Downgrade protection works only for the app_core -image-and not for the net-core -image

[Georg]

Hallo,

we are using the nrf5340 and the ncs Version 2.6.1.

I activated the software downgrade protection as described here Downgrade protection (nordicsemi.com). 

Then I made some simultaneious FOTA updates (App-image + Net-image) by using the nRF Connect app with different versions.

What I see is that the downngrade protection works for the App-image. It is not possible to update an App-image V2.0.0. with an App-image V1.0.0.

But it is possible to downgrade the Net- image V2.0.0 with the Net-image V1.0.0

How can I activate the downgrade protection also for the net-core ?

 

Best regards,

Georg

[Amanda Hsieh]

Hi, 

Do you test the MCUBoot version by adjusting CONFIG_MCUBOOT_HW_DOWNGRADE_PREVENTION_COUNTER_VALUE?

How do you check the version number? You can check the version by 

imgtool verify build/zephyr/net_core_app_update.bin

Regards,
Amanda H.

[Georg]

Hi,

I checked the version information by looking into the header of the net_core_app update.bin file.  

Here are the configuration switches which I have added to activate the downgrade prevention:

CONFIG_BOOT_VERSION_CMP_USE_BUILD_NUMBER=y
CONFIG_MCUBOOT_DOWNGRADE_PREVENTION=y

In the build configuration I added:

-DSB_CONFIG_MCUBOOT_MODE_OVERWRITE_ONLY=y

And  there is also a VERSION file which looks like this:

Some additional information:

We are using a serial external flash to store the secondary images of the app-core and the net-core.

After making an simultaineious update by using dfu_application.zip it seems that the header ifnormation of the net_core_app_update.bin is corrupt when lokking into the memory of the nrf5340-net-core. So there is no version information any more.

When looking into the memory of the app-core the header information seems to be ok 

Best regards,

Georg

[Georg]

Hi Amanda,

thank you for your answer.

When looking in the google play store I can't find the nRF Device app.

There is a nRF Device Manager app but here I can't find the option to read out the version.

Which app do you mean?

To get different versions for the net-image I added a version string in the main program of the net-core-image like this:

After updating the device I read out the memory of the nrf5340 (with the Programmer) and check the version string like this:

What I found out during debugging is that the version of the net image get lost when MCUboot transfers the net-core-image from the secondary slot to the primary slot. The version information which is placed in the header of the net_core_app_update.bin image is not programmed into the net core (primary slot). MCUboot assumes that the version of the net-core-image is 0.0.0, this means that downgrade prevention doesn’t work.

See the function boot_read_image_header_hook_in the file nrf_hooks.c

int boot_read_image_header_hook_(int img_index, int slot, struct image_header *img_head)
{
	if (img_index == 1 && slot == 0) {
		img_head->ih_magic = IMAGE_MAGIC;
		img_head->ih_hdr_size = PM_MCUBOOT_PAD_SIZE;
		img_head->ih_load_addr = PM_MCUBOOT_PRIMARY_1_ADDRESS;
		img_head->ih_img_size = PM_CPUNET_APP_SIZE;
		img_head->ih_flags = 0;
		img_head->ih_ver.iv_major = 0;
		img_head->ih_ver.iv_minor = 0;
		img_head->ih_ver.iv_revision = 0;
		img_head->ih_ver.iv_build_num = 0;
		img_head->_pad1 = 0;
		return 0;
	}

	return BOOT_HOOK_REGULAR;
}

Best regards,

Georg

[Amanda Hsieh]

Hi, 

Sorry, it's nRF Connect Device Manager. 

Thanks for finding the root cause. I will report to the internal. 

-Amanda H.

[responsible_duck]

Hi just wanted to add that we just found the same issue so can confirm a reproducible offender. 

[Georg]

Hi,

thank you.

I hope you find a solution because we want to use this feature in our product.

Best regards,

Georg

[Amanda Hsieh]

I will update if the team has anything.