[PATCH v3 00/14] KEYS: Add support for PGP keys and signatures

Roberto Sassu
2024-09-11T12:29:48Z

From: Roberto Sassu <roberto.sassu@huawei.com>

Support for PGP keys and signatures was proposed by David long time ago,
before the decision of using PKCS#7 for kernel modules signatures
verification was made. After that, there has been not enough interest to
support PGP too.

Lately, there is renewed interest in supporting PGP keys and signatures for
the following use cases:

- EFI variables in modern Lenovo laptops are in PGP form:
https://lore.kernel.org/keyrings/2493611.1723748374@warthog.procyon.org.uk/

- Appraisal of RPM package headers for integrity check
https://lore.kernel.org/linux-integrity/20240905152512.3781098-1-roberto.sassu@huaweicloud.com/

To make these use cases possible, introduce support for PGP keys and
signatures in the kernel, and load provided PGP keys (e.g. Linux
distribution own PGP keys) in the built-in keyring and .ima keyrings.

This feature does not interfere with existing signature verification
mechanisms, such as the one for kernel modules. One has to explicitly call
verify_pgp_signature() to take advantage of it.

For the envisioned use cases, PGP operations cannot be done in user space,
since the consumers are in the kernel itself (Integrity Digest Cache and
IMA). Also they cannot be done in a trusted initial ram disk, since PGP
operations can occur also while the system is running (e.g. after software
package installation).

In addition to the original version of the patch set, also introduce
support for signature verification of PGP keys, so that those keys can be
added to keyrings with a signature-based restriction (e.g. .ima). PGP keys
are searched with partial IDs, provided with signature subtype 16 (Issuer).
However, due to the possibility of ID collisions, the key_or_keyring
restriction is not supported.

The patch set includes two preliminary patches: patch 1 introduces
mpi_key_length(), to get the number of bits and bytes of an MPI; patch 2
introduces rsa_parse_priv_key_raw() and rsa_parse_pub_key_raw(), to parse
an RSA key in RAW format if the ASN.1 parser returns an error.

Patches 3-5 introduce the library necessary to parse PGP keys and
signatures, whose support is added with patches 6-10. Patch 11 introduces
verify_pgp_signature() to be used by kernel subsystems (e.g. IMA). Patch 12
is for testing of PGP signatures. Finally, patches 13-14 allow loading a
set of PGP keys from a supplied blob at boot time.

Changelog

v2 [3]:
- Fix description of verify_pgp_signature()
- Change references from RFC 4880 to RFC 9580 (suggested by Jonathan
McDowell)
- Remove support for v2 and v3 PGP keys (suggested by Jonathan McDowell)
- Explain better CONFIG_PGP_TEST_KEY
- Add MODULE_DESCRIPTION() for all kernel modules (suggested by Jeff
Johnson)
- Don't fill capabilities and MPIs for unsupported key algorithms
- Check if there is enough data when parsing PGP key MPIs and RSA RAW keys
- Fix style issues
- Fix debug messages in pgp_request_asymmetric_key()
- Search verification key in the secondary keyring for the pgp_test key
type

v1 [2]:
- Remove quiet_cmd_extract_certs (redundant, likely leftover from
conflict resolution)
- Load PGP keys embedded in the kernel image within load_module_cert()
and load_system_certificate_list(), instead of using a separate initcall
- Style bug fixes found by checkpatch.pl
- Add <crypto/pgp.h> include in crypto/asymmetric_keys/pgp_preload.c, to
remove no previous prototype warning
- Correctly check returned tfm in pgp_generate_fingerprint()
- Fix printing message in pgp_generate_fingerprint()
- Don't create a public key if the key blob does not contain a PGP key
packet
- Remove unused pgp_pubkey_hash array
- Set KEY_EFLAG_DIGITALSIG key flag if the key has the capability
- Allow PGP_SIG_GENERAL_CERT_OF_UID_PUBKEY signature type (for key sigs)
- Add is_key_sig parameter to pgp_sig_get_sig() to ensure the key
signature type is PGP_SIG_GENERAL_CERT_OF_UID_PUBKEY or
PGP_SIG_POSTITIVE_CERT_OF_UID_PUBKEY

