Re: [Xen-devel] Xen Security Advisory 155 (CVE-2015-8550) - paravirtualized drivers incautious about shared memory

[Marek Marczykowski-GÃrecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Jan 04, 2016 at 04:22:32PM +0000, David Vrabel wrote:
> On 04/01/16 13:06, Marek Marczykowski-GÃrecki wrote:
> > On Tue, Dec 22, 2015 at 10:06:25AM -0500, Eric Shelton wrote:
> >> The XSA mentions that "PV frontend patches will be developed and
> >> released (publicly) after the embargo date."  Has anything been done
> >> towards this that should also be incorporated into MiniOS?  On a
> >> system utilizing a "driver domain," where a backend is running on a
> >> domain that is considered unprivileged and untrusted (such as the
> >> example described in http://wiki.xenproject.org/wiki/Driver_Domain),
> >> it seems XSA-155-style double fetch vulnerabilities in the frontends
> >> are also a potential security concern, and should be eliminated.
> >> However, perhaps that does not include pcifront, since pciback would
> >> always be running in dom0.
> > 
> > And BTW the same applies to Linux frontends, for which also I haven't seen
> > any public development. In attachment my email to
> > xen-security-issues-discuss list (sent during embargo), with patches
> > attached there. I haven't got any response.
> 
> There are no similar security concerns with frontends since they trust
> the backend.
> 
> I note that you say:
> 
>   "But in some cases (namely: if driver domains are in use), frontends
>    may be more trusted/privileged than backends."
> 
> But this cannot be the case since the backend can always trivially DoS
> the frontend by (for example) not unmapping grant references when
> required by the protocol.

DoS is one thing, code execution is another.

-- 
Best Regards,
Marek Marczykowski-GÃrecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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