--- /dev/null
+Kernel module signing facility
+------------------------------
+
+.. CONTENTS
+..
+.. - Overview.
+.. - Configuring module signing.
+.. - Generating signing keys.
+.. - Public keys in the kernel.
+.. - Manually signing modules.
+.. - Signed modules and stripping.
+.. - Loading signed modules.
+.. - Non-valid signatures and unsigned modules.
+.. - Administering/protecting the private key.
+
+
+========
+Overview
+========
+
+The kernel module signing facility cryptographically signs modules during
+installation and then checks the signature upon loading the module. This
+allows increased kernel security by disallowing the loading of unsigned modules
+or modules signed with an invalid key. Module signing increases security by
+making it harder to load a malicious module into the kernel. The module
+signature checking is done by the kernel so that it is not necessary to have
+trusted userspace bits.
+
+This facility uses X.509 ITU-T standard certificates to encode the public keys
+involved. The signatures are not themselves encoded in any industrial standard
+type. The facility currently only supports the RSA public key encryption
+standard (though it is pluggable and permits others to be used). The possible
+hash algorithms that can be used are SHA-1, SHA-224, SHA-256, SHA-384, and
+SHA-512 (the algorithm is selected by data in the signature).
+
+
+==========================
+Configuring module signing
+==========================
+
+The module signing facility is enabled by going to the
+:menuselection:`Enable Loadable Module Support` section of
+the kernel configuration and turning on::
+
+ CONFIG_MODULE_SIG "Module signature verification"
+
+This has a number of options available:
+
+ (1) :menuselection:`Require modules to be validly signed`
+ (``CONFIG_MODULE_SIG_FORCE``)
+
+ This specifies how the kernel should deal with a module that has a
+ signature for which the key is not known or a module that is unsigned.
+
+ If this is off (ie. "permissive"), then modules for which the key is not
+ available and modules that are unsigned are permitted, but the kernel will
+ be marked as being tainted, and the concerned modules will be marked as
+ tainted, shown with the character 'E'.
+
+ If this is on (ie. "restrictive"), only modules that have a valid
+ signature that can be verified by a public key in the kernel's possession
+ will be loaded. All other modules will generate an error.
+
+ Irrespective of the setting here, if the module has a signature block that
+ cannot be parsed, it will be rejected out of hand.
+
+
+ (2) :menuselection:`Automatically sign all modules`
+ (``CONFIG_MODULE_SIG_ALL``)
+
+ If this is on then modules will be automatically signed during the
+ modules_install phase of a build. If this is off, then the modules must
+ be signed manually using::
+
+ scripts/sign-file
+
+
+ (3) :menuselection:`Which hash algorithm should modules be signed with?`
+
+ This presents a choice of which hash algorithm the installation phase will
+ sign the modules with:
+
+ =============================== ==========================================
+ ``CONFIG_MODULE_SIG_SHA1`` :menuselection:`Sign modules with SHA-1`
+ ``CONFIG_MODULE_SIG_SHA224`` :menuselection:`Sign modules with SHA-224`
+ ``CONFIG_MODULE_SIG_SHA256`` :menuselection:`Sign modules with SHA-256`
+ ``CONFIG_MODULE_SIG_SHA384`` :menuselection:`Sign modules with SHA-384`
+ ``CONFIG_MODULE_SIG_SHA512`` :menuselection:`Sign modules with SHA-512`
+ =============================== ==========================================
+
+ The algorithm selected here will also be built into the kernel (rather
+ than being a module) so that modules signed with that algorithm can have
+ their signatures checked without causing a dependency loop.
+
+
+ (4) :menuselection:`File name or PKCS#11 URI of module signing key`
+ (``CONFIG_MODULE_SIG_KEY``)
+
+ Setting this option to something other than its default of
+ ``certs/signing_key.pem`` will disable the autogeneration of signing keys
+ and allow the kernel modules to be signed with a key of your choosing.
+ The string provided should identify a file containing both a private key
+ and its corresponding X.509 certificate in PEM form, or — on systems where
+ the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI as defined by
+ RFC7512. In the latter case, the PKCS#11 URI should reference both a
+ certificate and a private key.
