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SubjectRe: There is a null-ptr-deref bug in kvm_dirty_ring_get in virt/kvm/dirty_ring.c
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On 11/17/21 10:46, Woodhouse, David wrote:
>> The remaining
>> option would be just "do not mark the page as dirty if the ring buffer
>> is active". This is feasible because userspace itself has passed the
>> shared info gfn; but again, it's ugly...
> I think I am coming to quite like that 'remaining option' as long as we
> rephrase it as follows:
>
> KVM does not mark the shared_info page as dirty, and userspace is
> expected to*assume* that it is dirty at all times. It's used for
> delivering event channel interrupts and the overhead of marking it
> dirty each time is just pointless.

For the case of dirty-bitmap, one solution could be to only set a bool
and actually mark the page dirty lazily, at the time of
KVM_GET_DIRTY_LOG. For dirty-ring, I agree that it's easiest if
userspace just "knows" the page is dirty.

Paolo

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