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Restoring EFI Boot Variables Externally
#1
I have a Wyse Z90 thin-client that I wanted to re-purpose as a router with OpenWRT (which had to be manually installed with the router. For some possibly stupid reason that escaped my mind, I set the boot options except PXE to inactive. Upon reboot, PXE was the only option on the boot list.

I removed the CMOS battery, hopint that it would clear the changes I made. It would seem the variables are stored in some persistent memory as they are still there.

Is is possible to edit the variables on the bin file backups? I've found 2 SPI chips and have backed up their contents with Flashrom on my Linux install.

Any help would be greatly appreciated.
Thanks.


Attached Files
.bin   bios.bin (Size: 2 MB / Downloads: 3)
.bin   otherspichip.bin (Size: 64 KB / Downloads: 0)
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#2
Lightbulb 
I found out a way around this, using Flashrom and UEFItool on Linux.

I located the 2nd_Gen_Compatibility_Kit(WES2009).zip file for my device. It contained 2 bios files with an exe suffix (they can be opened with archive software). The bios bin file is inside that executable's folders, with AZA0_ at the beginning, and is compressed with the gzip format - putting .gz at the end of the filename should ensure you can decompress with an archiver.

I dumped the bios from the chip and opened it up with UEFItool. The GUID beginning with FFF is where the boot variables are, and has to be replaced with the same GUID from the bios file extracted from the archives. I don't think I could flash the extracted bin file due to it being bigger than the size of the chip and the file structure in UEFItool seemed very different from the original.

I flashed the modified dump file to the chip and fired up the computer, and it now shows all the boot devices in the setup. I have yet to boot into the OS yet, but it all seems to have been rectified.


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.zip   2nd_Gen_Compatibility_Kit(WES2009).zip (Size: 3.34 MB / Downloads: 5)
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