[Feature]add MT2731_MP2_MR2_SVN388 baseline version
Change-Id: Ief04314834b31e27effab435d3ca8ba33b499059
diff --git a/src/kernel/linux/v4.14/Documentation/crypto/asymmetric-keys.txt b/src/kernel/linux/v4.14/Documentation/crypto/asymmetric-keys.txt
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+ =============================================
+ ASYMMETRIC / PUBLIC-KEY CRYPTOGRAPHY KEY TYPE
+ =============================================
+
+Contents:
+
+ - Overview.
+ - Key identification.
+ - Accessing asymmetric keys.
+ - Signature verification.
+ - Asymmetric key subtypes.
+ - Instantiation data parsers.
+ - Keyring link restrictions.
+
+
+========
+OVERVIEW
+========
+
+The "asymmetric" key type is designed to be a container for the keys used in
+public-key cryptography, without imposing any particular restrictions on the
+form or mechanism of the cryptography or form of the key.
+
+The asymmetric key is given a subtype that defines what sort of data is
+associated with the key and provides operations to describe and destroy it.
+However, no requirement is made that the key data actually be stored in the
+key.
+
+A completely in-kernel key retention and operation subtype can be defined, but
+it would also be possible to provide access to cryptographic hardware (such as
+a TPM) that might be used to both retain the relevant key and perform
+operations using that key. In such a case, the asymmetric key would then
+merely be an interface to the TPM driver.
+
+Also provided is the concept of a data parser. Data parsers are responsible
+for extracting information from the blobs of data passed to the instantiation
+function. The first data parser that recognises the blob gets to set the
+subtype of the key and define the operations that can be done on that key.
+
+A data parser may interpret the data blob as containing the bits representing a
+key, or it may interpret it as a reference to a key held somewhere else in the
+system (for example, a TPM).
+
+
+==================
+KEY IDENTIFICATION
+==================
+
+If a key is added with an empty name, the instantiation data parsers are given
+the opportunity to pre-parse a key and to determine the description the key
+should be given from the content of the key.
+
+This can then be used to refer to the key, either by complete match or by
+partial match. The key type may also use other criteria to refer to a key.
+
+The asymmetric key type's match function can then perform a wider range of
+comparisons than just the straightforward comparison of the description with
+the criterion string:
+
+ (1) If the criterion string is of the form "id:<hexdigits>" then the match
+ function will examine a key's fingerprint to see if the hex digits given
+ after the "id:" match the tail. For instance:
+
+ keyctl search @s asymmetric id:5acc2142
+
+ will match a key with fingerprint:
+
+ 1A00 2040 7601 7889 DE11 882C 3823 04AD 5ACC 2142
+
+ (2) If the criterion string is of the form "<subtype>:<hexdigits>" then the
+ match will match the ID as in (1), but with the added restriction that
+ only keys of the specified subtype (e.g. tpm) will be matched. For
+ instance:
+
+ keyctl search @s asymmetric tpm:5acc2142
+
+Looking in /proc/keys, the last 8 hex digits of the key fingerprint are
+displayed, along with the subtype:
+
+ 1a39e171 I----- 1 perm 3f010000 0 0 asymmetric modsign.0: DSA 5acc2142 []
+
+
+=========================
+ACCESSING ASYMMETRIC KEYS
+=========================
+
+For general access to asymmetric keys from within the kernel, the following
+inclusion is required:
+
+ #include <crypto/public_key.h>
+
+This gives access to functions for dealing with asymmetric / public keys.
+Three enums are defined there for representing public-key cryptography
+algorithms:
+
+ enum pkey_algo
+
+digest algorithms used by those:
+
+ enum pkey_hash_algo
+
+and key identifier representations:
+
+ enum pkey_id_type
+
+Note that the key type representation types are required because key
+identifiers from different standards aren't necessarily compatible. For
+instance, PGP generates key identifiers by hashing the key data plus some
+PGP-specific metadata, whereas X.509 has arbitrary certificate identifiers.
+
+The operations defined upon a key are:
+
+ (1) Signature verification.
+
+Other operations are possible (such as encryption) with the same key data
+required for verification, but not currently supported, and others
+(eg. decryption and signature generation) require extra key data.
+
+
+SIGNATURE VERIFICATION
+----------------------
+
+An operation is provided to perform cryptographic signature verification, using
+an asymmetric key to provide or to provide access to the public key.
+
+ int verify_signature(const struct key *key,
+ const struct public_key_signature *sig);
+
+The caller must have already obtained the key from some source and can then use
+it to check the signature. The caller must have parsed the signature and
+transferred the relevant bits to the structure pointed to by sig.
+
+ struct public_key_signature {
+ u8 *digest;
+ u8 digest_size;
+ enum pkey_hash_algo pkey_hash_algo : 8;
+ u8 nr_mpi;
+ union {
+ MPI mpi[2];
+ ...
+ };
+ };
+
+The algorithm used must be noted in sig->pkey_hash_algo, and all the MPIs that
+make up the actual signature must be stored in sig->mpi[] and the count of MPIs
+placed in sig->nr_mpi.
