Re: [PATCH 00/03] Preventing zero GPU virtual address allocation

Chris Wilson
2015-05-21T08:43:11Z

On Thu, May 21, 2015 at 11:08:42AM +0300, David Weinehall wrote:
> On Wed, May 20, 2015 at 05:10:58PM +0100, Chris Wilson wrote:
> > On Wed, May 20, 2015 at 06:00:43PM +0200, Daniel Vetter wrote:
> > > On Wed, May 20, 2015 at 03:14:06PM +0100, Chris Wilson wrote:
> > > > On Wed, May 20, 2015 at 03:09:43PM +0100, Chris Wilson wrote:
> > > > > On Wed, May 20, 2015 at 04:54:19PM +0300, David Weinehall wrote:
> > > > > > This patch series (one patch each for libdrm, the kernel, and beignet)
> > > > > > aims to provide a means to add a context-specific means to prevent
> > > > > > a mapping to GPU virtual address zero. This is needed at least by
> > > > > > Beignet (possibly in other use-cases too, though I don't know of any
> > > > > > other) to allow use of address zero to represent NULL.
> > > > >
> > > > > Urm, you cannot allow absolute addressing period. What happens to the
> > > > > object at 0 when the user reads from it or writes to it? You have to
> > > > > have an object at 0 for the user's NULL pointer access.
> > > >
> > > > I'll mollify that: outside of full-ppgtt where you need to share the VM.
> > >
> > > The description is misleading, the new flag doesn't prevent anything from
> > > getting mapped at 0 but only prevents any bo submitted through execbuf on
> > > the given context from being bound at address 0. If that would happen
> > > compute kernels using NULL checks for some things would fall over.
>
> Any suggestion for a better description?
>
> > That does not address the issue that *0 is an untrapped runtime bug that
> > allows writing to other objects or reading from them.
>
> Not exactly sure what you suggest here?

That you have an unmitigated security hole in your design.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre