Back to x86 again everyone, for responsible to curious feedback from 王御多, here's some little explain for PFAT aka. BIOS Guard.
Alright, I know some might feel it's too short for explaining the PFAT, however, it's really necessary to understand the basis of RSA first. If you do familiar with RSA, the only mist of PFAT to you is "Use HW solution to replace SMI method".
Using SMI method to verify and update BIOS package is okay in traditional way since in early days, people aren't so familiar with SMI. However, now days we have various software tools and spec. help us to catch and hijack the SMI.
So here's the PFAT (HW solution), the main idea is extremely simple, doing the verify and update in the hideout, block the interrupt and fetch the package data from HW-specified memory part. See, it's really simple so say so, PFAT is doing the exactly same thing except it's hiding in specified HW place.
Well, it's pretty nice, isn't?
However, someone just forgot a little thing about compatibility with BIOS recovery...what? how they get messed up since BIOS recovery is so conventional? Well, they did forget it. You may seem BIOS recovery as another kind BIOS update package only difference is the package itself is previously stored in BIOS ROM and it runs in PEI phase. Sounds fine...but PFAT module only runs in DXE phase....WTF?! BIOS recovery module could never pass the verify phase!
Anyway, I'm pretty sure it's just a little flaw had been fixed by now, just to share the experience that even the mighty one would make such funny issue.
Please leave me any comments or questions, I'd be thankful and response as soon as possible! Thanks!
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