Re: [ANNOUNCE] Introducing Codezero

[Sam Mason]

On Tue, Jul 28, 2009 at 08:37:36AM +0200, Bas Wijnen wrote:
> On Sun, Jul 26, 2009 at 01:53:29PM +0200, Bas Wijnen wrote:
> > The ability to contact a thread is one thing you need a capability for.
> > But to contact a thread with a certain request (and no other) is also
> > something capabilities should allow for.  That is hard to implement
> > without kernel protection, AFAICS.
> 
> I forgot to mention a feature that is not possible without kernel
> protection: encapsulation.  If the server is responsible for its access
> control, it is impossible to forbid it to _receive_ messages from
> untrusted sources.  If there is a program that is willing to listen, it
> can simply not do access control, and allow any request.  That means
> that you never know if a program can communicate (in fact both incoming
> and outgoing) with other programs.  AFAICS, the only solution to this is
> kernel support.

Strictly speaking, encapsulation of this kind is possible without kernel
support; just look at qemu or similar---run your untrusted code in a
system emulator and all is safe.  The problem is doing this efficiently;
kernel support is required if you want to solve the problem with less of
a sledge hammer.

-- 
  Sam  http://samason.me.uk/