linux-kernel - Re: [PATCH] drm: Use kvzalloc for allocating blob property memory

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Date:   Mon, 2 Jul 2018 10:07:04 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Michel Dänzer <michel@...nzer.net>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: Use kvzalloc for allocating blob property memory

On Fri, Jun 29, 2018 at 07:38:32PM +0300, Ville Syrjälä wrote:
> On Fri, Jun 29, 2018 at 06:27:28PM +0200, Michel Dänzer wrote:
> > On 2018-06-29 06:12 PM, Ville Syrjälä wrote:
> > > On Fri, Jun 29, 2018 at 04:27:10PM +0200, Michel Dänzer wrote:
> > >> From: Michel Dänzer <michel.daenzer@....com>
> > >>
> > >> The property size may be controlled by userspace, can be large (I've
> > >> seen failure with order 4, i.e. 16 pages / 64 KB) and doesn't need to be
> > >> physically contiguous.
> > > 
> > > I wonder if we should enforce some kind of reasonable limit
> > > on the blob size. Looks like we allow anything up to
> > > ULONG_MAX currently. We can't tell at createblob time how
> > > the thing is going to be used, so can't have any kind
> > > of property specific limit unfortunately.
> > 
> > The failure I was seeing was for a gamma LUT, so a size limit alone
> > cannot solve the issue.
> 
> Sure. I was just thinking that maybe we shouldn't allow someone to
> allocate unlimited amounts of kernel memory via this interface. But
> to do that effectively we'd also need to limit the total amount used
> by all blobs.

People with drm master rights are allowed to pin enormous amounts of
memory (through pinning of display buffers) ... I think simply requiring
DRM_MASTER for the ioctl would be good enough. Atm anyone can abuse
createblob to waste memory, which is a bit much.

We haven't marked it with DRM_RENDER_ALLOW, so I think this is just an
oversight really. I'll type a patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch