linux-kernel - Re: [RFC][PATCH 0/5 v2] DMA-BUF Heaps (destaging ION)

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Message-ID: <CA+M3ks61BGPkPjNd01g32LV7YZfDpy8t100KxQhScOFgGO4KjA@mail.gmail.com>
Date:   Wed, 20 Mar 2019 10:16:47 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, "Andrew F. Davis" <afd@...com>,
        Alistair Strachan <astrachan@...gle.com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Chenbo Feng <fengc@...gle.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Liam Mark <lmark@...eaurora.org>,
        Marissa Wall <marissaw@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 0/5 v2] DMA-BUF Heaps (destaging ION)

Le mar. 19 mars 2019 à 23:36, John Stultz <john.stultz@...aro.org> a écrit :
>
> On Tue, Mar 19, 2019 at 2:58 PM Rob Clark <robdclark@...il.com> wrote:
> >
> > On Tue, Mar 19, 2019 at 1:00 PM Andrew F. Davis <afd@...com> wrote:
> > >
> > > On 3/19/19 11:54 AM, Benjamin Gaignard wrote:
> > > > Le mer. 13 mars 2019 à 23:31, John Stultz <john.stultz@...aro.org> a écrit :
> > > >>
> > > >> On Wed, Mar 13, 2019 at 1:11 PM Liam Mark <lmark@...eaurora.org> wrote:
> > > >>> On Tue, 5 Mar 2019, John Stultz wrote:
> > > >>>>
> > > >>>> Eventual TODOS:
> > > >>>> * Reimplement page-pool for system heap (working on this)
> > > >>>> * Add stats accounting to system/cma heaps
> > > >>>> * Make the kselftest actually useful
> > > >>>> * Add other heaps folks see as useful (would love to get
> > > >>>>   some help from actual carveout/chunk users)!
> > > >>>
> > > >>> We use a modified carveout heap for certain secure use cases.
> > > >>
> > > >> Cool! It would be great to see if you have any concerns about adding
> > > >> such a secure-carveout heap to this framework. I suspect it would be
> > > >> fairly similar to how its integrated into ION, but particularly I'd be
> > > >> interested in issues around the lack of private flags and other
> > > >> allocation arguments like alignment.
> > > >>
> > > >>> Although there would probably be some benefit in discssing how the dma-buf
> > > >>> heap framework may want to support
> > > >>> secure heaps in the future it is a large topic which I assume you don't
> > > >>> want to tackle now.
> > > >>
> > > >> So I suspect others (Benjamin?) would have a more informed opinion on
> > > >> the details, but the intent is to allow secure heap implementations.
> > > >> I'm not sure what areas of concern you have for this allocation
> > > >> framework in particular?
> > > >
> > > > yes I would be great to understand how you provide the information to
> > > > tell that a dmabuf
> > > > is secure (or not) since we can't add flag in dmabuf structure itself.
> > > > An option is manage
> > > > the access rights when a device attach itself to the dmabuf but in
> > > > this case you need define
> > > > a list of allowed devices per heap...
> > > > If you have a good solution for secure heaps you are welcome :-)
> > > >
> > >
> > > Do we really need any of that? A secure buffer is secured by the
> > > hardware firewalls that keep out certain IP (including often the
> > > processor running Linux). So the only thing we need to track internally
> > > is that we should not allow mmap/kmap on the buffer. That can be done in
> > > the per-heap layer, everything else stays the same as a standard
> > > carveout heap.
> >
> > For at least some hw the importing driver needs to configure things
> > differently for secure buffers :-/
>
> Does the import ioctl need/use a flag for that then? Userland already
> has to keep meta-data about dmabufs around.

To secure a buffer you need to know who is allowed to write/read it and
hardware block involved in the dataflow may need to know that the buffer
is secure to configure themself.
As example for a video decoding you allow hw video decoder to read in
a buffer and display to read it. You can also allow cpu to write on the buffer
to add subtitles. For that we need to be able to mmap/kmap the buffer.
Using a carveout heap for secure buffer mean that you reserved a large
memory region only for this purpose, that isn't possible on embedded device
where we are always limited in memory so we use CMA.
In the past I have used dmabuf's attach function to know who write into
the buffer and then configure who will be able to read it. It was working well
but the issue was how to in generic way this behavior.

>
> thanks
> -john