[linux.git] / security / Kconfig.hardening

# SPDX-License-Identifier: GPL-2.0-only
menu "Kernel hardening options"

config GCC_PLUGIN_STRUCTLEAK
	bool
	help
	  While the kernel is built with warnings enabled for any missed
	  stack variable initializations, this warning is silenced for
	  anything passed by reference to another function, under the
	  occasionally misguided assumption that the function will do
	  the initialization. As this regularly leads to exploitable
	  flaws, this plugin is available to identify and zero-initialize
	  such variables, depending on the chosen level of coverage.

	  This plugin was originally ported from grsecurity/PaX. More
	  information at:
	   * https://grsecurity.net/
	   * https://pax.grsecurity.net/

menu "Memory initialization"

config CC_HAS_AUTO_VAR_INIT_PATTERN
	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)

config CC_HAS_AUTO_VAR_INIT_ZERO
	# GCC ignores the -enable flag, so we can test for the feature with
	# a single invocation using the flag, but drop it as appropriate in
	# the Makefile, depending on the presence of Clang.
	def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)

choice
	prompt "Initialize kernel stack variables at function entry"
	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
	default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
	default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
	default INIT_STACK_NONE
	help
	  This option enables initialization of stack variables at
	  function entry time. This has the possibility to have the
	  greatest coverage (since all functions can have their
	  variables initialized), but the performance impact depends
	  on the function calling complexity of a given workload's
	  syscalls.

	  This chooses the level of coverage over classes of potentially
	  uninitialized variables. The selected class of variable will be
	  initialized before use in a function.

	config INIT_STACK_NONE
		bool "no automatic stack variable initialization (weakest)"
		help
		  Disable automatic stack variable initialization.
		  This leaves the kernel vulnerable to the standard
		  classes of uninitialized stack variable exploits
		  and information exposures.

	config GCC_PLUGIN_STRUCTLEAK_USER
		bool "zero-init structs marked for userspace (weak)"
		# Plugin can be removed once the kernel only supports GCC 12+
		depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
		select GCC_PLUGIN_STRUCTLEAK
		help
		  Zero-initialize any structures on the stack containing
		  a __user attribute. This can prevent some classes of
		  uninitialized stack variable exploits and information
		  exposures, like CVE-2013-2141:
		  https://git.kernel.org/linus/b9e146d8eb3b9eca

	config GCC_PLUGIN_STRUCTLEAK_BYREF
		bool "zero-init structs passed by reference (strong)"
		# Plugin can be removed once the kernel only supports GCC 12+
		depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
		depends on !(KASAN && KASAN_STACK)
		select GCC_PLUGIN_STRUCTLEAK
		help
		  Zero-initialize any structures on the stack that may
		  be passed by reference and had not already been
		  explicitly initialized. This can prevent most classes
		  of uninitialized stack variable exploits and information
		  exposures, like CVE-2017-1000410:
		  https://git.kernel.org/linus/06e7e776ca4d3654

		  As a side-effect, this keeps a lot of variables on the
		  stack that can otherwise be optimized out, so combining
		  this with CONFIG_KASAN_STACK can lead to a stack overflow
		  and is disallowed.

	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
		bool "zero-init everything passed by reference (very strong)"
		# Plugin can be removed once the kernel only supports GCC 12+
		depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
		depends on !(KASAN && KASAN_STACK)
		select GCC_PLUGIN_STRUCTLEAK
		help
		  Zero-initialize any stack variables that may be passed
		  by reference and had not already been explicitly
		  initialized. This is intended to eliminate all classes
		  of uninitialized stack variable exploits and information
		  exposures.

		  As a side-effect, this keeps a lot of variables on the
		  stack that can otherwise be optimized out, so combining
		  this with CONFIG_KASAN_STACK can lead to a stack overflow
		  and is disallowed.

	config INIT_STACK_ALL_PATTERN
		bool "pattern-init everything (strongest)"
		depends on CC_HAS_AUTO_VAR_INIT_PATTERN
		help
		  Initializes everything on the stack (including padding)
		  with a specific debug value. This is intended to eliminate
		  all classes of uninitialized stack variable exploits and
		  information exposures, even variables that were warned about
		  having been left uninitialized.

		  Pattern initialization is known to provoke many existing bugs
		  related to uninitialized locals, e.g. pointers receive
		  non-NULL values, buffer sizes and indices are very big. The
		  pattern is situation-specific; Clang on 64-bit uses 0xAA
		  repeating for all types and padding except float and double
		  which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
		  repeating for all types and padding.

	config INIT_STACK_ALL_ZERO
		bool "zero-init everything (strongest and safest)"
		depends on CC_HAS_AUTO_VAR_INIT_ZERO
		help
		  Initializes everything on the stack (including padding)
		  with a zero value. This is intended to eliminate all
		  classes of uninitialized stack variable exploits and
		  information exposures, even variables that were warned
		  about having been left uninitialized.

