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MODSIGN: Implement module signature checking

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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 <[email protected]>
Signed-off-by: Rusty Russell <[email protected]> (minor Kconfig fix)
This commit is contained in:
David Howells 2012-09-26 10:11:03 +01:00 • committed by Rusty Russell
commit 48ba2462ac
2 changed files with 229 additions and 1 deletions
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8
init/Kconfig
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@ -1588,6 +1588,14 @@ config MODULE_SRCVERSION_ALL
config MODULE_SIG
bool "Module signature verification"
depends on MODULES
select KEYS
select CRYPTO
select ASYMMETRIC_KEY_TYPE
select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
select PUBLIC_KEY_ALGO_RSA
select ASN1
select OID_REGISTRY
select X509_CERTIFICATE_PARSER
help
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see