Check the signature on the module against the keys compiled into the kernel or
available in a hardware key store.
Currently, only RSA keys are supported - though that's easy enough to change,
and the signature is expected to contain raw components (so not a PGP or
PKCS#7 formatted blob).
The signature blob is expected to consist of the following pieces in order:
(1) The binary identifier for the key. This is expected to match the
SubjectKeyIdentifier from an X.509 certificate. Only X.509 type
identifiers are currently supported.
(2) The signature data, consisting of a series of MPIs in which each is in
the format of a 2-byte BE word sizes followed by the content data.
(3) A 12 byte information block of the form:
struct module_signature {
enum pkey_algo algo : 8;
enum pkey_hash_algo hash : 8;
enum pkey_id_type id_type : 8;
u8 __pad;
__be32 id_length;
__be32 sig_length;
};
The three enums are defined in crypto/public_key.h.
'algo' contains the public-key algorithm identifier (0->DSA, 1->RSA).
'hash' contains the digest algorithm identifier (0->MD4, 1->MD5, 2->SHA1,
etc.).
'id_type' contains the public-key identifier type (0->PGP, 1->X.509).
'__pad' should be 0.
'id_length' should contain in the binary identifier length in BE form.
'sig_length' should contain in the signature data length in BE form.
The lengths are in BE order rather than CPU order to make dealing with
cross-compilation easier.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (minor Kconfig fix)
We do a very simple search for a particular string appended to the module
(which is cache-hot and about to be SHA'd anyway). There's both a config
option and a boot parameter which control whether we accept or fail with
unsigned modules and modules that are signed with an unknown key.
If module signing is enabled, the kernel will be tainted if a module is
loaded that is unsigned or has a signature for which we don't have the
key.
(Useful feedback and tweaks by David Howells <dhowells@redhat.com>)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
David Howells