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: linux-fbdev@vger.kernel.org
Signed-off-by: Daniel Vetter <redacted>

Acked-by: Bartlomiej Zolnierkiewicz <redacted>

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