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 && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1))
   9         help
  10           For the list of compilers that support KCSAN, please see
  11           <file:Documentation/dev-tools/kcsan.rst>.
  12
  13 config KCSAN_KCOV_BROKEN
  14         def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
  15         depends on CC_IS_CLANG
  16         depends on !$(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
  23 menuconfig 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
  41 if KCSAN
  42
  43 # Compiler capabilities that should not fail the test if they are unavailable.
  44 config 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
  48 config 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
  61 config KCSAN_DEBUG
  62         bool "Debugging of KCSAN internals"
  63
  64 config 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
  72 config 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
  92 config 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
  99 config 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
 111 config 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
 117 config 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
 125 config 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
 133 config 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
 143 config 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
 151 config 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
 162 config 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
 180 config 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
 189 config 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
 197 config 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
 210 config 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
 227 endif # KCSAN