modsign: Enable ML-DSA module signing

Allow ML-DSA module signing to be enabled.

Note that OpenSSL's CMS_*() function suite does not, as of OpenSSL-3.6,
support the use of CMS_NOATTR with ML-DSA, so the prohibition against using
signedAttrs with module signing has to be removed.  The selected digest
then applies only to the algorithm used to calculate the digest stored in
the messageDigest attribute.  The OpenSSL development branch has patches
applied that fix this[1], but it appears that that will only be available
in OpenSSL-4.

[1] https://github.com/openssl/openssl/pull/28923

sign-file won't set CMS_NOATTR if openssl is earlier than v4, resulting in
the use of signed attributes.

The ML-DSA algorithm takes the raw data to be signed without regard to what
digest algorithm is specified in the CMS message.  The CMS specified digest
algorithm is ignored unless signedAttrs are used; in such a case, only
SHA512 is permitted.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: Eric Biggers <ebiggers@kernel.org>
cc: Lukas Wunner <lukas@wunner.de>
cc: Ignat Korchagin <ignat@cloudflare.com>
cc: Stephan Mueller <smueller@chronox.de>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: keyrings@vger.kernel.org
cc: linux-crypto@vger.kernel.org

1 files changed, 9 insertions, 7 deletions

diff --git a/Documentation/admin-guide/module-signing.rst b/Documentation/admin-guide/module-signing.rst
index a8667a777490..7f2f127dc76f 100644
--- a/Documentation/admin-guide/module-signing.rst
+++ b/Documentation/admin-guide/module-signing.rst
@@ -28,10 +28,12 @@ trusted userspace bits.
 
 This facility uses X.509 ITU-T standard certificates to encode the public keys
 involved.  The signatures are not themselves encoded in any industrial standard
-type.  The built-in facility currently only supports the RSA & NIST P-384 ECDSA
-public key signing standard (though it is pluggable and permits others to be
-used).  The possible hash algorithms that can be used are SHA-2 and SHA-3 of
-sizes 256, 384, and 512 (the algorithm is selected by data in the signature).
+type.  The built-in facility currently only supports the RSA, NIST P-384 ECDSA
+and NIST FIPS-204 ML-DSA public key signing standards (though it is pluggable
+and permits others to be used).  For RSA and ECDSA, the possible hash
+algorithms that can be used are SHA-2 and SHA-3 of sizes 256, 384, and 512 (the
+algorithm is selected by data in the signature); ML-DSA does its own hashing,
+but is allowed to be used with a SHA512 hash for signed attributes.
 
 
 ==========================
@@ -146,9 +148,9 @@ into vmlinux) using parameters in the::
 
 file (which is also generated if it does not already exist).
 
-One can select between RSA (``MODULE_SIG_KEY_TYPE_RSA``) and ECDSA
-(``MODULE_SIG_KEY_TYPE_ECDSA``) to generate either RSA 4k or NIST
-P-384 keypair.
+One can select between RSA (``MODULE_SIG_KEY_TYPE_RSA``), ECDSA
+(``MODULE_SIG_KEY_TYPE_ECDSA``) and ML-DSA (``MODULE_SIG_KEY_TYPE_MLDSA_*``) to
+generate an RSA 4k, a NIST P-384 keypair or an ML-DSA 44, 65 or 87 keypair.
 
 It is strongly recommended that you provide your own x509.genkey file.