Qubes Developers’ FAQ

Why does dom0 need to be 64-bit?

Since 2013 Xen has not supported 32-bit x86 architecture and Intel VT-d, which Qubes uses to isolate devices and drivers, is available on Intel 64-bit processors only.

In addition, often it is more difficult to exploit a bug on the x64 Linux than it is on x86 Linux (e.g. ASLR is sometimes harder to get around). While we designed Qubes with the emphasis on limiting any potential attack vectors in the first place, still we realize that some of the code running in Dom0, e.g. our GUI daemon or xen-store daemon, even though it is very simple code, might contain some bugs. Plus currently we haven’t implemented a separate storage domain, so also the disk backends are in Dom0 and are “reachable” from the VMs, which adds up to the potential attack surface. So, having faced a choice between 32-bit and 64-bit OS for Dom0, it was almost a no-brainer, as the 64-bit option provides some (little perhaps, but still) more protection against some classes of attacks, and at the same time does not have any disadvantages (except that it requires a 64-bit processor, but all systems on which it makes sense to run Qubes, e.g. that have at least 3-4GB memory, they do have 64-bit CPUs anyway).

Any rpm-based, 64-bit. Preferred Fedora.

How to build Qubes from sources?

See the instruction

How do I submit a patch?

See Qubes Source Code Repositories.

What is Qubes’ attitude toward changing guest distros?

We try to respect each distro’s culture, where possible. See the discussion on issue #1014 for an example.

The policy is there mostly to ease maintenance, on several levels:

  • Less modifications means easier migration to new upstream distribution releases
  • Upstream documentation matching the distribution running in Qubes VM
  • Less likely to introduce Qubes-specific issues
  • Each officially supported distribution (ideally) should offer the same set of Qubes-specific features - a change in one supported distribution should be followed also in others (including some new in the future)

Is QEMU part of the TCB?

No. Unlike many other virtualization systems, Qubes takes special effort to keep the I/O emulation component (QEMU) outside of the TCB. This has been achieved thanks to the careful use of Xen’s stub domain feature. For more details about how we improved on Xen’s native stub domain use, see here.