		  Zero initialization provides safe defaults for strings
		  (immediately NUL-terminated), pointers (NULL), indices
		  (index 0), and sizes (0 length), so it is therefore more
		  suitable as a production security mitigation than pattern
		  initialization.

endchoice

config GCC_PLUGIN_STRUCTLEAK_VERBOSE
	bool "Report forcefully initialized variables"
	depends on GCC_PLUGIN_STRUCTLEAK
	depends on !COMPILE_TEST	# too noisy
	help
	  This option will cause a warning to be printed each time the
	  structleak plugin finds a variable it thinks needs to be
	  initialized. Since not all existing initializers are detected
	  by the plugin, this can produce false positive warnings.

config GCC_PLUGIN_STACKLEAK
	bool "Poison kernel stack before returning from syscalls"
	depends on GCC_PLUGINS
	depends on HAVE_ARCH_STACKLEAK
	help
	  This option makes the kernel erase the kernel stack before
	  returning from system calls. This has the effect of leaving
	  the stack initialized to the poison value, which both reduces
	  the lifetime of any sensitive stack contents and reduces
	  potential for uninitialized stack variable exploits or information
	  exposures (it does not cover functions reaching the same stack
	  depth as prior functions during the same syscall). This blocks
	  most uninitialized stack variable attacks, with the performance
	  impact being driven by the depth of the stack usage, rather than
	  the function calling complexity.

	  The performance impact on a single CPU system kernel compilation
	  sees a 1% slowdown, other systems and workloads may vary and you
	  are advised to test this feature on your expected workload before
	  deploying it.

	  This plugin was ported from grsecurity/PaX. More information at:
	   * https://grsecurity.net/
	   * https://pax.grsecurity.net/

config STACKLEAK_TRACK_MIN_SIZE
	int "Minimum stack frame size of functions tracked by STACKLEAK"
	default 100
	range 0 4096
	depends on GCC_PLUGIN_STACKLEAK
	help
	  The STACKLEAK gcc plugin instruments the kernel code for tracking
	  the lowest border of the kernel stack (and for some other purposes).
	  It inserts the stackleak_track_stack() call for the functions with
	  a stack frame size greater than or equal to this parameter.
	  If unsure, leave the default value 100.

config STACKLEAK_METRICS
	bool "Show STACKLEAK metrics in the /proc file system"
	depends on GCC_PLUGIN_STACKLEAK
	depends on PROC_FS
	help
	  If this is set, STACKLEAK metrics for every task are available in
	  the /proc file system. In particular, /proc/<pid>/stack_depth
	  shows the maximum kernel stack consumption for the current and
	  previous syscalls. Although this information is not precise, it
	  can be useful for estimating the STACKLEAK performance impact for
	  your workloads.

config STACKLEAK_RUNTIME_DISABLE
	bool "Allow runtime disabling of kernel stack erasing"
	depends on GCC_PLUGIN_STACKLEAK
	help
	  This option provides 'stack_erasing' sysctl, which can be used in
	  runtime to control kernel stack erasing for kernels built with
	  CONFIG_GCC_PLUGIN_STACKLEAK.

config INIT_ON_ALLOC_DEFAULT_ON
	bool "Enable heap memory zeroing on allocation by default"
	help
	  This has the effect of setting "init_on_alloc=1" on the kernel
	  command line. This can be disabled with "init_on_alloc=0".
	  When "init_on_alloc" is enabled, all page allocator and slab
	  allocator memory will be zeroed when allocated, eliminating
	  many kinds of "uninitialized heap memory" flaws, especially
	  heap content exposures. The performance impact varies by
	  workload, but most cases see <1% impact. Some synthetic
	  workloads have measured as high as 7%.

config INIT_ON_FREE_DEFAULT_ON
	bool "Enable heap memory zeroing on free by default"
	help
	  This has the effect of setting "init_on_free=1" on the kernel
	  command line. This can be disabled with "init_on_free=0".
	  Similar to "init_on_alloc", when "init_on_free" is enabled,
	  all page allocator and slab allocator memory will be zeroed
	  when freed, eliminating many kinds of "uninitialized heap memory"
	  flaws, especially heap content exposures. The primary difference
	  with "init_on_free" is that data lifetime in memory is reduced,
	  as anything freed is wiped immediately, making live forensics or
	  cold boot memory attacks unable to recover freed memory contents.
	  The performance impact varies by workload, but is more expensive
	  than "init_on_alloc" due to the negative cache effects of
	  touching "cold" memory areas. Most cases see 3-5% impact. Some
	  synthetic workloads have measured as high as 8%.

