tpm: Mask TPM RC in tpm2_start_auth_session()

tpm2_start_auth_session() does not mask TPM RC correctly from the callers:

[   28.766528] tpm tpm0: A TPM error (2307) occurred start auth session

Process TPM RCs inside tpm2_start_auth_session(), and map them to POSIX
error codes.

Cc: stable@vger.kernel.org # v6.10+
Fixes: 699e3ef ("tpm: Add HMAC session start and end functions")
Reported-by: Herbert Xu <herbert@gondor.apana.org.au>
Closes: https://lore.kernel.org/linux-integrity/Z_NgdRHuTKP6JK--@gondor.apana.org.au/
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Author: jarkkojs

drivers/char/tpm/tpm2-sessions.c

@@ -40,11 +40,6 @@
  *
  * These are the usage functions:
  *
- * tpm2_start_auth_session() which allocates the opaque auth structure
- *	and gets a session from the TPM.  This must be called before
- *	any of the following functions.  The session is protected by a
- *	session_key which is derived from a random salt value
- *	encrypted to the NULL seed.
  * tpm2_end_auth_session() kills the session and frees the resources.
  *	Under normal operation this function is done by
  *	tpm_buf_check_hmac_response(), so this is only to be used on
@@ -963,16 +958,13 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 }
 
 /**
- * tpm2_start_auth_session() - create a HMAC authentication session with the TPM
- * @chip: the TPM chip structure to create the session with
+ * tpm2_start_auth_session() - Create an a HMAC authentication session
+ * @chip:	A TPM chip
  *
- * This function loads the NULL seed from its saved context and starts
- * an authentication session on the null seed, fills in the
- * @chip->auth structure to contain all the session details necessary
- * for performing the HMAC, encrypt and decrypt operations and
- * returns.  The NULL seed is flushed before this function returns.
+ * Loads the ephemeral key (null seed), and starts an HMAC authenticated
+ * session. The null seed is flushed before the return.
  *
- * Return: zero on success or actual error encountered.
+ * Returns zero on success, or a POSIX error code.
  */
 int tpm2_start_auth_session(struct tpm_chip *chip)
 {
@@ -1024,7 +1016,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	/* hash algorithm for session */
 	tpm_buf_append_u16(&buf, TPM_ALG_SHA256);
 
-	rc = tpm_transmit_cmd(chip, &buf, 0, "start auth session");
+	rc = tpm_ret_to_err(tpm_transmit_cmd(chip, &buf, 0, "StartAuthSession"));
 	tpm2_flush_context(chip, null_key);
 
 	if (rc == TPM2_RC_SUCCESS)

include/linux/tpm.h

@@ -257,6 +257,7 @@ enum tpm2_return_codes {
 	TPM2_RC_TESTING		= 0x090A, /* RC_WARN */
 	TPM2_RC_REFERENCE_H0	= 0x0910,
 	TPM2_RC_RETRY		= 0x0922,
+	TPM2_RC_SESSION_MEMORY	= 0x0903,
 };
 
 enum tpm2_command_codes {
@@ -437,6 +438,24 @@ static inline u32 tpm2_rc_value(u32 rc)
 	return (rc & BIT(7)) ? rc & 0xbf : rc;
 }
 
+/*
+ * Convert a return value from tpm_transmit_cmd() to POSIX error code.
+ */
+static inline ssize_t tpm_ret_to_err(ssize_t ret)
+{
+	if (ret < 0)
+		return ret;
+
+	switch (tpm2_rc_value(ret)) {
+	case TPM2_RC_SUCCESS:
+		return 0;
+	case TPM2_RC_SESSION_MEMORY:
+		return -ENOMEM;
+	default:
+		return -EFAULT;
+	}
+}
+
 #if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE)
 
 extern int tpm_is_tpm2(struct tpm_chip *chip);