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 CONSTRUCTORS 18 select STACKTRACE 19 help 20 The Kernel Concurrency Sanitizer (KCSAN) is a dynamic 21 data-race detector that relies on compile-time instrumentation. 22 KCSAN uses a watchpoint-based sampling approach to detect races. 23 24 While KCSAN's primary purpose is to detect data races, it 25 also provides assertions to check data access constraints. 26 These assertions can expose bugs that do not manifest as 27 data races. 28 29 See <file:Documentation/dev-tools/kcsan.rst> for more details. 30 31if KCSAN 32 33config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE 34 def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \ 35 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1)) 36 help 37 The compiler instruments plain compound read-write operations 38 differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to 39 distinguish them from other plain accesses. This is currently 40 supported by Clang 12 or later. 41 42config KCSAN_VERBOSE 43 bool "Show verbose reports with more information about system state" 44 depends on PROVE_LOCKING 45 help 46 If enabled, reports show more information about the system state that 47 may help better analyze and debug races. This includes held locks and 48 IRQ trace events. 49 50 While this option should generally be benign, we call into more 51 external functions on report generation; if a race report is 52 generated from any one of them, system stability may suffer due to 53 deadlocks or recursion. If in doubt, say N. 54 55config KCSAN_SELFTEST 56 bool "Perform short selftests on boot" 57 default y 58 help 59 Run KCSAN selftests on boot. On test failure, causes the kernel to 60 panic. Recommended to be enabled, ensuring critical functionality 61 works as intended. 62 63config KCSAN_KUNIT_TEST 64 tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS 65 default KUNIT_ALL_TESTS 66 depends on TRACEPOINTS && KUNIT 67 select TORTURE_TEST 68 help 69 KCSAN test focusing on behaviour of the integrated runtime. Tests 70 various race scenarios, and verifies the reports generated to 71 console. Makes use of KUnit for test organization, and the Torture 72 framework for test thread control. 73 74 Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS 75 milliseconds. Test run duration may be optimized by building the 76 kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower 77 than default value. 78 79 Say Y here if you want the test to be built into the kernel and run 80 during boot; say M if you want the test to build as a module; say N 81 if you are unsure. 82 83config KCSAN_EARLY_ENABLE 84 bool "Early enable during boot" 85 default y 86 help 87 If KCSAN should be enabled globally as soon as possible. KCSAN can 88 later be enabled/disabled via debugfs. 89 90config KCSAN_NUM_WATCHPOINTS 91 int "Number of available watchpoints" 92 default 64 93 help 94 Total number of available watchpoints. An address range maps into a 95 specific watchpoint slot as specified in kernel/kcsan/encoding.h. 96 Although larger number of watchpoints may not be usable due to 97 limited number of CPUs, a larger value helps to improve performance 98 due to reducing cache-line contention. The chosen default is a 99 conservative value; we should almost never observe "no_capacity" 100 events (see /sys/kernel/debug/kcsan). 101 102config KCSAN_UDELAY_TASK 103 int "Delay in microseconds (for tasks)" 104 default 80 105 help 106 For tasks, the microsecond delay after setting up a watchpoint. 107 108config KCSAN_UDELAY_INTERRUPT 109 int "Delay in microseconds (for interrupts)" 110 default 20 111 help 112 For interrupts, the microsecond delay after setting up a watchpoint. 113 Interrupts have tighter latency requirements, and their delay should 114 be lower than for tasks. 115 116config KCSAN_DELAY_RANDOMIZE 117 bool "Randomize above delays" 118 default y 119 help 120 If delays should be randomized, where the maximum is KCSAN_UDELAY_*. 121 If false, the chosen delays are always the KCSAN_UDELAY_* values 122 as defined above. 123 124config KCSAN_SKIP_WATCH 125 int "Skip instructions before setting up watchpoint" 126 default 4000 127 help 128 The number of per-CPU memory operations to skip, before another 129 watchpoint is set up, i.e. one in KCSAN_SKIP_WATCH per-CPU 130 memory operations are used to set up a watchpoint. A smaller value 131 results in more aggressive race detection, whereas a larger value 132 improves system performance at the cost of missing some races. 133 134config KCSAN_SKIP_WATCH_RANDOMIZE 135 bool "Randomize watchpoint instruction skip count" 136 default y 137 help 138 If instruction skip count should be randomized, where the maximum is 139 KCSAN_SKIP_WATCH. If false, the chosen value is always 140 KCSAN_SKIP_WATCH. 