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
86	  than default value.
87
88	  Say Y here if you want the test to be built into the kernel and run
89	  during boot; say M if you want the test to build as a module; say N
90	  if you are unsure.
91
92config KCSAN_EARLY_ENABLE
93	bool "Early enable during boot"
94	default y
95	help
96	  If KCSAN should be enabled globally as soon as possible. KCSAN can
97	  later be enabled/disabled via debugfs.
98
99config KCSAN_NUM_WATCHPOINTS
100	int "Number of available watchpoints"
101	default 64
102	help
103	  Total number of available watchpoints. An address range maps into a
104	  specific watchpoint slot as specified in kernel/kcsan/encoding.h.
105	  Although larger number of watchpoints may not be usable due to
106	  limited number of CPUs, a larger value helps to improve performance
107	  due to reducing cache-line contention. The chosen default is a
108	  conservative value; we should almost never observe "no_capacity"
109	  events (see /sys/kernel/debug/kcsan).
110
111config KCSAN_UDELAY_TASK
112	int "Delay in microseconds (for tasks)"
113	default 80
114	help
115	  For tasks, the microsecond delay after setting up a watchpoint.
116
117config KCSAN_UDELAY_INTERRUPT
118	int "Delay in microseconds (for interrupts)"
119	default 20
120	help
121	  For interrupts, the microsecond delay after setting up a watchpoint.
122	  Interrupts have tighter latency requirements, and their delay should
123	  be lower than for tasks.
124
125config KCSAN_DELAY_RANDOMIZE
126	bool "Randomize above delays"
127	default y
128	help
129	  If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
130	  If false, the chosen delays are always the KCSAN_UDELAY_* values
131	  as defined above.
132
133config KCSAN_SKIP_WATCH
134	int "Skip instructions before setting up watchpoint"
135	default 4000
136	help
137	  The number of per-CPU memory operations to skip, before another
138	  watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
139	  memory operations are used to set up a watchpoint. A smaller value
140	  results in more aggressive race detection, whereas a larger value
141	  improves system performance at the cost of missing some races.
142
143config KCSAN_SKIP_WATCH_RANDOMIZE
144	bool "Randomize watchpoint instruction skip count"
145	default y
146	help
147	  If instruction skip count should be randomized, where the maximum is
148	  KCSAN_WATCH_SKIP. If false, the chosen value is always
149	  KCSAN_WATCH_SKIP.
150
151config KCSAN_INTERRUPT_WATCHER
152	bool "Interruptible watchers"
153	help
154	  If enabled, a task that set up a watchpoint may be interrupted while
155	  delayed. This option will allow KCSAN to detect races between
156	  interrupted tasks and other threads of execution on the same CPU.
157
158	  Currently disabled by default, because not all safe per-CPU access
159	  primitives and patterns may be accounted for, and therefore could
160	  result in false positives.
161
162config KCSAN_REPORT_ONCE_IN_MS
163	int "Duration in milliseconds, in which any given race is only reported once"
164	default 3000
165	help
166	  Any given race is only reported once in the defined time window.
167	  Different races may still generate reports within a duration that is
168	  smaller than the duration defined here. This allows rate limiting
169	  reporting to avoid flooding the console with reports.  Setting this
170	  to 0 disables rate limiting.
171
172# The main purpose of the below options is to control reported data races (e.g.
173# in fuzzer configs), and are not expected to be switched frequently by other
174# users. We could turn some of them into boot parameters, but given they should
175# not be switched normally, let's keep them here to simplify configuration.
176#
177# The defaults below are chosen to be very conservative, and may miss certain
178# bugs.
179
180config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
181	bool "Report races of unknown origin"
182	default y
183	help
184	  If KCSAN should report races where only one access is known, and the
185	  conflicting access is of unknown origin. This type of race is
186	  reported if it was only possible to infer a race due to a data value
187	  change while an access is being delayed on a watchpoint.
188
189config KCSAN_REPORT_VALUE_CHANGE_ONLY
190	bool "Only report races where watcher observed a data value change"
191	default y
192	help
193	  If enabled and a conflicting write is observed via a watchpoint, but
194	  the data value of the memory location was observed to remain
195	  unchanged, do not report the data race.
196
197config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
198	bool "Assume that plain aligned writes up to word size are atomic"
199	default y
200	help
201	  Assume that plain aligned writes up to word size are atomic by
202	  default, and also not subject to other unsafe compiler optimizations
203	  resulting in data races. This will cause KCSAN to not report data
204	  races due to conflicts where the only plain accesses are aligned
205	  writes up to word size: conflicts between marked reads and plain
206	  aligned writes up to word size will not be reported as data races;
207	  notice that data races between two conflicting plain aligned writes
208	  will also not be reported.
209
210config KCSAN_IGNORE_ATOMICS
211	bool "Do not instrument marked atomic accesses"
212	help
213	  Never instrument marked atomic accesses. This option can be used for
214	  additional filtering. Conflicting marked atomic reads and plain
215	  writes will never be reported as a data race, however, will cause
216	  plain reads and marked writes to result in "unknown origin" reports.
217	  If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
218	  races where at least one access is marked atomic will never be
219	  reported.
220
221	  Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
222	  accesses, conflicting marked atomic reads and plain writes will not
223	  be reported as data races; however, unlike that option, data races
224	  due to two conflicting plain writes will be reported (aligned and
225	  unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
226
227endif # KCSAN
228