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Date: Mon, 23 Nov 2009 13:17:26 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios
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To: Kevin O'Connor <kevin@koconnor.net>
Cc: qemu-devel@nongnu.org, Sebastian Herbszt <herbszt@gmx.de>

On Sun, Nov 22, 2009 at 12:40:24PM -0500, Kevin O'Connor wrote:
> On Sun, Nov 22, 2009 at 05:38:09PM +0200, Gleb Natapov wrote:
> > On Sun, Nov 22, 2009 at 04:31:24PM +0100, Sebastian Herbszt wrote:
> > >    // Write protect bios memory.
> > >    make_bios_readonly();
> > Hmmm. How is tpr patching works then? It relies on ability of a guest to
> > write into BIOS memory region. Need to retest if it actually works I
> > guess.
> 
> The last time I looked, the TPR patching backend forced the "vapic"
> pages to be writable (effectively overriding the bios decision to make
> it readonly).
> 
Don't see where it does this. But now I recall that KVM doesn't support
ROM slots, so BIOS area is always writable under KVM.

> > > Bad things could happen if someone modifies the BIOS because it's unprotected
> > > (e.g. VM crash).
> 
> I'm not sure why modification of the BIOS would cause a VM crash.  If
> this is true, then a malicious guest could unlock the ram and write to
> it for the same effect.
> 
> -Kevin

--
			Gleb.