# 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>.

config KCSAN_KCOV_BROKEN

def_bool KCOV && CC_HAS_SANCOV_TRACE_PC

depends on CC_IS_CLANG

depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)

help

Some versions of clang support either KCSAN and KCOV but not the

combination of the two.

See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status

in newer releases.

menuconfig KCSAN

bool "KCSAN: dynamic data race detector"

depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER

depends on DEBUG_KERNEL && !KASAN

depends on !KCSAN_KCOV_BROKEN

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_WATCH_SKIP 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_WATCH_SKIP. If false, the chosen value is always

KCSAN_WATCH_SKIP.

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 STACK_VALIDATION || CC_IS_GCC || CLANG_VERSION >= 140000

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