[linux.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

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
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	config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
	44	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) \|\| \
	45	(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
eb32f9f9 ME	46	help
	47	The compiler instruments plain compound read-write operations
	48	differently (++, --, +=, -=, \|=, &=, etc.), which allows KCSAN to
	49	distinguish them from other plain accesses. This is currently
	50	supported by Clang 12 or later.
bec4a247	51
2402d0ea ME	52	config KCSAN_VERBOSE
	53	bool "Show verbose reports with more information about system state"
	54	depends on PROVE_LOCKING
	55	help
	56	If enabled, reports show more information about the system state that
	57	may help better analyze and debug races. This includes held locks and
	58	IRQ trace events.
	59
	60	While this option should generally be benign, we call into more
	61	external functions on report generation; if a race report is
	62	generated from any one of them, system stability may suffer due to
	63	deadlocks or recursion. If in doubt, say N.
	64
dfd402a4 ME	65	config KCSAN_SELFTEST
	66	bool "Perform short selftests on boot"
	67	default y
	68	help
1fe84fd4 ME	69	Run KCSAN selftests on boot. On test failure, causes the kernel to
	70	panic. Recommended to be enabled, ensuring critical functionality
	71	works as intended.
	72
a146fed5 ME	73	config KCSAN_KUNIT_TEST
	74	tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS
	75	default KUNIT_ALL_TESTS
1fe84fd4 ME	76	depends on TRACEPOINTS && KUNIT
	77	select TORTURE_TEST
	78	help
	79	KCSAN test focusing on behaviour of the integrated runtime. Tests
	80	various race scenarios, and verifies the reports generated to
	81	console. Makes use of KUnit for test organization, and the Torture
	82	framework for test thread control.
	83
	84	Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
	85	milliseconds. Test run duration may be optimized by building the
	86	kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
	87	than default value.
	88
	89	Say Y here if you want the test to be built into the kernel and run
	90	during boot; say M if you want the test to build as a module; say N
	91	if you are unsure.
dfd402a4 ME	92
	93	config KCSAN_EARLY_ENABLE
	94	bool "Early enable during boot"
	95	default y
	96	help
	97	If KCSAN should be enabled globally as soon as possible. KCSAN can
	98	later be enabled/disabled via debugfs.
	99
	100	config KCSAN_NUM_WATCHPOINTS
	101	int "Number of available watchpoints"
	102	default 64
	103	help
	104	Total number of available watchpoints. An address range maps into a
	105	specific watchpoint slot as specified in kernel/kcsan/encoding.h.
	106	Although larger number of watchpoints may not be usable due to
	107	limited number of CPUs, a larger value helps to improve performance
	108	due to reducing cache-line contention. The chosen default is a
	109	conservative value; we should almost never observe "no_capacity"
	110	events (see /sys/kernel/debug/kcsan).
	111
	112	config KCSAN_UDELAY_TASK
	113	int "Delay in microseconds (for tasks)"
	114	default 80
	115	help
	116	For tasks, the microsecond delay after setting up a watchpoint.
	117
	118	config KCSAN_UDELAY_INTERRUPT
	119	int "Delay in microseconds (for interrupts)"
	120	default 20
	121	help
	122	For interrupts, the microsecond delay after setting up a watchpoint.
	123	Interrupts have tighter latency requirements, and their delay should
	124	be lower than for tasks.
	125
	126	config KCSAN_DELAY_RANDOMIZE
	127	bool "Randomize above delays"
	128	default y
	129	help
	130	If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
5cbaefe9 IM	131	If false, the chosen delays are always the KCSAN_UDELAY_* values
5cbaefe9 IM	132	as defined above.
dfd402a4 ME	133
	134	config KCSAN_SKIP_WATCH
	135	int "Skip instructions before setting up watchpoint"
	136	default 4000
	137	help
	138	The number of per-CPU memory operations to skip, before another
	139	watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
	140	memory operations are used to set up a watchpoint. A smaller value
	141	results in more aggressive race detection, whereas a larger value
	142	improves system performance at the cost of missing some races.
	143
	144	config KCSAN_SKIP_WATCH_RANDOMIZE
	145	bool "Randomize watchpoint instruction skip count"
	146	default y
	147	help
	148	If instruction skip count should be randomized, where the maximum is
	149	KCSAN_WATCH_SKIP. If false, the chosen value is always
	150	KCSAN_WATCH_SKIP.
	151
48b1fc19	152	config KCSAN_INTERRUPT_WATCHER
e0493804 ME	153	bool "Interruptible watchers" if !KCSAN_STRICT
e0493804 ME	154	default KCSAN_STRICT
48b1fc19 ME	155	help
	156	If enabled, a task that set up a watchpoint may be interrupted while
	157	delayed. This option will allow KCSAN to detect races between
	158	interrupted tasks and other threads of execution on the same CPU.
