Commit 3f1e1bea authored by David Howells's avatar David Howells

MODSIGN: Use PKCS#7 messages as module signatures

Move to using PKCS#7 messages as module signatures because:

 (1) We have to be able to support the use of X.509 certificates that don't
     have a subjKeyId set.  We're currently relying on this to look up the
     X.509 certificate in the trusted keyring list.

 (2) PKCS#7 message signed information blocks have a field that supplies the
     data required to match with the X.509 certificate that signed it.

 (3) The PKCS#7 certificate carries fields that specify the digest algorithm
     used to generate the signature in a standardised way and the X.509
     certificates specify the public key algorithm in a standardised way - so
     we don't need our own methods of specifying these.

 (4) We now have PKCS#7 message support in the kernel for signed kexec purposes
     and we can make use of this.

To make this work, the old sign-file script has been replaced with a program
that needs compiling in a previous patch.  The rules to build it are added
here.
Signed-off-by: 's avatarDavid Howells <dhowells@redhat.com>
Tested-by: 's avatarVivek Goyal <vgoyal@redhat.com>
parent bc1c373d
......@@ -873,7 +873,7 @@ ifdef CONFIG_MODULE_SIG_ALL
MODSECKEY = ./signing_key.priv
MODPUBKEY = ./signing_key.x509
export MODPUBKEY
mod_sign_cmd = perl $(srctree)/scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(MODSECKEY) $(MODPUBKEY)
mod_sign_cmd = scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(MODSECKEY) $(MODPUBKEY)
else
mod_sign_cmd = true
endif
......
......@@ -1869,6 +1869,7 @@ config MODULE_SIG
select ASN1
select OID_REGISTRY
select X509_CERTIFICATE_PARSER
select PKCS7_MESSAGE_PARSER
help
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see
......
......@@ -11,10 +11,9 @@
#include <linux/kernel.h>
#include <linux/err.h>
#include <crypto/public_key.h>
#include <crypto/hash.h>
#include <keys/asymmetric-type.h>
#include <keys/system_keyring.h>
#include <crypto/public_key.h>
#include <crypto/pkcs7.h>
#include "module-internal.h"
/*
......@@ -28,157 +27,53 @@
* - Information block
*/
struct module_signature {
u8 algo; /* Public-key crypto algorithm [enum pkey_algo] */
u8 hash; /* Digest algorithm [enum hash_algo] */
u8 id_type; /* Key identifier type [enum pkey_id_type] */
u8 signer_len; /* Length of signer's name */
u8 key_id_len; /* Length of key identifier */
u8 algo; /* Public-key crypto algorithm [0] */
u8 hash; /* Digest algorithm [0] */
u8 id_type; /* Key identifier type [PKEY_ID_PKCS7] */
u8 signer_len; /* Length of signer's name [0] */
u8 key_id_len; /* Length of key identifier [0] */
u8 __pad[3];
__be32 sig_len; /* Length of signature data */
};
/*
* Digest the module contents.
* Verify a PKCS#7-based signature on a module.
*/
static struct public_key_signature *mod_make_digest(enum hash_algo hash,
const void *mod,
unsigned long modlen)
static int mod_verify_pkcs7(const void *mod, unsigned long modlen,
const void *raw_pkcs7, size_t pkcs7_len)
{
struct public_key_signature *pks;
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t digest_size, desc_size;
struct pkcs7_message *pkcs7;
bool trusted;
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(hash_algo_name[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;
desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
ret = crypto_shash_init(desc);
pkcs7 = pkcs7_parse_message(raw_pkcs7, pkcs7_len);
if (IS_ERR(pkcs7))
return PTR_ERR(pkcs7);
/* The data should be detached - so we need to supply it. */
if (pkcs7_supply_detached_data(pkcs7, mod, modlen) < 0) {
pr_err("PKCS#7 signature with non-detached data\n");
ret = -EBADMSG;
goto error;
}
ret = pkcs7_verify(pkcs7);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
if (ret < 0)
goto error;
crypto_free_shash(tfm);
pr_devel("<==%s() = ok\n", __func__);
return pks;
if (!trusted) {
pr_err("PKCS#7 signature not signed with a trusted key\n");
ret = -ENOKEY;
}
error:
kfree(pks);
error_no_pks:
crypto_free_shash(tfm);
pkcs7_free_message(pkcs7);
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(system_trusted_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));
kfree(id);
if (IS_ERR(key)) {
switch (PTR_ERR(key)) {
/* Hide some search errors */
case -EACCES:
case -ENOTDIR:
case -EAGAIN:
return ERR_PTR(-ENOKEY);
default:
return ERR_CAST(key);
}
}
pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
return key_ref_to_ptr(key);
return ret;
}
/*
......@@ -186,12 +81,8 @@ static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
*/
int mod_verify_sig(const void *mod, unsigned long *_modlen)
{
struct public_key_signature *pks;
struct module_signature ms;
struct key *key;
const void *sig;
size_t modlen = *_modlen, sig_len;
int ret;
pr_devel("==>%s(,%zu)\n", __func__, modlen);
......@@ -205,46 +96,23 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen)
if (sig_len >= modlen)
return -EBADMSG;
modlen -= sig_len;
if ((size_t)ms.signer_len + ms.key_id_len >= modlen)
return -EBADMSG;
modlen -= (size_t)ms.signer_len + ms.key_id_len;
*_modlen = modlen;
sig = mod + modlen;
/* 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 ||
!hash_algo_name[ms.hash])
if (ms.id_type != PKEY_ID_PKCS7) {
pr_err("Module is not signed with expected PKCS#7 message\n");
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,
sig_len);
if (ret < 0)
goto error_free_pks;
ret = verify_signature(key, pks);
pr_devel("verify_signature() = %d\n", ret);
if (ms.algo != 0 ||
ms.hash != 0 ||
ms.signer_len != 0 ||
ms.key_id_len != 0 ||
ms.__pad[0] != 0 ||
ms.__pad[1] != 0 ||
ms.__pad[2] != 0) {
pr_err("PKCS#7 signature info has unexpected non-zero params\n");
return -EBADMSG;
}
error_free_pks:
mpi_free(pks->rsa.s);
kfree(pks);
error_put_key:
key_put(key);
pr_devel("<==%s() = %d\n", __func__, ret);
return ret;
return mod_verify_pkcs7(mod, modlen, mod + modlen, sig_len);
}
......@@ -16,9 +16,11 @@ hostprogs-$(CONFIG_VT) += conmakehash
hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
hostprogs-$(CONFIG_ASN1) += asn1_compiler
hostprogs-$(CONFIG_MODULE_SIG) += sign-file
HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
HOSTLOADLIBES_sign-file = -lcrypto
always := $(hostprogs-y) $(hostprogs-m)
......
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