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
43config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
44	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
45		 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
46	help
47	  The compiler instruments plain compound read-write operations
48	  differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to
49	  distinguish them from other plain accesses. This is currently
50	  supported by Clang 12 or later.
51
52config KCSAN_VERBOSE
53	bool "Show verbose reports with more information about system state"
54	depends on PROVE_LOCKING
55	help
56	  If enabled, reports show more information about the system state that
57	  may help better analyze and debug races. This includes held locks and
58	  IRQ trace events.
59
60	  While this option should generally be benign, we call into more
61	  external functions on report generation; if a race report is
62	  generated from any one of them, system stability may suffer due to
63	  deadlocks or recursion.  If in doubt, say N.
64
65config KCSAN_SELFTEST
66	bool "Perform short selftests on boot"
67	default y
68	help
69	  Run KCSAN selftests on boot. On test failure, causes the kernel to
70	  panic. Recommended to be enabled, ensuring critical functionality
71	  works as intended.
72
73config KCSAN_KUNIT_TEST
74	tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
75	default KUNIT_ALL_TESTS
76	depends on TRACEPOINTS && KUNIT
77	select TORTURE_TEST
78	help
79	  KCSAN test focusing on behaviour of the integrated runtime. Tests
80	  various race scenarios, and verifies the reports generated to
81	  console. Makes use of KUnit for test organization, and the Torture
82	  framework for test thread control.
83
84	  Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
85	  milliseconds. Test run duration may be optimized by building the
86	  kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
87	  than default value.
88
89	  Say Y here if you want the test to be built into the kernel and run
90	  during boot; say M if you want the test to build as a module; say N
91	  if you are unsure.
92
93config KCSAN_EARLY_ENABLE
94	bool "Early enable during boot"
95	default y
96	help
97	  If KCSAN should be enabled globally as soon as possible. KCSAN can
98	  later be enabled/disabled via debugfs.
99
100config KCSAN_NUM_WATCHPOINTS
101	int "Number of available watchpoints"
102	default 64
103	help
104	  Total number of available watchpoints. An address range maps into a
105	  specific watchpoint slot as specified in kernel/kcsan/encoding.h.
106	  Although larger number of watchpoints may not be usable due to
107	  limited number of CPUs, a larger value helps to improve performance
108	  due to reducing cache-line contention. The chosen default is a
109	  conservative value; we should almost never observe "no_capacity"
110	  events (see /sys/kernel/debug/kcsan).
111
112config KCSAN_UDELAY_TASK
113	int "Delay in microseconds (for tasks)"
114	default 80
115	help
116	  For tasks, the microsecond delay after setting up a watchpoint.
117
118config KCSAN_UDELAY_INTERRUPT
119	int "Delay in microseconds (for interrupts)"
120	default 20
121	help
122	  For interrupts, the microsecond delay after setting up a watchpoint.
123	  Interrupts have tighter latency requirements, and their delay should
124	  be lower than for tasks.
125
126config KCSAN_DELAY_RANDOMIZE
127	bool "Randomize above delays"
128	default y
129	help
130	  If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
131	  If false, the chosen delays are always the KCSAN_UDELAY_* values
132	  as defined above.
133
134config KCSAN_SKIP_WATCH
135	int "Skip instructions before setting up watchpoint"
136	default 4000
137	help
138	  The number of per-CPU memory operations to skip, before another
139	  watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
140	  memory operations are used to set up a watchpoint. A smaller value
141	  results in more aggressive race detection, whereas a larger value
142	  improves system performance at the cost of missing some races.
143
144config KCSAN_SKIP_WATCH_RANDOMIZE
145	bool "Randomize watchpoint instruction skip count"
146	default y
147	help
148	  If instruction skip count should be randomized, where the maximum is
149	  KCSAN_WATCH_SKIP. If false, the chosen value is always
150	  KCSAN_WATCH_SKIP.
151
152config KCSAN_INTERRUPT_WATCHER
153	bool "Interruptible watchers" if !KCSAN_STRICT
154	default KCSAN_STRICT
155	help
156	  If enabled, a task that set up a watchpoint may be interrupted while
157	  delayed. This option will allow KCSAN to detect races between
158	  interrupted tasks and other threads of execution on the same CPU.
159
160	  Currently disabled by default, because not all safe per-CPU access
161	  primitives and patterns may be accounted for, and therefore could
162	  result in false positives.
163
164config KCSAN_REPORT_ONCE_IN_MS
165	int "Duration in milliseconds, in which any given race is only reported once"
166	default 3000
167	help
168	  Any given race is only reported once in the defined time window.
169	  Different races may still generate reports within a duration that is
170	  smaller than the duration defined here. This allows rate limiting
171	  reporting to avoid flooding the console with reports.  Setting this
172	  to 0 disables rate limiting.
173
174# The main purpose of the below options is to control reported data races, and
175# are not expected to be switched frequently by non-testers or at runtime.
176# The defaults are chosen to be conservative, and can miss certain bugs.
177
178config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
179	bool "Report races of unknown origin"
180	default y
181	help
182	  If KCSAN should report races where only one access is known, and the
183	  conflicting access is of unknown origin. This type of race is
184	  reported if it was only possible to infer a race due to a data value
185	  change while an access is being delayed on a watchpoint.
186
187config KCSAN_STRICT
188	bool "Strict data-race checking"
189	help
190	  KCSAN will report data races with the strictest possible rules, which
191	  closely aligns with the rules defined by the Linux-kernel memory
192	  consistency model (LKMM).
193
194config KCSAN_REPORT_VALUE_CHANGE_ONLY
195	bool "Only report races where watcher observed a data value change"
196	default y
197	depends on !KCSAN_STRICT
198	help
199	  If enabled and a conflicting write is observed via a watchpoint, but
200	  the data value of the memory location was observed to remain
201	  unchanged, do not report the data race.
202
203config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
204	bool "Assume that plain aligned writes up to word size are atomic"
205	default y
206	depends on !KCSAN_STRICT
207	help
208	  Assume that plain aligned writes up to word size are atomic by
209	  default, and also not subject to other unsafe compiler optimizations
210	  resulting in data races. This will cause KCSAN to not report data
211	  races due to conflicts where the only plain accesses are aligned
212	  writes up to word size: conflicts between marked reads and plain
213	  aligned writes up to word size will not be reported as data races;
214	  notice that data races between two conflicting plain aligned writes
215	  will also not be reported.
216
217config KCSAN_IGNORE_ATOMICS
218	bool "Do not instrument marked atomic accesses"
219	depends on !KCSAN_STRICT
220	help
221	  Never instrument marked atomic accesses. This option can be used for
222	  additional filtering. Conflicting marked atomic reads and plain
223	  writes will never be reported as a data race, however, will cause
224	  plain reads and marked writes to result in "unknown origin" reports.
225	  If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
226	  races where at least one access is marked atomic will never be
227	  reported.
228
229	  Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
230	  accesses, conflicting marked atomic reads and plain writes will not
231	  be reported as data races; however, unlike that option, data races
232	  due to two conflicting plain writes will be reported (aligned and
233	  unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
234
235config KCSAN_PERMISSIVE
236	bool "Enable all additional permissive rules"
237	depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
238	help
239	  Enable additional permissive rules to ignore certain classes of data
240	  races (also see kernel/kcsan/permissive.h). None of the permissive
241	  rules imply that such data races are generally safe, but can be used
242	  to further reduce reported data races due to data-racy patterns
243	  common across the kernel.
244
245endif # KCSAN
246