lib/Kconfig.kcsan

   1 # SPDX-License-Identifier: GPL-2.0-only
   2
   3 config HAVE_ARCH_KCSAN
   4         bool
   5
   6 config KCSAN_KCOV_BROKEN
   7         def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
   8         depends on CC_IS_CLANG
   9         depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)
  10         help
  11           Some versions of clang support either KCSAN and KCOV but not the
  12           combination of the two.
  13           See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
  14           in newer releases.
  15
  16 menuconfig KCSAN
  17         bool "KCSAN: dynamic data race detector"
  18         depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN
  19         depends on !KCSAN_KCOV_BROKEN
  20         select STACKTRACE
  21         help
  22           The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
  23           data-race detector that relies on compile-time instrumentation.
  24           KCSAN uses a watchpoint-based sampling approach to detect races.
  25
  26           While KCSAN's primary purpose is to detect data races, it
  27           also provides assertions to check data access constraints.
  28           These assertions can expose bugs that do not manifest as
  29           data races.
  30
  31           See <file:Documentation/dev-tools/kcsan.rst> for more details.
  32
  33 if KCSAN
  34
  35 config KCSAN_VERBOSE
  36         bool "Show verbose reports with more information about system state"
  37         depends on PROVE_LOCKING
  38         help
  39           If enabled, reports show more information about the system state that
  40           may help better analyze and debug races. This includes held locks and
  41           IRQ trace events.
  42
  43           While this option should generally be benign, we call into more
  44           external functions on report generation; if a race report is
  45           generated from any one of them, system stability may suffer due to
  46           deadlocks or recursion.  If in doubt, say N.
  47
  48 config KCSAN_DEBUG
  49         bool "Debugging of KCSAN internals"
  50
  51 config KCSAN_SELFTEST
  52         bool "Perform short selftests on boot"
  53         default y
  54         help
  55           Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
  56
  57 config KCSAN_EARLY_ENABLE
  58         bool "Early enable during boot"
  59         default y
  60         help
  61           If KCSAN should be enabled globally as soon as possible. KCSAN can
  62           later be enabled/disabled via debugfs.
  63
  64 config KCSAN_NUM_WATCHPOINTS
  65         int "Number of available watchpoints"
  66         default 64
  67         help
  68           Total number of available watchpoints. An address range maps into a
  69           specific watchpoint slot as specified in kernel/kcsan/encoding.h.
  70           Although larger number of watchpoints may not be usable due to
  71           limited number of CPUs, a larger value helps to improve performance
  72           due to reducing cache-line contention. The chosen default is a
  73           conservative value; we should almost never observe "no_capacity"
  74           events (see /sys/kernel/debug/kcsan).
  75
  76 config KCSAN_UDELAY_TASK
  77         int "Delay in microseconds (for tasks)"
  78         default 80
  79         help
  80           For tasks, the microsecond delay after setting up a watchpoint.
  81
  82 config KCSAN_UDELAY_INTERRUPT
  83         int "Delay in microseconds (for interrupts)"
  84         default 20
  85         help
  86           For interrupts, the microsecond delay after setting up a watchpoint.
  87           Interrupts have tighter latency requirements, and their delay should
  88           be lower than for tasks.
  89
  90 config KCSAN_DELAY_RANDOMIZE
  91         bool "Randomize above delays"
  92         default y
  93         help
  94           If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
  95           If false, the chosen delays are always the KCSAN_UDELAY_* values
  96           as defined above.
  97
  98 config KCSAN_SKIP_WATCH
  99         int "Skip instructions before setting up watchpoint"
 100         default 4000
 101         help
 102           The number of per-CPU memory operations to skip, before another
 103           watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
 104           memory operations are used to set up a watchpoint. A smaller value
 105           results in more aggressive race detection, whereas a larger value
 106           improves system performance at the cost of missing some races.
 107
 108 config KCSAN_SKIP_WATCH_RANDOMIZE
 109         bool "Randomize watchpoint instruction skip count"
 110         default y
 111         help
 112           If instruction skip count should be randomized, where the maximum is
 113           KCSAN_WATCH_SKIP. If false, the chosen value is always
 114           KCSAN_WATCH_SKIP.
 115
 116 config KCSAN_INTERRUPT_WATCHER
 117         bool "Interruptible watchers"
 118         help
 119           If enabled, a task that set up a watchpoint may be interrupted while
 120           delayed. This option will allow KCSAN to detect races between
 121           interrupted tasks and other threads of execution on the same CPU.
 122
 123           Currently disabled by default, because not all safe per-CPU access
 124           primitives and patterns may be accounted for, and therefore could
 125           result in false positives.
 126
 127 config KCSAN_REPORT_ONCE_IN_MS
 128         int "Duration in milliseconds, in which any given race is only reported once"
 129         default 3000
 130         help
 131           Any given race is only reported once in the defined time window.
 132           Different races may still generate reports within a duration that is
 133           smaller than the duration defined here. This allows rate limiting
 134           reporting to avoid flooding the console with reports.  Setting this
 135           to 0 disables rate limiting.
 136
 137 # The main purpose of the below options is to control reported data races (e.g.
 138 # in fuzzer configs), and are not expected to be switched frequently by other
 139 # users. We could turn some of them into boot parameters, but given they should
 140 # not be switched normally, let's keep them here to simplify configuration.
 141 #
 142 # The defaults below are chosen to be very conservative, and may miss certain
 143 # bugs.
 144
 145 config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
 146         bool "Report races of unknown origin"
 147         default y
 148         help
 149           If KCSAN should report races where only one access is known, and the
 150           conflicting access is of unknown origin. This type of race is
 151           reported if it was only possible to infer a race due to a data value
 152           change while an access is being delayed on a watchpoint.
 153
 154 config KCSAN_REPORT_VALUE_CHANGE_ONLY
 155         bool "Only report races where watcher observed a data value change"
 156         default y
 157         help
 158           If enabled and a conflicting write is observed via a watchpoint, but
 159           the data value of the memory location was observed to remain
 160           unchanged, do not report the data race.
 161
 162 config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
 163         bool "Assume that plain aligned writes up to word size are atomic"
 164         default y
 165         help
 166           Assume that plain aligned writes up to word size are atomic by
 167           default, and also not subject to other unsafe compiler optimizations
 168           resulting in data races. This will cause KCSAN to not report data
 169           races due to conflicts where the only plain accesses are aligned
 170           writes up to word size: conflicts between marked reads and plain
 171           aligned writes up to word size will not be reported as data races;
 172           notice that data races between two conflicting plain aligned writes
 173           will also not be reported.
 174
 175 config KCSAN_IGNORE_ATOMICS
 176         bool "Do not instrument marked atomic accesses"
 177         help
 178           Never instrument marked atomic accesses. This option can be used for
 179           additional filtering. Conflicting marked atomic reads and plain
 180           writes will never be reported as a data race, however, will cause
 181           plain reads and marked writes to result in "unknown origin" reports.
 182           If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
 183           races where at least one access is marked atomic will never be
 184           reported.
 185
 186           Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
 187           accesses, conflicting marked atomic reads and plain writes will not
 188           be reported as data races; however, unlike that option, data races
 189           due to two conflicting plain writes will be reported (aligned and
 190           unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
 191
 192 endif # KCSAN