linux-kernel - Re: [RFC] How implement Secure Data Path ?

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Message-ID: <20150507174003.2a5b42e6@lxorguk.ukuu.org.uk>
Date:	Thu, 7 May 2015 17:40:03 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Thierry Reding <treding@...dia.com>,
	Benjamin Gaignard <benjamin.gaignard@...aro.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Rob Clark <robdclark@...il.com>,
	Dave Airlie <airlied@...hat.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Tom Gall <tom.gall@...aro.org>
Subject: Re: [RFC] How implement Secure Data Path ?

On Thu, 7 May 2015 15:52:12 +0200
Daniel Vetter <daniel@...ll.ch> wrote:

> On Thu, May 07, 2015 at 03:22:20PM +0200, Thierry Reding wrote:
> > On Wed, May 06, 2015 at 03:15:32PM +0200, Daniel Vetter wrote:
> > > Yes the idea would be a special-purpose allocater thing like ion. Might
> > > even want that to be a syscall to do it properly.
> > 
> > Would you care to elaborate why a syscall would be more proper? Not that
> > I'm objecting to it, just for my education.
> 
> It seems to be the theme with someone proposing a global /dev node for a
> few system wide ioctls, then reviewers ask to make a proper ioctl out of
> it. E.g. kdbus, but I have vague memory of this happening a lot.

kdbus is not necessarily an advert for how to do anything 8)

If it can be user allocated then it really ought to be one or more device
nodes IMHO, because you want the resource to be passable between users,
you need a handle to it and you want it to go away nicely on last close.
In the cases where the CPU is allowed to or expected to have write only
access you also might want an mmap of it.

I guess the same kind of logic as with GEM (except preferably without
the DoS security holes) applies as to why its useful to have handles to
the DMA buffers.

Alan
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