Date:   Mon, 11 Jul 2022 18:33:08 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "atomlin@...hat.com" <atomlin@...hat.com>
Subject: Re: [PATCH] modules: move module symbols from init/Kconfig



Le 11/07/2022 à 18:20, Luis Chamberlain a écrit :
> This moves all the module symbols from init/Kconfig to its
> own dedicated file now that we have all of the module code in
> its own directory.
> 
> This does not introduce any functional changes.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>

It is similar to the patch I sent in February, isn't it ? 
(https://patchwork.kernel.org/project/linux-modules/patch/4042712961d42186c449734c253511ea7076c780.1645543105.git.christophe.leroy@csgroup.eu/)

> ---
>   init/Kconfig          | 298 +-----------------------------------------
>   kernel/module/Kconfig | 296 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 297 insertions(+), 297 deletions(-)
>   create mode 100644 kernel/module/Kconfig
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index c7900e8975f1..afb45347b775 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1918,303 +1918,6 @@ config BASE_SMALL
>   	default 0 if BASE_FULL
>   	default 1 if !BASE_FULL
>   
> -config MODULE_SIG_FORMAT
> -	def_bool n
> -	select SYSTEM_DATA_VERIFICATION
> -

MODULE_SIG_FORMAT is not used in kernel/module/Makefile but still in 
kernel/Makefile, that's the reason why in my patch I left it in init/Kconfig

