linux-yocto/certs/Kconfig

SPDX-License-Identifier: GPL-2.0

menu "Certificates for signature checking"

config MODULE_SIG_KEY string "File name or PKCS#11 URI of module signing key" default "certs/signing_key.pem" depends on MODULE_SIG || (IMA_APPRAISE_MODSIG && MODULES) help Provide the file name of a private key/certificate in PEM format, or a PKCS#11 URI according to RFC7512. The file should contain, or the URI should identify, both the certificate and its corresponding private key.

     If this option is unchanged from its default "certs/signing_key.pem",
     then the kernel will automatically generate the private key and
     certificate as described in Documentation/admin-guide/module-signing.rst

choice prompt "Type of module signing key to be generated" depends on MODULE_SIG || (IMA_APPRAISE_MODSIG && MODULES) help The type of module signing key type to generate. This option does not apply if a #PKCS11 URI is used.

config MODULE_SIG_KEY_TYPE_RSA bool "RSA" help Use an RSA key for module signing.

config MODULE_SIG_KEY_TYPE_ECDSA bool "ECDSA" select CRYPTO_ECDSA depends on !(MODULE_SIG_SHA256 || MODULE_SIG_SHA3_256) help Use an elliptic curve key (NIST P384) for module signing. Use a strong hash of same or higher bit length, i.e. sha384 or sha512 for hashing modules.

 Note: Remove all ECDSA signing keys, e.g. certs/signing_key.pem,
 when falling back to building Linux 5.14 and older kernels.

endchoice

config SYSTEM_TRUSTED_KEYRING bool "Provide system-wide ring of trusted keys" depends on KEYS depends on ASYMMETRIC_KEY_TYPE depends on X509_CERTIFICATE_PARSER = y help Provide a system keyring to which trusted keys can be added. Keys in the keyring are considered to be trusted. Keys may be added at will by the kernel from compiled-in data and from hardware key stores, but userspace may only add extra keys if those keys can be verified by keys already in the keyring.

  Keys in this keyring are used by module signature checking.

config SYSTEM_TRUSTED_KEYS string "Additional X.509 keys for default system keyring" depends on SYSTEM_TRUSTED_KEYRING help If set, this option should be the filename of a PEM-formatted file containing trusted X.509 certificates to be included in the default system keyring. Any certificate used for module signing is implicitly also trusted.

  NOTE: If you previously provided keys for the system keyring in the
  form of DER-encoded *.x509 files in the top-level build directory,
  those are no longer used. You will need to set this option instead.

config SYSTEM_EXTRA_CERTIFICATE bool "Reserve area for inserting a certificate without recompiling" depends on SYSTEM_TRUSTED_KEYRING help If set, space for an extra certificate will be reserved in the kernel image. This allows introducing a trusted certificate to the default system keyring without recompiling the kernel.

config SYSTEM_EXTRA_CERTIFICATE_SIZE int "Number of bytes to reserve for the extra certificate" depends on SYSTEM_EXTRA_CERTIFICATE default 4096 help This is the number of bytes reserved in the kernel image for a certificate to be inserted.

config SECONDARY_TRUSTED_KEYRING bool "Provide a keyring to which extra trustable keys may be added" depends on SYSTEM_TRUSTED_KEYRING help If set, provide a keyring to which extra keys may be added, provided those keys are not blacklisted and are vouched for by a key built into the kernel, machine keyring (if configured), or already in the secondary trusted keyring.

config SECONDARY_TRUSTED_KEYRING_SIGNED_BY_BUILTIN bool "Only allow additional certs signed by keys on the builtin trusted keyring" depends on SECONDARY_TRUSTED_KEYRING help If set, only certificates signed by keys on the builtin trusted keyring may be loaded onto the secondary trusted keyring.

  Note: The machine keyring, if configured, will be linked to the
  secondary keyring.  When enabling this option, it is recommended
  to also configure INTEGRITY_CA_MACHINE_KEYRING_MAX to prevent
  linking code signing keys with imputed trust to the secondary
  trusted keyring.

config SYSTEM_BLACKLIST_KEYRING bool "Provide system-wide ring of blacklisted keys" depends on KEYS help Provide a system keyring to which blacklisted keys can be added. Keys in the keyring are considered entirely untrusted. Keys in this keyring are used by the module signature checking to reject loading of modules signed with a blacklisted key.

config SYSTEM_BLACKLIST_HASH_LIST string "Hashes to be preloaded into the system blacklist keyring" depends on SYSTEM_BLACKLIST_KEYRING help If set, this option should be the filename of a list of hashes in the form "", "", ... . This will be included into a C wrapper to incorporate the list into the kernel. Each must be a string starting with a prefix ("tbs" or "bin"), then a colon (":"), and finally an even number of hexadecimal lowercase characters (up to 128). Certificate hashes can be generated with tools/certs/print-cert-tbs-hash.sh .

config SYSTEM_REVOCATION_LIST bool "Provide system-wide ring of revocation certificates" depends on SYSTEM_BLACKLIST_KEYRING depends on PKCS7_MESSAGE_PARSER=y help If set, this allows revocation certificates to be stored in the blacklist keyring and implements a hook whereby a PKCS#7 message can be checked to see if it matches such a certificate.

config SYSTEM_REVOCATION_KEYS string "X.509 certificates to be preloaded into the system blacklist keyring" depends on SYSTEM_REVOCATION_LIST help If set, this option should be the filename of a PEM-formatted file containing X.509 certificates to be included in the default blacklist keyring.

config SYSTEM_BLACKLIST_AUTH_UPDATE bool "Allow root to add signed blacklist keys" depends on SYSTEM_BLACKLIST_KEYRING depends on SYSTEM_DATA_VERIFICATION help If set, provide the ability to load new blacklist keys at run time if they are signed and vouched by a certificate from the builtin trusted keyring. The PKCS#7 signature of the description is set in the key payload. Blacklist keys cannot be removed.

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