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

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Date:   Fri, 21 Dec 2018 10:04:12 +0100
From:   Michel Dänzer <michel@...nzer.net>
To:     Yu Zhao <yuzhao@...gle.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König <christian.koenig@....com>,
        Alex Deucher <alexander.deucher@....com>
Cc:     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 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);
> +
> +	if (mode_cmd->pitches[0] != pitch) {
> +		dev_err(&dev->pdev->dev, "Invalid pitch: expecting %d but got %d\n",
> +			pitch, mode_cmd->pitches[0]);

This message shouldn't be printed by default, or buggy / malicious
userspace can spam dmesg. I suggest using DRM_DEBUG_KMS or DRM_DEBUG_DRIVER.


> +		return ERR_PTR(-EINVAL);
> +	}
>  
>  	obj = drm_gem_object_lookup(file_priv, mode_cmd->handles[0]);
>  	if (obj ==  NULL) {
> 

Other than that, looks good to me.


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