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by monocasa 2956 days ago
OK, neat, it looks like they haven't changed it in eons. It's PCI device 00:1f.5 and is documented in all of the PCH docs (so Vol 1 for overview, Vol 2 for registers). Sometimes it's disabled by firmware as a sort of 'security' mechanism.

Yeah, there's not a whole lot there in the docs, but it's PIO SPI that handles most of the flash addressing for you, so it's not the most complex thing in the world to begin with. More "fill the buffer and go" sort of deal.
2 comments
amluto 2956 days ago
But, if your firmware cares about preventing flashable rootkits, then these registers should be locked such that you can only flash from SMM or during initial boot. The fact that AFUEFI works at all on a System76 laptop is a bad sign IMO.
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jackpot51 2956 days ago
It absolutely is locked, and needs to be unlocked and flashed while in EFI mode.
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amluto 2956 days ago
What do you mean “in EFI mode”? Do you mean EFI Boot Services or something else? I’m trying to understand what makes AFUEFI special that causes it to be able to write the SPI flash when regular software can’t. If I understand your blog post right, AFUEFI run like any other .efi program, which seems insufficiently locked down to me.
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jackpot51 2956 days ago
That is good to know. We will also need to unlock the flash descriptor, which is more proprietary code to reverse engineer.
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monocasa 2956 days ago
For just doing updates, you shouldn't have to (or be able to) touch the flash descriptor, AFAIK. It's fixed at manufacturing time (without touching the flash with an external programmer of course).
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