linux-yocto/kernel/module/Kconfig

SPDX-License-Identifier: GPL-2.0-only

menuconfig MODULES bool "Enable loadable module support" modules select EXECMEM help Kernel modules are small pieces of compiled code which can be inserted in the running kernel, rather than being permanently built into the kernel. You use the "modprobe" tool to add (and sometimes remove) them. If you say Y here, many parts of the kernel can be built as modules (by answering M instead of Y where indicated): this is most useful for infrequently used options which are not required for booting. For more information, see the man pages for modprobe, lsmod, modinfo, insmod and rmmod.

  If you say Y here, you will need to run "make
  modules_install" to put the modules under /lib/modules/
  where modprobe can find them (you may need to be root to do
  this).

  If unsure, say Y.

if MODULES

config MODULE_DEBUGFS bool

config MODULE_DEBUG bool "Module debugging" depends on DEBUG_FS help Allows you to enable / disable features which can help you debug modules. You don't need these options on production systems.

if MODULE_DEBUG

config MODULE_STATS bool "Module statistics" depends on DEBUG_FS select MODULE_DEBUGFS help This option allows you to maintain a record of module statistics. For example, size of all modules, average size, text size, a list of failed modules and the size for each of those. For failed modules we keep track of modules which failed due to either the existing module taking too long to load or that module was already loaded.

  You should enable this if you are debugging production loads
  and want to see if userspace or the kernel is doing stupid things
  with loading modules when it shouldn't or if you want to help
  optimize userspace / kernel space module autoloading schemes.
  You might want to do this because failed modules tend to use
  up significant amount of memory, and so you'd be doing everyone a
  favor in avoiding these failures proactively.

  This functionality is also useful for those experimenting with
  module .text ELF section optimization.

  If unsure, say N.

config MODULE_DEBUG_AUTOLOAD_DUPS bool "Debug duplicate modules with auto-loading" help Module autoloading allows in-kernel code to request modules through the request_module() API calls. This in turn just calls userspace modprobe. Although modprobe checks to see if a module is already loaded before trying to load a module there is a small time window in which multiple duplicate requests can end up in userspace and multiple modprobe calls race calling finit_module() around the same time for duplicate modules. The finit_module() system call can consume in the worst case more than twice the respective module size in virtual memory for each duplicate module requests. Although duplicate module requests are non-fatal virtual memory is a limited resource and each duplicate module request ends up just unnecessarily straining virtual memory.

  This debugging facility will create pr_warn() splats for duplicate
  module requests to help identify if module auto-loading may be the
  culprit to your early boot virtual memory pressure. Since virtual
  memory abuse caused by duplicate module requests could render a
  system unusable this functionality will also converge races in
  requests for the same module to a single request. You can boot with
  the module.enable_dups_trace=1 kernel parameter to use WARN_ON()
  instead of the pr_warn().

  If the first module request used request_module_nowait() we cannot
  use that as the anchor to wait for duplicate module requests, since
  users of request_module() do want a proper return value. If a call
  for the same module happened earlier with request_module() though,
  then a duplicate request_module_nowait() would be detected. The
  non-wait request_module() call is synchronous and waits until modprobe
  completes. Subsequent auto-loading requests for the same module do
  not trigger a new finit_module() calls and do not strain virtual
  memory, and so as soon as modprobe successfully completes we remove
  tracking for duplicates for that module.

  Enable this functionality to try to debug virtual memory abuse during
  boot on systems which are failing to boot or if you suspect you may be
  straining virtual memory during boot, and you want to identify if the
  abuse was due to module auto-loading. These issues are currently only
  known to occur on systems with many CPUs (over 400) and is likely the
  result of udev issuing duplicate module requests for each CPU, and so
  module auto-loading is not the culprit. There may very well still be
  many duplicate module auto-loading requests which could be optimized
  for and this debugging facility can be used to help identify them.

  Only enable this for debugging system functionality, never have it
  enabled on real systems.

config MODULE_DEBUG_AUTOLOAD_DUPS_TRACE bool "Force full stack trace when duplicates are found" depends on MODULE_DEBUG_AUTOLOAD_DUPS help Enabling this will force a full stack trace for duplicate module auto-loading requests using WARN_ON() instead of pr_warn(). You should keep this disabled at all times unless you are a developer and are doing a manual inspection and want to debug exactly why these duplicates occur.

endif # MODULE_DEBUG

config MODULE_FORCE_LOAD bool "Forced module loading" default n help Allow loading of modules without version information (ie. modprobe --force). Forced module loading sets the 'F' (forced) taint flag and is usually a really bad idea.

config MODULE_UNLOAD bool "Module unloading" help Without this option you will not be able to unload any modules (note that some modules may not be unloadable anyway), which makes your kernel smaller, faster and simpler. If unsure, say Y.

