xref: /openbmc/linux/kernel/module/Kconfig (revision 8660484e)
1# SPDX-License-Identifier: GPL-2.0-only
2menuconfig MODULES
3	bool "Enable loadable module support"
4	modules
5	help
6	  Kernel modules are small pieces of compiled code which can
7	  be inserted in the running kernel, rather than being
8	  permanently built into the kernel.  You use the "modprobe"
9	  tool to add (and sometimes remove) them.  If you say Y here,
10	  many parts of the kernel can be built as modules (by
11	  answering M instead of Y where indicated): this is most
12	  useful for infrequently used options which are not required
13	  for booting.  For more information, see the man pages for
14	  modprobe, lsmod, modinfo, insmod and rmmod.
15
16	  If you say Y here, you will need to run "make
17	  modules_install" to put the modules under /lib/modules/
18	  where modprobe can find them (you may need to be root to do
19	  this).
20
21	  If unsure, say Y.
22
23if MODULES
24
25config MODULE_DEBUGFS
26	bool
27
28config MODULE_DEBUG
29	bool "Module debugging"
30	depends on DEBUG_FS
31	help
32	  Allows you to enable / disable features which can help you debug
33	  modules. You don't need these options on production systems.
34
35if MODULE_DEBUG
36
37config MODULE_STATS
38	bool "Module statistics"
39	depends on DEBUG_FS
40	select MODULE_DEBUGFS
41	help
42	  This option allows you to maintain a record of module statistics.
43	  For example, size of all modules, average size, text size, a list
44	  of failed modules and the size for each of those. For failed
45	  modules we keep track of modules which failed due to either the
46	  existing module taking too long to load or that module was already
47	  loaded.
48
49	  You should enable this if you are debugging production loads
50	  and want to see if userspace or the kernel is doing stupid things
51	  with loading modules when it shouldn't or if you want to help
52	  optimize userspace / kernel space module autoloading schemes.
53	  You might want to do this because failed modules tend to use
54	  up significant amount of memory, and so you'd be doing everyone a
55	  favor in avoiding these failures proactively.
56
57	  This functionality is also useful for those experimenting with
58	  module .text ELF section optimization.
59
60	  If unsure, say N.
61
62config MODULE_DEBUG_AUTOLOAD_DUPS
63	bool "Debug duplicate modules with auto-loading"
64	help
65	  Module autoloading allows in-kernel code to request modules through
66	  the *request_module*() API calls. This in turn just calls userspace
67	  modprobe. Although modprobe checks to see if a module is already
68	  loaded before trying to load a module there is a small time window in
69	  which multiple duplicate requests can end up in userspace and multiple
70	  modprobe calls race calling finit_module() around the same time for
71	  duplicate modules. The finit_module() system call can consume in the
72	  worst case more than twice the respective module size in virtual
73	  memory for each duplicate module requests. Although duplicate module
74	  requests are non-fatal virtual memory is a limited resource and each
75	  duplicate module request ends up just unnecessarily straining virtual
76	  memory.
77
78	  This debugging facility will create pr_warn() splats for duplicate
79	  module requests to help identify if module auto-loading may be the
80	  culprit to your early boot virtual memory pressure. Since virtual
81	  memory abuse caused by duplicate module requests could render a
82	  system unusable this functionality will also converge races in
83	  requests for the same module to a single request. You can boot with
84	  the module.enable_dups_trace=1 kernel parameter to use WARN_ON()
85	  instead of the pr_warn().
86
87	  If the first module request used request_module_nowait() we cannot
88	  use that as the anchor to wait for duplicate module requests, since
89	  users of request_module() do want a proper return value. If a call
90	  for the same module happened earlier with request_module() though,
91	  then a duplicate request_module_nowait() would be detected. The
92	  non-wait request_module() call is synchronous and waits until modprobe
93	  completes. Subsequent auto-loading requests for the same module do
94	  not trigger a new finit_module() calls and do not strain virtual
95	  memory, and so as soon as modprobe successfully completes we remove
96	  tracking for duplicates for that module.
97
98	  Enable this functionality to try to debug virtual memory abuse during
99	  boot on systems which are failing to boot or if you suspect you may be
100	  straining virtual memory during boot, and you want to identify if the
101	  abuse was due to module auto-loading. These issues are currently only
102	  known to occur on systems with many CPUs (over 400) and is likely the
103	  result of udev issuing duplicate module requests for each CPU, and so
104	  module auto-loading is not the culprit. There may very well still be
105	  many duplicate module auto-loading requests which could be optimized
106	  for and this debugging facility can be used to help identify them.
107
108	  Only enable this for debugging system functionality, never have it
109	  enabled on real systems.
110
111config MODULE_DEBUG_AUTOLOAD_DUPS_TRACE
112	bool "Force full stack trace when duplicates are found"
113	depends on MODULE_DEBUG_AUTOLOAD_DUPS
114	help
115	  Enabling this will force a full stack trace for duplicate module
116	  auto-loading requests using WARN_ON() instead of pr_warn(). You
117	  should keep this disabled at all times unless you are a developer
118	  and are doing a manual inspection and want to debug exactly why
119	  these duplicates occur.
