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Add a kernel option SYSTEM_BLACKLIST_AUTH_UPDATE to enable the root user to dynamically add new keys to the blacklist keyring. This enables to invalidate new certificates, either from being loaded in a keyring, or from being trusted in a PKCS#7 certificate chain. This also enables to add new file hashes to be denied by the integrity infrastructure. Being able to untrust a certificate which could have normaly been trusted is a sensitive operation. This is why adding new hashes to the blacklist keyring is only allowed when these hashes are signed and vouched by the builtin trusted keyring. A blacklist hash is stored as a key description. The PKCS#7 signature of this description must be provided as the key payload. Marking a certificate as untrusted should be enforced while the system is running. It is then forbiden to remove such blacklist keys. Update blacklist keyring, blacklist key and revoked certificate access rights: * allows the root user to search for a specific blacklisted hash, which make sense because the descriptions are already viewable; * forbids key update (blacklist and asymmetric ones); * restricts kernel rights on the blacklist keyring to align with the root user rights. See help in tools/certs/print-cert-tbs-hash.sh . Cc: David Howells <dhowells@redhat.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Eric Snowberg <eric.snowberg@oracle.com> Cc: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210712170313.884724-6-mic@digikod.net Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Tested-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
141 lines
5.4 KiB
Plaintext
141 lines
5.4 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0
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menu "Certificates for signature checking"
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config MODULE_SIG_KEY
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string "File name or PKCS#11 URI of module signing key"
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default "certs/signing_key.pem"
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depends on MODULE_SIG || (IMA_APPRAISE_MODSIG && MODULES)
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help
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Provide the file name of a private key/certificate in PEM format,
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or a PKCS#11 URI according to RFC7512. The file should contain, or
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the URI should identify, both the certificate and its corresponding
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private key.
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If this option is unchanged from its default "certs/signing_key.pem",
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then the kernel will automatically generate the private key and
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certificate as described in Documentation/admin-guide/module-signing.rst
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choice
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prompt "Type of module signing key to be generated"
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depends on MODULE_SIG || (IMA_APPRAISE_MODSIG && MODULES)
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help
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The type of module signing key type to generate. This option
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does not apply if a #PKCS11 URI is used.
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config MODULE_SIG_KEY_TYPE_RSA
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bool "RSA"
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help
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Use an RSA key for module signing.
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config MODULE_SIG_KEY_TYPE_ECDSA
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bool "ECDSA"
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select CRYPTO_ECDSA
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help
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Use an elliptic curve key (NIST P384) for module signing. Consider
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using a strong hash like sha256 or sha384 for hashing modules.
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Note: Remove all ECDSA signing keys, e.g. certs/signing_key.pem,
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when falling back to building Linux 5.14 and older kernels.
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endchoice
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config SYSTEM_TRUSTED_KEYRING
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bool "Provide system-wide ring of trusted keys"
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depends on KEYS
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depends on ASYMMETRIC_KEY_TYPE
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help
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Provide a system keyring to which trusted keys can be added. Keys in
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the keyring are considered to be trusted. Keys may be added at will
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by the kernel from compiled-in data and from hardware key stores, but
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userspace may only add extra keys if those keys can be verified by
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keys already in the keyring.
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Keys in this keyring are used by module signature checking.
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config SYSTEM_TRUSTED_KEYS
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string "Additional X.509 keys for default system keyring"
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depends on SYSTEM_TRUSTED_KEYRING
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help
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If set, this option should be the filename of a PEM-formatted file
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containing trusted X.509 certificates to be included in the default
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system keyring. Any certificate used for module signing is implicitly
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also trusted.
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NOTE: If you previously provided keys for the system keyring in the
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form of DER-encoded *.x509 files in the top-level build directory,
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those are no longer used. You will need to set this option instead.
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config SYSTEM_EXTRA_CERTIFICATE
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bool "Reserve area for inserting a certificate without recompiling"
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depends on SYSTEM_TRUSTED_KEYRING
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help
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If set, space for an extra certificate will be reserved in the kernel
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image. This allows introducing a trusted certificate to the default
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system keyring without recompiling the kernel.
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config SYSTEM_EXTRA_CERTIFICATE_SIZE
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int "Number of bytes to reserve for the extra certificate"
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depends on SYSTEM_EXTRA_CERTIFICATE
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default 4096
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help
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This is the number of bytes reserved in the kernel image for a
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certificate to be inserted.
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config SECONDARY_TRUSTED_KEYRING
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bool "Provide a keyring to which extra trustable keys may be added"
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depends on SYSTEM_TRUSTED_KEYRING
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help
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If set, provide a keyring to which extra keys may be added, provided
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those keys are not blacklisted and are vouched for by a key built
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into the kernel or already in the secondary trusted keyring.
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config SYSTEM_BLACKLIST_KEYRING
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bool "Provide system-wide ring of blacklisted keys"
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depends on KEYS
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help
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Provide a system keyring to which blacklisted keys can be added.
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Keys in the keyring are considered entirely untrusted. Keys in this
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keyring are used by the module signature checking to reject loading
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of modules signed with a blacklisted key.
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config SYSTEM_BLACKLIST_HASH_LIST
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string "Hashes to be preloaded into the system blacklist keyring"
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depends on SYSTEM_BLACKLIST_KEYRING
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help
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If set, this option should be the filename of a list of hashes in the
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form "<hash>", "<hash>", ... . This will be included into a C
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wrapper to incorporate the list into the kernel. Each <hash> must be a
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string starting with a prefix ("tbs" or "bin"), then a colon (":"), and
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finally an even number of hexadecimal lowercase characters (up to 128).
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Certificate hashes can be generated with
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tools/certs/print-cert-tbs-hash.sh .
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config SYSTEM_REVOCATION_LIST
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bool "Provide system-wide ring of revocation certificates"
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depends on SYSTEM_BLACKLIST_KEYRING
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depends on PKCS7_MESSAGE_PARSER=y
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help
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If set, this allows revocation certificates to be stored in the
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blacklist keyring and implements a hook whereby a PKCS#7 message can
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be checked to see if it matches such a certificate.
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config SYSTEM_REVOCATION_KEYS
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string "X.509 certificates to be preloaded into the system blacklist keyring"
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depends on SYSTEM_REVOCATION_LIST
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help
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If set, this option should be the filename of a PEM-formatted file
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containing X.509 certificates to be included in the default blacklist
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keyring.
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config SYSTEM_BLACKLIST_AUTH_UPDATE
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bool "Allow root to add signed blacklist keys"
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depends on SYSTEM_BLACKLIST_KEYRING
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depends on SYSTEM_DATA_VERIFICATION
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help
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If set, provide the ability to load new blacklist keys at run time if
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they are signed and vouched by a certificate from the builtin trusted
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keyring. The PKCS#7 signature of the description is set in the key
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payload. Blacklist keys cannot be removed.
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endmenu
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