config CC_HAS_ZERO_CALL_USED_REGS
	def_bool $(cc-option,-fzero-call-used-regs=used-gpr)

config ZERO_CALL_USED_REGS
	bool "Enable register zeroing on function exit"
	depends on CC_HAS_ZERO_CALL_USED_REGS
	help
	  At the end of functions, always zero any caller-used register
	  contents. This helps ensure that temporary values are not
	  leaked beyond the function boundary. This means that register
	  contents are less likely to be available for side channels
	  and information exposures. Additionally, this helps reduce the
	  number of useful ROP gadgets by about 20% (and removes compiler
	  generated "write-what-where" gadgets) in the resulting kernel
	  image. This has a less than 1% performance impact on most
	  workloads. Image size growth depends on architecture, and should
	  be evaluated for suitability. For example, x86_64 grows by less
	  than 1%, and arm64 grows by about 5%.

endmenu

endmenu
Commit	Line	Data
ec8f24b7	1	# SPDX-License-Identifier: GPL-2.0-only
9f671e58 KC	2	menu "Kernel hardening options"
	3
	4	config GCC_PLUGIN_STRUCTLEAK
	5	bool
	6	help
	7	While the kernel is built with warnings enabled for any missed
	8	stack variable initializations, this warning is silenced for
	9	anything passed by reference to another function, under the
	10	occasionally misguided assumption that the function will do
	11	the initialization. As this regularly leads to exploitable
	12	flaws, this plugin is available to identify and zero-initialize
	13	such variables, depending on the chosen level of coverage.
	14
	15	This plugin was originally ported from grsecurity/PaX. More
	16	information at:
	17	* https://grsecurity.net/
	18	* https://pax.grsecurity.net/
	19
	20	menu "Memory initialization"
	21
f0fe00d4	22	config CC_HAS_AUTO_VAR_INIT_PATTERN
709a972e KC	23	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
709a972e KC	24
f0fe00d4	25	config CC_HAS_AUTO_VAR_INIT_ZERO
f02003c8 KC	26	# GCC ignores the -enable flag, so we can test for the feature with
	27	# a single invocation using the flag, but drop it as appropriate in
	28	# the Makefile, depending on the presence of Clang.
f0fe00d4	29	def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)
f0fe00d4	30
9f671e58 KC	31	choice
	32	prompt "Initialize kernel stack variables at function entry"
	33	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
f0fe00d4	34	default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
f02003c8	35	default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
9f671e58 KC	36	default INIT_STACK_NONE
	37	help
	38	This option enables initialization of stack variables at
	39	function entry time. This has the possibility to have the
	40	greatest coverage (since all functions can have their
	41	variables initialized), but the performance impact depends
	42	on the function calling complexity of a given workload's
	43	syscalls.
	44
	45	This chooses the level of coverage over classes of potentially
dcb7c0b9	46	uninitialized variables. The selected class of variable will be
9f671e58 KC	47	initialized before use in a function.
	48
	49	config INIT_STACK_NONE
dcb7c0b9	50	bool "no automatic stack variable initialization (weakest)"
9f671e58 KC	51	help
	52	Disable automatic stack variable initialization.
	53	This leaves the kernel vulnerable to the standard
	54	classes of uninitialized stack variable exploits
	55	and information exposures.
	56
	57	config GCC_PLUGIN_STRUCTLEAK_USER
	58	bool "zero-init structs marked for userspace (weak)"
8bd51a2b KC	59	# Plugin can be removed once the kernel only supports GCC 12+
8bd51a2b KC	60	depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
9f671e58 KC	61	select GCC_PLUGIN_STRUCTLEAK
	62	help
	63	Zero-initialize any structures on the stack containing
	64	a __user attribute. This can prevent some classes of
	65	uninitialized stack variable exploits and information
	66	exposures, like CVE-2013-2141:
	67	https://git.kernel.org/linus/b9e146d8eb3b9eca
	68
	69	config GCC_PLUGIN_STRUCTLEAK_BYREF
	70	bool "zero-init structs passed by reference (strong)"
8bd51a2b KC	71	# Plugin can be removed once the kernel only supports GCC 12+
8bd51a2b KC	72	depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
02c58773	73	depends on !(KASAN && KASAN_STACK)
9f671e58 KC	74	select GCC_PLUGIN_STRUCTLEAK
	75	help
	76	Zero-initialize any structures on the stack that may
