tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure

1. Use tpm_buf in tpm1_get_random()
2. Fix comment in tpm_get_random() so it is clear that
the function is expected to return number of random bytes.
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm-interface.c

@@ -600,7 +600,7 @@ EXPORT_SYMBOL_GPL(tpm_pm_resume);
  * @out:	destination buffer for the random bytes
  * @max:	the max number of bytes to write to @out
  *
- * Return: same as with tpm_transmit_cmd()
+ * Return: number of random bytes read or a negative error value.
  */
 int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max)
 {

drivers/char/tpm/tpm.h

@@ -396,20 +396,9 @@ struct tpm_pcrread_in {
  * compiler warnings about stack frame size. */
 #define TPM_MAX_RNG_DATA	128
 
-struct tpm_getrandom_out {
-	__be32 rng_data_len;
-	u8     rng_data[TPM_MAX_RNG_DATA];
-} __packed;
-
-struct tpm_getrandom_in {
-	__be32 num_bytes;
-} __packed;
-
 typedef union {
 	struct	tpm_pcrread_in	pcrread_in;
 	struct	tpm_pcrread_out	pcrread_out;
-	struct	tpm_getrandom_in getrandom_in;
-	struct	tpm_getrandom_out getrandom_out;
 } tpm_cmd_params;
 
 struct tpm_cmd_t {

drivers/char/tpm/tpm1-cmd.c

@@ -505,58 +505,70 @@ ssize_t tpm1_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
 EXPORT_SYMBOL_GPL(tpm1_getcap);
 
 #define TPM_ORD_GET_RANDOM 70
-#define TPM_GETRANDOM_RESULT_SIZE	18
-static const struct tpm_input_header tpm_getrandom_header = {
-	.tag = cpu_to_be16(TPM_TAG_RQU_COMMAND),
-	.length = cpu_to_be32(14),
-	.ordinal = cpu_to_be32(TPM_ORD_GET_RANDOM)
-};
+struct tpm1_get_random_out {
+	__be32 rng_data_len;
+	u8 rng_data[TPM_MAX_RNG_DATA];
+} __packed;
 
-int tpm1_get_random(struct tpm_chip *chip, u8 *out, size_t max)
+/**
+ * tpm1_get_random() - get random bytes from the TPM's RNG
+ * @chip:	a &struct tpm_chip instance
+ * @dest:	destination buffer for the random bytes
+ * @max:	the maximum number of bytes to write to @dest
+ *
+ * Return:
+ * *  number of bytes read
+ * * -errno or a TPM return code otherwise
+ */
+int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
 {
-	struct tpm_cmd_t tpm_cmd;
-	u32 recd;
+	struct tpm1_get_random_out *out;
 	u32 num_bytes =  min_t(u32, max, TPM_MAX_RNG_DATA);
-	u32 rlength;
-	int err, total = 0, retries = 5;
-	u8 *dest = out;
+	struct tpm_buf buf;
+	u32 total = 0;
+	int retries = 5;
+	u32 recd;
+	int rc;
 
-	if (!out || !num_bytes || max > TPM_MAX_RNG_DATA)
-		return -EINVAL;
+	rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_GET_RANDOM);
+	if (rc)
+		return rc;
 
 	do {
-		tpm_cmd.header.in = tpm_getrandom_header;
-		tpm_cmd.params.getrandom_in.num_bytes = cpu_to_be32(num_bytes);
-
-		err = tpm_transmit_cmd(chip, NULL, &tpm_cmd,
-				       TPM_GETRANDOM_RESULT_SIZE + num_bytes,
-				       offsetof(struct tpm_getrandom_out,
-						rng_data),
-				       0, "attempting get random");
-		if (err)
-			break;
+		tpm_buf_append_u32(&buf, num_bytes);
 
-		recd = be32_to_cpu(tpm_cmd.params.getrandom_out.rng_data_len);
+		rc = tpm_transmit_cmd(chip, NULL, buf.data, PAGE_SIZE,
+				      sizeof(out->rng_data_len), 0,
+				      "attempting get random");
+		if (rc)
+			goto out;
+
+		out = (struct tpm1_get_random_out *)&buf.data[TPM_HEADER_SIZE];
+
+		recd = be32_to_cpu(out->rng_data_len);
 		if (recd > num_bytes) {
-			total = -EFAULT;
-			break;
+			rc = -EFAULT;
+			goto out;
 		}
 
-		rlength = be32_to_cpu(tpm_cmd.header.out.length);
-		if (rlength < TPM_HEADER_SIZE +
-			      offsetof(struct tpm_getrandom_out, rng_data) +
-			      recd) {
-			total = -EFAULT;
-			break;
+		if (tpm_buf_length(&buf) < TPM_HEADER_SIZE +
+					   sizeof(out->rng_data_len) + recd) {
+			rc = -EFAULT;
+			goto out;
 		}
-		memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
+		memcpy(dest, out->rng_data, recd);
 
 		dest += recd;
 		total += recd;
 		num_bytes -= recd;
-	} while (retries-- && (size_t)total < max);
 
-	return total ? total : -EIO;
+		tpm_buf_reset(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_GET_RANDOM);
+	} while (retries-- && total < max);
+
+	rc = total ? (int)total : -EIO;
+out:
+	tpm_buf_destroy(&buf);
+	return rc;
 }
 
 #define TPM_ORDINAL_PCRREAD 21