ASUS CM3401 Chromebook Plus / FrostFlow UEFI Unbootable

Apparently things changed in 2023, and I followed Read-only firmware unlock on 2023+ devices to unlock the WP bit of the system.

Using the firmware-util.sh script, I was able to flash the UEFI full firmware, and it reported success. However, I went and did a reboot (not shutdown) from ChromeOS. After that reboot, I let it sit for 3-5 minutes, and nothing ever appreared on the screen.

I force powered it down, and retired and nothing.

I have one of these: GSC Debug Board (aka "Chromebook Debug Cable" / "SuzyQ", for Cr50 / Ti50) | eBay on order, so I’m hoping the closed case debugging will at least allow me to restore the stock firmware (which produced a 16MB backup file) and figure out what went wrong.

The only thing I can think of is even after following the instructions in the Google docs, the utility asked about unlocking something else and said if you were going to do the UEFI firmware to do that, so I said yes. However, now I’m wondering if that was the correct course of action, as I thought I already did everything needed beforehand.

Any thoughts or things to try?

-Matt

There’s a chance that it was a general brick unrelated to the new security feature. A SuzyQ is needed to debug this further.

Ok, I’d love some suggested things to do / run once I get the cable to help debug this before I attempt to restore the firmware.

-Matt

I’d have to check on my device, but there may be logs about the new RO verification failing or something. Coreboot itself doesn’t output any logs by default though, so not much we can debug with that other than flashing it again. If that fails, you can flash a custom build that does output to the serial console.

That’s interesting. No errors listed, all green text when I did the flash.

I’ve seen a few people have issues flashing this model. Not really sure why though.

Maybe the docs should show a warning not to flash firmware on this model until the issue is fixed.

Using a chip programmer and a not-very-fun-to-use WSON8 probe (5x6mm for this model), I was able to flash enough of the chip for it to boot. I then did a flashrom verifym which failed, did firmware restore (using a modified version of the firmware-util script to not check if I was on ChromeOS), and then the verify was good.

It has been restored to factory, is in its box, and it will be returned to Best Buy this evening. Definitely not the model for me.

-Matt

I’m curious why you bought a new Chromebook from BestBuy for running Linux / Windows. If you’re buying new then are you really saving any money vs buying a laptop that can officially run Windows / Linux?

I was interested in Coreboot support, and figured this was the easiest way to get a modern platform that supported it.

-Matt

Why coreboot?

Coreboot is based.

the issue with your inital flash aside, you could have just reflashed the UEFI firmware and all would have been fine. FROSTFLOW works fantastically under Linux.

Ah. Well, in any case I overpaid for it, so it was gonna get returned anyway. I got a Chromebook 515 Plus (OMNIGUL) for $199 refurb, which is good for this experiment…I eventually want to get Heads / Qubes on it. I did get the UEFI firmware on there, and the installer booted successfuly…so now trying to get heads to build. bzImage too big is where I am at the moment…

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