+
+In addition, the data must have been digested by the caller and the resulting
+hash must be pointed to by sig->digest and the size of the hash be placed in
+sig->digest_size.
+
+The function will return 0 upon success or -EKEYREJECTED if the signature
+doesn't match.
+
+The function may also return -ENOTSUPP if an unsupported public-key algorithm
+or public-key/hash algorithm combination is specified or the key doesn't
+support the operation; -EBADMSG or -ERANGE if some of the parameters have weird
+data; or -ENOMEM if an allocation can't be performed. -EINVAL can be returned
+if the key argument is the wrong type or is incompletely set up.
+
+
+=======================
+ASYMMETRIC KEY SUBTYPES
+=======================
+
+Asymmetric keys have a subtype that defines the set of operations that can be
+performed on that key and that determines what data is attached as the key
+payload. The payload format is entirely at the whim of the subtype.
+
+The subtype is selected by the key data parser and the parser must initialise
+the data required for it. The asymmetric key retains a reference on the
+subtype module.
+
+The subtype definition structure can be found in:
+
+ #include <keys/asymmetric-subtype.h>
+
+and looks like the following:
+
+ struct asymmetric_key_subtype {
+ struct module *owner;
+ const char *name;
+
+ void (*describe)(const struct key *key, struct seq_file *m);
+ void (*destroy)(void *payload);
+ int (*verify_signature)(const struct key *key,
+ const struct public_key_signature *sig);
+ };
+
+Asymmetric keys point to this with their payload[asym_subtype] member.
+
+The owner and name fields should be set to the owning module and the name of
+the subtype. Currently, the name is only used for print statements.
+
+There are a number of operations defined by the subtype:
+
+ (1) describe().
+
+ Mandatory. This allows the subtype to display something in /proc/keys
+ against the key. For instance the name of the public key algorithm type
+ could be displayed. The key type will display the tail of the key
+ identity string after this.
+
+ (2) destroy().
+
+ Mandatory. This should free the memory associated with the key. The
+ asymmetric key will look after freeing the fingerprint and releasing the
+ reference on the subtype module.
+
+ (3) verify_signature().
+
+ Optional. These are the entry points for the key usage operations.
+ Currently there is only the one defined. If not set, the caller will be
+ given -ENOTSUPP. The subtype may do anything it likes to implement an
+ operation, including offloading to hardware.
+
+
+==========================
+INSTANTIATION DATA PARSERS
+==========================
+
+The asymmetric key type doesn't generally want to store or to deal with a raw
+blob of data that holds the key data. It would have to parse it and error
+check it each time it wanted to use it. Further, the contents of the blob may
+have various checks that can be performed on it (eg. self-signatures, validity
+dates) and may contain useful data about the key (identifiers, capabilities).
+
+Also, the blob may represent a pointer to some hardware containing the key
+rather than the key itself.
+
+Examples of blob formats for which parsers could be implemented include:
+
+ - OpenPGP packet stream [RFC 4880].
+ - X.509 ASN.1 stream.
+ - Pointer to TPM key.
+ - Pointer to UEFI key.
+
+During key instantiation each parser in the list is tried until one doesn't
+return -EBADMSG.
+
+The parser definition structure can be found in:
+
+ #include <keys/asymmetric-parser.h>
+
+and looks like the following:
+
+ struct asymmetric_key_parser {
+ struct module *owner;
+ const char *name;
+
+ int (*parse)(struct key_preparsed_payload *prep);
+ };
+
+The owner and name fields should be set to the owning module and the name of
+the parser.
+
+There is currently only a single operation defined by the parser, and it is
+mandatory:
+
+ (1) parse().
+
+ This is called to preparse the key from the key creation and update paths.
+ In particular, it is called during the key creation _before_ a key is
+ allocated, and as such, is permitted to provide the key's description in
+ the case that the caller declines to do so.
+
+ The caller passes a pointer to the following struct with all of the fields
+ cleared, except for data, datalen and quotalen [see
+ Documentation/security/keys/core.rst].
+
+ struct key_preparsed_payload {
+ char *description;
+ void *payload[4];
+ const void *data;
+ size_t datalen;
+ size_t quotalen;
+ };
+
+ The instantiation data is in a blob pointed to by data and is datalen in
+ size. The parse() function is not permitted to change these two values at
+ all, and shouldn't change any of the other values _unless_ they are
+ recognise the blob format and will not return -EBADMSG to indicate it is
+ not theirs.
+
+ If the parser is happy with the blob, it should propose a description for
+ the key and attach it to ->description, ->payload[asym_subtype] should be
+ set to point to the subtype to be used, ->payload[asym_crypto] should be
+ set to point to the initialised data for that subtype,
+ ->payload[asym_key_ids] should point to one or more hex fingerprints and
+ quotalen should be updated to indicate how much quota this key should
+ account for.
+
+ When clearing up, the data attached to ->payload[asym_key_ids] and
+ ->description will be kfree()'d and the data attached to
+ ->payload[asm_crypto] will be passed to the subtype's ->destroy() method
+ to be disposed of. A module reference for the subtype pointed to by
+ ->payload[asym_subtype] will be put.
