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SubjectRe: [tip:x86/setup] x86, setup: "glove box" BIOS calls -- infrastructure
Ingo Molnar wrote:
> * Avi Kivity <avi@redhat.com> wrote:
>
>
>> Ingo Molnar wrote:
>>
>>>> Sure, go ahead and wrap them in some kind of "save and restore all
>>>> registers" wrapping, but nothing fancier than that. It would just be
>>>> overkill, and likely to break more than it fixes.
>>>>
>>>>
>>> Yeah. I only brought up the virtualization thing as a
>>> hypothetical: "if" corrupting the main OS ever became a
>>> widespread problem. Then i made the argument that this is
>>> unlikely to happen, because Windows will be affected by it just
>>> as much. (while register state corruptions might go unnoticed
>>> much more easily, just via the random call-environment clobbering
>>> of registers by Windows itself.)
>>>
>>> The only case where i could see virtualization to be useful is
>>> the low memory RAM corruption pattern that some people have
>>> observed.
>>>
>> You could easily check that by checksumming pages (or actually
>> copying them to high memory) before the call, and verifying after
>> the call.
>>
>
> Yes, we could do memory checks, and ... hey, we already do that:
>
> bb577f9: x86: add periodic corruption check
> 5394f80: x86: check for and defend against BIOS memory corruption
>
> ... and i seem to be the one who implemented it! ;-)
>
> That check resulted in logs showing the BIOS corrupting Linux memory
> across s2ram cycles or HDMI plug/unplug events on certain boxes (are
> Hollywood rootkits in the BIOS now?), and resulted in some
> head-scratching but not much more.
>

Then there's definitely no point in putting it into a container, is
there? I mean, we could track down the exact instruction which caused
the corruption, but how would it help us?

>> I don't think the effort is worth the benefit in this case, but
>> there actually is an interesting use case for this. SMM is known
>> to be harmful to deterministic replay games and to real time
>> response. If we can virtualize SMM, we can increase the range of
>> hardware on which the real time kernel is able to deliver real
>> time guarantees.
>>
>
> Hey, i do have a real sweet spot for deterministic execution - but
> SMM, while not problem-free (like most of firmware), also has a very
> real role in not letting various hardware melt. So SMM should be
> thought of as a flexible extended arm of hardware - not some sw bit.
>
> So i think that the memory of that SMM virtualization chapter you've
> almost read should be quickly erased from your mind. (Via forceful
> means if prompt corrective self-action is not forthcoming.)
>

I'll keep my remaining neurons, thanks.


--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.



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