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Subject: Re: [PATCH 3/3] drm/amd: validate user GEM object size
To:     Yu Zhao <yuzhao@google.com>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>
Cc:     David Zhou <David1.Zhou@amd.com>,
        Daniel Stone <daniels@collabora.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, Samuel Li <Samuel.Li@amd.com>,
        Junwei Zhang <Jerry.Zhang@amd.com>,
        Harry Wentland <harry.wentland@amd.com>
References: <20181221031053.240161-1-yuzhao@google.com>
 <20181221031053.240161-3-yuzhao@google.com>
From:   =?UTF-8?Q?Michel_D=c3=a4nzer?= <michel@daenzer.net>
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Message-ID: <1e804635-e7a4-2cf6-956a-3e140f8d0e7d@daenzer.net>
Date:   Fri, 21 Dec 2018 10:09:24 +0100
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On 2018-12-21 4:10 a.m., Yu Zhao wrote:
> When creating frame buffer, userspace may request to attach to a
> previously allocated GEM object that is smaller than what GPU
> requires. Validation must be done to prevent out-of-bound DMA,
> which could not only corrupt memory but also reveal sensitive data.
> 
> This fix is not done in a common code path because individual
> driver might have different requirement.
> 
> Signed-off-by: Yu Zhao <yuzhao@google.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> index 755daa332f8a..bb48b016cc68 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> @@ -527,6 +527,7 @@ amdgpu_display_user_framebuffer_create(struct drm_device *dev,
>  	struct drm_gem_object *obj;
>  	struct amdgpu_framebuffer *amdgpu_fb;
>  	int ret;
> +	int height;
>  	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);
> @@ -550,6 +551,13 @@ amdgpu_display_user_framebuffer_create(struct drm_device *dev,
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	height = ALIGN(mode_cmd->height, 8);
> +	if (obj->size < pitch * height) {
> +		dev_err(&dev->pdev->dev, "Invalid GEM size: expecting %d but got %d\n",
> +			pitch * height, obj->size);

Same comment as patch 2, and maybe write "expecting >= %d but got %d"
for clarity.


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