120
121endif # MODULE_DEBUG
122
123config MODULE_FORCE_LOAD
124	bool "Forced module loading"
125	default n
126	help
127	  Allow loading of modules without version information (ie. modprobe
128	  --force).  Forced module loading sets the 'F' (forced) taint flag and
129	  is usually a really bad idea.
130
131config MODULE_UNLOAD
132	bool "Module unloading"
133	help
134	  Without this option you will not be able to unload any
135	  modules (note that some modules may not be unloadable
136	  anyway), which makes your kernel smaller, faster
137	  and simpler.  If unsure, say Y.
138
139config MODULE_FORCE_UNLOAD
140	bool "Forced module unloading"
141	depends on MODULE_UNLOAD
142	help
143	  This option allows you to force a module to unload, even if the
144	  kernel believes it is unsafe: the kernel will remove the module
145	  without waiting for anyone to stop using it (using the -f option to
146	  rmmod).  This is mainly for kernel developers and desperate users.
147	  If unsure, say N.
148
149config MODULE_UNLOAD_TAINT_TRACKING
150	bool "Tainted module unload tracking"
151	depends on MODULE_UNLOAD
152	select MODULE_DEBUGFS
153	help
154	  This option allows you to maintain a record of each unloaded
155	  module that tainted the kernel. In addition to displaying a
156	  list of linked (or loaded) modules e.g. on detection of a bad
157	  page (see bad_page()), the aforementioned details are also
158	  shown. If unsure, say N.
159
160config MODVERSIONS
161	bool "Module versioning support"
162	help
163	  Usually, you have to use modules compiled with your kernel.
164	  Saying Y here makes it sometimes possible to use modules
165	  compiled for different kernels, by adding enough information
166	  to the modules to (hopefully) spot any changes which would
167	  make them incompatible with the kernel you are running.  If
168	  unsure, say N.
169
170config ASM_MODVERSIONS
171	bool
172	default HAVE_ASM_MODVERSIONS && MODVERSIONS
173	help
174	  This enables module versioning for exported symbols also from
175	  assembly. This can be enabled only when the target architecture
176	  supports it.
177
178config MODULE_SRCVERSION_ALL
179	bool "Source checksum for all modules"
180	help
181	  Modules which contain a MODULE_VERSION get an extra "srcversion"
182	  field inserted into their modinfo section, which contains a
183	  sum of the source files which made it.  This helps maintainers
184	  see exactly which source was used to build a module (since
185	  others sometimes change the module source without updating
186	  the version).  With this option, such a "srcversion" field
187	  will be created for all modules.  If unsure, say N.
188
189config MODULE_SIG
190	bool "Module signature verification"
191	select MODULE_SIG_FORMAT
192	help
193	  Check modules for valid signatures upon load: the signature
194	  is simply appended to the module. For more information see
195	  <file:Documentation/admin-guide/module-signing.rst>.
196
197	  Note that this option adds the OpenSSL development packages as a
198	  kernel build dependency so that the signing tool can use its crypto
199	  library.
200
201	  You should enable this option if you wish to use either
202	  CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
203	  another LSM - otherwise unsigned modules will be loadable regardless
204	  of the lockdown policy.
205
206	  !!!WARNING!!!  If you enable this option, you MUST make sure that the
207	  module DOES NOT get stripped after being signed.  This includes the
208	  debuginfo strip done by some packagers (such as rpmbuild) and
209	  inclusion into an initramfs that wants the module size reduced.
210
211config MODULE_SIG_FORCE
212	bool "Require modules to be validly signed"
213	depends on MODULE_SIG
214	help
215	  Reject unsigned modules or signed modules for which we don't have a
216	  key.  Without this, such modules will simply taint the kernel.
217
218config MODULE_SIG_ALL
219	bool "Automatically sign all modules"
220	default y
221	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
222	help
223	  Sign all modules during make modules_install. Without this option,
224	  modules must be signed manually, using the scripts/sign-file tool.
225
226comment "Do not forget to sign required modules with scripts/sign-file"
227	depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
228
229choice
230	prompt "Which hash algorithm should modules be signed with?"
231	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
232	help
233	  This determines which sort of hashing algorithm will be used during
234	  signature generation.  This algorithm _must_ be built into the kernel
235	  directly so that signature verification can take place.  It is not
236	  possible to load a signed module containing the algorithm to check
237	  the signature on that module.
