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Re: [Qemu-devel] Stack corruption problem with SeaBIOS/gPXE under QEMU

From: Kevin O'Connor
Subject: Re: [Qemu-devel] Stack corruption problem with SeaBIOS/gPXE under QEMU
Date: Wed, 18 Nov 2009 20:07:06 -0500
User-agent: Mutt/1.5.19 (2009-01-05)

On Wed, Nov 18, 2009 at 04:22:17PM +0200, Gleb Natapov wrote:
> On Wed, Nov 18, 2009 at 08:06:26AM -0500, Kevin O'Connor wrote:
> > On Wed, Nov 18, 2009 at 11:39:49AM +0200, Gleb Natapov wrote:
> > > On Mon, Nov 16, 2009 at 09:26:20PM -0500, Kevin O'Connor wrote:
> > > > I do see an issue if SeaBIOS's reboot vector is called (eg, by using
> > > > "sendkey ctrl-alt-delete" while still in the bios) because seabios
> > > > allows gpxe to modify itself, and on a seabios only reboot the gpxe
> > > > rom isn't recopied and gpxe therefore gets confused.  However, on a
> > > > linux invoked reboot, it looks like a full machine reset occurs and
> > > > qemu recopies the gpxe rom, so that doesn't seem to be an issue.
> > > > 
> > > Do we have the same problem with tpr patching rom (vapic,bin)? It modifies
> > > itself too.
> > 
> > I don't know, but I wouldn't think so.  The issue is only if the
> > option rom init code doesn't like getting run twice.  (Gpxe allocates
> If rom modifies itself its checksum changes so SeaBIOS thinks that rom
> is invalid and does not call its init code second time. Is this correct?

An option rom that modifies itself is required to update its checksum
before returning to the bios.

If the vapic is modified without updating the checksum then SeaBIOS
wont execute its init vector.  I'm guessing that isn't really a
problem, though.


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