[libvirt] Do different Virgil3D users running have the same CANVAS fingerprint?

Martin Kletzander mkletzan at redhat.com
Mon Jan 9 10:17:28 UTC 2017

On Sun, Jan 08, 2017 at 07:17:07PM +0100, bancfc at openmailbox.org wrote:
>On 2016-12-27 04:05, bancfc at openmailbox.org wrote:
>> Background:
>> Canvas fingerprinting is a technique to track users based on their
>> GPUs. https://en.wikipedia.org/wiki/Canvas_fingerprinting
>> Someone did some testing and the good news is the fingerprint is
>> common for all users of the same OS across all KVM users because it
>> presents the same virtual GPU/drivers for everybody.
>> What I need your help to find out is whether this holds for Virgil3D
>> users that enable graphics acceleration. (I am running on Debian and
>> the libvirt version in the repos is too old to have this included also

$ ./configure && make && make install # O:-)

>> I don't have multiple machines)

Oh, not even nested VMs won't hep here :(

>> To test this you need:
>> To run plain FireFox on a virtualized distro (with GL acceleration
>> enabled in libvirt) of your choice and visit
>> https://browserleaks.com/canvas . Then repeat the same steps with that
>> same distro (in a VM) on another physical machine and compare values.
>> A good result is if you see the same numbers for both machines. That
>> means the virtual device  fingerprint is uniform for all virtual
>> users.
>Bumping. I realized I post this in holiday season when it was easily

Not only were even patches discussed during that time, but people will
catch up on things after the break, don't worry.

>Since CANVAS is about graphics drivers version the question can be
>simplified: Is the virtio-gpu driver version uniform across KVM

I think the drivers and versions will not be the same nor different *all
the time*.  Based on what the method says, the main difference is done
by font selection, hinting and antialiasing settings.  I don't think
that will be dependent on the graphics hardware.  Although the hardware
description might look the same.  The details about that should probably
be asked somewhere else than libvirt, e.g. whoever does virglrenderer or
qemu or...

I don't have another machine handy and my graphics guests are borked for
some reason (and I spent a lot of time trying to fix those already), so
I won't help much there.  I tried it with some live media, but then
realized it's not going to help.  I'd have to try the same VM (not only
distro), I guess.

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