141 142config KCSAN_INTERRUPT_WATCHER 143 bool "Interruptible watchers" if !KCSAN_STRICT 144 default KCSAN_STRICT 145 help 146 If enabled, a task that set up a watchpoint may be interrupted while 147 delayed. This option will allow KCSAN to detect races between 148 interrupted tasks and other threads of execution on the same CPU. 149 150 Currently disabled by default, because not all safe per-CPU access 151 primitives and patterns may be accounted for, and therefore could 152 result in false positives. 153 154config KCSAN_REPORT_ONCE_IN_MS 155 int "Duration in milliseconds, in which any given race is only reported once" 156 default 3000 157 help 158 Any given race is only reported once in the defined time window. 159 Different races may still generate reports within a duration that is 160 smaller than the duration defined here. This allows rate limiting 161 reporting to avoid flooding the console with reports. Setting this 162 to 0 disables rate limiting. 163 164# The main purpose of the below options is to control reported data races, and 165# are not expected to be switched frequently by non-testers or at runtime. 166# The defaults are chosen to be conservative, and can miss certain bugs. 167 168config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN 169 bool "Report races of unknown origin" 170 default y 171 help 172 If KCSAN should report races where only one access is known, and the 173 conflicting access is of unknown origin. This type of race is 174 reported if it was only possible to infer a race due to a data value 175 change while an access is being delayed on a watchpoint. 176 177config KCSAN_STRICT 178 bool "Strict data-race checking" 179 help 180 KCSAN will report data races with the strictest possible rules, which 181 closely aligns with the rules defined by the Linux-kernel memory 182 consistency model (LKMM). 183 184config KCSAN_WEAK_MEMORY 185 bool "Enable weak memory modeling to detect missing memory barriers" 186 default y 187 depends on KCSAN_STRICT 188 # We can either let objtool nop __tsan_func_{entry,exit}() and builtin 189 # atomics instrumentation in .noinstr.text, or use a compiler that can 190 # implement __no_kcsan to really remove all instrumentation. 191 depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \ 192 CC_IS_GCC || CLANG_VERSION >= 140000 193 select OBJTOOL if HAVE_NOINSTR_HACK 194 help 195 Enable support for modeling a subset of weak memory, which allows 196 detecting a subset of data races due to missing memory barriers. 197 198 Depends on KCSAN_STRICT, because the options strengthening certain 199 plain accesses by default (depending on !KCSAN_STRICT) reduce the 200 ability to detect any data races invoving reordered accesses, in 201 particular reordered writes. 202 203 Weak memory modeling relies on additional instrumentation and may 204 affect performance. 205 206config KCSAN_REPORT_VALUE_CHANGE_ONLY 207 bool "Only report races where watcher observed a data value change" 208 default y 209 depends on !KCSAN_STRICT 210 help 211 If enabled and a conflicting write is observed via a watchpoint, but 212 the data value of the memory location was observed to remain 213 unchanged, do not report the data race. 214 215config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC 216 bool "Assume that plain aligned writes up to word size are atomic" 217 default y 218 depends on !KCSAN_STRICT 219 help 220 Assume that plain aligned writes up to word size are atomic by 221 default, and also not subject to other unsafe compiler optimizations 222 resulting in data races. This will cause KCSAN to not report data 223 races due to conflicts where the only plain accesses are aligned 224 writes up to word size: conflicts between marked reads and plain 225 aligned writes up to word size will not be reported as data races; 226 notice that data races between two conflicting plain aligned writes 227 will also not be reported. 228 229config KCSAN_IGNORE_ATOMICS 230 bool "Do not instrument marked atomic accesses" 231 depends on !KCSAN_STRICT 232 help 233 Never instrument marked atomic accesses. This option can be used for 234 additional filtering. Conflicting marked atomic reads and plain 235 writes will never be reported as a data race, however, will cause 236 plain reads and marked writes to result in "unknown origin" reports. 237 If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data 238 races where at least one access is marked atomic will never be 239 reported. 240 241 Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned 242 accesses, conflicting marked atomic reads and plain writes will not 243 be reported as data races; however, unlike that option, data races 244 due to two conflicting plain writes will be reported (aligned and 245 unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n). 246 247config KCSAN_PERMISSIVE 248 bool "Enable all additional permissive rules" 249 depends on KCSAN_REPORT_VALUE_CHANGE_ONLY 250 help 251 Enable additional permissive rules to ignore certain classes of data 252 races (also see kernel/kcsan/permissive.h). None of the permissive 253 rules imply that such data races are generally safe, but can be used 254 to further reduce reported data races due to data-racy patterns 255 common across the kernel. 256 257endif # KCSAN 258