+
+ If the PEM file containing the private key is encrypted, or if the
+ PKCS#11 token requries a PIN, this can be provided at build time by
+ means of the ``KBUILD_SIGN_PIN`` variable.
+
+
+ (5) :menuselection:`Additional X.509 keys for default system keyring`
+ (``CONFIG_SYSTEM_TRUSTED_KEYS``)
+
+ This option can be set to the filename of a PEM-encoded file containing
+ additional certificates which will be included in the system keyring by
+ default.
+
+Note that enabling module signing adds a dependency on the OpenSSL devel
+packages to the kernel build processes for the tool that does the signing.
+
+
+=======================
+Generating signing keys
+=======================
+
+Cryptographic keypairs are required to generate and check signatures. A
+private key is used to generate a signature and the corresponding public key is
+used to check it. The private key is only needed during the build, after which
+it can be deleted or stored securely. The public key gets built into the
+kernel so that it can be used to check the signatures as the modules are
+loaded.
+
+Under normal conditions, when ``CONFIG_MODULE_SIG_KEY`` is unchanged from its
+default, the kernel build will automatically generate a new keypair using
+openssl if one does not exist in the file::
+
+ certs/signing_key.pem
+
+during the building of vmlinux (the public part of the key needs to be built
+into vmlinux) using parameters in the::
+
+ certs/x509.genkey
+
+file (which is also generated if it does not already exist).
+
+It is strongly recommended that you provide your own x509.genkey file.
+
+Most notably, in the x509.genkey file, the req_distinguished_name section
+should be altered from the default::
+
+ [ req_distinguished_name ]
+ #O = Unspecified company
+ CN = Build time autogenerated kernel key
+ #emailAddress = unspecified.user@unspecified.company
+
+The generated RSA key size can also be set with::
+
+ [ req ]
+ default_bits = 4096
+
+
+It is also possible to manually generate the key private/public files using the
+x509.genkey key generation configuration file in the root node of the Linux
+kernel sources tree and the openssl command. The following is an example to
+generate the public/private key files::
+
+ openssl req -new -nodes -utf8 -sha256 -days 36500 -batch -x509 \
+ -config x509.genkey -outform PEM -out kernel_key.pem \
+ -keyout kernel_key.pem
+
+The full pathname for the resulting kernel_key.pem file can then be specified
+in the ``CONFIG_MODULE_SIG_KEY`` option, and the certificate and key therein will
+be used instead of an autogenerated keypair.
+
+
+=========================
+Public keys in the kernel
+=========================
+
+The kernel contains a ring of public keys that can be viewed by root. They're
+in a keyring called ".system_keyring" that can be seen by::
+
+ [root@deneb ~]# cat /proc/keys
+ ...
+ 223c7853 I------ 1 perm 1f030000 0 0 keyring .system_keyring: 1
+ 302d2d52 I------ 1 perm 1f010000 0 0 asymmetri Fedora kernel signing key: d69a84e6bce3d216b979e9505b3e3ef9a7118079: X509.RSA a7118079 []
+ ...
+
+Beyond the public key generated specifically for module signing, additional
+trusted certificates can be provided in a PEM-encoded file referenced by the
+``CONFIG_SYSTEM_TRUSTED_KEYS`` configuration option.
+
+Further, the architecture code may take public keys from a hardware store and
+add those in also (e.g. from the UEFI key database).
+
+Finally, it is possible to add additional public keys by doing::
+
+ keyctl padd asymmetric "" [.system_keyring-ID] <[key-file]
+
+e.g.::
+
+ keyctl padd asymmetric "" 0x223c7853 <my_public_key.x509
+
+Note, however, that the kernel will only permit keys to be added to
+``.system_keyring _if_`` the new key's X.509 wrapper is validly signed by a key
+that is already resident in the .system_keyring at the time the key was added.
+
+
+========================
+Manually signing modules
+========================
+
+To manually sign a module, use the scripts/sign-file tool available in
+the Linux kernel source tree. The script requires 4 arguments:
+
+ 1. The hash algorithm (e.g., sha256)
+ 2. The private key filename or PKCS#11 URI
+ 3. The public key filename
+ 4. The kernel module to be signed
+
+The following is an example to sign a kernel module::
+
+ scripts/sign-file sha512 kernel-signkey.priv \
+ kernel-signkey.x509 module.ko
+
+The hash algorithm used does not have to match the one configured, but if it
+doesn't, you should make sure that hash algorithm is either built into the
+kernel or can be loaded without requiring itself.
