1 # SPDX-License-Identifier: GPL-2.0-only
2 menu "Kernel hardening options"
4 config GCC_PLUGIN_STRUCTLEAK
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.
15 This plugin was originally ported from grsecurity/PaX. More
17 * https://grsecurity.net/
18 * https://pax.grsecurity.net/
20 menu "Memory initialization"
22 config CC_HAS_AUTO_VAR_INIT_PATTERN
23 def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
25 config CC_HAS_AUTO_VAR_INIT_ZERO_BARE
26 def_bool $(cc-option,-ftrivial-auto-var-init=zero)
28 config CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER
29 # Clang 16 and later warn about using the -enable flag, but it
30 # is required before then.
31 def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)
32 depends on !CC_HAS_AUTO_VAR_INIT_ZERO_BARE
34 config CC_HAS_AUTO_VAR_INIT_ZERO
35 def_bool CC_HAS_AUTO_VAR_INIT_ZERO_BARE || CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER
38 prompt "Initialize kernel stack variables at function entry"
39 default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
40 default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
41 default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
42 default INIT_STACK_NONE
44 This option enables initialization of stack variables at
45 function entry time. This has the possibility to have the
46 greatest coverage (since all functions can have their
47 variables initialized), but the performance impact depends
48 on the function calling complexity of a given workload's
51 This chooses the level of coverage over classes of potentially
52 uninitialized variables. The selected class of variable will be
53 initialized before use in a function.
55 config INIT_STACK_NONE
56 bool "no automatic stack variable initialization (weakest)"
58 Disable automatic stack variable initialization.
59 This leaves the kernel vulnerable to the standard
60 classes of uninitialized stack variable exploits
61 and information exposures.
63 config GCC_PLUGIN_STRUCTLEAK_USER
64 bool "zero-init structs marked for userspace (weak)"
65 # Plugin can be removed once the kernel only supports GCC 12+
66 depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
67 select GCC_PLUGIN_STRUCTLEAK
69 Zero-initialize any structures on the stack containing
70 a __user attribute. This can prevent some classes of
71 uninitialized stack variable exploits and information
72 exposures, like CVE-2013-2141:
73 https://git.kernel.org/linus/b9e146d8eb3b9eca
75 config GCC_PLUGIN_STRUCTLEAK_BYREF
76 bool "zero-init structs passed by reference (strong)"
77 # Plugin can be removed once the kernel only supports GCC 12+
78 depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
79 depends on !(KASAN && KASAN_STACK)
80 select GCC_PLUGIN_STRUCTLEAK
82 Zero-initialize any structures on the stack that may
83 be passed by reference and had not already been
84 explicitly initialized. This can prevent most classes
85 of uninitialized stack variable exploits and information
86 exposures, like CVE-2017-1000410:
87 https://git.kernel.org/linus/06e7e776ca4d3654
89 As a side-effect, this keeps a lot of variables on the
90 stack that can otherwise be optimized out, so combining
91 this with CONFIG_KASAN_STACK can lead to a stack overflow
94 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
95 bool "zero-init everything passed by reference (very strong)"
96 # Plugin can be removed once the kernel only supports GCC 12+
97 depends on GCC_PLUGINS && !CC_HAS_AUTO_VAR_INIT_ZERO
98 depends on !(KASAN && KASAN_STACK)
99 select GCC_PLUGIN_STRUCTLEAK
101 Zero-initialize any stack variables that may be passed
102 by reference and had not already been explicitly
103 initialized. This is intended to eliminate all classes
104 of uninitialized stack variable exploits and information
107 As a side-effect, this keeps a lot of variables on the
108 stack that can otherwise be optimized out, so combining
109 this with CONFIG_KASAN_STACK can lead to a stack overflow
112 config INIT_STACK_ALL_PATTERN
113 bool "pattern-init everything (strongest)"
114 depends on CC_HAS_AUTO_VAR_INIT_PATTERN
117 Initializes everything on the stack (including padding)
118 with a specific debug value. This is intended to eliminate
119 all classes of uninitialized stack variable exploits and
120 information exposures, even variables that were warned about
121 having been left uninitialized.
123 Pattern initialization is known to provoke many existing bugs
124 related to uninitialized locals, e.g. pointers receive
125 non-NULL values, buffer sizes and indices are very big. The
126 pattern is situation-specific; Clang on 64-bit uses 0xAA
127 repeating for all types and padding except float and double
128 which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
129 repeating for all types and padding.
131 config INIT_STACK_ALL_ZERO
132 bool "zero-init everything (strongest and safest)"
133 depends on CC_HAS_AUTO_VAR_INIT_ZERO
136 Initializes everything on the stack (including padding)
137 with a zero value. This is intended to eliminate all
138 classes of uninitialized stack variable exploits and
139 information exposures, even variables that were warned
140 about having been left uninitialized.
