keys, trusted: seal with a TPM2 authorization policy

TPM2 supports authorization policies, which are essentially
combinational logic statements repsenting the conditions where the data
can be unsealed based on the TPM state. This patch enables to use
authorization policies to seal trusted keys.

Two following new options have been added for trusted keys:

* 'policydigest=': provide an auth policy digest for sealing.
* 'policyhandle=': provide a policy session handle for unsealing.

If 'hash=' option is supplied after 'policydigest=' option, this
will result an error because the state of the option would become
mixed.
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Peter Huewe <peterhuewe@gmx.de>

Documentation/security/keys-trusted-encrypted.txt

@@ -41,6 +41,12 @@ Usage:
        hash=         hash algorithm name as a string. For TPM 1.x the only
                      allowed value is sha1. For TPM 2.x the allowed values
                      are sha1, sha256, sha384, sha512 and sm3-256.
+       policydigest= digest for the authorization policy. must be calculated
+                     with the same hash algorithm as specified by the 'hash='
+                     option.
+       policyhandle= handle to an authorization policy session that defines the
+                     same policy and with the same hash algorithm as was used to
+                     seal the key.
 
 "keyctl print" returns an ascii hex copy of the sealed key, which is in standard
 TPM_STORED_DATA format.  The key length for new keys are always in bytes.

drivers/char/tpm/tpm2-cmd.c

@@ -478,12 +478,26 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	tpm_buf_append_u8(&buf, payload->migratable);
 
 	/* public */
+	if (options->policydigest)
+		tpm_buf_append_u16(&buf, 14 + options->digest_len);
+	else
 		tpm_buf_append_u16(&buf, 14);
 
 	tpm_buf_append_u16(&buf, TPM2_ALG_KEYEDHASH);
 	tpm_buf_append_u16(&buf, hash);
+
+	/* policy */
+	if (options->policydigest) {
+		tpm_buf_append_u32(&buf, 0);
+		tpm_buf_append_u16(&buf, options->digest_len);
+		tpm_buf_append(&buf, options->policydigest,
+			       options->digest_len);
+	} else {
 		tpm_buf_append_u32(&buf, TPM2_ATTR_USER_WITH_AUTH);
-	tpm_buf_append_u16(&buf, 0); /* policy digest size */
+		tpm_buf_append_u16(&buf, 0);
+	}
+
+	/* public parameters */
 	tpm_buf_append_u16(&buf, TPM2_ALG_NULL);
 	tpm_buf_append_u16(&buf, 0);
 
@@ -613,7 +627,9 @@ static int tpm2_unseal(struct tpm_chip *chip,
 		return rc;
 
 	tpm_buf_append_u32(&buf, blob_handle);
-	tpm2_buf_append_auth(&buf, TPM2_RS_PW,
+	tpm2_buf_append_auth(&buf,
+			     options->policyhandle ?
+			     options->policyhandle : TPM2_RS_PW,
 			     NULL /* nonce */, 0,
 			     0 /* session_attributes */,
 			     options->blobauth /* hmac */,

include/keys/trusted-type.h

@@ -18,6 +18,7 @@
 #define MAX_KEY_SIZE			128
 #define MAX_BLOB_SIZE			512
 #define MAX_PCRINFO_SIZE		64
+#define MAX_DIGEST_SIZE			64
 
 struct trusted_key_payload {
 	struct rcu_head rcu;
@@ -37,6 +38,9 @@ struct trusted_key_options {
 	unsigned char pcrinfo[MAX_PCRINFO_SIZE];
 	int pcrlock;
 	uint32_t hash;
+	uint32_t digest_len;
+	unsigned char policydigest[MAX_DIGEST_SIZE];
+	uint32_t policyhandle;
 };
 
 extern struct key_type key_type_trusted;

security/keys/trusted.c

@@ -713,6 +713,8 @@ enum {
 	Opt_keyhandle, Opt_keyauth, Opt_blobauth,
 	Opt_pcrinfo, Opt_pcrlock, Opt_migratable,
 	Opt_hash,
+	Opt_policydigest,
+	Opt_policyhandle,
 };
 
 static const match_table_t key_tokens = {
@@ -726,6 +728,8 @@ static const match_table_t key_tokens = {
 	{Opt_pcrlock, "pcrlock=%s"},
 	{Opt_migratable, "migratable=%s"},
 	{Opt_hash, "hash=%s"},
+	{Opt_policydigest, "policydigest=%s"},
+	{Opt_policyhandle, "policyhandle=%s"},
 	{Opt_err, NULL}
 };
 
@@ -748,6 +752,7 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
 		return tpm2;
 
 	opt->hash = tpm2 ? HASH_ALGO_SHA256 : HASH_ALGO_SHA1;
+	opt->digest_len = hash_digest_size[opt->hash];
 
 	while ((p = strsep(&c, " \t"))) {
 		if (*p == '\0' || *p == ' ' || *p == '\t')
@@ -802,9 +807,13 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
 			opt->pcrlock = lock;
 			break;
 		case Opt_hash:
+			if (test_bit(Opt_policydigest, &token_mask))
+				return -EINVAL;
 			for (i = 0; i < HASH_ALGO__LAST; i++) {
 				if (!strcmp(args[0].from, hash_algo_name[i])) {
 					opt->hash = i;
+					opt->digest_len =
+						hash_digest_size[opt->hash];
 					break;
 				}
 			}
@@ -815,6 +824,23 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
 				return -EINVAL;
 			}
 			break;
+		case Opt_policydigest:
+			if (!tpm2 ||
+			    strlen(args[0].from) != (2 * opt->digest_len))
+				return -EINVAL;
+			res = hex2bin(opt->policydigest, args[0].from,
+				      opt->digest_len);
+			if (res < 0)
+				return -EINVAL;
+			break;
+		case Opt_policyhandle:
+			if (!tpm2)
+				return -EINVAL;
+			res = kstrtoul(args[0].from, 16, &handle);
+			if (res < 0)
+				return -EINVAL;
+			opt->policyhandle = handle;
+			break;
 		default:
 			return -EINVAL;
 		}