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 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
  31 if KCSAN
  32
  33 config 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
  42 config 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
  55 config 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
  63 config 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
  83 config 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
  90 config 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
 102 config 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
 108 config 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
 116 config 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
 124 config 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
 134 config 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
 142 config 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
 154 config 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
 168 config 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
 177 config 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
 184 config 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
 206 config 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
 215 config 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
 229 config 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
 247 config 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
 257 endif # KCSAN