| # SPDX-License-Identifier: GPL-2.0-only |
| |
| config HAVE_ARCH_KCSAN |
| bool |
| |
| config HAVE_KCSAN_COMPILER |
| def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)) || \ |
| (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1)) |
| help |
| For the list of compilers that support KCSAN, please see |
| <file:Documentation/dev-tools/kcsan.rst>. |
| |
| menuconfig KCSAN |
| bool "KCSAN: dynamic data race detector" |
| depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER |
| depends on DEBUG_KERNEL && !KASAN |
| select STACKTRACE |
| help |
| The Kernel Concurrency Sanitizer (KCSAN) is a dynamic |
| data-race detector that relies on compile-time instrumentation. |
| KCSAN uses a watchpoint-based sampling approach to detect races. |
| |
| While KCSAN's primary purpose is to detect data races, it |
| also provides assertions to check data access constraints. |
| These assertions can expose bugs that do not manifest as |
| data races. |
| |
| See <file:Documentation/dev-tools/kcsan.rst> for more details. |
| |
| if KCSAN |
| |
| config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE |
| def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \ |
| (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1)) |
| help |
| The compiler instruments plain compound read-write operations |
| differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to |
| distinguish them from other plain accesses. This is currently |
| supported by Clang 12 or later. |
| |
| config KCSAN_VERBOSE |
| bool "Show verbose reports with more information about system state" |
| depends on PROVE_LOCKING |
| help |
| If enabled, reports show more information about the system state that |
| may help better analyze and debug races. This includes held locks and |
| IRQ trace events. |
| |
| While this option should generally be benign, we call into more |
| external functions on report generation; if a race report is |
| generated from any one of them, system stability may suffer due to |
| deadlocks or recursion. If in doubt, say N. |
| |
| config KCSAN_SELFTEST |
| bool "Perform short selftests on boot" |
| default y |
| help |
| Run KCSAN selftests on boot. On test failure, causes the kernel to |
| panic. Recommended to be enabled, ensuring critical functionality |
| works as intended. |
| |
| config KCSAN_KUNIT_TEST |
| tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS |
| default KUNIT_ALL_TESTS |
| depends on TRACEPOINTS && KUNIT |
| select TORTURE_TEST |
| help |
| KCSAN test focusing on behaviour of the integrated runtime. Tests |
| various race scenarios, and verifies the reports generated to |
| console. Makes use of KUnit for test organization, and the Torture |
| framework for test thread control. |
| |
| Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS |
| milliseconds. Test run duration may be optimized by building the |
| kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower |
| than default value. |
| |
| Say Y here if you want the test to be built into the kernel and run |
| during boot; say M if you want the test to build as a module; say N |
| if you are unsure. |
| |
| config KCSAN_EARLY_ENABLE |
| bool "Early enable during boot" |
| default y |
| help |
| If KCSAN should be enabled globally as soon as possible. KCSAN can |
| later be enabled/disabled via debugfs. |
| |
| config KCSAN_NUM_WATCHPOINTS |
| int "Number of available watchpoints" |
| default 64 |
| help |
| Total number of available watchpoints. An address range maps into a |
| specific watchpoint slot as specified in kernel/kcsan/encoding.h. |
| Although larger number of watchpoints may not be usable due to |
| limited number of CPUs, a larger value helps to improve performance |
| due to reducing cache-line contention. The chosen default is a |
| conservative value; we should almost never observe "no_capacity" |
| events (see /sys/kernel/debug/kcsan). |
| |
| config KCSAN_UDELAY_TASK |
| int "Delay in microseconds (for tasks)" |
| default 80 |
| help |
| For tasks, the microsecond delay after setting up a watchpoint. |
| |
| config KCSAN_UDELAY_INTERRUPT |
| int "Delay in microseconds (for interrupts)" |
| default 20 |
| help |
| For interrupts, the microsecond delay after setting up a watchpoint. |
| Interrupts have tighter latency requirements, and their delay should |
| be lower than for tasks. |
| |
| config KCSAN_DELAY_RANDOMIZE |
| bool "Randomize above delays" |
| default y |
| help |
| If delays should be randomized, where the maximum is KCSAN_UDELAY_*. |
| If false, the chosen delays are always the KCSAN_UDELAY_* values |
| as defined above. |
| |
| config KCSAN_SKIP_WATCH |
| int "Skip instructions before setting up watchpoint" |
| default 4000 |
| help |
| The number of per-CPU memory operations to skip, before another |
| watchpoint is set up, i.e. one in KCSAN_SKIP_WATCH per-CPU |
| memory operations are used to set up a watchpoint. A smaller value |
| results in more aggressive race detection, whereas a larger value |
| improves system performance at the cost of missing some races. |
| |
| config KCSAN_SKIP_WATCH_RANDOMIZE |
| bool "Randomize watchpoint instruction skip count" |
| default y |
| help |
| If instruction skip count should be randomized, where the maximum is |
| KCSAN_SKIP_WATCH. If false, the chosen value is always |
