[linux-block.git] / lib / Kconfig.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>.

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

# Compiler capabilities that should not fail the test if they are unavailable.
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))

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_DEBUG
	bool "Debugging of KCSAN internals"

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"
	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 (e.g.
# in fuzzer configs), and are not expected to be switched frequently by other
# users. We could turn some of them into boot parameters, but given they should
# not be switched normally, let's keep them here to simplify configuration.
#
# The defaults below are chosen to be very conservative, and may 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_REPORT_VALUE_CHANGE_ONLY
	bool "Only report races where watcher observed a data value change"
	default y
	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
	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"
	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).

endif # KCSAN
Commit	Line	Data
dfd402a4 ME	1	# SPDX-License-Identifier: GPL-2.0-only
	2
	3	config HAVE_ARCH_KCSAN
	4	bool
	5
0e1aa5b6	6	config HAVE_KCSAN_COMPILER
e68dcd8e ME	7	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)) \|\| \
e68dcd8e ME	8	(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1))
0e1aa5b6 ME	9	help
	10	For the list of compilers that support KCSAN, please see
	11	<file:Documentation/dev-tools/kcsan.rst>.
	12
ea91a1d4 AB	13	config KCSAN_KCOV_BROKEN
	14	def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
	15	depends on CC_IS_CLANG
	16	depends on !$(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
dfd402a4	23	menuconfig KCSAN
eba9c444	24	bool "KCSAN: dynamic data race detector"
0e1aa5b6 ME	25	depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
0e1aa5b6 ME	26	depends on DEBUG_KERNEL && !KASAN
ea91a1d4	27	depends on !KCSAN_KCOV_BROKEN
8cfbb04f	28	select STACKTRACE
dfd402a4	29	help
eba9c444 IM	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.
d591ec3d	33
eba9c444 IM	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.
8cfbb04f ME	38
8cfbb04f ME	39	See <file:Documentation/dev-tools/kcsan.rst> for more details.
dfd402a4 ME	40
	41	if KCSAN
	42
bec4a247 ME	43	# Compiler capabilities that should not fail the test if they are unavailable.
	44	config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
	45	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) \|\| \
	46	(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
	47
2402d0ea ME	48	config KCSAN_VERBOSE
	49	bool "Show verbose reports with more information about system state"
	50	depends on PROVE_LOCKING
	51	help
	52	If enabled, reports show more information about the system state that
	53	may help better analyze and debug races. This includes held locks and
	54	IRQ trace events.
	55
	56	While this option should generally be benign, we call into more
	57	external functions on report generation; if a race report is
	58	generated from any one of them, system stability may suffer due to
	59	deadlocks or recursion. If in doubt, say N.
	60
dfd402a4 ME	61	config KCSAN_DEBUG
dfd402a4 ME	62	bool "Debugging of KCSAN internals"
dfd402a4 ME	63
	64	config KCSAN_SELFTEST
	65	bool "Perform short selftests on boot"
	66	default y
	67	help
1fe84fd4 ME	68	Run KCSAN selftests on boot. On test failure, causes the kernel to
	69	panic. Recommended to be enabled, ensuring critical functionality
	70	works as intended.
	71
a146fed5 ME	72	config KCSAN_KUNIT_TEST
	73	tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
	74	default KUNIT_ALL_TESTS
1fe84fd4 ME	75	depends on TRACEPOINTS && KUNIT
	76	select TORTURE_TEST
	77	help
	78	KCSAN test focusing on behaviour of the integrated runtime. Tests
	79	various race scenarios, and verifies the reports generated to
	80	console. Makes use of KUnit for test organization, and the Torture
	81	framework for test thread control.
	82
	83	Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
	84	milliseconds. Test run duration may be optimized by building the
	85	kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
	86	than default value.
	87
	88	Say Y here if you want the test to be built into the kernel and run
	89	during boot; say M if you want the test to build as a module; say N
	90	if you are unsure.
dfd402a4 ME	91
	92	config KCSAN_EARLY_ENABLE
	93	bool "Early enable during boot"
	94	default y
	95	help
	96	If KCSAN should be enabled globally as soon as possible. KCSAN can
	97	later be enabled/disabled via debugfs.
	98
	99	config KCSAN_NUM_WATCHPOINTS
	100	int "Number of available watchpoints"
	101	default 64
	102	help
	103	Total number of available watchpoints. An address range maps into a
	104	specific watchpoint slot as specified in kernel/kcsan/encoding.h.
	105	Although larger number of watchpoints may not be usable due to
	106	limited number of CPUs, a larger value helps to improve performance
	107	due to reducing cache-line contention. The chosen default is a
	108	conservative value; we should almost never observe "no_capacity"
	109	events (see /sys/kernel/debug/kcsan).
	110
	111	config KCSAN_UDELAY_TASK
	112	int "Delay in microseconds (for tasks)"
	113	default 80
	114	help
