# Re: \[PATCH 3/4\] fbdev: Add FBINFO\_HIDE\_SMEM\_START flag

- From: Bartlomiej Zolnierkiewicz \<hidden\>
- Date: 2018-09-10 12:51:08 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2018/09/5376682
- Thread: https://ratatoskr.run/dri-devel/2018/08/5361306/t.md

```text

On 08/22/2018 10:54 AM, Daniel Vetter wrote:
> DRM drivers really, really, really don't want random userspace to
> share buffer behind it's back, bypassing the dma-buf buffer sharing
> machanism. For that reason we've ruthlessly rejected any IOCTL
> exposing the physical address of any graphics buffer.
> 
> Unfortunately fbdev comes with that built-in. We could just set
> smem_start to 0, but that means we'd have to hand-roll our own fb_mmap
> implementation. For good reasons many drivers do that, but
> smem_start/length is still super convenient.
> 
> Hence instead just stop the leak in the ioctl, to keep fb mmap working
> as-is. A second patch will set this flag for all drm drivers.
> 
> Cc: Bartlomiej Zolnierkiewicz <redacted>
> Cc: Kees Cook <redacted>
> Cc: Daniel Vetter <redacted>
> Cc: <redacted>
> Signed-off-by: Daniel Vetter <redacted>

Acked-by: Bartlomiej Zolnierkiewicz <redacted>

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics
```