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SubjectRe: [PATCH 2/3] drm/amd: validate user pitch alignment
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On 2018-12-23 10:44 p.m., Yu Zhao wrote:
> 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@google.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].

Use mode_cmd->pitches[0] / cpp then?


> And I'm not sure if the hardware works with larger alignment

It does.

> (it certainly ignores smaller alignment).

Yeah, pitch must be >= width. Maybe this patch could check that as well.


--
Earthling Michel Dänzer | http://www.amd.com
Libre software enthusiast | Mesa and X developer

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