KEYS: asym_tpm: extract key size & public key [ver #2]

The parsed BER/DER blob obtained from user space contains a TPM_Key
structure.  This structure has some information about the key as well as
the public key portion.

This patch extracts this information for future use.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
This commit is contained in:
Denis Kenzior 2018-10-09 17:48:10 +01:00 committed by James Morris
parent 903be6bb84
commit f8c54e1ac4
2 changed files with 115 additions and 0 deletions

View File

@ -7,6 +7,7 @@
#include <linux/seq_file.h>
#include <linux/scatterlist.h>
#include <linux/tpm.h>
#include <asm/unaligned.h>
#include <keys/asymmetric-subtype.h>
#include <crypto/asym_tpm_subtype.h>
@ -37,6 +38,110 @@ static void asym_tpm_destroy(void *payload0, void *payload3)
kfree(tk);
}
/*
* Parse enough information out of TPM_KEY structure:
* TPM_STRUCT_VER -> 4 bytes
* TPM_KEY_USAGE -> 2 bytes
* TPM_KEY_FLAGS -> 4 bytes
* TPM_AUTH_DATA_USAGE -> 1 byte
* TPM_KEY_PARMS -> variable
* UINT32 PCRInfoSize -> 4 bytes
* BYTE* -> PCRInfoSize bytes
* TPM_STORE_PUBKEY
* UINT32 encDataSize;
* BYTE* -> encDataSize;
*
* TPM_KEY_PARMS:
* TPM_ALGORITHM_ID -> 4 bytes
* TPM_ENC_SCHEME -> 2 bytes
* TPM_SIG_SCHEME -> 2 bytes
* UINT32 parmSize -> 4 bytes
* BYTE* -> variable
*/
static int extract_key_parameters(struct tpm_key *tk)
{
const void *cur = tk->blob;
uint32_t len = tk->blob_len;
const void *pub_key;
uint32_t sz;
uint32_t key_len;
if (len < 11)
return -EBADMSG;
/* Ensure this is a legacy key */
if (get_unaligned_be16(cur + 4) != 0x0015)
return -EBADMSG;
/* Skip to TPM_KEY_PARMS */
cur += 11;
len -= 11;
if (len < 12)
return -EBADMSG;
/* Make sure this is an RSA key */
if (get_unaligned_be32(cur) != 0x00000001)
return -EBADMSG;
/* Make sure this is TPM_ES_RSAESPKCSv15 encoding scheme */
if (get_unaligned_be16(cur + 4) != 0x0002)
return -EBADMSG;
/* Make sure this is TPM_SS_RSASSAPKCS1v15_DER signature scheme */
if (get_unaligned_be16(cur + 6) != 0x0003)
return -EBADMSG;
sz = get_unaligned_be32(cur + 8);
if (len < sz + 12)
return -EBADMSG;
/* Move to TPM_RSA_KEY_PARMS */
len -= 12;
cur += 12;
/* Grab the RSA key length */
key_len = get_unaligned_be32(cur);
switch (key_len) {
case 512:
case 1024:
case 1536:
case 2048:
break;
default:
return -EINVAL;
}
/* Move just past TPM_KEY_PARMS */
cur += sz;
len -= sz;
if (len < 4)
return -EBADMSG;
sz = get_unaligned_be32(cur);
if (len < 4 + sz)
return -EBADMSG;
/* Move to TPM_STORE_PUBKEY */
cur += 4 + sz;
len -= 4 + sz;
/* Grab the size of the public key, it should jive with the key size */
sz = get_unaligned_be32(cur);
if (sz > 256)
return -EINVAL;
pub_key = cur + 4;
tk->key_len = key_len;
tk->pub_key = pub_key;
tk->pub_key_len = sz;
return 0;
}
/* Given the blob, parse it and load it into the TPM */
struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
{
@ -64,8 +169,15 @@ struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
tk->blob_len = blob_len;
r = extract_key_parameters(tk);
if (r < 0)
goto error_extract;
return tk;
error_extract:
kfree(tk->blob);
tk->blob_len = 0;
error_memdup:
kfree(tk);
error:

View File

@ -7,6 +7,9 @@
struct tpm_key {
void *blob;
u32 blob_len;
uint16_t key_len; /* Size in bits of the key */
const void *pub_key; /* pointer inside blob to the public key bytes */
uint16_t pub_key_len; /* length of the public key */
};
struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len);