Messages in this thread | | | Subject | Re: [PATCH RFC 00/24] userfaultfd: write protection support | From | David Hildenbrand <> | Date | Tue, 22 Jan 2019 09:59:34 +0100 |
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On 22.01.19 04:18, Peter Xu wrote: > On Mon, Jan 21, 2019 at 03:33:21PM +0100, David Hildenbrand wrote: > > [...] > >> Does this series fix the "false positives" case I experienced on early >> prototypes of uffd-wp? (getting notified about a write access although >> it was not a write access?) > > Hi, David, > > Yes it should solve it.
Terrific, as my use case for uffd-wp really rely on not having false positives these are good news :)
... however it will take a while until I actually have time to look back into it (too much stuff on my table).
Just for reference (we talked about this offline once):
My plan is to use this for virtio-mem in QEMU. Memory that a virtio-mem device provides to a guest can either be plugged or unplugged. When unplugging, memory will be MADVISE_DONTNEED'ed and uffd-wp'ed. The guest can still read memory (e.g. for dumping) but writing to it is considered bad (as the guest could this way consume more memory as intended). So I can detect malicious guests without too much overhead this way.
False positives would mean that I would detect guests as malicious although they are not. So it really would be harmful.
Thanks!
> > The early prototype in Andrea's tree hasn't yet applied the new > PTE/swap bits for uffd-wp hence it was not able to avoid those fause > positives. This series has applied all those ideas (which actually > come from Andrea as well) so the protection information will be > persisent per PTE rather than per VMA and it will be kept even through > swapping and page migrations. > > Thanks, >
--
Thanks,
David / dhildenb
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