	77	be passed by reference and had not already been
	78	explicitly initialized. This can prevent most classes
	79	of uninitialized stack variable exploits and information
	80	exposures, like CVE-2017-1000410:
	81	https://git.kernel.org/linus/06e7e776ca4d3654
	82
173e6ee2 AB	83	As a side-effect, this keeps a lot of variables on the
	84	stack that can otherwise be optimized out, so combining
	85	this with CONFIG_KASAN_STACK can lead to a stack overflow
	86	and is disallowed.
	87
9f671e58	88	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
dcb7c0b9	89	bool "zero-init everything passed by reference (very strong)"
8bd51a2b KC	90	# Plugin can be removed once the kernel only supports GCC 12+
8bd51a2b KC	91	depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
02c58773	92	depends on !(KASAN && KASAN_STACK)
9f671e58 KC	93	select GCC_PLUGIN_STRUCTLEAK
	94	help
	95	Zero-initialize any stack variables that may be passed
	96	by reference and had not already been explicitly
	97	initialized. This is intended to eliminate all classes
	98	of uninitialized stack variable exploits and information
	99	exposures.
	100
dcb7c0b9 KC	101	As a side-effect, this keeps a lot of variables on the
	102	stack that can otherwise be optimized out, so combining
	103	this with CONFIG_KASAN_STACK can lead to a stack overflow
	104	and is disallowed.
	105
f0fe00d4	106	config INIT_STACK_ALL_PATTERN
dcb7c0b9	107	bool "pattern-init everything (strongest)"
f0fe00d4	108	depends on CC_HAS_AUTO_VAR_INIT_PATTERN
709a972e	109	help
dcb7c0b9 KC	110	Initializes everything on the stack (including padding)
	111	with a specific debug value. This is intended to eliminate
	112	all classes of uninitialized stack variable exploits and
	113	information exposures, even variables that were warned about
	114	having been left uninitialized.
709a972e	115
f0fe00d4	116	Pattern initialization is known to provoke many existing bugs
f0fe00d4	117	related to uninitialized locals, e.g. pointers receive
dcb7c0b9 KC	118	non-NULL values, buffer sizes and indices are very big. The
	119	pattern is situation-specific; Clang on 64-bit uses 0xAA
	120	repeating for all types and padding except float and double
	121	which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
	122	repeating for all types and padding.
f0fe00d4	123
f0fe00d4	124	config INIT_STACK_ALL_ZERO
dcb7c0b9	125	bool "zero-init everything (strongest and safest)"
f0fe00d4	126	depends on CC_HAS_AUTO_VAR_INIT_ZERO
f0fe00d4	127	help
dcb7c0b9 KC	128	Initializes everything on the stack (including padding)
	129	with a zero value. This is intended to eliminate all
	130	classes of uninitialized stack variable exploits and
	131	information exposures, even variables that were warned
	132	about having been left uninitialized.
	133
	134	Zero initialization provides safe defaults for strings
	135	(immediately NUL-terminated), pointers (NULL), indices
	136	(index 0), and sizes (0 length), so it is therefore more
	137	suitable as a production security mitigation than pattern
	138	initialization.
f0fe00d4	139
9f671e58 KC	140	endchoice
	141
	142	config GCC_PLUGIN_STRUCTLEAK_VERBOSE
	143	bool "Report forcefully initialized variables"
	144	depends on GCC_PLUGIN_STRUCTLEAK
	145	depends on !COMPILE_TEST # too noisy
	146	help
	147	This option will cause a warning to be printed each time the
	148	structleak plugin finds a variable it thinks needs to be
	149	initialized. Since not all existing initializers are detected
	150	by the plugin, this can produce false positive warnings.
	151
b6a6a377 KC	152	config GCC_PLUGIN_STACKLEAK
	153	bool "Poison kernel stack before returning from syscalls"
	154	depends on GCC_PLUGINS
	155	depends on HAVE_ARCH_STACKLEAK
	156	help
	157	This option makes the kernel erase the kernel stack before
	158	returning from system calls. This has the effect of leaving
	159	the stack initialized to the poison value, which both reduces
	160	the lifetime of any sensitive stack contents and reduces
	161	potential for uninitialized stack variable exploits or information
	162	exposures (it does not cover functions reaching the same stack
	163	depth as prior functions during the same syscall). This blocks
	164	most uninitialized stack variable attacks, with the performance
	165	impact being driven by the depth of the stack usage, rather than
	166	the function calling complexity.
	167
