Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 424 insertions, 0 deletions

diff --git a/Documentation/crypto/asymmetric-keys.rst b/Documentation/crypto/asymmetric-keys.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+=============================================
+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 (*query)(const struct kernel_pkey_params *params,
+			     struct kernel_pkey_query *info);
+		int (*eds_op)(struct kernel_pkey_params *params,
+			      const void *in, void *out);
+		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) query().
+
+     Mandatory.  This is a function for querying the capabilities of a key.
+
+  4) eds_op().
+
+     Optional.  This is the entry point for the encryption, decryption and
+     signature creation operations (which are distinguished by the operation ID
+     in the parameter struct).  The subtype may do anything it likes to
+     implement an operation, including offloading to hardware.
+
+  5) verify_signature().
+
+     Optional.  This is the entry point for signature verification.  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.
+ - PKCS#8 private key [RFC 5208].
+ - PKCS#5 encrypted private key [RFC 2898].
+
+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.