Christophe

> -menuconfig MODULES
> -	bool "Enable loadable module support"
> -	modules
> -	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_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
> -	default n
> -	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"
> -	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.
> -
> -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 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 "Which hash algorithm should modules be signed with?"
> -	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> -	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 "Sign modules with SHA-1"
> -	select CRYPTO_SHA1
> -
> -config MODULE_SIG_SHA224
> -	bool "Sign modules with SHA-224"
> -	select CRYPTO_SHA256
> -
> -config MODULE_SIG_SHA256
> -	bool "Sign modules with SHA-256"
> -	select CRYPTO_SHA256
> -
> -config MODULE_SIG_SHA384
> -	bool "Sign modules with SHA-384"
> -	select CRYPTO_SHA512
> -
> -config MODULE_SIG_SHA512
> -	bool "Sign modules with SHA-512"
> -	select CRYPTO_SHA512
> -
> -endchoice
> -
> -config MODULE_SIG_HASH
> -	string
> -	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> -	default "sha1" if MODULE_SIG_SHA1
> -	default "sha224" if MODULE_SIG_SHA224
> -	default "sha256" if MODULE_SIG_SHA256
> -	default "sha384" if MODULE_SIG_SHA384
> -	default "sha512" if MODULE_SIG_SHA512
> -
> -choice
> -	prompt "Module compression mode"
> -	help
> -	  This option allows you to choose the algorithm which will be used to
> -	  compress modules when 'make modules_install' is run. (or, you can
> -	  choose to not compress modules at all.)
> -
> -	  External modules will also be compressed in the same way during the
> -	  installation.
> -
> -	  For modules inside an initrd or initramfs, it's more efficient to
> -	  compress the whole initrd or initramfs instead.
> -
> -	  This is fully compatible with signed modules.
> -
> -	  Please note that the tool used to load modules needs to support the
> -	  corresponding algorithm. module-init-tools MAY support gzip, and kmod
> -	  MAY support gzip, xz and zstd.
> -
> -	  Your build system needs to provide the appropriate compression tool
> -	  to compress the modules.
> -
> -	  If in doubt, select 'None'.
> -
> -config MODULE_COMPRESS_NONE
> -	bool "None"
> -	help
> -	  Do not compress modules. The installed modules are suffixed
> -	  with .ko.
> -
> -config MODULE_COMPRESS_GZIP
> -	bool "GZIP"
> -	help
> -	  Compress modules with GZIP. The installed modules are suffixed
> -	  with .ko.gz.
> -
> -config MODULE_COMPRESS_XZ
> -	bool "XZ"
> -	help
> -	  Compress modules with XZ. The installed modules are suffixed
> -	  with .ko.xz.
> -
> -config MODULE_COMPRESS_ZSTD
> -	bool "ZSTD"
> -	help
> -	  Compress modules with ZSTD. The installed modules are suffixed
> -	  with .ko.zst.
> -
> -endchoice
> -
> -config MODULE_DECOMPRESS
> -	bool "Support in-kernel module decompression"
> -	depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
> -	select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
> -	select XZ_DEC if MODULE_COMPRESS_XZ
> -	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" if EXPERT
> -	depends on !COMPILE_TEST
> -	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 tree.
> -
> -endif # MODULES
> -
> -config MODULES_TREE_LOOKUP
> -	def_bool y
> -	depends on PERF_EVENTS || TRACING || CFI_CLANG
> -
>   config INIT_ALL_POSSIBLE
>   	bool
>   	help
> @@ -2224,6 +1927,7 @@ config INIT_ALL_POSSIBLE
>   	  it was better to provide this option than to break all the archs
>   	  and have several arch maintainers pursuing me down dark alleys.
>   
> +source "kernel/module/Kconfig"
>   source "block/Kconfig"
>   
>   config PREEMPT_NOTIFIERS
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> new file mode 100644
> index 000000000000..5aff8a40c58e
> --- /dev/null
> +++ b/kernel/module/Kconfig
> @@ -0,0 +1,296 @@
> +config MODULE_SIG_FORMAT
> +	def_bool n
> +	select SYSTEM_DATA_VERIFICATION
> +
> +menuconfig MODULES
> +	bool "Enable loadable module support"
> +	modules
> +	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_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
> +	default n
> +	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"
> +	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.
> +
> +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 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 "Which hash algorithm should modules be signed with?"
> +	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> +	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 "Sign modules with SHA-1"
> +	select CRYPTO_SHA1
> +
> +config MODULE_SIG_SHA224
> +	bool "Sign modules with SHA-224"
> +	select CRYPTO_SHA256
> +
> +config MODULE_SIG_SHA256
> +	bool "Sign modules with SHA-256"
> +	select CRYPTO_SHA256
> +
> +config MODULE_SIG_SHA384
> +	bool "Sign modules with SHA-384"
> +	select CRYPTO_SHA512
> +
> +config MODULE_SIG_SHA512
> +	bool "Sign modules with SHA-512"
> +	select CRYPTO_SHA512
> +
> +endchoice
> +
> +config MODULE_SIG_HASH
> +	string
> +	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> +	default "sha1" if MODULE_SIG_SHA1
> +	default "sha224" if MODULE_SIG_SHA224
> +	default "sha256" if MODULE_SIG_SHA256
> +	default "sha384" if MODULE_SIG_SHA384
> +	default "sha512" if MODULE_SIG_SHA512
> +
> +choice
> +	prompt "Module compression mode"
> +	help
> +	  This option allows you to choose the algorithm which will be used to
> +	  compress modules when 'make modules_install' is run. (or, you can
> +	  choose to not compress modules at all.)
> +
> +	  External modules will also be compressed in the same way during the
> +	  installation.
> +
> +	  For modules inside an initrd or initramfs, it's more efficient to
> +	  compress the whole initrd or initramfs instead.
> +
> +	  This is fully compatible with signed modules.
> +
> +	  Please note that the tool used to load modules needs to support the
> +	  corresponding algorithm. module-init-tools MAY support gzip, and kmod
> +	  MAY support gzip, xz and zstd.
> +
> +	  Your build system needs to provide the appropriate compression tool
> +	  to compress the modules.
> +
> +	  If in doubt, select 'None'.
> +
> +config MODULE_COMPRESS_NONE
> +	bool "None"
> +	help
> +	  Do not compress modules. The installed modules are suffixed
> +	  with .ko.
> +
> +config MODULE_COMPRESS_GZIP
> +	bool "GZIP"
> +	help
> +	  Compress modules with GZIP. The installed modules are suffixed
> +	  with .ko.gz.
> +
> +config MODULE_COMPRESS_XZ
> +	bool "XZ"
> +	help
> +	  Compress modules with XZ. The installed modules are suffixed
> +	  with .ko.xz.
> +
> +config MODULE_COMPRESS_ZSTD
> +	bool "ZSTD"
> +	help
> +	  Compress modules with ZSTD. The installed modules are suffixed
> +	  with .ko.zst.
> +
> +endchoice
> +
> +config MODULE_DECOMPRESS
> +	bool "Support in-kernel module decompression"
> +	depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
> +	select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
> +	select XZ_DEC if MODULE_COMPRESS_XZ
> +	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" if EXPERT
> +	depends on !COMPILE_TEST
> +	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 tree.
> +
> +endif # MODULES
> +
> +config MODULES_TREE_LOOKUP
> +	def_bool y
> +	depends on PERF_EVENTS || TRACING || CFI_CLANG

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