KEYS: trusted: allow trusted.ko to initialize w/o a TPM

Allow trusted.ko to initialize w/o a TPM. This commit also adds checks
to the exported functions to fail when a TPM is not available.

Fixes: 24073043 ("KEYS: trusted: explicitly use tpm_chip structure...")
Cc: James Morris <jmorris@namei.org>
Reported-by: NDan Williams <dan.j.williams@intel.com>
Tested-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: NJames Morris <james.morris@microsoft.com>

security/keys/trusted.c

@@ -135,6 +135,9 @@ int TSS_authhmac(unsigned char *digest, const unsigned char *key,
 	int ret;
 	va_list argp;
 
+	if (!chip)
+		return -ENODEV;
+
 	sdesc = init_sdesc(hashalg);
 	if (IS_ERR(sdesc)) {
 		pr_info("trusted_key: can't alloc %s\n", hash_alg);
@@ -196,6 +199,9 @@ int TSS_checkhmac1(unsigned char *buffer,
 	va_list argp;
 	int ret;
 
+	if (!chip)
+		return -ENODEV;
+
 	bufsize = LOAD32(buffer, TPM_SIZE_OFFSET);
 	tag = LOAD16(buffer, 0);
 	ordinal = command;
@@ -363,6 +369,9 @@ int trusted_tpm_send(unsigned char *cmd, size_t buflen)
 {
 	int rc;
 
+	if (!chip)
+		return -ENODEV;
+
 	dump_tpm_buf(cmd);
 	rc = tpm_send(chip, cmd, buflen);
 	dump_tpm_buf(cmd);
@@ -429,6 +438,9 @@ int oiap(struct tpm_buf *tb, uint32_t *handle, unsigned char *nonce)
 {
 	int ret;
 
+	if (!chip)
+		return -ENODEV;
+
 	INIT_BUF(tb);
 	store16(tb, TPM_TAG_RQU_COMMAND);
 	store32(tb, TPM_OIAP_SIZE);
@@ -1245,9 +1257,13 @@ static int __init init_trusted(void)
 {
 	int ret;
 
+	/* encrypted_keys.ko depends on successful load of this module even if
+	 * TPM is not used.
+	 */
 	chip = tpm_default_chip();
 	if (!chip)
-		return -ENOENT;
+		return 0;
+
 	ret = init_digests();
 	if (ret < 0)
 		goto err_put;
@@ -1269,10 +1285,12 @@ static int __init init_trusted(void)
 
 static void __exit cleanup_trusted(void)
 {
-	put_device(&chip->dev);
-	kfree(digests);
-	trusted_shash_release();
-	unregister_key_type(&key_type_trusted);
+	if (chip) {
+		put_device(&chip->dev);
+		kfree(digests);
+		trusted_shash_release();
+		unregister_key_type(&key_type_trusted);
+	}
 }
 
 late_initcall(init_trusted);