linux-kernel - Re: [RFC v2 8/8] drm: tegra: Add gr2d device

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Message-ID: <20121127103739.GA3329@avionic-0098.adnet.avionic-design.de>
Date:	Tue, 27 Nov 2012 11:37:39 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Lucas Stach <dev@...xeye.de>
Cc:	Terje Bergström <tbergstrom@...dia.com>,
	Dave Airlie <airlied@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arto Merilainen <amerilainen@...dia.com>
Subject: Re: [RFC v2 8/8] drm: tegra: Add gr2d device

On Tue, Nov 27, 2012 at 11:22:56AM +0100, Lucas Stach wrote:
> Am Dienstag, den 27.11.2012, 10:45 +0200 schrieb Terje Bergström:
> > On 27.11.2012 10:32, Dave Airlie wrote:
> > > On Tue, Nov 27, 2012 at 8:16 AM, Terje Bergström <tbergstrom@...dia.com> wrote:
> > >> Thanks for the pointer, I looked at exynos code. It indeed checks the
> > >> registers written to, but it doesn't prevent overrun by checking sizes
> > >> of buffers and compare against requests.
> > > They probably need to add that, its not as important as the base
> > > addresses, unless it takes negative strides, generally base addresses
> > > means you can target current->uid quite easily!
> > 
> > Ok. We'll implement the firewall, unless we come up with even a better
> > choice.
> > 
> > >> If this is the way to go, I'll put the firewall behind a Kconfig flag so
> > >> that system integrator can decide if his system needs it.
> > > We don't generally make security like this optional :-)
> > > 
> > > If you do that you should restrict the drm device to root users only,
> > > and never let a user with a browser anywhere near it.
> > 
> Personally I would never trust any binary, but that's just my personal
> opinion.
> 
> But I'm in favour of having the command stream checking optional, simply
> backed by the fact that we are likely to use the same 2D driver
> infrastructure for Tegra 2 and 3. On Tegra 3 we can most likely go
> without in-depth command stream checking as the graphics core there sits
> behind the IOMMU, which can provide an appropriate level of security.

But in that case it should be made mandatory at first until proper IOMMU
support is enabled on Tegra30. Then it can be checked at driver probe
time whether or not to enable the extra checks. That way we don't need a
special Kconfig option and we still get all the security that we need,
right?

Thierry

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