Cannot update bios on Asus CN60 Panther

I’ve been running Linux on an Asus CN60 (Panther) chromebox with the RW_Legacy firmware for years with no issues. I want to update to use UEFI, but have been unsuccessful. Running the firmware-util script gives the following:

Downloading supporting files...

Downloading required tools...

Getting device/system info...

Flashrom is unable to read current firmware; cannot continue:

flashrom MrChromebox-v1.5.0 (git:v1.5.0-5-g255f289445) on Linux 6.1.0-31-amd64 (x86_64)
flashrom is free software, get the source code at https://flashrom.org

coreboot table found at 0x7f757000.
Found chipset "Intel Lynx Point LP Mainstream".
This chipset is marked as untested. If you are using an up-to-date version
of flashrom *and* were (not) able to successfully update your firmware with it,
then please email a report to [email protected] including a verbose (-V) log.
Thank you!
Enabling flash write... Error accessing ICH RCRB, 0x4000 bytes at 0x00000000fed1c000
/dev/mem mmap failed: Operation not permitted
FAILED!
FATAL ERROR!
Error: Programmer initialization failed.

You may need to add 'iomem=relaxed' to your kernel parameters,
or trying running from a Live USB with a more permissive kernel (eg, Ubuntu 23.04+).

If you have UEFI SecureBoot enabled, you need to disable it to run the script/update your firmware.

Secureboot is not enabled. I’m running Debian Bookworm, stable. I’ve also tried running the Debian live DVD, same issue.

Well, it was somewhat unpleasant, but I think I got it updated. I had to do a full install of Ubuntu, which I don’t like. The live version wouldn’t do it. At least it said finished, and it rebooted. Now to purge Ubuntu…

Debian locks down the kernel so that the firmware can’t be read/written.

Ubuntu live works perfectly fine for flashing, I use it for that all of the time