tpm: fix byte order related arithmetic inconsistency in tpm_getcap()

You should not do arithmetic with __be32 or __le32 types because
sometimes it results incorrect results. Calculations must be done only
with integers that are in in the CPU byte order. This commit migrates
tpm_getcap() to struct tpm_buf in order to sort out these issues.

Signed-off-by: Jarkko Sakkinen <[e-mail]>
Reviewed-by: Jason Gunthorpe <[e-mail]>

drivers/char/tpm/tpm-interface.c

···
 ssize_t tpm_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
 		   const char *desc, size_t min_cap_length)
 {
-	struct tpm_cmd_t tpm_cmd;
+	struct tpm_buf buf;
 	int rc;
 
-	tpm_cmd.header.in = tpm_getcap_header;
+	rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_GET_CAP);
+	if (rc)
+		return rc;
+
 	if (subcap_id == TPM_CAP_VERSION_1_1 ||
 	    subcap_id == TPM_CAP_VERSION_1_2) {
-		tpm_cmd.params.getcap_in.cap = cpu_to_be32(subcap_id);
-		/*subcap field not necessary */
-		tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(0);
-		tpm_cmd.header.in.length -= cpu_to_be32(sizeof(__be32));
+		tpm_buf_append_u32(&buf, subcap_id);
+		tpm_buf_append_u32(&buf, 0);
 	} else {
 		if (subcap_id == TPM_CAP_FLAG_PERM ||
 		    subcap_id == TPM_CAP_FLAG_VOL)
-			tpm_cmd.params.getcap_in.cap =
-				cpu_to_be32(TPM_CAP_FLAG);
+			tpm_buf_append_u32(&buf, TPM_CAP_FLAG);
 		else
-			tpm_cmd.params.getcap_in.cap =
-				cpu_to_be32(TPM_CAP_PROP);
-		tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
-		tpm_cmd.params.getcap_in.subcap = cpu_to_be32(subcap_id);
+			tpm_buf_append_u32(&buf, TPM_CAP_PROP);
+
+		tpm_buf_append_u32(&buf, 4);
+		tpm_buf_append_u32(&buf, subcap_id);
 	}
-	rc = tpm_transmit_cmd(chip, NULL, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, NULL, buf.data, PAGE_SIZE,
 			      min_cap_length, 0, desc);
 	if (!rc)
-		*cap = tpm_cmd.params.getcap_out.cap;
+		*cap = *(cap_t *)&buf.data[TPM_HEADER_SIZE + 4];
+
+	tpm_buf_destroy(&buf);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm_getcap);

drivers/char/tpm/tpm.h

···
 	TPM_CAP_PROP_TIS_DURATION = 0x120,
 };
 
-struct	tpm_getcap_params_in {
-	__be32	cap;
-	__be32	subcap_size;
-	__be32	subcap;
-} __packed;
-
-struct	tpm_getcap_params_out {
-	__be32	cap_size;
-	cap_t	cap;
-} __packed;
-
 struct	tpm_readpubek_params_out {
 	u8	algorithm[4];
 	u8	encscheme[2];
···
 } __packed;
 
 typedef union {
-	struct	tpm_getcap_params_out getcap_out;
 	struct	tpm_readpubek_params_out readpubek_out;
 	u8	readpubek_out_buffer[sizeof(struct tpm_readpubek_params_out)];
-	struct	tpm_getcap_params_in getcap_in;
 	struct	tpm_pcrread_in	pcrread_in;
 	struct	tpm_pcrread_out	pcrread_out;
 	struct	tpm_pcrextend_in pcrextend_in;