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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
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
13menuconfig KCSAN
14 bool "KCSAN: dynamic data race detector"
15 depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
16 depends on DEBUG_KERNEL && !KASAN
17 select STACKTRACE
18 help
19 The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
20 data-race detector that relies on compile-time instrumentation.
21 KCSAN uses a watchpoint-based sampling approach to detect races.
22
23 While KCSAN's primary purpose is to detect data races, it
24 also provides assertions to check data access constraints.
25 These assertions can expose bugs that do not manifest as
26 data races.
27
28 See <file:Documentation/dev-tools/kcsan.rst> for more details.
29
30if KCSAN
31
32config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
33 def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
34 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
35 help
36 The compiler instruments plain compound read-write operations
37 differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to
38 distinguish them from other plain accesses. This is currently
39 supported by Clang 12 or later.
40
41config KCSAN_VERBOSE
42 bool "Show verbose reports with more information about system state"
43 depends on PROVE_LOCKING
44 help
45 If enabled, reports show more information about the system state that
46 may help better analyze and debug races. This includes held locks and
47 IRQ trace events.
48
49 While this option should generally be benign, we call into more
50 external functions on report generation; if a race report is
51 generated from any one of them, system stability may suffer due to
52 deadlocks or recursion. If in doubt, say N.
53
54config KCSAN_SELFTEST
55 bool "Perform short selftests on boot"
56 default y
57 help
58 Run KCSAN selftests on boot. On test failure, causes the kernel to
59 panic. Recommended to be enabled, ensuring critical functionality
60 works as intended.
61
62config KCSAN_KUNIT_TEST
63 tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
64 default KUNIT_ALL_TESTS
65 depends on TRACEPOINTS && KUNIT
66 select TORTURE_TEST
67 help
68 KCSAN test focusing on behaviour of the integrated runtime. Tests
69 various race scenarios, and verifies the reports generated to
70 console. Makes use of KUnit for test organization, and the Torture
71 framework for test thread control.
72
73 Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
74 milliseconds. Test run duration may be optimized by building the
75 kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
76 than default value.
77
78 Say Y here if you want the test to be built into the kernel and run
79 during boot; say M if you want the test to build as a module; say N
80 if you are unsure.
81
82config KCSAN_EARLY_ENABLE
83 bool "Early enable during boot"
84 default y
85 help
86 If KCSAN should be enabled globally as soon as possible. KCSAN can
87 later be enabled/disabled via debugfs.
88
89config KCSAN_NUM_WATCHPOINTS
90 int "Number of available watchpoints"
91 default 64
92 help
93 Total number of available watchpoints. An address range maps into a
94 specific watchpoint slot as specified in kernel/kcsan/encoding.h.
95 Although larger number of watchpoints may not be usable due to
96 limited number of CPUs, a larger value helps to improve performance
97 due to reducing cache-line contention. The chosen default is a
98 conservative value; we should almost never observe "no_capacity"
99 events (see /sys/kernel/debug/kcsan).
100
101config KCSAN_UDELAY_TASK
102 int "Delay in microseconds (for tasks)"
103 default 80
104 help
105 For tasks, the microsecond delay after setting up a watchpoint.
106
107config KCSAN_UDELAY_INTERRUPT
108 int "Delay in microseconds (for interrupts)"
109 default 20
110 help
111 For interrupts, the microsecond delay after setting up a watchpoint.
112 Interrupts have tighter latency requirements, and their delay should
113 be lower than for tasks.
114
115config KCSAN_DELAY_RANDOMIZE
116 bool "Randomize above delays"
117 default y
118 help
119 If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
120 If false, the chosen delays are always the KCSAN_UDELAY_* values
121 as defined above.
122
123config KCSAN_SKIP_WATCH
124 int "Skip instructions before setting up watchpoint"
125 default 4000
126 help
127 The number of per-CPU memory operations to skip, before another
128 watchpoint is set up, i.e. one in KCSAN_SKIP_WATCH per-CPU
129 memory operations are used to set up a watchpoint. A smaller value
130 results in more aggressive race detection, whereas a larger value
131 improves system performance at the cost of missing some races.
132
133config KCSAN_SKIP_WATCH_RANDOMIZE
134 bool "Randomize watchpoint instruction skip count"
135 default y
136 help
137 If instruction skip count should be randomized, where the maximum is
138 KCSAN_SKIP_WATCH. If false, the chosen value is always
139 KCSAN_SKIP_WATCH.
140
141config KCSAN_INTERRUPT_WATCHER
142 bool "Interruptible watchers" if !KCSAN_STRICT
143 default KCSAN_STRICT
144 help
145 If enabled, a task that set up a watchpoint may be interrupted while
146 delayed. This option will allow KCSAN to detect races between
147 interrupted tasks and other threads of execution on the same CPU.
