Re: [Xen-devel] [PATCH] hvmloader / qemu-xen: Getting rid of resource conflict for OpRegion.

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

>> >> More importantly I am pointing out that if
>> >> you are trying to find out information like the location/size/layout
>> of
>> >> the IGD OpRegion, you can get that information from the host BIOS.
>> That
>> >> sounded like what your original issues centered around. Sorry if I
>> >> confused things.
>> >
>>
>> Ross, your help is highly appreciated. I think it's not you that
>> confused things.
>> The problem comes from my side, I'm far from familiar with all these
>> ACPI / BIOS related stuff.
>> I dumped && disassembled the ACPI table. But have no idea how to read
>> the output...
>> I attached the DSDT.dsl dumped from my system, in case you would like
>> to take a quick check.
>>

>> Just one more question -- is the layout specific to the bios, or common?
>> I wonder how can we judge the security risk if the layout is not
>> constant.
>
> I would say the layout of the IGD stuff is common per the Intel spec for it 
> and the OEMs have to follow that spec when writing the BIOS. But it could 
> change for newer hardware (with a new rev of the spec for example that 
> extended the IGD functionality).

I understand that the layout within OpRegion  is defined by the spec
and should be common.
But I don't see any words (may be I missed something) about the layout
of the outside world (e.g. what region is adjacent to OpRegion?).
So my question is actually can we expect a constant layout with regard
to OpRegion's neighbors?

My impression from Ian's feedback is that the patch cannot be accepted
before the concern being resolved.
(Let alone the existing code in the tree has already open a hole
(first 18 bytes in my example))
And you mentioned that such info can be obtained from my host bios.
I've dumped the ACPI table from my host system and had it disassembled by iasl.
But I lack of the knowledge to interpret the content.
Could you lend me a hand in case that's a trivial task for you?
You can find the DSDT.dsl file attached in my previous mail (@2012-12-23).

If you don't have time to help, could you point me to a proper spec /
documentation to start with?

Thanks,
Timothy

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