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

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Date:	Thu, 26 May 2011 13:16:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	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, gnatapov@...hat.com,
	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


* Avi Kivity <avi@...hat.com> wrote:

> > It would be possible to further increase isolation there by also 
> > passing the IO/MMIO decoding to the worker thread - but i'm not 
> > sure that's truly needed. Most of the risk is where most of the 
> > code is - and the code is in the worker task which interprets 
> > on-disk data, protocols, etc.
> 
> I've suggested in the past to add an "mmiofd" facility to kvm, 
> similar to ioeventfd.  This is how it would work:
> 
> - userspace configures kvm with an mmio range and a pipe
> - guest writes to that range write a packet to the pipe describing the write
> - guest reads from that range write a packet to the pipe describing
> the read, then wait for a reply packet with the result
> 
> The advantages would be
> - avoid heavyweight exit; kvm can simply wake up a thread on another
> core and resume processing
> - writes can be pipelined, similar to how PCI writes are posted
> - supports process separation

Yes, that was my exact thought, a per transport channel fd.

> So far no one has posted an implementation but it should be pretty 
> simple.

tools/kvm/ could make quick use of it - and it's a performance 
optimization mainly IMO, not primarily a security feature.

If you whip up a quick untested prototype for the KVM side we could 
look into adding tooling support for it and could test it.

As long as it's provided as an opt-in ioctl() which if fails (on 
older kernels) we fall back to the vcpu-fd, it should be relatively 
straightforward to support on the tooling side as well AFAICS.

Thanks,

	Ingo
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