Re: [Xen-users] beginners question concerning security

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> as I'm a real beginner I would be pleased if someone can answer a maybe
> simple question.

No probs, welcome to the community!

> I'm looking for a virtaul server system to be used by diffrent entities. As
> I heard from other solutions there are often (at least small) security
> problems.
>
> Now I would like to know if it's (at least theoretical possible) that one
> user from domU_a can access domU_b or even dom0.

Nothing we know of.  If there was, it'd be a bug and we'd be all over it, 
getting it fixed :-)  In non-trivial software it's always possible such a bug 
exists but we're aiming to get high-assurance from the fact that Xen itself 
is relatively small and well-reviewed.

> Btw, what makes the difference between dom0 and domU?

Dom0 is privileged to access the real machine hardware and map other domain's 
memory.  DomUs are only privileged to access their own resources - if they 
want to do IO, they have to ask dom0.  This separation is enforced by Xen, so 
you can run whatever you want in a domU without compromising this privilege 
difference.  It is safe to allow users to compile their own kernel, for 
instance.

Btw, we supply a "xen0" kernel and a "xenU" kernel for XenLinux.  The 
difference is that the xen0 kernel may run in *any* domain, the xenU kernel 
is smaller but can only run in a domU because it doesn't have the drivers for 
the "real" hardware.

> Any hint would be apprecitated..
>
> btw (I already read tfm :-))

Thanks, it's appreciated :-)

Cheers,
Mark

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