142 Zero initialization provides safe defaults for strings
143 (immediately NUL-terminated), pointers (NULL), indices
144 (index 0), and sizes (0 length), so it is therefore more
145 suitable as a production security mitigation than pattern
150 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
151 bool "Report forcefully initialized variables"
152 depends on GCC_PLUGIN_STRUCTLEAK
153 depends on !COMPILE_TEST # too noisy
155 This option will cause a warning to be printed each time the
156 structleak plugin finds a variable it thinks needs to be
157 initialized. Since not all existing initializers are detected
158 by the plugin, this can produce false positive warnings.
160 config GCC_PLUGIN_STACKLEAK
161 bool "Poison kernel stack before returning from syscalls"
162 depends on GCC_PLUGINS
163 depends on HAVE_ARCH_STACKLEAK
165 This option makes the kernel erase the kernel stack before
166 returning from system calls. This has the effect of leaving
167 the stack initialized to the poison value, which both reduces
168 the lifetime of any sensitive stack contents and reduces
169 potential for uninitialized stack variable exploits or information
170 exposures (it does not cover functions reaching the same stack
171 depth as prior functions during the same syscall). This blocks
172 most uninitialized stack variable attacks, with the performance
173 impact being driven by the depth of the stack usage, rather than
174 the function calling complexity.
176 The performance impact on a single CPU system kernel compilation
177 sees a 1% slowdown, other systems and workloads may vary and you
178 are advised to test this feature on your expected workload before
181 This plugin was ported from grsecurity/PaX. More information at:
182 * https://grsecurity.net/
183 * https://pax.grsecurity.net/
185 config GCC_PLUGIN_STACKLEAK_VERBOSE
186 bool "Report stack depth analysis instrumentation" if EXPERT
187 depends on GCC_PLUGIN_STACKLEAK
188 depends on !COMPILE_TEST # too noisy
190 This option will cause a warning to be printed each time the
191 stackleak plugin finds a function it thinks needs to be
192 instrumented. This is useful for comparing coverage between
195 config STACKLEAK_TRACK_MIN_SIZE
196 int "Minimum stack frame size of functions tracked by STACKLEAK"
199 depends on GCC_PLUGIN_STACKLEAK
201 The STACKLEAK gcc plugin instruments the kernel code for tracking
202 the lowest border of the kernel stack (and for some other purposes).
203 It inserts the stackleak_track_stack() call for the functions with
204 a stack frame size greater than or equal to this parameter.
205 If unsure, leave the default value 100.
207 config STACKLEAK_METRICS
208 bool "Show STACKLEAK metrics in the /proc file system"
209 depends on GCC_PLUGIN_STACKLEAK
212 If this is set, STACKLEAK metrics for every task are available in
213 the /proc file system. In particular, /proc/<pid>/stack_depth
214 shows the maximum kernel stack consumption for the current and
215 previous syscalls. Although this information is not precise, it
216 can be useful for estimating the STACKLEAK performance impact for
219 config STACKLEAK_RUNTIME_DISABLE
220 bool "Allow runtime disabling of kernel stack erasing"
221 depends on GCC_PLUGIN_STACKLEAK
223 This option provides 'stack_erasing' sysctl, which can be used in
224 runtime to control kernel stack erasing for kernels built with
225 CONFIG_GCC_PLUGIN_STACKLEAK.
227 config INIT_ON_ALLOC_DEFAULT_ON
228 bool "Enable heap memory zeroing on allocation by default"
231 This has the effect of setting "init_on_alloc=1" on the kernel
232 command line. This can be disabled with "init_on_alloc=0".
233 When "init_on_alloc" is enabled, all page allocator and slab
234 allocator memory will be zeroed when allocated, eliminating
235 many kinds of "uninitialized heap memory" flaws, especially
236 heap content exposures. The performance impact varies by
237 workload, but most cases see <1% impact. Some synthetic
238 workloads have measured as high as 7%.
240 config INIT_ON_FREE_DEFAULT_ON
241 bool "Enable heap memory zeroing on free by default"
244 This has the effect of setting "init_on_free=1" on the kernel
245 command line. This can be disabled with "init_on_free=0".
246 Similar to "init_on_alloc", when "init_on_free" is enabled,
247 all page allocator and slab allocator memory will be zeroed
248 when freed, eliminating many kinds of "uninitialized heap memory"
249 flaws, especially heap content exposures. The primary difference
250 with "init_on_free" is that data lifetime in memory is reduced,
251 as anything freed is wiped immediately, making live forensics or
252 cold boot memory attacks unable to recover freed memory contents.