	168	The performance impact on a single CPU system kernel compilation
	169	sees a 1% slowdown, other systems and workloads may vary and you
	170	are advised to test this feature on your expected workload before
	171	deploying it.
	172
	173	This plugin was ported from grsecurity/PaX. More information at:
	174	* https://grsecurity.net/
	175	* https://pax.grsecurity.net/
	176
	177	config STACKLEAK_TRACK_MIN_SIZE
	178	int "Minimum stack frame size of functions tracked by STACKLEAK"
	179	default 100
	180	range 0 4096
	181	depends on GCC_PLUGIN_STACKLEAK
	182	help
	183	The STACKLEAK gcc plugin instruments the kernel code for tracking
	184	the lowest border of the kernel stack (and for some other purposes).
	185	It inserts the stackleak_track_stack() call for the functions with
	186	a stack frame size greater than or equal to this parameter.
	187	If unsure, leave the default value 100.
	188
	189	config STACKLEAK_METRICS
	190	bool "Show STACKLEAK metrics in the /proc file system"
	191	depends on GCC_PLUGIN_STACKLEAK
	192	depends on PROC_FS
	193	help
	194	If this is set, STACKLEAK metrics for every task are available in
	195	the /proc file system. In particular, /proc/<pid>/stack_depth
	196	shows the maximum kernel stack consumption for the current and
	197	previous syscalls. Although this information is not precise, it
	198	can be useful for estimating the STACKLEAK performance impact for
	199	your workloads.
	200
	201	config STACKLEAK_RUNTIME_DISABLE
	202	bool "Allow runtime disabling of kernel stack erasing"
	203	depends on GCC_PLUGIN_STACKLEAK
	204	help
	205	This option provides 'stack_erasing' sysctl, which can be used in
	206	runtime to control kernel stack erasing for kernels built with
	207	CONFIG_GCC_PLUGIN_STACKLEAK.
	208
6471384a AP	209	config INIT_ON_ALLOC_DEFAULT_ON
	210	bool "Enable heap memory zeroing on allocation by default"
	211	help
	212	This has the effect of setting "init_on_alloc=1" on the kernel
	213	command line. This can be disabled with "init_on_alloc=0".
	214	When "init_on_alloc" is enabled, all page allocator and slab
	215	allocator memory will be zeroed when allocated, eliminating
	216	many kinds of "uninitialized heap memory" flaws, especially
	217	heap content exposures. The performance impact varies by
	218	workload, but most cases see <1% impact. Some synthetic
	219	workloads have measured as high as 7%.
	220
	221	config INIT_ON_FREE_DEFAULT_ON
	222	bool "Enable heap memory zeroing on free by default"
	223	help
	224	This has the effect of setting "init_on_free=1" on the kernel
	225	command line. This can be disabled with "init_on_free=0".
	226	Similar to "init_on_alloc", when "init_on_free" is enabled,
	227	all page allocator and slab allocator memory will be zeroed
	228	when freed, eliminating many kinds of "uninitialized heap memory"
	229	flaws, especially heap content exposures. The primary difference
	230	with "init_on_free" is that data lifetime in memory is reduced,
	231	as anything freed is wiped immediately, making live forensics or
	232	cold boot memory attacks unable to recover freed memory contents.
	233	The performance impact varies by workload, but is more expensive
	234	than "init_on_alloc" due to the negative cache effects of
	235	touching "cold" memory areas. Most cases see 3-5% impact. Some
	236	synthetic workloads have measured as high as 8%.
	237
a82adfd5 KC	238	config CC_HAS_ZERO_CALL_USED_REGS
	239	def_bool $(cc-option,-fzero-call-used-regs=used-gpr)
	240
	241	config ZERO_CALL_USED_REGS
	242	bool "Enable register zeroing on function exit"
	243	depends on CC_HAS_ZERO_CALL_USED_REGS
	244	help
	245	At the end of functions, always zero any caller-used register
	246	contents. This helps ensure that temporary values are not
	247	leaked beyond the function boundary. This means that register
	248	contents are less likely to be available for side channels
	249	and information exposures. Additionally, this helps reduce the
	250	number of useful ROP gadgets by about 20% (and removes compiler
	251	generated "write-what-where" gadgets) in the resulting kernel
	252	image. This has a less than 1% performance impact on most
	253	workloads. Image size growth depends on architecture, and should
	254	be evaluated for suitability. For example, x86_64 grows by less
	255	than 1%, and arm64 grows by about 5%.
	256
9f671e58 KC	257	endmenu
	258
	259	endmenu