kernel/module/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0-only
   2 menuconfig 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
  23 if MODULES
  24
  25 config MODULE_DEBUGFS
  26         bool
  27
  28 config 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
  35 if MODULE_DEBUG
  36
  37 config 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
  62 config 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
 111 config 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
 121 endif # MODULE_DEBUG
 122
 123 config 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
 131 config 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
 139 config 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
 149 config 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
 160 config 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
 170 config 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
 178 config 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
 189 config 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
 211 config 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
 218 config 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
 226 comment "Do not forget to sign required modules with scripts/sign-file"
 227         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
 228
 229 choice
 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
 239 config MODULE_SIG_SHA256
 240         bool "Sign modules with SHA-256"
 241         select CRYPTO_SHA256
 242
 243 config MODULE_SIG_SHA384
 244         bool "Sign modules with SHA-384"
 245         select CRYPTO_SHA512
 246
 247 config MODULE_SIG_SHA512
 248         bool "Sign modules with SHA-512"
 249         select CRYPTO_SHA512
 250
 251 config MODULE_SIG_SHA3_256
 252         bool "Sign modules with SHA3-256"
 253         select CRYPTO_SHA3
 254
 255 config MODULE_SIG_SHA3_384
 256         bool "Sign modules with SHA3-384"
 257         select CRYPTO_SHA3
 258
 259 config MODULE_SIG_SHA3_512
 260         bool "Sign modules with SHA3-512"
 261         select CRYPTO_SHA3
 262
 263 endchoice
 264
 265 config MODULE_SIG_HASH
 266         string
 267         depends on MODULE_SIG || IMA_APPRAISE_MODSIG
 268         default "sha256" if MODULE_SIG_SHA256
 269         default "sha384" if MODULE_SIG_SHA384
 270         default "sha512" if MODULE_SIG_SHA512
 271         default "sha3-256" if MODULE_SIG_SHA3_256
 272         default "sha3-384" if MODULE_SIG_SHA3_384
 273         default "sha3-512" if MODULE_SIG_SHA3_512
 274
 275 choice
 276         prompt "Module compression mode"
 277         help
 278           This option allows you to choose the algorithm which will be used to
 279           compress modules when 'make modules_install' is run. (or, you can
 280           choose to not compress modules at all.)
 281
 282           External modules will also be compressed in the same way during the
 283           installation.
 284
 285           For modules inside an initrd or initramfs, it's more efficient to
 286           compress the whole initrd or initramfs instead.
 287
 288           This is fully compatible with signed modules.
 289
 290           Please note that the tool used to load modules needs to support the
 291           corresponding algorithm. module-init-tools MAY support gzip, and kmod
 292           MAY support gzip, xz and zstd.
 293
 294           Your build system needs to provide the appropriate compression tool
 295           to compress the modules.
 296
 297           If in doubt, select 'None'.
 298
 299 config MODULE_COMPRESS_NONE
 300         bool "None"
 301         help
 302           Do not compress modules. The installed modules are suffixed
 303           with .ko.
 304
 305 config MODULE_COMPRESS_GZIP
 306         bool "GZIP"
 307         help
 308           Compress modules with GZIP. The installed modules are suffixed
 309           with .ko.gz.
 310
 311 config MODULE_COMPRESS_XZ
 312         bool "XZ"
 313         help
 314           Compress modules with XZ. The installed modules are suffixed
 315           with .ko.xz.
 316
 317 config MODULE_COMPRESS_ZSTD
 318         bool "ZSTD"
 319         help
 320           Compress modules with ZSTD. The installed modules are suffixed
 321           with .ko.zst.
 322
 323 endchoice
 324
 325 config MODULE_DECOMPRESS
 326         bool "Support in-kernel module decompression"
 327         depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ || MODULE_COMPRESS_ZSTD
 328         select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
 329         select XZ_DEC if MODULE_COMPRESS_XZ
 330         select ZSTD_DECOMPRESS if MODULE_COMPRESS_ZSTD
 331         help
 332
 333           Support for decompressing kernel modules by the kernel itself
 334           instead of relying on userspace to perform this task. Useful when
 335           load pinning security policy is enabled.
 336
 337           If unsure, say N.
 338
 339 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
 340         bool "Allow loading of modules with missing namespace imports"
 341         help
 342           Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
 343           a namespace. A module that makes use of a symbol exported with such a
 344           namespace is required to import the namespace via MODULE_IMPORT_NS().
 345           There is no technical reason to enforce correct namespace imports,
 346           but it creates consistency between symbols defining namespaces and
 347           users importing namespaces they make use of. This option relaxes this
 348           requirement and lifts the enforcement when loading a module.
 349
 350           If unsure, say N.
 351
 352 config MODPROBE_PATH
 353         string "Path to modprobe binary"
 354         default "/sbin/modprobe"
 355         help
 356           When kernel code requests a module, it does so by calling
 357           the "modprobe" userspace utility. This option allows you to
 358           set the path where that binary is found. This can be changed
 359           at runtime via the sysctl file
 360           /proc/sys/kernel/modprobe. Setting this to the empty string
 361           removes the kernel's ability to request modules (but
 362           userspace can still load modules explicitly).
 363
 364 config TRIM_UNUSED_KSYMS
 365         bool "Trim unused exported kernel symbols" if EXPERT
 366         depends on !COMPILE_TEST
 367         help
 368           The kernel and some modules make many symbols available for
 369           other modules to use via EXPORT_SYMBOL() and variants. Depending
 370           on the set of modules being selected in your kernel configuration,
 371           many of those exported symbols might never be used.
 372
 373           This option allows for unused exported symbols to be dropped from
 374           the build. In turn, this provides the compiler more opportunities
 375           (especially when using LTO) for optimizing the code and reducing
 376           binary size.  This might have some security advantages as well.
 377
 378           If unsure, or if you need to build out-of-tree modules, say N.
 379
 380 config UNUSED_KSYMS_WHITELIST
 381         string "Whitelist of symbols to keep in ksymtab"
 382         depends on TRIM_UNUSED_KSYMS
 383         help
 384           By default, all unused exported symbols will be un-exported from the
 385           build when TRIM_UNUSED_KSYMS is selected.
 386
 387           UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
 388           exported at all times, even in absence of in-tree users. The value to
 389           set here is the path to a text file containing the list of symbols,
 390           one per line. The path can be absolute, or relative to the kernel
 391           source tree.
 392
 393 config MODULES_TREE_LOOKUP
 394         def_bool y
 395         depends on PERF_EVENTS || TRACING || CFI_CLANG
 396
 397 endif # MODULES