[Intel-gfx] [PATCH v4 14/19] vfio: Make vfio_device_open() single open for device cdev path

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu at intel.com>
> Sent: Tuesday, February 21, 2023 11:48 AM
> 
> VFIO group has historically allowed multi-open of the device FD. This
> was made secure because the "open" was executed via an ioctl to the
> group FD which is itself only single open.
> 
> However, no known use of multiple device FDs today. It is kind of a
> strange thing to do because new device FDs can naturally be created
> via dup().
> 
> When we implement the new device uAPI (only used in cdev path) there is
> no natural way to allow the device itself from being multi-opened in a
> secure manner. Without the group FD we cannot prove the security context
> of the opener.
> 
> Thus, when moving to the new uAPI we block the ability to multi-open
> the device. Old group path still allows it.
> 
> vfio_device_open() needs to sustain both the legacy behavior i.e. multi-open
> in the group path and the new behavior i.e. single-open in the cdev path.
> This mixture leads to the introduction of a new is_cdev_device flag in struct
> vfio_device_file.
> 
> Signed-off-by: Yi Liu <yi.l.liu at intel.com>

Reviewed-by: Kevin Tian <kevin.tian at intel.com>