On Mon, Nov 14, 2016 at 5:49 AM, Sec Tester <sectesting0...@gmail.com> wrote:
> Could open up a vulnerability if not done carefully.
>
> VM could use it to query and identify other VMs in existence on the system.

There are already several timing side-channel ways to do that.

Example:

AppVM$ time /usr/lib/qubes/qrexec-client-vm sys-net qubes.VMShell
Request refused
/usr/lib/qubes/qrexec-client-vm sys-net qubes.VMShell  0.00s user
0.00s system 1% cpu 0.180 total

AppVM$ time /usr/lib/qubes/qrexec-client-vm does-not-exist qubes.VMShell
Request refused
/usr/lib/qubes/qrexec-client-vm does-not-exist qubes.VMShell  0.00s
user 0.00s system 0% cpu 1.565 total

In this case the difference in time is quite obvious because it blocks
while an error dialog is open in dom0.

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