Re: (pv)?grub and PVHv2

[George Dunlap <dunlapg@umich.edu>]

On Mon, Jun 5, 2017 at 1:08 PM, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
> On 05/06/17 11:55, George Dunlap wrote:
>> On Fri, Jun 2, 2017 at 10:58 AM, Roger Pau Monné <roger.pau@citrix.com> wrote:
>>> On Fri, Jun 02, 2017 at 11:33:50AM +0200, Marek Marczykowski-Górecki wrote:
>>>> Hi,
>>>>
>>>> Is there any method to boot PVHv2 domain using a kernel fetched from
>>>> that domain's disk image, _without_ mounting it in dom0? Something like
>>>> pvgrub was for PV.
>>> Hello,
>>>
>>> Anthony (Cced) is working on an OVMF port, so it can be used as
>>> firmware for PVHv2 guests.
>> I think in theory it shouldn't be too hard to port the pvgrub2 code to
>> boot into PVH, since it already boots in PV, right?
>>
>> Is this something we should try to encourage, or do you think it would
>> be better to route everyone through EFI?
>
> Even a PVH pvgrub still suffers the a priori problem which makes booting
> PV guests extremely difficult.  You don't know ahead-of-time which
> bootloader the guest is using without peering at its disks, which opens
> a massive attack surface in dom0.
>
> Using things like EFI allows any compatible OS to function, not just
> ones which use grub.

I wasn't suggesting loading the grub bootloader off the disk image; I
was suggesting using a fixed pvgrub supplied by the host.  That's what
happens for PV guests using pvgrub at the moment.

Using pvgrub allows any grub-compatible OS to function; using EFI
allows any EFI-compatible OS to function.  There are many which would
be one but not the other.  (But I suppose, there would not be many
that were both PVH compatible and not EFI compatible.)

 -George

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