linux-kernel - Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

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Date:	Thu, 26 May 2011 13:46:36 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Pekka Enberg <penberg@...nel.org>, Avi Kivity <avi@...hat.com>,
	James Morris <jmorris@...ei.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <kees.cook@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Will Drewry <wad@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call
 filtering

On Thu, May 26, 2011 at 12:38:36PM +0200, Ingo Molnar wrote:
> 
> * Gleb Natapov <gleb@...hat.com> wrote:
> 
> > On Thu, May 26, 2011 at 11:57:51AM +0300, Pekka Enberg wrote:
> > > Hi Avi,
> > > 
> > > On Thu, May 26, 2011 at 11:49 AM, Avi Kivity <avi@...hat.com> wrote:
> > >
> > > > You mean each thread will have a different security context?  I 
> > > > don't see the point.  All threads share all of memory so it 
> > > > would be trivial for one thread to exploit another and gain all 
> > > > of its privileges.
> > > 
> > > So how would that happen? I'm assuming that once the security 
> > > context has been set up for a thread, you're not able to change 
> > > it after that. You'd be able to exploit other threads through 
> > > shared memory but how would you gain privileges?
> > 
> > By tricking other threads to execute code for you. Just replace 
> > return address on the other's thread stack.
> 
> That kind of exploit is not possible if the worker pool consists of 
> processes - which would be rather easy to achieve with tools/kvm/.
> 
Well, of course. There original question was about threads.

> In that model each process has its own stack, not accessible to other 
> worker processes. They'd only share the guest RAM image and some 
> (minimal) global state.
> 
> This way the individual devices are (optionally) isolated from each 
> other. In a way this is a microkernel done right ;-)
> 
But doesn't this design suffer the same problem as microkernel? Namely
a lot of slow IPCs?

--
			Gleb.
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