+
+
+ If the data format is not recognised, -EBADMSG should be returned. If it
+ is recognised, but the key cannot for some reason be set up, some other
+ negative error code should be returned. On success, 0 should be returned.
+
+ The key's fingerprint string may be partially matched upon. For a
+ public-key algorithm such as RSA and DSA this will likely be a printable
+ hex version of the key's fingerprint.
+
+Functions are provided to register and unregister parsers:
+
+ int register_asymmetric_key_parser(struct asymmetric_key_parser *parser);
+ void unregister_asymmetric_key_parser(struct asymmetric_key_parser *subtype);
+
+Parsers may not have the same name. The names are otherwise only used for
+displaying in debugging messages.
+
+
+=========================
+KEYRING LINK RESTRICTIONS
+=========================
+
+Keyrings created from userspace using add_key can be configured to check the
+signature of the key being linked. Keys without a valid signature are not
+allowed to link.
+
+Several restriction methods are available:
+
+ (1) Restrict using the kernel builtin trusted keyring
+
+ - Option string used with KEYCTL_RESTRICT_KEYRING:
+ - "builtin_trusted"
+
+ The kernel builtin trusted keyring will be searched for the signing key.
+ If the builtin trusted keyring is not configured, all links will be
+ rejected. The ca_keys kernel parameter also affects which keys are used
+ for signature verification.
+
+ (2) Restrict using the kernel builtin and secondary trusted keyrings
+
+ - Option string used with KEYCTL_RESTRICT_KEYRING:
+ - "builtin_and_secondary_trusted"
+
+ The kernel builtin and secondary trusted keyrings will be searched for the
+ signing key. If the secondary trusted keyring is not configured, this
+ restriction will behave like the "builtin_trusted" option. The ca_keys
+ kernel parameter also affects which keys are used for signature
+ verification.
+
+ (3) Restrict using a separate key or keyring
+
+ - Option string used with KEYCTL_RESTRICT_KEYRING:
+ - "key_or_keyring:<key or keyring serial number>[:chain]"
+
+ Whenever a key link is requested, the link will only succeed if the key
+ being linked is signed by one of the designated keys. This key may be
+ specified directly by providing a serial number for one asymmetric key, or
+ a group of keys may be searched for the signing key by providing the
+ serial number for a keyring.
+
+ When the "chain" option is provided at the end of the string, the keys
+ within the destination keyring will also be searched for signing keys.
+ This allows for verification of certificate chains by adding each
+ certificate in order (starting closest to the root) to a keyring. For
+ instance, one keyring can be populated with links to a set of root
+ certificates, with a separate, restricted keyring set up for each
+ certificate chain to be validated:
+
+ # Create and populate a keyring for root certificates
+ root_id=`keyctl add keyring root-certs "" @s`
+ keyctl padd asymmetric "" $root_id < root1.cert
+ keyctl padd asymmetric "" $root_id < root2.cert
+
+ # Create and restrict a keyring for the certificate chain
+ chain_id=`keyctl add keyring chain "" @s`
+ keyctl restrict_keyring $chain_id asymmetric key_or_keyring:$root_id:chain
+
+ # Attempt to add each certificate in the chain, starting with the
+ # certificate closest to the root.
+ keyctl padd asymmetric "" $chain_id < intermediateA.cert
+ keyctl padd asymmetric "" $chain_id < intermediateB.cert
+ keyctl padd asymmetric "" $chain_id < end-entity.cert
+
+ If the final end-entity certificate is successfully added to the "chain"
+ keyring, we can be certain that it has a valid signing chain going back to
+ one of the root certificates.
+
+ A single keyring can be used to verify a chain of signatures by
+ restricting the keyring after linking the root certificate:
+
+ # Create a keyring for the certificate chain and add the root
+ chain2_id=`keyctl add keyring chain2 "" @s`
+ keyctl padd asymmetric "" $chain2_id < root1.cert
+
+ # Restrict the keyring that already has root1.cert linked. The cert
+ # will remain linked by the keyring.
+ keyctl restrict_keyring $chain2_id asymmetric key_or_keyring:0:chain
+
+ # Attempt to add each certificate in the chain, starting with the
+ # certificate closest to the root.
+ keyctl padd asymmetric "" $chain2_id < intermediateA.cert
+ keyctl padd asymmetric "" $chain2_id < intermediateB.cert
+ keyctl padd asymmetric "" $chain2_id < end-entity.cert
+
+ If the final end-entity certificate is successfully added to the "chain2"
+ keyring, we can be certain that there is a valid signing chain going back
+ to the root certificate that was added before the keyring was restricted.
+
+
+In all of these cases, if the signing key is found the signature of the key to
+be linked will be verified using the signing key. The requested key is added
+to the keyring only if the signature is successfully verified. -ENOKEY is
+returned if the parent certificate could not be found, or -EKEYREJECTED is
+returned if the signature check fails or the key is blacklisted. Other errors
+may be returned if the signature check could not be performed.