lib/Kconfig.kcsan - third_party/kernel - Git at Google

 # 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_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 !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
	# 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_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 !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