Re: [DISCUSSION] Allow ACPI default OEM ID and OEM table ID fields to be set.

[Michael S. Tsirkin]

On Thu, Nov 26, 2020 at 01:51:43PM +0100, Laszlo Ersek wrote:
> On 11/26/20 12:09, Michael S. Tsirkin wrote:
> > On Wed, Nov 25, 2020 at 09:13:22PM +0100, Antoine Damhet wrote:
> >> On Wed, Nov 25, 2020 at 11:04:55AM -0500, Michael S. Tsirkin wrote:
> >>> On Wed, Nov 25, 2020 at 01:32:51PM +0000, Richard W.M. Jones wrote:
> >>>> On Wed, Nov 25, 2020 at 02:27:11PM +0100, Antoine Damhet wrote:
> >>>>> Hello,
> >>>>>
> >>>>> We recently found out that some softwares are effectively crashing
> >>>>> when they detect qemu's `OEM ID` or `OEM table ID` in the ACPI tables.
> >>>>>
> >>>>> I see no reason not to expose the setting to the user/command-line. A
> >>>>> previous patch has been submitted in 2015[1] but did not get through
> >>>>> because (if I understand correctly) using the IDs on the `SLIC`, `BXPC`
> >>>>> and `RSDT` tables were enough at the time.
> >>>>>
> >>>>> If you agree, I am willing to forward port the patches of M. Jones but I
> >>>>> need to ask how it would work `Signed-Off`-wise ?
> >>>>
> >>>> On this point, the patch I sent was actually written by
> >>>> Michael Tokarev, I was only trying to get them upstream.
> >>>>
> >>>> Rich.
> >>>
> >>> I think at least one of the issues is that e.g. UEFI at least
> >>> seems to assume unique OEM table IDs e.g. for SSDTs.
> >>>
> >>> So let's try to be more specific please, which software
> >>> crashes, what does it want to see and in which table.
> >>
> >> I'm sorry I cannot give you the name of the crashing software due to a
> >> company policy. But I can tell you that if either `BOCHS ` or `BXPC` is
> >> present in any of the tables it will crash. Any (or at least the few
> >> that I threw at it) other string will work so it seems it's some kind
> >> of DRM-related hypervisor detection.
> > 
> > Hmm I'm not sure how far we want to go with this. If software vendors
> > want to detect a hypervisor there will always be a way.
> > How are we sure we are not starting an arms race here?
> > 
> > Also which of the IDs matter?  OEMID? OEM Table ID? Creator ID?
> > 
> > 
> >> As for the uniqueness of the table IDs, I guess it would be sane to keep
> >> the same pattern (id+table sig) but allowing the first 4 bytes to be
> >> overridden.
> >>
> >> [...]
> > 
> > It's certainly possible, it's just very specific to just this DRM scheme.
> > Not sure what's a better way to do it:
> >   qemu -acpidefault oem_id=ABCD,oem_table_id=EFGHIJKL
> > is probably going too far since then table IDs are not unique.
> > 
> > Also I'd probably use machine properties for this, the need here
> > is baroque enough that we don't want a dedicated option.
> 
> Minimally, I dislike the partial overlap with the existent "-acpitable"
> switch.
> 
> Thanks
> Laszlo

Well the existing -acpitable is very powerful and easy to break guests
with, it can not really be fully supported.

> > 
> >>
> >> -- 
> >> Antoine 'xdbob' Damhet
> >