Bottomley: Owning your Windows 8 UEFI Platform [LWN.net]

Bottomley: Owning your Windows 8 UEFI Platform

Posted Feb 25, 2013 20:33 UTC (Mon) by etienne (guest, #25256)
In reply to: Bottomley: Owning your Windows 8 UEFI Platform by nix
Parent article: Bottomley: Owning your Windows 8 UEFI Platform

Are all EFI PC able to run the EFI stack, init the memory and processor, and reboot to BIOS if they detect the user wants to boot the BIOS way (for instance to run an El-Torito CDROM), or are they loading the EFI stack and try to simulate a real mode BIOS - and then good luck if you try to run memtester which would overwrite the EFI code.

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Bottomley: Owning your Windows 8 UEFI Platform

Posted Feb 25, 2013 21:26 UTC (Mon) by khim (subscriber, #9252) [Link]

Are all EFI PC able to run the EFI stack, init the memory and processor, and reboot to BIOS if they detect the user wants to boot the BIOS way (for instance to run an El-Torito CDROM), or are they loading the EFI stack and try to simulate a real mode BIOS

Usually it's a combination: they start as EFI and then at some point switch to old real mode BIOS+SMM code mix.

And then good luck if you try to run memtester which would overwrite the EFI code.

YMMV: some will survive memtester (if they keep the important bits hidden away in SMM), some may crash — especially when USB is involved (the first example Google found).