On 07/11/2016 05:24 PM, Duncan Guthrie wrote:
> On 11/07/16 15:14, [email protected] wrote:
>> Is it possible that someone who compromised QUBES, could re-write 
>> the AppVM in a way that whenever it is loaded up, it re-infects the
>> entire system all over again...?
> 
> 
> If someone compromised dom0, then they would have to firstly have 
> compromised some AppVM in order to run arbitrary code. They would
> [....]
> the key) as you would revoke it. Just back up with Qubes tools,
> assuming dom0 is clean. It is really hard to compromise dom0 so you
> as an average person would probably be all right.
I agree, it is extremely hard to actually compromise dom0 (i.e., escape
Xen), and this type of attack will likely have to be so targeted that it
will most likely affect ring -2/-3 (System Management Mode / Management
Engine), so a simple restore will not be enough. A new machine will be
better, and a completely free/libre hardware platform is the top of line
for this paranoia.

Still I agree with Duncan, this easily borders on paranoia, and then we
have the good ol' thermorectal cryptanalysis, which would be way more
cost-effective than crafting such a complicated piece of software.

To answer your actual question, it would not be possible to re-write an
AppVM to re-infect the system if the hole through which the system was
hacked in the first place is fixed before restoring the backup. There
would be no good in formatting and restoring the backup, only a waste of
time, if you are not going to fix the hole.

It is possible to write auto-starting code in your AppVM, just add your
commands to .bashrc / .bash_profile in your home directory (which is
persisted across reboots).

-- 
Alex

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