148
149 Currently disabled by default, because not all safe per-CPU access
150 primitives and patterns may be accounted for, and therefore could
151 result in false positives.
152
153config KCSAN_REPORT_ONCE_IN_MS
154 int "Duration in milliseconds, in which any given race is only reported once"
155 default 3000
156 help
157 Any given race is only reported once in the defined time window.
158 Different races may still generate reports within a duration that is
159 smaller than the duration defined here. This allows rate limiting
160 reporting to avoid flooding the console with reports. Setting this
161 to 0 disables rate limiting.
162
163# The main purpose of the below options is to control reported data races, and
164# are not expected to be switched frequently by non-testers or at runtime.
165# The defaults are chosen to be conservative, and can miss certain bugs.
166
167config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
168 bool "Report races of unknown origin"
169 default y
170 help
171 If KCSAN should report races where only one access is known, and the
172 conflicting access is of unknown origin. This type of race is
173 reported if it was only possible to infer a race due to a data value
174 change while an access is being delayed on a watchpoint.
175
176config KCSAN_STRICT
177 bool "Strict data-race checking"
178 help
179 KCSAN will report data races with the strictest possible rules, which
180 closely aligns with the rules defined by the Linux-kernel memory
181 consistency model (LKMM).
182
183config KCSAN_WEAK_MEMORY
184 bool "Enable weak memory modeling to detect missing memory barriers"
185 default y
186 depends on KCSAN_STRICT
187 # We can either let objtool nop __tsan_func_{entry,exit}() and builtin
188 # atomics instrumentation in .noinstr.text, or use a compiler that can
189 # implement __no_kcsan to really remove all instrumentation.
190 depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
191 CC_IS_GCC || CLANG_VERSION >= 140000
192 select OBJTOOL if HAVE_NOINSTR_HACK
193 help
194 Enable support for modeling a subset of weak memory, which allows
195 detecting a subset of data races due to missing memory barriers.
196
197 Depends on KCSAN_STRICT, because the options strengthening certain
198 plain accesses by default (depending on !KCSAN_STRICT) reduce the
199 ability to detect any data races invoving reordered accesses, in
200 particular reordered writes.
201
202 Weak memory modeling relies on additional instrumentation and may
203 affect performance.
204
205config KCSAN_REPORT_VALUE_CHANGE_ONLY
206 bool "Only report races where watcher observed a data value change"
207 default y
208 depends on !KCSAN_STRICT
209 help
210 If enabled and a conflicting write is observed via a watchpoint, but
211 the data value of the memory location was observed to remain
212 unchanged, do not report the data race.
213
214config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
215 bool "Assume that plain aligned writes up to word size are atomic"
216 default y
217 depends on !KCSAN_STRICT
218 help
219 Assume that plain aligned writes up to word size are atomic by
220 default, and also not subject to other unsafe compiler optimizations
221 resulting in data races. This will cause KCSAN to not report data
222 races due to conflicts where the only plain accesses are aligned
223 writes up to word size: conflicts between marked reads and plain
224 aligned writes up to word size will not be reported as data races;
225 notice that data races between two conflicting plain aligned writes
226 will also not be reported.
227
228config KCSAN_IGNORE_ATOMICS
229 bool "Do not instrument marked atomic accesses"
230 depends on !KCSAN_STRICT
231 help
232 Never instrument marked atomic accesses. This option can be used for
233 additional filtering. Conflicting marked atomic reads and plain
234 writes will never be reported as a data race, however, will cause
235 plain reads and marked writes to result in "unknown origin" reports.
236 If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
237 races where at least one access is marked atomic will never be
238 reported.
239
240 Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
241 accesses, conflicting marked atomic reads and plain writes will not
242 be reported as data races; however, unlike that option, data races
243 due to two conflicting plain writes will be reported (aligned and
244 unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
245
246config KCSAN_PERMISSIVE
247 bool "Enable all additional permissive rules"
248 depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
249 help
250 Enable additional permissive rules to ignore certain classes of data
251 races (also see kernel/kcsan/permissive.h). None of the permissive
252 rules imply that such data races are generally safe, but can be used
253 to further reduce reported data races due to data-racy patterns
254 common across the kernel.
255
256endif # KCSAN