Attest: Handle discrepancy in tlv_len definitions
The definition of the 'tlv_len' field in the shared boot data entry
header differs in upstream MCUboot repo and in its TF-M fork.
In the upstream repo the 'tlv_len' only covers the length of the payload
but not the size of the entry header. But in the TF-M fork the 'tlv_len'
covers the size of entry header and payload together. This discrepancy
is distinguished during the shared boot data processing based on which
MCUboot version is used along with TF-M runtime.
Change-Id: I0cc4b2a2e6c53d125514b1da7e44be474abdd9e4
Signed-off-by: David Vincze <david.vincze@linaro.org>
diff --git a/docs/reference/services/tfm_attestation_integration_guide.rst b/docs/reference/services/tfm_attestation_integration_guide.rst
index d3457cd..5d29861 100644
--- a/docs/reference/services/tfm_attestation_integration_guide.rst
+++ b/docs/reference/services/tfm_attestation_integration_guide.rst
@@ -356,8 +356,21 @@
entry header structure: ``struct shared_data_tlv_entry`` and the data. In
the entry header is a type field ``tlv_type`` which identify the consumer of
the entry in the runtime software and specify the subtype of that data item.
- There is a size field ``tlv_len`` which covers the size of the entry header
- and the data. After this structure comes the actual data.
+
+ .. Note::
+
+ There is a size field ``tlv_len`` which has different definitions in the
+ upstream MCUboot repository and in its TF-M forked version:
+
+ - Upstream MCUboot: Covers only the length of data but not the header
+ size.
+ - TF-M MCUboot: Covers the size of the entry header and the data
+ together.
+
+ This difference is handled by TF-M code based on which bootloader is used
+ along with TF-M runtime.
+
+ After the entry header structure comes the actual data.
.. code-block:: c