| KCSAN_SKIP_WATCH. |
| |
| config KCSAN_INTERRUPT_WATCHER |
| bool "Interruptible watchers" if !KCSAN_STRICT |
| default KCSAN_STRICT |
| help |
| If enabled, a task that set up a watchpoint may be interrupted while |
| delayed. This option will allow KCSAN to detect races between |
| interrupted tasks and other threads of execution on the same CPU. |
| |
| Currently disabled by default, because not all safe per-CPU access |
| primitives and patterns may be accounted for, and therefore could |
| result in false positives. |
| |
| config KCSAN_REPORT_ONCE_IN_MS |
| int "Duration in milliseconds, in which any given race is only reported once" |
| default 3000 |
| help |
| Any given race is only reported once in the defined time window. |
| Different races may still generate reports within a duration that is |
| smaller than the duration defined here. This allows rate limiting |
| reporting to avoid flooding the console with reports. Setting this |
| to 0 disables rate limiting. |
| |
| # The main purpose of the below options is to control reported data races, and |
| # are not expected to be switched frequently by non-testers or at runtime. |
| # The defaults are chosen to be conservative, and can miss certain bugs. |
| |
| config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN |
| bool "Report races of unknown origin" |
| default y |
| help |
| If KCSAN should report races where only one access is known, and the |
| conflicting access is of unknown origin. This type of race is |
| reported if it was only possible to infer a race due to a data value |
| change while an access is being delayed on a watchpoint. |
| |
| config KCSAN_STRICT |
| bool "Strict data-race checking" |
| help |
| KCSAN will report data races with the strictest possible rules, which |
| closely aligns with the rules defined by the Linux-kernel memory |
| consistency model (LKMM). |
| |
| config KCSAN_WEAK_MEMORY |
| bool "Enable weak memory modeling to detect missing memory barriers" |
| default y |
| depends on KCSAN_STRICT |
| # We can either let objtool nop __tsan_func_{entry,exit}() and builtin |
| # atomics instrumentation in .noinstr.text, or use a compiler that can |
| # implement __no_kcsan to really remove all instrumentation. |
| depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \ |
| CC_IS_GCC || CLANG_VERSION >= 140000 |
| select OBJTOOL if HAVE_NOINSTR_HACK |
| help |
| Enable support for modeling a subset of weak memory, which allows |
| detecting a subset of data races due to missing memory barriers. |
| |
| Depends on KCSAN_STRICT, because the options strenghtening certain |
| plain accesses by default (depending on !KCSAN_STRICT) reduce the |
| ability to detect any data races invoving reordered accesses, in |
| particular reordered writes. |
| |
| Weak memory modeling relies on additional instrumentation and may |
| affect performance. |
| |
| config KCSAN_REPORT_VALUE_CHANGE_ONLY |
| bool "Only report races where watcher observed a data value change" |
| default y |
| depends on !KCSAN_STRICT |
| help |
| If enabled and a conflicting write is observed via a watchpoint, but |
| the data value of the memory location was observed to remain |
| unchanged, do not report the data race. |
| |
| config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC |
| bool "Assume that plain aligned writes up to word size are atomic" |
| default y |
| depends on !KCSAN_STRICT |
| help |
| Assume that plain aligned writes up to word size are atomic by |
| default, and also not subject to other unsafe compiler optimizations |
| resulting in data races. This will cause KCSAN to not report data |
| races due to conflicts where the only plain accesses are aligned |
| writes up to word size: conflicts between marked reads and plain |
| aligned writes up to word size will not be reported as data races; |
| notice that data races between two conflicting plain aligned writes |
| will also not be reported. |
| |
| config KCSAN_IGNORE_ATOMICS |
| bool "Do not instrument marked atomic accesses" |
| depends on !KCSAN_STRICT |
| help |
| Never instrument marked atomic accesses. This option can be used for |
| additional filtering. Conflicting marked atomic reads and plain |
| writes will never be reported as a data race, however, will cause |
| plain reads and marked writes to result in "unknown origin" reports. |
| If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data |
| races where at least one access is marked atomic will never be |
| reported. |
| |
| Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned |
| accesses, conflicting marked atomic reads and plain writes will not |
| be reported as data races; however, unlike that option, data races |
| due to two conflicting plain writes will be reported (aligned and |
| unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n). |
| |
| config KCSAN_PERMISSIVE |
| bool "Enable all additional permissive rules" |
| depends on KCSAN_REPORT_VALUE_CHANGE_ONLY |
| help |
| Enable additional permissive rules to ignore certain classes of data |
| races (also see kernel/kcsan/permissive.h). None of the permissive |
| rules imply that such data races are generally safe, but can be used |
| to further reduce reported data races due to data-racy patterns |
| common across the kernel. |
| |
| endif # KCSAN |