238
239config MODULE_SIG_SHA1
240	bool "Sign modules with SHA-1"
241	select CRYPTO_SHA1
242
243config MODULE_SIG_SHA224
244	bool "Sign modules with SHA-224"
245	select CRYPTO_SHA256
246
247config MODULE_SIG_SHA256
248	bool "Sign modules with SHA-256"
249	select CRYPTO_SHA256
250
251config MODULE_SIG_SHA384
252	bool "Sign modules with SHA-384"
253	select CRYPTO_SHA512
254
255config MODULE_SIG_SHA512
256	bool "Sign modules with SHA-512"
257	select CRYPTO_SHA512
258
259endchoice
260
261config MODULE_SIG_HASH
262	string
263	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
264	default "sha1" if MODULE_SIG_SHA1
265	default "sha224" if MODULE_SIG_SHA224
266	default "sha256" if MODULE_SIG_SHA256
267	default "sha384" if MODULE_SIG_SHA384
268	default "sha512" if MODULE_SIG_SHA512
269
270choice
271	prompt "Module compression mode"
272	help
273	  This option allows you to choose the algorithm which will be used to
274	  compress modules when 'make modules_install' is run. (or, you can
275	  choose to not compress modules at all.)
276
277	  External modules will also be compressed in the same way during the
278	  installation.
279
280	  For modules inside an initrd or initramfs, it's more efficient to
281	  compress the whole initrd or initramfs instead.
282
283	  This is fully compatible with signed modules.
284
285	  Please note that the tool used to load modules needs to support the
286	  corresponding algorithm. module-init-tools MAY support gzip, and kmod
287	  MAY support gzip, xz and zstd.
288
289	  Your build system needs to provide the appropriate compression tool
290	  to compress the modules.
291
292	  If in doubt, select 'None'.
293
294config MODULE_COMPRESS_NONE
295	bool "None"
296	help
297	  Do not compress modules. The installed modules are suffixed
298	  with .ko.
299
300config MODULE_COMPRESS_GZIP
301	bool "GZIP"
302	help
303	  Compress modules with GZIP. The installed modules are suffixed
304	  with .ko.gz.
305
306config MODULE_COMPRESS_XZ
307	bool "XZ"
308	help
309	  Compress modules with XZ. The installed modules are suffixed
310	  with .ko.xz.
311
312config MODULE_COMPRESS_ZSTD
313	bool "ZSTD"
314	help
315	  Compress modules with ZSTD. The installed modules are suffixed
316	  with .ko.zst.
317
318endchoice
319
320config MODULE_DECOMPRESS
321	bool "Support in-kernel module decompression"
322	depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ || MODULE_COMPRESS_ZSTD
323	select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
324	select XZ_DEC if MODULE_COMPRESS_XZ
325	select ZSTD_DECOMPRESS if MODULE_COMPRESS_ZSTD
326	help
327
328	  Support for decompressing kernel modules by the kernel itself
329	  instead of relying on userspace to perform this task. Useful when
330	  load pinning security policy is enabled.
331
332	  If unsure, say N.
333
334config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
335	bool "Allow loading of modules with missing namespace imports"
336	help
337	  Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
338	  a namespace. A module that makes use of a symbol exported with such a
339	  namespace is required to import the namespace via MODULE_IMPORT_NS().
340	  There is no technical reason to enforce correct namespace imports,
341	  but it creates consistency between symbols defining namespaces and
342	  users importing namespaces they make use of. This option relaxes this
343	  requirement and lifts the enforcement when loading a module.
344
345	  If unsure, say N.
346
347config MODPROBE_PATH
348	string "Path to modprobe binary"
349	default "/sbin/modprobe"
350	help
351	  When kernel code requests a module, it does so by calling
352	  the "modprobe" userspace utility. This option allows you to
353	  set the path where that binary is found. This can be changed
354	  at runtime via the sysctl file
355	  /proc/sys/kernel/modprobe. Setting this to the empty string
356	  removes the kernel's ability to request modules (but
357	  userspace can still load modules explicitly).
358
359config TRIM_UNUSED_KSYMS
360	bool "Trim unused exported kernel symbols" if EXPERT
361	depends on !COMPILE_TEST
362	help
363	  The kernel and some modules make many symbols available for
364	  other modules to use via EXPORT_SYMBOL() and variants. Depending
365	  on the set of modules being selected in your kernel configuration,
366	  many of those exported symbols might never be used.
367
368	  This option allows for unused exported symbols to be dropped from
369	  the build. In turn, this provides the compiler more opportunities
370	  (especially when using LTO) for optimizing the code and reducing
371	  binary size.  This might have some security advantages as well.
372
373	  If unsure, or if you need to build out-of-tree modules, say N.
374
375config UNUSED_KSYMS_WHITELIST
376	string "Whitelist of symbols to keep in ksymtab"
377	depends on TRIM_UNUSED_KSYMS
378	help
379	  By default, all unused exported symbols will be un-exported from the
380	  build when TRIM_UNUSED_KSYMS is selected.
381
382	  UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
383	  exported at all times, even in absence of in-tree users. The value to
384	  set here is the path to a text file containing the list of symbols,
385	  one per line. The path can be absolute, or relative to the kernel
386	  source tree.
387
388config MODULES_TREE_LOOKUP
389	def_bool y
390	depends on PERF_EVENTS || TRACING || CFI_CLANG
391
392endif # MODULES
393