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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 |
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23 | def_bool $(cc-option,-ftrivial-auto-var-init=pattern) |
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) |
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+ |
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+ |
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+ |
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 |
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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 |
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 | |
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 |
127 | help | |
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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 | ||
f154066b KC |
177 | config GCC_PLUGIN_STACKLEAK_VERBOSE |
178 | bool "Report stack depth analysis instrumentation" if EXPERT | |
179 | depends on GCC_PLUGIN_STACKLEAK | |
180 | depends on !COMPILE_TEST # too noisy | |
181 | help | |
182 | This option will cause a warning to be printed each time the | |
183 | stackleak plugin finds a function it thinks needs to be | |
184 | instrumented. This is useful for comparing coverage between | |
185 | builds. | |
186 | ||
b6a6a377 KC |
187 | config STACKLEAK_TRACK_MIN_SIZE |
188 | int "Minimum stack frame size of functions tracked by STACKLEAK" | |
189 | default 100 | |
190 | range 0 4096 | |
191 | depends on GCC_PLUGIN_STACKLEAK | |
192 | help | |
193 | The STACKLEAK gcc plugin instruments the kernel code for tracking | |
194 | the lowest border of the kernel stack (and for some other purposes). | |
195 | It inserts the stackleak_track_stack() call for the functions with | |
196 | a stack frame size greater than or equal to this parameter. | |
197 | If unsure, leave the default value 100. | |
198 | ||
199 | config STACKLEAK_METRICS | |
200 | bool "Show STACKLEAK metrics in the /proc file system" | |
201 | depends on GCC_PLUGIN_STACKLEAK | |
202 | depends on PROC_FS | |
203 | help | |
204 | If this is set, STACKLEAK metrics for every task are available in | |
205 | the /proc file system. In particular, /proc/<pid>/stack_depth | |
206 | shows the maximum kernel stack consumption for the current and | |
207 | previous syscalls. Although this information is not precise, it | |
208 | can be useful for estimating the STACKLEAK performance impact for | |
209 | your workloads. | |
210 | ||
211 | config STACKLEAK_RUNTIME_DISABLE | |
212 | bool "Allow runtime disabling of kernel stack erasing" | |
213 | depends on GCC_PLUGIN_STACKLEAK | |
214 | help | |
215 | This option provides 'stack_erasing' sysctl, which can be used in | |
216 | runtime to control kernel stack erasing for kernels built with | |
217 | CONFIG_GCC_PLUGIN_STACKLEAK. | |
218 | ||
6471384a AP |
219 | config INIT_ON_ALLOC_DEFAULT_ON |
220 | bool "Enable heap memory zeroing on allocation by default" | |
221 | help | |
222 | This has the effect of setting "init_on_alloc=1" on the kernel | |
223 | command line. This can be disabled with "init_on_alloc=0". | |
224 | When "init_on_alloc" is enabled, all page allocator and slab | |
225 | allocator memory will be zeroed when allocated, eliminating | |
226 | many kinds of "uninitialized heap memory" flaws, especially | |
227 | heap content exposures. The performance impact varies by | |
228 | workload, but most cases see <1% impact. Some synthetic | |
229 | workloads have measured as high as 7%. | |
230 | ||
231 | config INIT_ON_FREE_DEFAULT_ON | |
232 | bool "Enable heap memory zeroing on free by default" | |
233 | help | |
234 | This has the effect of setting "init_on_free=1" on the kernel | |
235 | command line. This can be disabled with "init_on_free=0". | |
236 | Similar to "init_on_alloc", when "init_on_free" is enabled, | |
237 | all page allocator and slab allocator memory will be zeroed | |
238 | when freed, eliminating many kinds of "uninitialized heap memory" | |
239 | flaws, especially heap content exposures. The primary difference | |
240 | with "init_on_free" is that data lifetime in memory is reduced, | |
241 | as anything freed is wiped immediately, making live forensics or | |
242 | cold boot memory attacks unable to recover freed memory contents. | |
243 | The performance impact varies by workload, but is more expensive | |
244 | than "init_on_alloc" due to the negative cache effects of | |
245 | touching "cold" memory areas. Most cases see 3-5% impact. Some | |
246 | synthetic workloads have measured as high as 8%. | |
247 | ||
a82adfd5 KC |
248 | config CC_HAS_ZERO_CALL_USED_REGS |