+
+If the private key requires a passphrase or PIN, it can be provided in the
+$KBUILD_SIGN_PIN environment variable.
+
+
+============================
+Signed modules and stripping
+============================
+
+A signed module has a digital signature simply appended at the end. The string
+``~Module signature appended~.`` at the end of the module's file confirms that a
+signature is present but it does not confirm that the signature is valid!
+
+Signed modules are BRITTLE as the signature is outside of the defined ELF
+container. Thus they MAY NOT be stripped once the signature is computed and
+attached. Note the entire module is the signed payload, including any and all
+debug information present at the time of signing.
+
+
+======================
+Loading signed modules
+======================
+
+Modules are loaded with insmod, modprobe, ``init_module()`` or
+``finit_module()``, exactly as for unsigned modules as no processing is
+done in userspace. The signature checking is all done within the kernel.
+
+
+=========================================
+Non-valid signatures and unsigned modules
+=========================================
+
+If ``CONFIG_MODULE_SIG_FORCE`` is enabled or module.sig_enforce=1 is supplied on
+the kernel command line, the kernel will only load validly signed modules
+for which it has a public key. Otherwise, it will also load modules that are
+unsigned. Any module for which the kernel has a key, but which proves to have
+a signature mismatch will not be permitted to load.
+
+Any module that has an unparseable signature will be rejected.
+
+
+=========================================
+Administering/protecting the private key
+=========================================
+
+Since the private key is used to sign modules, viruses and malware could use
+the private key to sign modules and compromise the operating system. The
+private key must be either destroyed or moved to a secure location and not kept
+in the root node of the kernel source tree.
+
+If you use the same private key to sign modules for multiple kernel
+configurations, you must ensure that the module version information is
+sufficient to prevent loading a module into a different kernel. Either
+set ``CONFIG_MODVERSIONS=y`` or ensure that each configuration has a different
+kernel release string by changing ``EXTRAVERSION`` or ``CONFIG_LOCALVERSION``.
+++ /dev/null
- ==============================
- KERNEL MODULE SIGNING FACILITY
- ==============================
-
-CONTENTS
-
- - Overview.
- - Configuring module signing.
- - Generating signing keys.
- - Public keys in the kernel.
- - Manually signing modules.
- - Signed modules and stripping.
- - Loading signed modules.
- - Non-valid signatures and unsigned modules.
- - Administering/protecting the private key.
-
-
-========
-OVERVIEW
-========
-
-The kernel module signing facility cryptographically signs modules during
-installation and then checks the signature upon loading the module. This
-allows increased kernel security by disallowing the loading of unsigned modules
-or modules signed with an invalid key. Module signing increases security by
-making it harder to load a malicious module into the kernel. The module
-signature checking is done by the kernel so that it is not necessary to have
-trusted userspace bits.
-
-This facility uses X.509 ITU-T standard certificates to encode the public keys
-involved. The signatures are not themselves encoded in any industrial standard
-type. The facility currently only supports the RSA public key encryption
-standard (though it is pluggable and permits others to be used). The possible
-hash algorithms that can be used are SHA-1, SHA-224, SHA-256, SHA-384, and
-SHA-512 (the algorithm is selected by data in the signature).
-
-
-==========================
-CONFIGURING MODULE SIGNING
-==========================
-
-The module signing facility is enabled by going to the "Enable Loadable Module
-Support" section of the kernel configuration and turning on
-
- CONFIG_MODULE_SIG "Module signature verification"
-
-This has a number of options available:
-
- (1) "Require modules to be validly signed" (CONFIG_MODULE_SIG_FORCE)
-
- This specifies how the kernel should deal with a module that has a
- signature for which the key is not known or a module that is unsigned.
-
- If this is off (ie. "permissive"), then modules for which the key is not
- available and modules that are unsigned are permitted, but the kernel will
- be marked as being tainted, and the concerned modules will be marked as
- tainted, shown with the character 'E'.
