MCUBoot partition manager flash signature validation

[Andrew Sanders]

Hello all, I am following up on a related issue regarding mcuboots partitioning and image validation. (link to previous MCUBoot QA forum). I have devices out in the field that i would like to update and change the partition formatting to include a settings section in NVM. We previously discovered and confirmed that MCUboot uses SHA to validate an image. How ours got stuck is that the image initially starts as all 0xFF in the settings partition, matching the needed padding for the image validation. When we saved settings it "corrupted" the image, essentially locking the image in slot one due to verification errors. I have thought of a few ways to work around this issue (resetting the settings partition to all 0xFF before dfu, JTAG only), but all current solutions are complex and situational.

Question: Hoping to get insight into the MCUBoot process to understand paths to introduce features that modify partitions without breaking the DFU process. Restraints are that devices cannot come out of the field to be JTAG'd.

[Turbo J]

You might want to post your partitions.yml or pm_static.yml file here: The settings or storage partition should never be part of any code partition that mcuboot cares about.

Note that fixing this problem may require usage of the SWD debugger. I don't see how one could fix this in the field unless you opted for one of the "mutable" bootloader setups.

[Vidar Berg]

Hello,

As Turbo J  pointed out, the settings partition must not be placed within the MCUboot slot, and if MCUboot is immutable, it is not possible to change the size of these slots. However, from the thread you linked, it appears that you may have some free space in your external flash. Would it be an option to place your storage partition there without changing the secondary slot?

Best regards,

Vidar