	115	For tasks, the microsecond delay after setting up a watchpoint.
	116
	117	config KCSAN_UDELAY_INTERRUPT
	118	int "Delay in microseconds (for interrupts)"
	119	default 20
	120	help
	121	For interrupts, the microsecond delay after setting up a watchpoint.
	122	Interrupts have tighter latency requirements, and their delay should
	123	be lower than for tasks.
	124
	125	config KCSAN_DELAY_RANDOMIZE
	126	bool "Randomize above delays"
	127	default y
	128	help
	129	If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
5cbaefe9 IM	130	If false, the chosen delays are always the KCSAN_UDELAY_* values
5cbaefe9 IM	131	as defined above.
dfd402a4 ME	132
	133	config KCSAN_SKIP_WATCH
	134	int "Skip instructions before setting up watchpoint"
	135	default 4000
	136	help
	137	The number of per-CPU memory operations to skip, before another
	138	watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
	139	memory operations are used to set up a watchpoint. A smaller value
	140	results in more aggressive race detection, whereas a larger value
	141	improves system performance at the cost of missing some races.
	142
	143	config KCSAN_SKIP_WATCH_RANDOMIZE
	144	bool "Randomize watchpoint instruction skip count"
	145	default y
	146	help
	147	If instruction skip count should be randomized, where the maximum is
	148	KCSAN_WATCH_SKIP. If false, the chosen value is always
	149	KCSAN_WATCH_SKIP.
	150
48b1fc19 ME	151	config KCSAN_INTERRUPT_WATCHER
	152	bool "Interruptible watchers"
	153	help
	154	If enabled, a task that set up a watchpoint may be interrupted while
	155	delayed. This option will allow KCSAN to detect races between
	156	interrupted tasks and other threads of execution on the same CPU.
	157
	158	Currently disabled by default, because not all safe per-CPU access
	159	primitives and patterns may be accounted for, and therefore could
	160	result in false positives.
	161
05f9a406	162	config KCSAN_REPORT_ONCE_IN_MS
d591ec3d	163	int "Duration in milliseconds, in which any given race is only reported once"
05f9a406 ME	164	default 3000
05f9a406 ME	165	help
d591ec3d ME	166	Any given race is only reported once in the defined time window.
	167	Different races may still generate reports within a duration that is
	168	smaller than the duration defined here. This allows rate limiting
	169	reporting to avoid flooding the console with reports. Setting this
	170	to 0 disables rate limiting.
05f9a406	171
1e6ee2f0 ME	172	# The main purpose of the below options is to control reported data races (e.g.
	173	# in fuzzer configs), and are not expected to be switched frequently by other
	174	# users. We could turn some of them into boot parameters, but given they should
	175	# not be switched normally, let's keep them here to simplify configuration.
	176	#
	177	# The defaults below are chosen to be very conservative, and may miss certain
	178	# bugs.
dfd402a4 ME	179
	180	config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
	181	bool "Report races of unknown origin"
	182	default y
	183	help
	184	If KCSAN should report races where only one access is known, and the
	185	conflicting access is of unknown origin. This type of race is
	186	reported if it was only possible to infer a race due to a data value
	187	change while an access is being delayed on a watchpoint.
	188
	189	config KCSAN_REPORT_VALUE_CHANGE_ONLY
	190	bool "Only report races where watcher observed a data value change"
	191	default y
	192	help
5cbaefe9	193	If enabled and a conflicting write is observed via a watchpoint, but
dfd402a4 ME	194	the data value of the memory location was observed to remain
	195	unchanged, do not report the data race.
	196
1e6ee2f0 ME	197	config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
	198	bool "Assume that plain aligned writes up to word size are atomic"
	199	default y
	200	help
	201	Assume that plain aligned writes up to word size are atomic by
	202	default, and also not subject to other unsafe compiler optimizations
	203	resulting in data races. This will cause KCSAN to not report data
	204	races due to conflicts where the only plain accesses are aligned
	205	writes up to word size: conflicts between marked reads and plain
	206	aligned writes up to word size will not be reported as data races;
	207	notice that data races between two conflicting plain aligned writes
	208	will also not be reported.
	209
dfd402a4 ME	210	config KCSAN_IGNORE_ATOMICS
dfd402a4 ME	211	bool "Do not instrument marked atomic accesses"
dfd402a4	212	help
a249a732 ME	213	Never instrument marked atomic accesses. This option can be used for
	214	additional filtering. Conflicting marked atomic reads and plain
	215	writes will never be reported as a data race, however, will cause
	216	plain reads and marked writes to result in "unknown origin" reports.
	217	If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
	218	races where at least one access is marked atomic will never be
	219	reported.
	220
	221	Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
	222	accesses, conflicting marked atomic reads and plain writes will not
	223	be reported as data races; however, unlike that option, data races
	224	due to two conflicting plain writes will be reported (aligned and
	225	unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
dfd402a4 ME	226
dfd402a4 ME	227	endif # KCSAN