tpm: Open code tpm_buf_parameters()

With only single call site, this makes no sense (slipped out of the
radar during the review). Open code and document the action directly
to the site, to make it more readable.

Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()")
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/char/tpm/tpm-buf.c

···
 }
 EXPORT_SYMBOL_GPL(tpm_buf_read_u32);
 
-static u16 tpm_buf_tag(struct tpm_buf *buf)
-{
-	struct tpm_header *head = (struct tpm_header *)buf->data;
 
-	return be16_to_cpu(head->tag);
-}
-
-/**
- * tpm_buf_parameters - return the TPM response parameters area of the tpm_buf
- * @buf: tpm_buf to use
- *
- * Where the parameters are located depends on the tag of a TPM
- * command (it's immediately after the header for TPM_ST_NO_SESSIONS
- * or 4 bytes after for TPM_ST_SESSIONS). Evaluate this and return a
- * pointer to the first byte of the parameters area.
- *
- * @return: pointer to parameters area
- */
-u8 *tpm_buf_parameters(struct tpm_buf *buf)
-{
-	int offset = TPM_HEADER_SIZE;
-
-	if (tpm_buf_tag(buf) == TPM2_ST_SESSIONS)
-		offset += 4;
-
-	return &buf->data[offset];
-}

drivers/char/tpm/tpm2-cmd.c

···
 int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
 {
 	struct tpm2_get_random_out *out;
+	struct tpm_header *head;
 	struct tpm_buf buf;
 	u32 recd;
 	u32 num_bytes = max;
···
 	int total = 0;
 	int retries = 5;
 	u8 *dest_ptr = dest;
+	off_t offset;
 
 	if (!num_bytes || max > TPM_MAX_RNG_DATA)
 		return -EINVAL;
···
 			goto out;
 		}
 
-		out = (struct tpm2_get_random_out *)tpm_buf_parameters(&buf);
+		head = (struct tpm_header *)buf.data;
+		offset = TPM_HEADER_SIZE;
+		/* Skip the parameter size field: */
+		if (be16_to_cpu(head->tag) == TPM2_ST_SESSIONS)
+			offset += 4;
+
+		out = (struct tpm2_get_random_out *)&buf.data[offset];
 		recd = min_t(u32, be16_to_cpu(out->size), num_bytes);
 		if (tpm_buf_length(&buf) <
 		    TPM_HEADER_SIZE +

include/linux/tpm.h

···
 u16 tpm_buf_read_u16(struct tpm_buf *buf, off_t *offset);
 u32 tpm_buf_read_u32(struct tpm_buf *buf, off_t *offset);
 
-u8 *tpm_buf_parameters(struct tpm_buf *buf);
-
 /*
  * Check if TPM device is in the firmware upgrade mode.
  */