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

[Laszlo Ersek]

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

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