[PATCH v6 06/12] tpm-buf: add tpm_buf_parameters()

[James Bottomley <James.Bottomley@HansenPartnership.com>]

Introducing encryption sessions changes where the return parameters
are located in the buffer because if a return session is present
they're 4 bytes beyond the header with those 4 bytes showing the
parameter length.  If there is no return session, then they're in the
usual place immediately after the header.  The tpm_buf_parameters()
encapsulates this calculation and should be used everywhere
&buf.data[TPM_HEADER_SIZE] is used now

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 drivers/char/tpm/tpm-buf.c | 10 ++++++++++
 drivers/char/tpm/tpm.h     |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index f56350123a08..a5d793d8180d 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -190,3 +190,13 @@ u32 tpm_get_inc_u32(const u8 **ptr)
 	return val;
 }
 EXPORT_SYMBOL_GPL(tpm_get_inc_u32);
+
+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];
+}
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index ebead8e4c3fe..c88eee6376e4 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -311,6 +311,8 @@ u8 tpm_get_inc_u8(const u8 **ptr);
 u16 tpm_get_inc_u16(const u8 **ptr);
 u32 tpm_get_inc_u32(const u8 **ptr);
 
+u8 *tpm_buf_parameters(struct tpm_buf *buf);
+
 /* opaque structure, holds auth session parameters like the session key */
 struct tpm2_auth;
 
-- 
2.16.4