lib/Kconfig.kcsan

   1 # SPDX-License-Identifier: GPL-2.0-only
   2
   3 config HAVE_ARCH_KCSAN
   4         bool
   5
   6 config 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
  13 menuconfig 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
  30 if KCSAN
  31
  32 config 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
  41 config 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
  54 config 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
  62 config 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
  82 config 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
  89 config 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
 101 config 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
 107 config 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
 115 config 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
 123 config 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
 133 config 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
 141 config 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
 153 config 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
 167 config 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
 176 config 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
 183 config 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
 205 config 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
 214 config 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
 228 config 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
 246 config 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
 256 endif # KCSAN