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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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