249 | def_bool $(cc-option,-fzero-call-used-regs=used-gpr) | |
250 | ||
251 | config ZERO_CALL_USED_REGS | |
252 | bool "Enable register zeroing on function exit" | |
253 | depends on CC_HAS_ZERO_CALL_USED_REGS | |
254 | help | |
255 | At the end of functions, always zero any caller-used register | |
256 | contents. This helps ensure that temporary values are not | |
257 | leaked beyond the function boundary. This means that register | |
258 | contents are less likely to be available for side channels | |
259 | and information exposures. Additionally, this helps reduce the | |
260 | number of useful ROP gadgets by about 20% (and removes compiler | |
261 | generated "write-what-where" gadgets) in the resulting kernel | |
262 | image. This has a less than 1% performance impact on most | |
263 | workloads. Image size growth depends on architecture, and should | |
264 | be evaluated for suitability. For example, x86_64 grows by less | |
265 | than 1%, and arm64 grows by about 5%. | |
266 | ||
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267 | endmenu |
268 | ||
035f7f87 KC |
269 | config CC_HAS_RANDSTRUCT |
270 | def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null) | |
271 | ||
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272 | choice |
273 | prompt "Randomize layout of sensitive kernel structures" | |
035f7f87 | 274 | default RANDSTRUCT_FULL if COMPILE_TEST && (GCC_PLUGINS || CC_HAS_RANDSTRUCT) |
595b893e KC |
275 | default RANDSTRUCT_NONE |
276 | help | |
277 | If you enable this, the layouts of structures that are entirely | |
278 | function pointers (and have not been manually annotated with | |
279 | __no_randomize_layout), or structures that have been explicitly | |
280 | marked with __randomize_layout, will be randomized at compile-time. | |
281 | This can introduce the requirement of an additional information | |
282 | exposure vulnerability for exploits targeting these structure | |
283 | types. | |
284 | ||
285 | Enabling this feature will introduce some performance impact, | |
286 | slightly increase memory usage, and prevent the use of forensic | |
287 | tools like Volatility against the system (unless the kernel | |
288 | source tree isn't cleaned after kernel installation). | |
289 | ||
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290 | The seed used for compilation is in scripts/basic/randomize.seed. |
291 | It remains after a "make clean" to allow for external modules to | |
292 | be compiled with the existing seed and will be removed by a | |
293 | "make mrproper" or "make distclean". This file should not be made | |
294 | public, or the structure layout can be determined. | |
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295 | |
296 | config RANDSTRUCT_NONE | |
297 | bool "Disable structure layout randomization" | |
298 | help | |
299 | Build normally: no structure layout randomization. | |
300 | ||
301 | config RANDSTRUCT_FULL | |
302 | bool "Fully randomize structure layout" | |
035f7f87 | 303 | depends on CC_HAS_RANDSTRUCT || GCC_PLUGINS |
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304 | select MODVERSIONS if MODULES |
305 | help | |
306 | Fully randomize the member layout of sensitive | |
307 | structures as much as possible, which may have both a | |
308 | memory size and performance impact. | |
309 | ||
035f7f87 KC |
310 | One difference between the Clang and GCC plugin |
311 | implementations is the handling of bitfields. The GCC | |
312 | plugin treats them as fully separate variables, | |
313 | introducing sometimes significant padding. Clang tries | |
314 | to keep adjacent bitfields together, but with their bit | |
315 | ordering randomized. | |
316 | ||
595b893e KC |
317 | config RANDSTRUCT_PERFORMANCE |
318 | bool "Limit randomization of structure layout to cache-lines" | |
319 | depends on GCC_PLUGINS | |
320 | select MODVERSIONS if MODULES | |
321 | help | |
322 | Randomization of sensitive kernel structures will make a | |
323 | best effort at restricting randomization to cacheline-sized | |
324 | groups of members. It will further not randomize bitfields | |
325 | in structures. This reduces the performance hit of RANDSTRUCT | |
326 | at the cost of weakened randomization. | |
327 | endchoice | |
328 | ||
329 | config RANDSTRUCT | |
330 | def_bool !RANDSTRUCT_NONE | |
331 | ||
332 | config GCC_PLUGIN_RANDSTRUCT | |
333 | def_bool GCC_PLUGINS && RANDSTRUCT | |
334 | help | |
335 | Use GCC plugin to randomize structure layout. | |
336 | ||
337 | This plugin was ported from grsecurity/PaX. More | |
338 | information at: | |
339 | * https://grsecurity.net/ | |
340 | * https://pax.grsecurity.net/ | |
341 | ||
9f671e58 | 342 | endmenu |