[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>.

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 strengthening 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
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
dfd402a4	13	menuconfig KCSAN
eba9c444	14	bool "KCSAN: dynamic data race detector"
0e1aa5b6 ME	15	depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
0e1aa5b6 ME	16	depends on DEBUG_KERNEL && !KASAN
8cfbb04f	17	select STACKTRACE
dfd402a4	18	help
eba9c444 IM	19	The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
	20	data-race detector that relies on compile-time instrumentation.
	21	KCSAN uses a watchpoint-based sampling approach to detect races.
d591ec3d	22
eba9c444 IM	23	While KCSAN's primary purpose is to detect data races, it
	24	also provides assertions to check data access constraints.
	25	These assertions can expose bugs that do not manifest as
	26	data races.
8cfbb04f ME	27
8cfbb04f ME	28	See <file:Documentation/dev-tools/kcsan.rst> for more details.
dfd402a4 ME	29
	30	if KCSAN
	31
bec4a247 ME	32	config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
	33	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) \|\| \
	34	(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
eb32f9f9 ME	35	help
	36	The compiler instruments plain compound read-write operations
	37	differently (++, --, +=, -=, \|=, &=, etc.), which allows KCSAN to
	38	distinguish them from other plain accesses. This is currently
	39	supported by Clang 12 or later.
bec4a247	40
2402d0ea ME	41	config KCSAN_VERBOSE
	42	bool "Show verbose reports with more information about system state"
	43	depends on PROVE_LOCKING
	44	help
	45	If enabled, reports show more information about the system state that
	46	may help better analyze and debug races. This includes held locks and
	47	IRQ trace events.
	48
	49	While this option should generally be benign, we call into more
	50	external functions on report generation; if a race report is
	51	generated from any one of them, system stability may suffer due to
	52	deadlocks or recursion. If in doubt, say N.
	53
dfd402a4 ME	54	config KCSAN_SELFTEST
	55	bool "Perform short selftests on boot"
	56	default y
	57	help
1fe84fd4 ME	58	Run KCSAN selftests on boot. On test failure, causes the kernel to
	59	panic. Recommended to be enabled, ensuring critical functionality
	60	works as intended.
	61
a146fed5 ME	62	config KCSAN_KUNIT_TEST
	63	tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
	64	default KUNIT_ALL_TESTS
1fe84fd4 ME	65	depends on TRACEPOINTS && KUNIT
	66	select TORTURE_TEST
	67	help
	68	KCSAN test focusing on behaviour of the integrated runtime. Tests
	69	various race scenarios, and verifies the reports generated to
	70	console. Makes use of KUnit for test organization, and the Torture
	71	framework for test thread control.
	72
	73	Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
	74	milliseconds. Test run duration may be optimized by building the
	75	kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
	76	than default value.
	77
	78	Say Y here if you want the test to be built into the kernel and run
	79	during boot; say M if you want the test to build as a module; say N
	80	if you are unsure.
dfd402a4 ME	81
	82	config KCSAN_EARLY_ENABLE
	83	bool "Early enable during boot"
	84	default y
	85	help
	86	If KCSAN should be enabled globally as soon as possible. KCSAN can
	87	later be enabled/disabled via debugfs.
	88
	89	config KCSAN_NUM_WATCHPOINTS
	90	int "Number of available watchpoints"
	91	default 64
	92	help
	93	Total number of available watchpoints. An address range maps into a
	94	specific watchpoint slot as specified in kernel/kcsan/encoding.h.
	95	Although larger number of watchpoints may not be usable due to
	96	limited number of CPUs, a larger value helps to improve performance
	97	due to reducing cache-line contention. The chosen default is a
	98	conservative value; we should almost never observe "no_capacity"
	99	events (see /sys/kernel/debug/kcsan).
	100
	101	config KCSAN_UDELAY_TASK
	102	int "Delay in microseconds (for tasks)"
	103	default 80
	104	help
	105	For tasks, the microsecond delay after setting up a watchpoint.
	106
	107	config KCSAN_UDELAY_INTERRUPT
	108	int "Delay in microseconds (for interrupts)"
	109	default 20
	110	help
	111	For interrupts, the microsecond delay after setting up a watchpoint.
	112	Interrupts have tighter latency requirements, and their delay should
	113	be lower than for tasks.
	114
	115	config KCSAN_DELAY_RANDOMIZE
	116	bool "Randomize above delays"
	117	default y
	118	help
	119	If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
5cbaefe9 IM	120	If false, the chosen delays are always the KCSAN_UDELAY_* values
5cbaefe9 IM	121	as defined above.
dfd402a4 ME	122
	123	config KCSAN_SKIP_WATCH
	124	int "Skip instructions before setting up watchpoint"
	125	default 4000
	126	help
	127	The number of per-CPU memory operations to skip, before another
144b9152	128	watchpoint is set up, i.e. one in KCSAN_SKIP_WATCH per-CPU
dfd402a4 ME	129	memory operations are used to set up a watchpoint. A smaller value
	130	results in more aggressive race detection, whereas a larger value
	131	improves system performance at the cost of missing some races.
	132
	133	config KCSAN_SKIP_WATCH_RANDOMIZE
	134	bool "Randomize watchpoint instruction skip count"
	135	default y
	136	help
	137	If instruction skip count should be randomized, where the maximum is
144b9152 RY	138	KCSAN_SKIP_WATCH. If false, the chosen value is always
144b9152 RY	139	KCSAN_SKIP_WATCH.
dfd402a4	140
48b1fc19	141	config KCSAN_INTERRUPT_WATCHER
e0493804 ME	142	bool "Interruptible watchers" if !KCSAN_STRICT
e0493804 ME	143	default KCSAN_STRICT
48b1fc19 ME	144	help
	145	If enabled, a task that set up a watchpoint may be interrupted while
	146	delayed. This option will allow KCSAN to detect races between
	147	interrupted tasks and other threads of execution on the same CPU.
