linux-kernel - Re: [PATCH 2/3] drm/amd: validate user pitch alignment

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Date:   Sun, 23 Dec 2018 14:44:39 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Michel Dänzer <michel@...nzer.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Christian König <christian.koenig@....com>,
        Alex Deucher <alexander.deucher@....com>,
        David Zhou <David1.Zhou@....com>,
        Daniel Stone <daniels@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, Samuel Li <Samuel.Li@....com>,
        Junwei Zhang <Jerry.Zhang@....com>,
        Harry Wentland <harry.wentland@....com>
Subject: Re: [PATCH 2/3] drm/amd: validate user pitch alignment

On Fri, Dec 21, 2018 at 10:07:26AM +0100, Michel Dänzer wrote:
> On 2018-12-21 4:10 a.m., Yu Zhao wrote:
> > Userspace may request pitch alignment that is not supported by GPU.
> > Some requests 32, but GPU ignores it and uses default 64 when cpp is
> > 4. If GEM object is allocated based on the smaller alignment, GPU
> > DMA will go out of bound.
> > 
> > For GPU that does frame buffer compression, DMA writing out of bound
> > memory will cause memory corruption.
> > 
> > Signed-off-by: Yu Zhao <yuzhao@...gle.com>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> > index e309d26170db..755daa332f8a 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> > @@ -527,6 +527,15 @@ amdgpu_display_user_framebuffer_create(struct drm_device *dev,
> >  	struct drm_gem_object *obj;
> >  	struct amdgpu_framebuffer *amdgpu_fb;
> >  	int ret;
> > +	struct amdgpu_device *adev = dev->dev_private;
> > +	int cpp = drm_format_plane_cpp(mode_cmd->pixel_format, 0);
> > +	int pitch = amdgpu_align_pitch(adev, mode_cmd->width, cpp, false);
> 
> Also, this needs to use mode_cmd->pitches[0] instead of mode_cmd->width,
> otherwise it'll spuriously fail for larger but well-aligned pitches.

Actually mode_cmd->pitches[0] is aligned mode_cmd->width multiplied
by cpp. So we can't just use mode_cmd->pitches[0]. And I'm not sure
if the hardware works with larger alignment (it certainly ignores
smaller alignment).