	159
	160	Currently disabled by default, because not all safe per-CPU access
	161	primitives and patterns may be accounted for, and therefore could
	162	result in false positives.
	163
05f9a406	164	config KCSAN_REPORT_ONCE_IN_MS
d591ec3d	165	int "Duration in milliseconds, in which any given race is only reported once"
05f9a406 ME	166	default 3000
05f9a406 ME	167	help
d591ec3d ME	168	Any given race is only reported once in the defined time window.
	169	Different races may still generate reports within a duration that is
	170	smaller than the duration defined here. This allows rate limiting
	171	reporting to avoid flooding the console with reports. Setting this
	172	to 0 disables rate limiting.
05f9a406	173
eb32f9f9 ME	174	# The main purpose of the below options is to control reported data races, and
	175	# are not expected to be switched frequently by non-testers or at runtime.
	176	# The defaults are chosen to be conservative, and can miss certain bugs.
dfd402a4 ME	177
	178	config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
	179	bool "Report races of unknown origin"
	180	default y
	181	help
	182	If KCSAN should report races where only one access is known, and the
	183	conflicting access is of unknown origin. This type of race is
	184	reported if it was only possible to infer a race due to a data value
	185	change while an access is being delayed on a watchpoint.
	186
e675d253 ME	187	config KCSAN_STRICT
	188	bool "Strict data-race checking"
	189	help
	190	KCSAN will report data races with the strictest possible rules, which
	191	closely aligns with the rules defined by the Linux-kernel memory
	192	consistency model (LKMM).
	193
69562e49 ME	194	config KCSAN_WEAK_MEMORY
	195	bool "Enable weak memory modeling to detect missing memory barriers"
	196	default y
	197	depends on KCSAN_STRICT
	198	# We can either let objtool nop __tsan_func_{entry,exit}() and builtin
	199	# atomics instrumentation in .noinstr.text, or use a compiler that can
	200	# implement __no_kcsan to really remove all instrumentation.
bd3d5bd1	201	depends on STACK_VALIDATION \|\| CC_IS_GCC \|\| CLANG_VERSION >= 140000
69562e49 ME	202	help
	203	Enable support for modeling a subset of weak memory, which allows
	204	detecting a subset of data races due to missing memory barriers.
	205
	206	Depends on KCSAN_STRICT, because the options strenghtening certain
	207	plain accesses by default (depending on !KCSAN_STRICT) reduce the
	208	ability to detect any data races invoving reordered accesses, in
	209	particular reordered writes.
	210
	211	Weak memory modeling relies on additional instrumentation and may
	212	affect performance.
	213
dfd402a4 ME	214	config KCSAN_REPORT_VALUE_CHANGE_ONLY
	215	bool "Only report races where watcher observed a data value change"
	216	default y
e675d253	217	depends on !KCSAN_STRICT
dfd402a4	218	help
5cbaefe9	219	If enabled and a conflicting write is observed via a watchpoint, but
dfd402a4 ME	220	the data value of the memory location was observed to remain
	221	unchanged, do not report the data race.
	222
1e6ee2f0 ME	223	config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
	224	bool "Assume that plain aligned writes up to word size are atomic"
	225	default y
e675d253	226	depends on !KCSAN_STRICT
1e6ee2f0 ME	227	help
	228	Assume that plain aligned writes up to word size are atomic by
	229	default, and also not subject to other unsafe compiler optimizations
	230	resulting in data races. This will cause KCSAN to not report data
	231	races due to conflicts where the only plain accesses are aligned
	232	writes up to word size: conflicts between marked reads and plain
	233	aligned writes up to word size will not be reported as data races;
	234	notice that data races between two conflicting plain aligned writes
	235	will also not be reported.
	236
dfd402a4 ME	237	config KCSAN_IGNORE_ATOMICS
dfd402a4 ME	238	bool "Do not instrument marked atomic accesses"
e675d253	239	depends on !KCSAN_STRICT
dfd402a4	240	help
a249a732 ME	241	Never instrument marked atomic accesses. This option can be used for
	242	additional filtering. Conflicting marked atomic reads and plain
	243	writes will never be reported as a data race, however, will cause
	244	plain reads and marked writes to result in "unknown origin" reports.
	245	If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
	246	races where at least one access is marked atomic will never be
	247	reported.
	248
	249	Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
	250	accesses, conflicting marked atomic reads and plain writes will not
	251	be reported as data races; however, unlike that option, data races
	252	due to two conflicting plain writes will be reported (aligned and
	253	unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
dfd402a4	254
49f72d53 ME	255	config KCSAN_PERMISSIVE
	256	bool "Enable all additional permissive rules"
	257	depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
	258	help
	259	Enable additional permissive rules to ignore certain classes of data
	260	races (also see kernel/kcsan/permissive.h). None of the permissive
	261	rules imply that such data races are generally safe, but can be used
	262	to further reduce reported data races due to data-racy patterns
	263	common across the kernel.
	264
dfd402a4	265	endif # KCSAN