Hi Bohdan,

It is just that the IAS doc has not been updated.
This distinction was removed from the code when we deleted the MCUboot fork from the TF-M repository (the commit hash is: e5cadb28ca650c16976bcf095d7259bc9717dbcc).
Since then the TF-M code is aligned to the TLV header definitions of upstream MCUBoot.

Thank you for spotting this in the documentation. I’ll push a patch to update it.

Best regards,
David Vincze

From: TF-M <tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Bohdan Hunko via TF-M
Sent: Thursday, 7 October, 2021 15:46
To: tf-m@lists.trustedfirmware.org; Hennadiy.Kytsun@infineon.com
Subject: [TF-M] Boot shared data TLV length

Hi everyone,

IAS docs have this note that says:

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.

I was wondering where in code is this difference handled?

When calculating next TLV entry address attest_core.c line 213 takes into account SHARED_DATA_ENTRY_HEADER_SIZE:

tlv_curr  = (*tlv_ptr) + SHARED_DATA_ENTRY_HEADER_SIZE + tlv_entry.tlv_len;

So tlv_entry.tlv_len then must cover only length of entry (without header). This way corresponds to: “Upstream MCUboot: Covers only the length of data but not the header size”

I was not able to find anything related to “TF-M MCUboot: Covers the size of the entry header and the data together”.

Is this difference handled in TF-M fork of MCUboot or is it just outdated IAS doc?

Best regards,

Bohdan Hunko

Cypress Semiconductor Ukraine

Engineer

CSUKR CSS ICW SW FW

Mobile: +38099 50 19 714
Bohdan.Hunko@infineon.com