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 config KCSAN_VERBOSE
  44         bool "Show verbose reports with more information about system state"
  45         depends on PROVE_LOCKING
  46         help
  47           If enabled, reports show more information about the system state that
  48           may help better analyze and debug races. This includes held locks and
  49           IRQ trace events.
  50
  51           While this option should generally be benign, we call into more
  52           external functions on report generation; if a race report is
  53           generated from any one of them, system stability may suffer due to
  54           deadlocks or recursion.  If in doubt, say N.
  55
  56 config KCSAN_DEBUG
  57         bool "Debugging of KCSAN internals"
  58
  59 config KCSAN_SELFTEST
  60         bool "Perform short selftests on boot"
  61         default y
  62         help
  63           Run KCSAN selftests on boot. On test failure, causes the kernel to
  64           panic. Recommended to be enabled, ensuring critical functionality
  65           works as intended.
  66
  67 config KCSAN_TEST
  68         tristate "KCSAN test for integrated runtime behaviour"
  69         depends on TRACEPOINTS && KUNIT
  70         select TORTURE_TEST
  71         help
  72           KCSAN test focusing on behaviour of the integrated runtime. Tests
  73           various race scenarios, and verifies the reports generated to
  74           console. Makes use of KUnit for test organization, and the Torture
  75           framework for test thread control.
  76
  77           Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
  78           milliseconds. Test run duration may be optimized by building the
  79           kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
  80           than default value.
  81
  82           Say Y here if you want the test to be built into the kernel and run
  83           during boot; say M if you want the test to build as a module; say N
  84           if you are unsure.
  85
  86 config KCSAN_EARLY_ENABLE
  87         bool "Early enable during boot"
  88         default y
  89         help
  90           If KCSAN should be enabled globally as soon as possible. KCSAN can
  91           later be enabled/disabled via debugfs.
  92
  93 config KCSAN_NUM_WATCHPOINTS
  94         int "Number of available watchpoints"
  95         default 64
  96         help
  97           Total number of available watchpoints. An address range maps into a
  98           specific watchpoint slot as specified in kernel/kcsan/encoding.h.
  99           Although larger number of watchpoints may not be usable due to
 100           limited number of CPUs, a larger value helps to improve performance
 101           due to reducing cache-line contention. The chosen default is a
 102           conservative value; we should almost never observe "no_capacity"
 103           events (see /sys/kernel/debug/kcsan).
 104
 105 config KCSAN_UDELAY_TASK
 106         int "Delay in microseconds (for tasks)"
 107         default 80
 108         help
 109           For tasks, the microsecond delay after setting up a watchpoint.
 110
 111 config KCSAN_UDELAY_INTERRUPT
 112         int "Delay in microseconds (for interrupts)"
 113         default 20
 114         help
 115           For interrupts, the microsecond delay after setting up a watchpoint.
 116           Interrupts have tighter latency requirements, and their delay should
 117           be lower than for tasks.
 118
 119 config KCSAN_DELAY_RANDOMIZE
 120         bool "Randomize above delays"
 121         default y
 122         help
 123           If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
 124           If false, the chosen delays are always the KCSAN_UDELAY_* values
 125           as defined above.
 126
 127 config KCSAN_SKIP_WATCH
 128         int "Skip instructions before setting up watchpoint"
 129         default 4000
 130         help
 131           The number of per-CPU memory operations to skip, before another
 132           watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
 133           memory operations are used to set up a watchpoint. A smaller value
 134           results in more aggressive race detection, whereas a larger value
 135           improves system performance at the cost of missing some races.
 136
 137 config KCSAN_SKIP_WATCH_RANDOMIZE
 138         bool "Randomize watchpoint instruction skip count"
 139         default y
 140         help
 141           If instruction skip count should be randomized, where the maximum is
 142           KCSAN_WATCH_SKIP. If false, the chosen value is always
 143           KCSAN_WATCH_SKIP.
 144
 145 config KCSAN_INTERRUPT_WATCHER
 146         bool "Interruptible watchers"
 147         help
 148           If enabled, a task that set up a watchpoint may be interrupted while
 149           delayed. This option will allow KCSAN to detect races between
 150           interrupted tasks and other threads of execution on the same CPU.
 151
 152           Currently disabled by default, because not all safe per-CPU access
 153           primitives and patterns may be accounted for, and therefore could
 154           result in false positives.
 155
 156 config KCSAN_REPORT_ONCE_IN_MS
 157         int "Duration in milliseconds, in which any given race is only reported once"
 158         default 3000
 159         help
 160           Any given race is only reported once in the defined time window.
 161           Different races may still generate reports within a duration that is
 162           smaller than the duration defined here. This allows rate limiting
 163           reporting to avoid flooding the console with reports.  Setting this
 164           to 0 disables rate limiting.
 165
 166 # The main purpose of the below options is to control reported data races (e.g.
 167 # in fuzzer configs), and are not expected to be switched frequently by other
 168 # users. We could turn some of them into boot parameters, but given they should
 169 # not be switched normally, let's keep them here to simplify configuration.
 170 #
 171 # The defaults below are chosen to be very conservative, and may miss certain
 172 # bugs.
 173
 174 config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
 175         bool "Report races of unknown origin"
 176         default y
 177         help
 178           If KCSAN should report races where only one access is known, and the
 179           conflicting access is of unknown origin. This type of race is
 180           reported if it was only possible to infer a race due to a data value
 181           change while an access is being delayed on a watchpoint.
 182
 183 config KCSAN_REPORT_VALUE_CHANGE_ONLY
 184         bool "Only report races where watcher observed a data value change"
 185         default y
 186         help
 187           If enabled and a conflicting write is observed via a watchpoint, but
 188           the data value of the memory location was observed to remain
 189           unchanged, do not report the data race.
 190
 191 config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
 192         bool "Assume that plain aligned writes up to word size are atomic"
 193         default y
 194         help
 195           Assume that plain aligned writes up to word size are atomic by
 196           default, and also not subject to other unsafe compiler optimizations
 197           resulting in data races. This will cause KCSAN to not report data
 198           races due to conflicts where the only plain accesses are aligned
 199           writes up to word size: conflicts between marked reads and plain
 200           aligned writes up to word size will not be reported as data races;
 201           notice that data races between two conflicting plain aligned writes
 202           will also not be reported.
 203
 204 config KCSAN_IGNORE_ATOMICS
 205         bool "Do not instrument marked atomic accesses"
 206         help
 207           Never instrument marked atomic accesses. This option can be used for
 208           additional filtering. Conflicting marked atomic reads and plain
 209           writes will never be reported as a data race, however, will cause
 210           plain reads and marked writes to result in "unknown origin" reports.
 211           If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
 212           races where at least one access is marked atomic will never be
 213           reported.
 214
 215           Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
 216           accesses, conflicting marked atomic reads and plain writes will not
 217           be reported as data races; however, unlike that option, data races
 218           due to two conflicting plain writes will be reported (aligned and
 219           unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
 220
 221 endif # KCSAN