-
- If this is on (ie. "restrictive"), only modules that have a valid
- signature that can be verified by a public key in the kernel's possession
- will be loaded. All other modules will generate an error.
-
- Irrespective of the setting here, if the module has a signature block that
- cannot be parsed, it will be rejected out of hand.
-
-
- (2) "Automatically sign all modules" (CONFIG_MODULE_SIG_ALL)
-
- If this is on then modules will be automatically signed during the
- modules_install phase of a build. If this is off, then the modules must
- be signed manually using:
-
- scripts/sign-file
-
-
- (3) "Which hash algorithm should modules be signed with?"
-
- This presents a choice of which hash algorithm the installation phase will
- sign the modules with:
-
- CONFIG_MODULE_SIG_SHA1 "Sign modules with SHA-1"
- CONFIG_MODULE_SIG_SHA224 "Sign modules with SHA-224"
- CONFIG_MODULE_SIG_SHA256 "Sign modules with SHA-256"
- CONFIG_MODULE_SIG_SHA384 "Sign modules with SHA-384"
- CONFIG_MODULE_SIG_SHA512 "Sign modules with SHA-512"
-
- The algorithm selected here will also be built into the kernel (rather
- than being a module) so that modules signed with that algorithm can have
- their signatures checked without causing a dependency loop.
-
-
- (4) "File name or PKCS#11 URI of module signing key" (CONFIG_MODULE_SIG_KEY)
-
- Setting this option to something other than its default of
- "certs/signing_key.pem" will disable the autogeneration of signing keys
- and allow the kernel modules to be signed with a key of your choosing.
- The string provided should identify a file containing both a private key
- and its corresponding X.509 certificate in PEM form, or — on systems where
- the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI as defined by
- RFC7512. In the latter case, the PKCS#11 URI should reference both a
- certificate and a private key.
-
- If the PEM file containing the private key is encrypted, or if the
- PKCS#11 token requries a PIN, this can be provided at build time by
- means of the KBUILD_SIGN_PIN variable.
-
-
- (5) "Additional X.509 keys for default system keyring" (CONFIG_SYSTEM_TRUSTED_KEYS)
-
- This option can be set to the filename of a PEM-encoded file containing
- additional certificates which will be included in the system keyring by
- default.
-
-Note that enabling module signing adds a dependency on the OpenSSL devel
-packages to the kernel build processes for the tool that does the signing.
-
-
-=======================
-GENERATING SIGNING KEYS
-=======================
-
-Cryptographic keypairs are required to generate and check signatures. A
-private key is used to generate a signature and the corresponding public key is
-used to check it. The private key is only needed during the build, after which
-it can be deleted or stored securely. The public key gets built into the
-kernel so that it can be used to check the signatures as the modules are
-loaded.
-
-Under normal conditions, when CONFIG_MODULE_SIG_KEY is unchanged from its
-default, the kernel build will automatically generate a new keypair using
-openssl if one does not exist in the file:
-
- certs/signing_key.pem
-
-during the building of vmlinux (the public part of the key needs to be built
-into vmlinux) using parameters in the:
-
- certs/x509.genkey
-
-file (which is also generated if it does not already exist).
-
-It is strongly recommended that you provide your own x509.genkey file.
-
-Most notably, in the x509.genkey file, the req_distinguished_name section
-should be altered from the default:
-
- [ req_distinguished_name ]
- #O = Unspecified company
- CN = Build time autogenerated kernel key
- #emailAddress = unspecified.user@unspecified.company
-
-The generated RSA key size can also be set with:
-
- [ req ]
- default_bits = 4096
-
-
-It is also possible to manually generate the key private/public files using the
-x509.genkey key generation configuration file in the root node of the Linux
-kernel sources tree and the openssl command. The following is an example to
-generate the public/private key files:
-
- openssl req -new -nodes -utf8 -sha256 -days 36500 -batch -x509 \
- -config x509.genkey -outform PEM -out kernel_key.pem \
- -keyout kernel_key.pem
-
-The full pathname for the resulting kernel_key.pem file can then be specified
-in the CONFIG_MODULE_SIG_KEY option, and the certificate and key therein will
-be used instead of an autogenerated keypair.