	148
	149	Currently disabled by default, because not all safe per-CPU access
	150	primitives and patterns may be accounted for, and therefore could
	151	result in false positives.
	152
05f9a406	153	config KCSAN_REPORT_ONCE_IN_MS
d591ec3d	154	int "Duration in milliseconds, in which any given race is only reported once"
05f9a406 ME	155	default 3000
05f9a406 ME	156	help
d591ec3d ME	157	Any given race is only reported once in the defined time window.
	158	Different races may still generate reports within a duration that is
	159	smaller than the duration defined here. This allows rate limiting
	160	reporting to avoid flooding the console with reports. Setting this
	161	to 0 disables rate limiting.
05f9a406	162
eb32f9f9 ME	163	# The main purpose of the below options is to control reported data races, and
	164	# are not expected to be switched frequently by non-testers or at runtime.
	165	# The defaults are chosen to be conservative, and can miss certain bugs.
dfd402a4 ME	166
	167	config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
	168	bool "Report races of unknown origin"
	169	default y
	170	help
	171	If KCSAN should report races where only one access is known, and the
	172	conflicting access is of unknown origin. This type of race is
	173	reported if it was only possible to infer a race due to a data value
	174	change while an access is being delayed on a watchpoint.
	175
e675d253 ME	176	config KCSAN_STRICT
	177	bool "Strict data-race checking"
	178	help
	179	KCSAN will report data races with the strictest possible rules, which
	180	closely aligns with the rules defined by the Linux-kernel memory
	181	consistency model (LKMM).
	182
69562e49 ME	183	config KCSAN_WEAK_MEMORY
	184	bool "Enable weak memory modeling to detect missing memory barriers"
	185	default y
	186	depends on KCSAN_STRICT
	187	# We can either let objtool nop __tsan_func_{entry,exit}() and builtin
	188	# atomics instrumentation in .noinstr.text, or use a compiler that can
	189	# implement __no_kcsan to really remove all instrumentation.
22102f45 JP	190	depends on !ARCH_WANTS_NO_INSTR \|\| HAVE_NOINSTR_HACK \|\| \
	191	CC_IS_GCC \|\| CLANG_VERSION >= 140000
	192	select OBJTOOL if HAVE_NOINSTR_HACK
69562e49 ME	193	help
	194	Enable support for modeling a subset of weak memory, which allows
	195	detecting a subset of data races due to missing memory barriers.
	196
ca0f2cfc	197	Depends on KCSAN_STRICT, because the options strengthening certain
69562e49 ME	198	plain accesses by default (depending on !KCSAN_STRICT) reduce the
	199	ability to detect any data races invoving reordered accesses, in
	200	particular reordered writes.
	201
	202	Weak memory modeling relies on additional instrumentation and may
	203	affect performance.
	204
dfd402a4 ME	205	config KCSAN_REPORT_VALUE_CHANGE_ONLY
	206	bool "Only report races where watcher observed a data value change"
	207	default y
e675d253	208	depends on !KCSAN_STRICT
dfd402a4	209	help
5cbaefe9	210	If enabled and a conflicting write is observed via a watchpoint, but
dfd402a4 ME	211	the data value of the memory location was observed to remain
	212	unchanged, do not report the data race.
	213
1e6ee2f0 ME	214	config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
	215	bool "Assume that plain aligned writes up to word size are atomic"
	216	default y
e675d253	217	depends on !KCSAN_STRICT
1e6ee2f0 ME	218	help
	219	Assume that plain aligned writes up to word size are atomic by
	220	default, and also not subject to other unsafe compiler optimizations
	221	resulting in data races. This will cause KCSAN to not report data
	222	races due to conflicts where the only plain accesses are aligned
	223	writes up to word size: conflicts between marked reads and plain
	224	aligned writes up to word size will not be reported as data races;
	225	notice that data races between two conflicting plain aligned writes
	226	will also not be reported.
	227
dfd402a4 ME	228	config KCSAN_IGNORE_ATOMICS
dfd402a4 ME	229	bool "Do not instrument marked atomic accesses"
e675d253	230	depends on !KCSAN_STRICT
dfd402a4	231	help
a249a732 ME	232	Never instrument marked atomic accesses. This option can be used for
	233	additional filtering. Conflicting marked atomic reads and plain
	234	writes will never be reported as a data race, however, will cause
	235	plain reads and marked writes to result in "unknown origin" reports.
	236	If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
	237	races where at least one access is marked atomic will never be
	238	reported.
	239
	240	Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
	241	accesses, conflicting marked atomic reads and plain writes will not
	242	be reported as data races; however, unlike that option, data races
	243	due to two conflicting plain writes will be reported (aligned and
	244	unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
dfd402a4	245
49f72d53 ME	246	config KCSAN_PERMISSIVE
	247	bool "Enable all additional permissive rules"
	248	depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
	249	help
	250	Enable additional permissive rules to ignore certain classes of data
	251	races (also see kernel/kcsan/permissive.h). None of the permissive
	252	rules imply that such data races are generally safe, but can be used
	253	to further reduce reported data races due to data-racy patterns
	254	common across the kernel.
	255
dfd402a4	256	endif # KCSAN