Re: [Qemu-devel] [PATCH 17/21] introduce memory_region_get_address() and use it in kvm/ioapic

[Paolo Bonzini]

Il 27/04/2013 22:57, Blue Swirl ha scritto:
>> The questions are, in order of importance:
>>
>> (1) what privileges would this require in the guest?  Answer: a lot.
>>
>> (2) is this likely to happen by chance?  Answer: no, not at all.
>>
>> (3) is there a workaround?  Answer: yes, disable in-kernel irqchip.
> 
> These questions ask if there is a risk of benevolent guests performing
> these activities and I agree that the chances are close to zero.
> 
> But the interesting question is to ask if a malevolent guest can bring
> down a VM uncontrollably this way and I think it only needs a few
> elevated privileges in a guest to do this.

If you have them, isn't it simpler to just turn off the VM (using APM or
ACPI)?  Also, killing your guest is not a very interesting thing to do
once you've gotten elevated privileges. ;)

>> Simply setting IO_APIC_DEFAULT_ADDRESS is also flawed in my opinion.
>> I'm not sure the in-kernel irqchip handles correctly an overlap between
>> the IOAPIC and LAPIC regions, maybe an abort is predictable after all.
> 
> At least the guest needs to be stopped. Perhaps we should have a
> common function which does this and logs the guest error so we can
> start replacing calls to abort() with it.

Yes, that's a good idea.  We can reuse the internal error runstate for that.

Paolo