CONFIG_DISABLE_FLASH_PATCH purpose

[robsrick]

Hi

I see i get a cmake warning with DFU enabled with the following message:

      ----------------------------------------------------------
      --- WARNING: To maintain the integrity of secure boot, ---
      --- enable CONFIG_DISABLE_FLASH_PATCH in production.   ---
      ----------------------------------------------------------

whats the purpose of this? should i just have it always enabled in my conf, or for prod only?

it seems to include https://github.com/NordicPlayground/nRF52-flash-patch/blob/master/example/flash_patch.c 

[Priyanka]

Hi,

The CONFIG_DIABLE_FLASH_PATCH is used in order to work with CONFIG_HW_UNIQUE_KEY_LOAD.

Please take a look at this: https://github.com/LairdCP/sdk-nrf/commit/9a9d1a5c4f5483a7c55b259df69346b702987238 

Best Regards,

Priyanka

[robsrick]

thanks. I saw even when CONFIG_DISABLE_FLASH_PATCH=y I still get this cmake warning? is this intended?

[Priyanka]

Well, the warning should go away if you have enabled it. So could be a config issue. Could you maybe check the .config in your build folder to see if the flash patch is actually enabled?

Because you can see here that in order for the warning to happen, FLASH_PATCH_WARN must be enabled.

-Priyanka

[robsrick]

I can see that the line 'CONFIG_DISABLE_FLASH_PATCH=y' is included in build/zephyr/.config but FLASH_PATCH_WARN /CONFIG_FLASH_PATCH_WARN is not mentioned at all in there. Just did a pristine build to confirm and i definitely see the warning.

[Priyanka]

Could you share your build folder as a zip file here?

[robsrick]

attached0878.build.zip

[Priyanka]

Hi,

Is it a multi-image build? If so, then the warning might be for another image or core. Not for the one that you have actually disabled it.

[robsrick]

I've got DFU enabled via the following configuration so i assume it is multi-image but I don't believe I control the other images?

# DFU Features

## MCUMGR

CONFIG_ZCBOR=y

CONFIG_MCUMGR=y

CONFIG_MCUMGR_CMD_IMG_MGMT=y

CONFIG_MCUMGR_CMD_OS_MGMT=y

CONFIG_DISABLE_FLASH_PATCH=y

# Ensure an MCUboot-compatible binary is generated.

CONFIG_BOOTLOADER_MCUBOOT=y

## Enable the Bluetooth (unauthenticated) and shell mcumgr transports.

CONFIG_MCUMGR_SMP_BT=y

CONFIG_MCUMGR_SMP_BT_AUTHEN=n

## Some command handlers require a large stack.

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=4096

[Priyanka]

Well, it is not required to add flash patch code to each of your images. This code flash_patch.c checks whether the flash_patch is disabled in the UICR and then disables it, if not already done. This is persistent until the next full chip erase. So maybe you can try doing something to suppress the warning in your code, but it's totally up to you. And as long as it doesn't interfere with your working, then I guess it's okay? 

You can see the conditions where you get warnings in the link I had mentioned in the earlier comments:

-Priyanka