drm/amdgpu: validate user GEM object size

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,
otherwise it could be exploited to reveal sensitive data.

This fix is not done in a common code path because individual
driver might have different requirement.

Cc: stable@vger.kernel.org # v4.2+
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_display.c

@@ -531,6 +531,7 @@ 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 = mode_cmd->pitches[0] / cpp;
@@ -555,6 +556,13 @@ amdgpu_display_user_framebuffer_create(struct drm_device *dev,
 		return ERR_PTR(-EINVAL);
 	}
 
+	height = ALIGN(mode_cmd->height, 8);
+	if (obj->size < pitch * height) {
+		DRM_DEBUG_KMS("Invalid GEM size: expecting >= %d but got %zu\n",
+			      pitch * height, obj->size);
+		return ERR_PTR(-EINVAL);
+	}
+
 	amdgpu_fb = kzalloc(sizeof(*amdgpu_fb), GFP_KERNEL);
 	if (amdgpu_fb == NULL) {
 		drm_gem_object_put_unlocked(obj);