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

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Message-ID: <20150508083735.GB15256@phenom.ffwll.local>
Date:	Fri, 8 May 2015 10:37:35 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	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, May 07, 2015 at 05:40:03PM +0100, One Thousand Gnomes wrote:
> 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.

dma-buf user handles are fds, which means anything allocated can be passed
around nicely already. The question really is whether we'll have one ioctl
on top of a special dev node or a syscall. I thought that in these cases
where the dev node is only ever used to allocate the real thing, a syscall
is the preferred way to go.

> 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.

We have handles (well file descriptors) to dma-bufs already, I'm a bit
confused what you mean?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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