lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Tue, 22 Jan 2019 09:59:34 +0100
From:   David Hildenbrand <>
To:     Peter Xu <>
        Hugh Dickins <>,
        Maya Gokhale <>,
        Jerome Glisse <>,
        Johannes Weiner <>,
        Martin Cracauer <>,
        Denis Plotnikov <>,
        Shaohua Li <>,
        Andrea Arcangeli <>,
        Pavel Emelyanov <>,
        Mike Kravetz <>,
        Marty McFadden <>,
        Mike Rapoport <>,
        Mel Gorman <>,
        "Kirill A . Shutemov" <>,
        "Dr . David Alan Gilbert" <>
Subject: Re: [PATCH RFC 00/24] userfaultfd: write protection support

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.


> 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,



David / dhildenb

Powered by blists - more mailing lists