[Kata-hypervisor] kata requirements for image formats and devices

Allison Randal allison at lohutok.net
Mon Aug 6 19:24:20 UTC 2018

On 08/06/2018 05:53 PM, Paolo Bonzini wrote:
> Nice.  This is a bit more tricky to assess; it's an (important) QoI
> issue but it's not a fundamental problem with virtual machines in
> general or KVM in particular.  In a perfect world, the device emulator
> would be confined using OS-level security features such as cgroups,
> capabilities, seccomp, etc.  However, this is not always the case and in
> particular it's not for Kata containers (though its predecessor Clear
> Containers did some OS-level isolation of the device emulator).

Nod, I'm not convinced that either virtual machines or containers are
fundamentally and universally a more secure approach. So much depends on
implementation, and if you get really, really fundamental both are just
a way of running an OS image as an isolated process on a kernel, so a
case could be made that the differences between the two are relatively

Some of the interesting future directions are hybrid approaches that
look at secure isolation features and how to combine them, without
getting too caught up in whether those features are commonly associated
with virtual machines or containers.

> Note that these same modular features can be applied to virtual machines
> simply by running the device emulation in a container.  This provides
> isolation for the parts that are most complex and deal the most with
> untrusted data from the guest.

Nod, more hybrid approaches.

> I think it would be disingenuous, and it somewhat reminds me to Theo de
> Raadt's famous virtualization quote[1], to say that OS-level containers
> can be more secure than virtual machines. 

I started with the preconception that virtual machines were more secure,
and didn't give it up lightly. Which doesn't mean that all arguments in
favor of container security are compelling. :) But, some are.

> Capabilities and the like are
> nice, but software has bugs and that's why you defend in depth.  Virtual
> machines are just an additional layer in the defend-in-depth onion.

That would be more compelling if the additional layer was substantially
more secure. Two weak layers of security is better than one weak layer
of security, but a single layer that combined the security features of
those two layers would be equivalent to them (and likely perform better).

No hacker ever has broken one weak layer of security and decided not to
go any farther because it wasn't worth the bother of breaking a second
weak layer of security.


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