On 4/3/23 17:39, James Bottomley wrote:
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@xxxxxxxxxxxxxxxxxxxxx>
---
v4: add kdoc
---
drivers/char/tpm/tpm-buf.c | 27 +++++++++++++++++++++++++++
include/linux/tpm.h | 2 ++
2 files changed, 29 insertions(+)
diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index da0f6e725c3f..d107321bcdff 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -277,3 +277,30 @@ u32 tpm_get_inc_u32(const u8 **ptr)
return val;
}
EXPORT_SYMBOL_GPL(tpm_get_inc_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 parameters area of the tpm_buf
in a TPM response
+ * @buf: tpm_buf to use
+ *
+ * Where the parameters are located depends on the tag of a TPM
+ * command. Evaluate this and return a pointer to the first byte of
+ * the parameters area.
I would also describe here what the non-obvious 4 bytes are that you are skipping over in case of TPM2_ST_SESSIONS.
With this:
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
+ *
+ * @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];
+}
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 845eadfed715..d2fea2afd37c 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -340,6 +340,8 @@ 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);
+
/*
* Check if TPM device is in the firmware upgrade mode.
*/
