Commit 48ba2462 authored by David Howells's avatar David Howells Committed by Rusty Russell

MODSIGN: Implement module signature checking

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,

     '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: 's avatarDavid Howells <>
Signed-off-by: Rusty Russell <> (minor Kconfig fix)
parent 631cc66e
......@@ -1588,6 +1588,14 @@ config MODULE_SRCVERSION_ALL
bool "Module signature verification"
depends on MODULES
select KEYS
select CRYPTO
select ASN1
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see
......@@ -11,13 +11,233 @@
#include <linux/kernel.h>
#include <linux/err.h>
#include <crypto/public_key.h>
#include <crypto/hash.h>
#include <keys/asymmetric-type.h>
#include "module-internal.h"
* Module signature information block.
* The constituents of the signature section are, in order:
* - Signer's name
* - Key identifier
* - Signature data
* - Information block
struct module_signature {
enum pkey_algo algo : 8; /* Public-key crypto algorithm */
enum pkey_hash_algo hash : 8; /* Digest algorithm */
enum pkey_id_type id_type : 8; /* Key identifier type */
u8 signer_len; /* Length of signer's name */
u8 key_id_len; /* Length of key identifier */
u8 __pad[3];
__be32 sig_len; /* Length of signature data */
* Digest the module contents.
static struct public_key_signature *mod_make_digest(enum pkey_hash_algo hash,
const void *mod,
unsigned long modlen)
struct public_key_signature *pks;
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t digest_size, desc_size;
int ret;
pr_devel("==>%s()\n", __func__);
/* Allocate the hashing algorithm we're going to need and find out how
* big the hash operational data will be.
tfm = crypto_alloc_shash(pkey_hash_algo[hash], 0, 0);
if (IS_ERR(tfm))
return (PTR_ERR(tfm) == -ENOENT) ? ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
digest_size = crypto_shash_digestsize(tfm);
/* We allocate the hash operational data storage on the end of our
* context data and the digest output buffer on the end of that.
ret = -ENOMEM;
pks = kzalloc(digest_size + sizeof(*pks) + desc_size, GFP_KERNEL);
if (!pks)
goto error_no_pks;
pks->pkey_hash_algo = hash;
pks->digest = (u8 *)pks + sizeof(*pks) + desc_size;
pks->digest_size = digest_size;
desc = (void *)pks + sizeof(*pks);
desc->tfm = tfm;
ret = crypto_shash_init(desc);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
if (ret < 0)
goto error;
pr_devel("<==%s() = ok\n", __func__);
return pks;
pr_devel("<==%s() = %d\n", __func__, ret);
return ERR_PTR(ret);
* Extract an MPI array from the signature data. This represents the actual
* signature. Each raw MPI is prefaced by a BE 2-byte value indicating the
* size of the MPI in bytes.
* RSA signatures only have one MPI, so currently we only read one.
static int mod_extract_mpi_array(struct public_key_signature *pks,
const void *data, size_t len)
size_t nbytes;
MPI mpi;
if (len < 3)
return -EBADMSG;
nbytes = ((const u8 *)data)[0] << 8 | ((const u8 *)data)[1];
data += 2;
len -= 2;
if (len != nbytes)
return -EBADMSG;
mpi = mpi_read_raw_data(data, nbytes);
if (!mpi)
return -ENOMEM;
pks->mpi[0] = mpi;
pks->nr_mpi = 1;
return 0;
* Request an asymmetric key.
static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
const u8 *key_id, size_t key_id_len)
key_ref_t key;
size_t i;
char *id, *q;
pr_devel("==>%s(,%zu,,%zu)\n", __func__, signer_len, key_id_len);
/* Construct an identifier. */
id = kmalloc(signer_len + 2 + key_id_len * 2 + 1, GFP_KERNEL);
if (!id)
return ERR_PTR(-ENOKEY);
memcpy(id, signer, signer_len);
q = id + signer_len;
*q++ = ':';
*q++ = ' ';
for (i = 0; i < key_id_len; i++) {
*q++ = hex_asc[*key_id >> 4];
*q++ = hex_asc[*key_id++ & 0x0f];
*q = 0;
pr_debug("Look up: \"%s\"\n", id);
key = keyring_search(make_key_ref(modsign_keyring, 1),
&key_type_asymmetric, id);
if (IS_ERR(key))
pr_warn("Request for unknown module key '%s' err %ld\n",
id, PTR_ERR(key));
if (IS_ERR(key)) {
switch (PTR_ERR(key)) {
/* Hide some search errors */
case -EACCES:
case -ENOTDIR:
case -EAGAIN:
return ERR_PTR(-ENOKEY);
return ERR_CAST(key);
pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
return key_ref_to_ptr(key);
* Verify the signature on a module.
int mod_verify_sig(const void *mod, unsigned long modlen,
const void *sig, unsigned long siglen)
return -ENOKEY;
struct public_key_signature *pks;
struct module_signature ms;
struct key *key;
size_t sig_len;
int ret;
pr_devel("==>%s(,%lu,,%lu,)\n", __func__, modlen, siglen);
if (siglen <= sizeof(ms))
return -EBADMSG;
memcpy(&ms, sig + (siglen - sizeof(ms)), sizeof(ms));
siglen -= sizeof(ms);
sig_len = be32_to_cpu(ms.sig_len);
if (sig_len >= siglen ||
siglen - sig_len != (size_t)ms.signer_len + ms.key_id_len)
return -EBADMSG;
/* For the moment, only support RSA and X.509 identifiers */
if (ms.algo != PKEY_ALGO_RSA ||
ms.id_type != PKEY_ID_X509)
return -ENOPKG;
if (ms.hash >= PKEY_HASH__LAST ||
return -ENOPKG;
key = request_asymmetric_key(sig, ms.signer_len,
sig + ms.signer_len, ms.key_id_len);
if (IS_ERR(key))
return PTR_ERR(key);
pks = mod_make_digest(ms.hash, mod, modlen);
if (IS_ERR(pks)) {
ret = PTR_ERR(pks);
goto error_put_key;
ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len,
if (ret < 0)
goto error_free_pks;
ret = verify_signature(key, pks);
pr_devel("verify_signature() = %d\n", ret);
pr_devel("<==%s() = %d\n", __func__, ret);
return ret;
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