MCUBOOT

RE: MCUBOOT

Einar Thorsrud — Thu, 08 Aug 2024 15:15:03 GMT

Hi,

I would not recomend this approach, but theoretically you could modfiy the version and security counter in some cases in a semi-safe way by writing to the image trailer without erasing. That would only let you flip bits from 1 to 0.

But why do you want to do this? If. you really need to downgrade while using downgrade protection, a possibility could be to build another variant of the old firmware with a higher version number. So that it is a higher version seen from the bootloader, but in fact is in other ways identical with the older version.

RE: MCUBOOT

YveWit — Mon, 05 Aug 2024 22:20:33 GMT

Hi Sorry for the late reply, but is it possible to modify the version number of the current image safely to allow downgrading? Creating a fork of the SDK is not really a viable option. If for example we were in the middle of modifying the version and we lost power would that essentially brick the unit as we would have no image with a valid version number a.k.a no bootable image?

RE: MCUBOOT

AHaug — Tue, 09 Jul 2024 06:34:19 GMT

This would mean that you don't remove all dependencies. The configuration is selected by something else, which you can see in the KConfig documentation: https://docs.nordicsemi.com/bundle/ncs-latest/page/kconfig/index.html#CONFIG_MCUBOOT_BOOTLOADER_NO_DOWNGRADE

You can modify the KConfigs in the SDK to make a custom fork of the SDK (disclaimer do not do this without knowing what you're doing) as an experiment to see if you're able to disable it.

Kind regards,
Andreas

RE: MCUBOOT

YveWit — Mon, 08 Jul 2024 19:17:19 GMT

When I set it to n it say that it is still set to y in build. I am not sure it is possible to actually disable it with DIRECT_XIP:

RE: MCUBOOT

AHaug — Thu, 04 Jul 2024 13:19:32 GMT

Hi,

What do you see when you set it to n and remove all dependencies?

Kind regards,
Andreas

RE: MCUBOOT

YveWit — Wed, 03 Jul 2024 14:45:34 GMT

Why Can I not enable DIRECT_XIP and just set CONFIG_MCUBOOT_BOOTLOADER_NO_DOWNGRADE to no. Why would that now work exactly?

RE: MCUBOOT

AHaug — Wed, 03 Jul 2024 08:52:47 GMT

The team says that this should be possible, but that doing so will cause you too loose out of the safetyfeatures that downgrade protection provides. Negating CONFIG_MCUBOOT_BOOTLOADER_NO_DOWNGRADE will also be quite hard due to how it's implemented.

The recommendation is to make CONFIG_MCUBOOT_BOOTLOADER_MODE_DIRECT_XIP_WITH_REVERT working with removing the selects.

Kind regards,
Andreas

RE: MCUBOOT

AHaug — Wed, 03 Jul 2024 07:13:56 GMT

Noted, thank you for elaborating.

Then the answer is unfortunately no, not currently and not without a feature request that will implement a workaround through the configuration or that you create your own custom MCUboot (which is possible) that does not select MCUBOOT_BOOTLOADER_NO_DOWNGRADE when building your project with DIRECT_XIP.

I've checked in internally w.r.t the last option to see if there is any pitfalls that I've not considered and I'll get back to you with an update when I hear back from them

Kind regards,
Andreas

RE: MCUBOOT

YveWit — Tue, 02 Jul 2024 18:52:19 GMT

We require the use of DIRECT_XIP for the boot speed. Because it does not copy over the secondary slot to the primary slot. As far as I know there is no other option that allows one to run directly from the slot that was updated. It is a requirement for our product to have the ability to update to any version. I just want to know if there is anyway to use DIRECT_XIP but disabling the version checking

RE: MCUBOOT

AHaug — Tue, 02 Jul 2024 07:28:17 GMT

Hi,

Currently this is not supported as all of the variations of CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT, i.e CONFIG_MCUBOOT_BOOTLOADER_MODE_DIRECT_XIP and CONFIG_MCUBOOT_BOOTLOADER_MODE_DIRECT_XIP_WITH_REVERT selects MCUBOOT_BOOTLOADER_NO_DOWNGRADE due it's not possible to downgrade a running application.

Could you expand a bit upon the motivation for the need of not having downgrade protection while using DIRECT_XIP? Is it an option to investigate the use of non-direct_xip with downgrade protection disabled?

Kind regards,
Andreas