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_WATCH_SKIP 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_WATCH_SKIP. If false, the chosen value is always 139 KCSAN_WATCH_SKIP. 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 strenghtening 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 257