v0 [1]:
- style fixes
- move include/linux/pgp.h and pgplib.h to crypto/asymmetric_keys
- introduce verify_pgp_signature()
- replace KEY_ALLOC_TRUSTED flag with KEY_ALLOC_BUILT_IN
- don't fetch PGP subkeys
- drop support for DSA
- store number of MPIs in pgp_key_algo_p_num_mpi array
- replace dynamic memory allocations with static ones in
pgp_generate_fingerprint()
- store only keys with capability of verifying signatures
- remember selection of PGP signature packet and don't repeat parsing
- move search of the PGP key to verify the signature from the beginning
to the end of the verification process (to be similar with PKCS#7)
- don't retry key search in the session keyring from the signature
verification code, let the caller pass the desired keyring
- for the PGP signature test key type, retry the key search in the session
keyring
- retry key search in restrict_link_by_signature() with a partial ID
(provided in the PGP signature)

[1] https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-modsign.git/log/?h=pgp-parser
[2] https://lore.kernel.org/linux-integrity/20220111180318.591029-1-roberto.sassu@huawei.com/
[3] https://lore.kernel.org/linux-integrity/20240818165756.629203-1-roberto.sassu@huaweicloud.com/

David Howells (8):
PGPLIB: PGP definitions (RFC 9580)
PGPLIB: Basic packet parser
PGPLIB: Signature parser
KEYS: PGP data parser
KEYS: Provide PGP key description autogeneration
KEYS: PGP-based public key signature verification
PGP: Provide a key type for testing PGP signatures
KEYS: Provide a function to load keys from a PGP keyring blob

Roberto Sassu (6):
mpi: Introduce mpi_key_length()
rsa: add parser of raw format
KEYS: Retry asym key search with partial ID in
restrict_link_by_signature()
KEYS: Calculate key digest and get signature of the key
verification: introduce verify_pgp_signature()
KEYS: Introduce load_pgp_public_keyring()

MAINTAINERS | 1 +
certs/Kconfig | 11 +
certs/Makefile | 7 +
certs/system_certificates.S | 18 +
certs/system_keyring.c | 94 ++++
crypto/asymmetric_keys/Kconfig | 39 ++
crypto/asymmetric_keys/Makefile | 13 +
crypto/asymmetric_keys/pgp.h | 216 +++++++++
crypto/asymmetric_keys/pgp_library.c | 610 ++++++++++++++++++++++++
crypto/asymmetric_keys/pgp_parser.h | 18 +
crypto/asymmetric_keys/pgp_preload.c | 111 +++++
crypto/asymmetric_keys/pgp_public_key.c | 482 +++++++++++++++++++
crypto/asymmetric_keys/pgp_signature.c | 510 ++++++++++++++++++++
crypto/asymmetric_keys/pgp_test_key.c | 131 +++++
crypto/asymmetric_keys/pgplib.h | 74 +++
crypto/asymmetric_keys/restrict.c | 10 +-
crypto/rsa.c | 14 +-
crypto/rsa_helper.c | 83 +++-
include/crypto/internal/rsa.h | 6 +
include/crypto/pgp.h | 36 ++
include/linux/mpi.h | 2 +
include/linux/verification.h | 23 +
lib/crypto/mpi/mpicoder.c | 33 +-
23 files changed, 2527 insertions(+), 15 deletions(-)
create mode 100644 crypto/asymmetric_keys/pgp.h
create mode 100644 crypto/asymmetric_keys/pgp_library.c
create mode 100644 crypto/asymmetric_keys/pgp_parser.h
create mode 100644 crypto/asymmetric_keys/pgp_preload.c
create mode 100644 crypto/asymmetric_keys/pgp_public_key.c
create mode 100644 crypto/asymmetric_keys/pgp_signature.c
create mode 100644 crypto/asymmetric_keys/pgp_test_key.c
create mode 100644 crypto/asymmetric_keys/pgplib.h
create mode 100644 include/crypto/pgp.h

--
2.34.1