253 The performance impact varies by workload, but is more expensive
254 than "init_on_alloc" due to the negative cache effects of
255 touching "cold" memory areas. Most cases see 3-5% impact. Some
256 synthetic workloads have measured as high as 8%.
258 config CC_HAS_ZERO_CALL_USED_REGS
259 def_bool $(cc-option,-fzero-call-used-regs=used-gpr)
260 # https://github.com/ClangBuiltLinux/linux/issues/1766
261 # https://github.com/llvm/llvm-project/issues/59242
262 depends on !CC_IS_CLANG || CLANG_VERSION > 150006
264 config ZERO_CALL_USED_REGS
265 bool "Enable register zeroing on function exit"
266 depends on CC_HAS_ZERO_CALL_USED_REGS
268 At the end of functions, always zero any caller-used register
269 contents. This helps ensure that temporary values are not
270 leaked beyond the function boundary. This means that register
271 contents are less likely to be available for side channels
272 and information exposures. Additionally, this helps reduce the
273 number of useful ROP gadgets by about 20% (and removes compiler
274 generated "write-what-where" gadgets) in the resulting kernel
275 image. This has a less than 1% performance impact on most
276 workloads. Image size growth depends on architecture, and should
277 be evaluated for suitability. For example, x86_64 grows by less
278 than 1%, and arm64 grows by about 5%.
282 menu "Hardening of kernel data structures"
285 bool "Check integrity of linked list manipulation"
287 Minimal integrity checking in the linked-list manipulation routines
288 to catch memory corruptions that are not guaranteed to result in an
289 immediate access fault.
293 config BUG_ON_DATA_CORRUPTION
294 bool "Trigger a BUG when data corruption is detected"
297 Select this option if the kernel should BUG when it encounters
298 data corruption in kernel memory structures when they get checked
305 config CC_HAS_RANDSTRUCT
306 def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null)
307 # Randstruct was first added in Clang 15, but it isn't safe to use until
308 # Clang 16 due to https://github.com/llvm/llvm-project/issues/60349
309 depends on !CC_IS_CLANG || CLANG_VERSION >= 160000
312 prompt "Randomize layout of sensitive kernel structures"
313 default RANDSTRUCT_FULL if COMPILE_TEST && (GCC_PLUGINS || CC_HAS_RANDSTRUCT)
314 default RANDSTRUCT_NONE
316 If you enable this, the layouts of structures that are entirely
317 function pointers (and have not been manually annotated with
318 __no_randomize_layout), or structures that have been explicitly
319 marked with __randomize_layout, will be randomized at compile-time.
320 This can introduce the requirement of an additional information
321 exposure vulnerability for exploits targeting these structure
324 Enabling this feature will introduce some performance impact,
325 slightly increase memory usage, and prevent the use of forensic
326 tools like Volatility against the system (unless the kernel
327 source tree isn't cleaned after kernel installation).
329 The seed used for compilation is in scripts/basic/randomize.seed.
330 It remains after a "make clean" to allow for external modules to
331 be compiled with the existing seed and will be removed by a
332 "make mrproper" or "make distclean". This file should not be made
333 public, or the structure layout can be determined.
335 config RANDSTRUCT_NONE
336 bool "Disable structure layout randomization"
338 Build normally: no structure layout randomization.
340 config RANDSTRUCT_FULL
341 bool "Fully randomize structure layout"
342 depends on CC_HAS_RANDSTRUCT || GCC_PLUGINS
343 select MODVERSIONS if MODULES
345 Fully randomize the member layout of sensitive
346 structures as much as possible, which may have both a
347 memory size and performance impact.
349 One difference between the Clang and GCC plugin
350 implementations is the handling of bitfields. The GCC
351 plugin treats them as fully separate variables,
352 introducing sometimes significant padding. Clang tries
353 to keep adjacent bitfields together, but with their bit
356 config RANDSTRUCT_PERFORMANCE
357 bool "Limit randomization of structure layout to cache-lines"
358 depends on GCC_PLUGINS
359 select MODVERSIONS if MODULES
361 Randomization of sensitive kernel structures will make a
362 best effort at restricting randomization to cacheline-sized
363 groups of members. It will further not randomize bitfields
364 in structures. This reduces the performance hit of RANDSTRUCT
365 at the cost of weakened randomization.
369 def_bool !RANDSTRUCT_NONE
371 config GCC_PLUGIN_RANDSTRUCT
372 def_bool GCC_PLUGINS && RANDSTRUCT
374 Use GCC plugin to randomize structure layout.
376 This plugin was ported from grsecurity/PaX. More
378 * https://grsecurity.net/
379 * https://pax.grsecurity.net/