Re: [PATCH v2] hw/i386: place setup_data at fixed place in memory

[Jason A. Donenfeld]

Hey Gerd,

On Tue, Aug 16, 2022 at 10:55:11AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > > We can make setup_data chaining work with OVMF, but the whole chain
> > > should be located in a GPA range that OVMF dictates.
> > 
> > It sounds like what you describe is pretty OVMF-specific though,
> > right? Do we want to tie things together so tightly like that?
> > 
> > Given we only need 48 bytes or so, isn't there a more subtle place we
> > could just throw this in ram that doesn't need such complex
> > coordination?
> 
> Joining the party late (and still catching up the thread).  Given we
> don't need that anyway with EFI, only with legacy BIOS:  Can't that just
> be a protocol between qemu and pc-bios/optionrom/*boot*.S on how to pass
> those 48 bytes random seed?

Actually, I want this to work with EFI, very much so.

If our objective was to just not break EFI, the solution would be
simple: in the kernel we can have EFISTUB ignore the setup_data field
from the image, and then bump the boot header protocol number. If QEMU
sees the boot protocol number is below this one, then it won't set
setup_data. Done, fixed.

Except I think there's value in passing seeds even through with EFI.

Your option ROM idea is interesting; somebody mentioned that elsewhere
too I think. I'm wondering, though: do option ROMs still run when
EFI/OVMF is being used?

Jason