config MODULE_FORCE_UNLOAD bool "Forced module unloading" depends on MODULE_UNLOAD help This option allows you to force a module to unload, even if the kernel believes it is unsafe: the kernel will remove the module without waiting for anyone to stop using it (using the -f option to rmmod). This is mainly for kernel developers and desperate users. If unsure, say N.

config MODULE_UNLOAD_TAINT_TRACKING bool "Tainted module unload tracking" depends on MODULE_UNLOAD select MODULE_DEBUGFS help This option allows you to maintain a record of each unloaded module that tainted the kernel. In addition to displaying a list of linked (or loaded) modules e.g. on detection of a bad page (see bad_page()), the aforementioned details are also shown. If unsure, say N.

config MODVERSIONS bool "Module versioning support" depends on !COMPILE_TEST help Usually, you have to use modules compiled with your kernel. Saying Y here makes it sometimes possible to use modules compiled for different kernels, by adding enough information to the modules to (hopefully) spot any changes which would make them incompatible with the kernel you are running. If unsure, say N.

choice prompt "Module versioning implementation" depends on MODVERSIONS help Select the tool used to calculate symbol versions for modules.

  If unsure, select GENKSYMS.

config GENKSYMS bool "genksyms (from source code)" help Calculate symbol versions from pre-processed source code using genksyms.

  If unsure, say Y.

config GENDWARFKSYMS bool "gendwarfksyms (from debugging information)" depends on DEBUG_INFO # Requires full debugging information, split DWARF not supported. depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT # Requires ELF object files. depends on !LTO # To avoid conflicts with the discarded __gendwarfksyms_ptr symbols on # X86, requires pahole before commit 47dcb534e253 ("btf_encoder: Stop # indexing symbols for VARs") or after commit 9810758003ce ("btf_encoder: # Verify 0 address DWARF variables are in ELF section"). depends on !X86 || !DEBUG_INFO_BTF || PAHOLE_VERSION < 128 || PAHOLE_VERSION > 129 help Calculate symbol versions from DWARF debugging information using gendwarfksyms. Requires DEBUG_INFO to be enabled.

  If unsure, say N.

endchoice

config ASM_MODVERSIONS bool default HAVE_ASM_MODVERSIONS && MODVERSIONS help This enables module versioning for exported symbols also from assembly. This can be enabled only when the target architecture supports it.

config EXTENDED_MODVERSIONS bool "Extended Module Versioning Support" depends on MODVERSIONS help This enables extended MODVERSIONs support, allowing long symbol names to be versioned.

  The most likely reason you would enable this is to enable Rust
  support. If unsure, say N.

config BASIC_MODVERSIONS bool "Basic Module Versioning Support" depends on MODVERSIONS default y help This enables basic MODVERSIONS support, allowing older tools or kernels to potentially load modules.

  Disabling this may cause older `modprobe` or `kmod` to be unable
  to read MODVERSIONS information from built modules. With this
  disabled, older kernels may treat this module as unversioned.

  This is enabled by default when MODVERSIONS are enabled.
  If unsure, say Y.

config MODULE_SRCVERSION_ALL bool "Source checksum for all modules" help Modules which contain a MODULE_VERSION get an extra "srcversion" field inserted into their modinfo section, which contains a sum of the source files which made it. This helps maintainers see exactly which source was used to build a module (since others sometimes change the module source without updating the version). With this option, such a "srcversion" field will be created for all modules. If unsure, say N.

config MODULE_SIG bool "Module signature verification" select MODULE_SIG_FORMAT help Check modules for valid signatures upon load: the signature is simply appended to the module. For more information see file:Documentation/admin-guide/module-signing.rst.

  Note that this option adds the OpenSSL development packages as a
  kernel build dependency so that the signing tool can use its crypto
  library.

  You should enable this option if you wish to use either
  CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
  another LSM - otherwise unsigned modules will be loadable regardless
  of the lockdown policy.

  !!!WARNING!!!  If you enable this option, you MUST make sure that the
  module DOES NOT get stripped after being signed.  This includes the
  debuginfo strip done by some packagers (such as rpmbuild) and
  inclusion into an initramfs that wants the module size reduced.

config MODULE_SIG_FORCE bool "Require modules to be validly signed" depends on MODULE_SIG help Reject unsigned modules or signed modules for which we don't have a key. Without this, such modules will simply taint the kernel.

config MODULE_SIG_ALL bool "Automatically sign all modules" default y depends on MODULE_SIG || IMA_APPRAISE_MODSIG help Sign all modules during make modules_install. Without this option, modules must be signed manually, using the scripts/sign-file tool.

comment "Do not forget to sign required modules with scripts/sign-file" depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL

choice prompt "Hash algorithm to sign modules" depends on MODULE_SIG || IMA_APPRAISE_MODSIG default MODULE_SIG_SHA512 help This determines which sort of hashing algorithm will be used during signature generation. This algorithm must be built into the kernel directly so that signature verification can take place. It is not possible to load a signed module containing the algorithm to check the signature on that module.