-
-
-=========================
-PUBLIC KEYS IN THE KERNEL
-=========================
-
-The kernel contains a ring of public keys that can be viewed by root. They're
-in a keyring called ".system_keyring" that can be seen by:
-
- [root@deneb ~]# cat /proc/keys
- ...
- 223c7853 I------ 1 perm 1f030000 0 0 keyring .system_keyring: 1
- 302d2d52 I------ 1 perm 1f010000 0 0 asymmetri Fedora kernel signing key: d69a84e6bce3d216b979e9505b3e3ef9a7118079: X509.RSA a7118079 []
- ...
-
-Beyond the public key generated specifically for module signing, additional
-trusted certificates can be provided in a PEM-encoded file referenced by the
-CONFIG_SYSTEM_TRUSTED_KEYS configuration option.
-
-Further, the architecture code may take public keys from a hardware store and
-add those in also (e.g. from the UEFI key database).
-
-Finally, it is possible to add additional public keys by doing:
-
- keyctl padd asymmetric "" [.system_keyring-ID] <[key-file]
-
-e.g.:
-
- keyctl padd asymmetric "" 0x223c7853 <my_public_key.x509
-
-Note, however, that the kernel will only permit keys to be added to
-.system_keyring _if_ the new key's X.509 wrapper is validly signed by a key
-that is already resident in the .system_keyring at the time the key was added.
-
-
-=========================
-MANUALLY SIGNING MODULES
-=========================
-
-To manually sign a module, use the scripts/sign-file tool available in
-the Linux kernel source tree. The script requires 4 arguments:
-
- 1. The hash algorithm (e.g., sha256)
- 2. The private key filename or PKCS#11 URI
- 3. The public key filename
- 4. The kernel module to be signed
-
-The following is an example to sign a kernel module:
-
- scripts/sign-file sha512 kernel-signkey.priv \
- kernel-signkey.x509 module.ko
-
-The hash algorithm used does not have to match the one configured, but if it
-doesn't, you should make sure that hash algorithm is either built into the
-kernel or can be loaded without requiring itself.
-
-If the private key requires a passphrase or PIN, it can be provided in the
-$KBUILD_SIGN_PIN environment variable.
-
-
-============================
-SIGNED MODULES AND STRIPPING
-============================
-
-A signed module has a digital signature simply appended at the end. The string
-"~Module signature appended~." at the end of the module's file confirms that a
-signature is present but it does not confirm that the signature is valid!
-
-Signed modules are BRITTLE as the signature is outside of the defined ELF
-container. Thus they MAY NOT be stripped once the signature is computed and
-attached. Note the entire module is the signed payload, including any and all
-debug information present at the time of signing.
-
-
-======================
-LOADING SIGNED MODULES
-======================
-
-Modules are loaded with insmod, modprobe, init_module() or finit_module(),
-exactly as for unsigned modules as no processing is done in userspace. The
-signature checking is all done within the kernel.
-
-
-=========================================
-NON-VALID SIGNATURES AND UNSIGNED MODULES
-=========================================
-
-If CONFIG_MODULE_SIG_FORCE is enabled or module.sig_enforce=1 is supplied on
-the kernel command line, the kernel will only load validly signed modules
-for which it has a public key. Otherwise, it will also load modules that are
-unsigned. Any module for which the kernel has a key, but which proves to have
-a signature mismatch will not be permitted to load.
-
-Any module that has an unparseable signature will be rejected.
-
-
-=========================================
-ADMINISTERING/PROTECTING THE PRIVATE KEY
-=========================================
-
-Since the private key is used to sign modules, viruses and malware could use
-the private key to sign modules and compromise the operating system. The
-private key must be either destroyed or moved to a secure location and not kept
-in the root node of the kernel source tree.
-
-If you use the same private key to sign modules for multiple kernel
-configurations, you must ensure that the module version information is
-sufficient to prevent loading a module into a different kernel. Either
-set CONFIG_MODVERSIONS=y or ensure that each configuration has a different
-kernel release string by changing EXTRAVERSION or CONFIG_LOCALVERSION.
projects / GitHub / moto-9609 / android_kernel_motorola_exynos9610.git / commitdiff