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_TEST
  73         tristate "KCSAN test for integrated runtime behaviour"
  74         depends on TRACEPOINTS && KUNIT
  75         select TORTURE_TEST
  76         help
  77           KCSAN test focusing on behaviour of the integrated runtime. Tests
  78           various race scenarios, and verifies the reports generated to
  79           console. Makes use of KUnit for test organization, and the Torture
  80           framework for test thread control.
  81
  82           Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
  83           milliseconds. Test run duration may be optimized by building the
  84           kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
  85           than default value.
  86
  87           Say Y here if you want the test to be built into the kernel and run
  88           during boot; say M if you want the test to build as a module; say N
  89           if you are unsure.
  90
  91 config KCSAN_EARLY_ENABLE
  92         bool "Early enable during boot"
  93         default y
  94         help
  95           If KCSAN should be enabled globally as soon as possible. KCSAN can
  96           later be enabled/disabled via debugfs.
  97
  98 config KCSAN_NUM_WATCHPOINTS
  99         int "Number of available watchpoints"
 100         default 64
 101         help
 102           Total number of available watchpoints. An address range maps into a
 103           specific watchpoint slot as specified in kernel/kcsan/encoding.h.
 104           Although larger number of watchpoints may not be usable due to
 105           limited number of CPUs, a larger value helps to improve performance
 106           due to reducing cache-line contention. The chosen default is a
 107           conservative value; we should almost never observe "no_capacity"
 108           events (see /sys/kernel/debug/kcsan).
 109
 110 config KCSAN_UDELAY_TASK
 111         int "Delay in microseconds (for tasks)"
 112         default 80
 113         help
 114           For tasks, the microsecond delay after setting up a watchpoint.
 115
 116 config KCSAN_UDELAY_INTERRUPT
 117         int "Delay in microseconds (for interrupts)"
 118         default 20
 119         help
 120           For interrupts, the microsecond delay after setting up a watchpoint.
 121           Interrupts have tighter latency requirements, and their delay should
 122           be lower than for tasks.
 123
 124 config KCSAN_DELAY_RANDOMIZE
 125         bool "Randomize above delays"
 126         default y
 127         help
 128           If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
 129           If false, the chosen delays are always the KCSAN_UDELAY_* values
 130           as defined above.
 131
 132 config KCSAN_SKIP_WATCH
 133         int "Skip instructions before setting up watchpoint"
 134         default 4000
 135         help
 136           The number of per-CPU memory operations to skip, before another
 137           watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
 138           memory operations are used to set up a watchpoint. A smaller value
 139           results in more aggressive race detection, whereas a larger value
 140           improves system performance at the cost of missing some races.
 141
 142 config KCSAN_SKIP_WATCH_RANDOMIZE
 143         bool "Randomize watchpoint instruction skip count"
 144         default y
 145         help
 146           If instruction skip count should be randomized, where the maximum is
 147           KCSAN_WATCH_SKIP. If false, the chosen value is always
 148           KCSAN_WATCH_SKIP.
 149
 150 config KCSAN_INTERRUPT_WATCHER
 151         bool "Interruptible watchers"
 152         help
 153           If enabled, a task that set up a watchpoint may be interrupted while
 154           delayed. This option will allow KCSAN to detect races between
 155           interrupted tasks and other threads of execution on the same CPU.
 156
 157           Currently disabled by default, because not all safe per-CPU access
 158           primitives and patterns may be accounted for, and therefore could
 159           result in false positives.
 160
 161 config KCSAN_REPORT_ONCE_IN_MS
 162         int "Duration in milliseconds, in which any given race is only reported once"
 163         default 3000
 164         help
 165           Any given race is only reported once in the defined time window.
 166           Different races may still generate reports within a duration that is
 167           smaller than the duration defined here. This allows rate limiting
 168           reporting to avoid flooding the console with reports.  Setting this
 169           to 0 disables rate limiting.
 170
 171 # The main purpose of the below options is to control reported data races (e.g.
 172 # in fuzzer configs), and are not expected to be switched frequently by other
 173 # users. We could turn some of them into boot parameters, but given they should
 174 # not be switched normally, let's keep them here to simplify configuration.
 175 #
 176 # The defaults below are chosen to be very conservative, and may miss certain
 177 # bugs.
 178
 179 config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
 180         bool "Report races of unknown origin"
 181         default y
 182         help
 183           If KCSAN should report races where only one access is known, and the
 184           conflicting access is of unknown origin. This type of race is
 185           reported if it was only possible to infer a race due to a data value
 186           change while an access is being delayed on a watchpoint.
 187
 188 config KCSAN_REPORT_VALUE_CHANGE_ONLY
 189         bool "Only report races where watcher observed a data value change"
 190         default y
 191         help
 192           If enabled and a conflicting write is observed via a watchpoint, but
 193           the data value of the memory location was observed to remain
 194           unchanged, do not report the data race.
 195
 196 config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
 197         bool "Assume that plain aligned writes up to word size are atomic"
 198         default y
 199         help
 200           Assume that plain aligned writes up to word size are atomic by
 201           default, and also not subject to other unsafe compiler optimizations
 202           resulting in data races. This will cause KCSAN to not report data
 203           races due to conflicts where the only plain accesses are aligned
 204           writes up to word size: conflicts between marked reads and plain
 205           aligned writes up to word size will not be reported as data races;
 206           notice that data races between two conflicting plain aligned writes
 207           will also not be reported.
 208
 209 config KCSAN_IGNORE_ATOMICS
 210         bool "Do not instrument marked atomic accesses"
 211         help
 212           Never instrument marked atomic accesses. This option can be used for
 213           additional filtering. Conflicting marked atomic reads and plain
 214           writes will never be reported as a data race, however, will cause
 215           plain reads and marked writes to result in "unknown origin" reports.
 216           If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
 217           races where at least one access is marked atomic will never be
 218           reported.
 219
 220           Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
 221           accesses, conflicting marked atomic reads and plain writes will not
 222           be reported as data races; however, unlike that option, data races
 223           due to two conflicting plain writes will be reported (aligned and
 224           unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
 225
 226 endif # KCSAN