config MODULE_SIG_SHA1 bool "SHA-1" select CRYPTO_SHA1

config MODULE_SIG_SHA256 bool "SHA-256" select CRYPTO_SHA256

config MODULE_SIG_SHA384 bool "SHA-384" select CRYPTO_SHA512

config MODULE_SIG_SHA512 bool "SHA-512" select CRYPTO_SHA512

config MODULE_SIG_SHA3_256 bool "SHA3-256" select CRYPTO_SHA3

config MODULE_SIG_SHA3_384 bool "SHA3-384" select CRYPTO_SHA3

config MODULE_SIG_SHA3_512 bool "SHA3-512" select CRYPTO_SHA3

endchoice

config MODULE_SIG_HASH string depends on MODULE_SIG || IMA_APPRAISE_MODSIG default "sha1" if MODULE_SIG_SHA1 default "sha256" if MODULE_SIG_SHA256 default "sha384" if MODULE_SIG_SHA384 default "sha512" if MODULE_SIG_SHA512 default "sha3-256" if MODULE_SIG_SHA3_256 default "sha3-384" if MODULE_SIG_SHA3_384 default "sha3-512" if MODULE_SIG_SHA3_512

config MODULE_COMPRESS bool "Module compression" help Enable module compression to reduce on-disk size of module binaries. This is fully compatible with signed modules.

  The tool used to work with modules needs to support the selected
  compression type. kmod MAY support gzip, xz and zstd. Other tools
  might have a limited selection of the supported types.

  Note that for modules inside an initrd or initramfs, it's more
  efficient to compress the whole ramdisk instead.

  If unsure, say N.

choice prompt "Module compression type" depends on MODULE_COMPRESS help Choose the supported algorithm for module compression.

config MODULE_COMPRESS_GZIP bool "GZIP" help Support modules compressed with GZIP. The installed modules are suffixed with .ko.gz.

config MODULE_COMPRESS_XZ bool "XZ" help Support modules compressed with XZ. The installed modules are suffixed with .ko.xz.

config MODULE_COMPRESS_ZSTD bool "ZSTD" help Support modules compressed with ZSTD. The installed modules are suffixed with .ko.zst.

endchoice

config MODULE_COMPRESS_ALL bool "Automatically compress all modules" default y depends on MODULE_COMPRESS help Compress all modules during 'make modules_install'.

  Your build system needs to provide the appropriate compression tool
  for the selected compression type. External modules will also be
  compressed in the same way during the installation.

config MODULE_DECOMPRESS bool "Support in-kernel module decompression" depends on MODULE_COMPRESS select ZLIB_INFLATE if MODULE_COMPRESS_GZIP select XZ_DEC if MODULE_COMPRESS_XZ select ZSTD_DECOMPRESS if MODULE_COMPRESS_ZSTD help Support for decompressing kernel modules by the kernel itself instead of relying on userspace to perform this task. Useful when load pinning security policy is enabled.

  If unsure, say N.

config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS bool "Allow loading of modules with missing namespace imports" help Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in a namespace. A module that makes use of a symbol exported with such a namespace is required to import the namespace via MODULE_IMPORT_NS(""). There is no technical reason to enforce correct namespace imports, but it creates consistency between symbols defining namespaces and users importing namespaces they make use of. This option relaxes this requirement and lifts the enforcement when loading a module.

  If unsure, say N.

config MODPROBE_PATH string "Path to modprobe binary" default "/sbin/modprobe" help When kernel code requests a module, it does so by calling the "modprobe" userspace utility. This option allows you to set the path where that binary is found. This can be changed at runtime via the sysctl file /proc/sys/kernel/modprobe. Setting this to the empty string removes the kernel's ability to request modules (but userspace can still load modules explicitly).

config TRIM_UNUSED_KSYMS bool "Trim unused exported kernel symbols" help The kernel and some modules make many symbols available for other modules to use via EXPORT_SYMBOL() and variants. Depending on the set of modules being selected in your kernel configuration, many of those exported symbols might never be used.

  This option allows for unused exported symbols to be dropped from
  the build. In turn, this provides the compiler more opportunities
  (especially when using LTO) for optimizing the code and reducing
  binary size.  This might have some security advantages as well.

  If unsure, or if you need to build out-of-tree modules, say N.

config UNUSED_KSYMS_WHITELIST string "Whitelist of symbols to keep in ksymtab" depends on TRIM_UNUSED_KSYMS help By default, all unused exported symbols will be un-exported from the build when TRIM_UNUSED_KSYMS is selected.

  UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
  exported at all times, even in absence of in-tree users. The value to
  set here is the path to a text file containing the list of symbols,
  one per line. The path can be absolute, or relative to the kernel
  source or obj tree.

config MODULES_TREE_LOOKUP def_bool y depends on PERF_EVENTS || TRACING || CFI_CLANG

endif # MODULES