tpm: fix RC value check in tpm2_seal_trusted

The error code handling is broken as any error code that has the same
bits set as TPM_RC_HASH passes. Implemented tpm2_rc_value() helper to
parse the error value from FMT0 and FMT1 error codes so that these types
of mistakes are prevented in the future.

Fixes: 5ca4c20cfd37 ("keys, trusted: select hash algorithm for TPM2 chips")
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>

drivers/char/tpm/tpm.h

@@ -519,6 +519,11 @@ static inline void tpm_add_ppi(struct tpm_chip *chip)
 }
 #endif
 
+static inline inline u32 tpm2_rc_value(u32 rc)
+{
+	return (rc & BIT(7)) ? rc & 0xff : rc;
+}
+
 int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 *res_buf);
 int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 *hash);
 int tpm2_get_random(struct tpm_chip *chip, u8 *out, size_t max);

drivers/char/tpm/tpm2-cmd.c

@@ -546,7 +546,7 @@ out:
 	tpm_buf_destroy(&buf);
 
 	if (rc > 0) {
-		if ((rc & TPM2_RC_HASH) == TPM2_RC_HASH)
+		if (tpm2_rc_value(rc) == TPM2_RC_HASH)
 			rc = -EINVAL;
 		else
 			rc = -EPERM;