Hi all,

Joanna Rutkowska has just published a new article titled "Qubes Air:
> Generalizing the Qubes Architecture." The article is available both on
> Joanna's blog:
>
> https://blog.invisiblethings.org/2018/01/22/qubes-air.html
>
> And on the Qubes website:
>
> https://www.qubes-os.org/news/2018/01/22/qubes-air/


I confess I found the writing a bit difficult to understand this time.  I
suggest adding some more example use cases.

Consider the following use case -- is this what Joanna had in mind?

Suppose you are a journalist, and you have received a PDF document on a USB
stick from an anonymous source.  Given all the recent
meltdown/rowhammer/spectre/xen debacles, you aren't thrilled about plugging
in the USB stick into your Qubes laptop.  And even if you did plug it in,
you wouldn't be thrilled about running the Qubes PDF converter on it either.

So what do you do?

On the USB front, you might buy a Raspberry Pi, and plug the USB stick into
that instead.  You could then scp the PDF document from the Rasbperry Pi
onto the Qubes laptop.  Qubes Air would make this easier by making using
the Raspberry Pi appear just like another USB VM (like sys-usb).

You could also do the PDF conversion on the same Raspberry Pi (specifically
the half of the conversion that would normally run inside a disposable
VM).  Qubes Air would also make this work smoothly, as if the disposable VM
were running on the Qubes laptop.

So, what are the security trade-offs?

First, this Raspberry Pi arrangement means that both steps are better
isolated from the Qubes laptop.  Previously, a successful attack on the
sys-usb VM or the disposable VM could be escalated via Meltdown et al to
take over the whole laptop.  Now they can't.

Second, the Raspberry Pi has inferior isolation within itself (e.g. no
IOMMU).  This means that if the journalist re-uses the same Raspberry Pi
for several different sources, those sources could interfere with each
other.  For instance, if source A is malicious, it could reprogram the
Raspberry Pi to destroy all data from source B.

Are you hoping that Qubes Air could overcome this obstacle?  For example,
are you hoping that a dedicated Raspberry Pi just for disposable VMs would
be able to isolate all disposable VMs from each other?

Kind regards,
Andrew

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