Re: [PATCH v9 10/25] vfio: Make vfio_device_open() single open for device cdev path

[Eric Auger <eric.auger@redhat.com>]

Hi Yi,

On 4/1/23 17:18, Yi Liu wrote:
> 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 of opening
> a device multiple times. Given old group path still allows it we store
> a vfio_group pointer in struct vfio_device_file to differentiate.
>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Tested-by: Terrence Xu <terrence.xu@intel.com>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Yanting Jiang <yanting.jiang@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
>  drivers/vfio/group.c     | 2 ++
>  drivers/vfio/vfio.h      | 2 ++
>  drivers/vfio/vfio_main.c | 7 +++++++
>  3 files changed, 11 insertions(+)
>
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index d55ce3ca44b7..1af4b9e012a7 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -245,6 +245,8 @@ static struct file *vfio_device_open_file(struct vfio_device *device)
>  		goto err_out;
>  	}
>  
> +	df->group = device->group;
> +
>  	ret = vfio_device_group_open(df);
>  	if (ret)
>  		goto err_free;
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index b2f20b78a707..f1a448f9d067 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -18,6 +18,8 @@ struct vfio_container;
>  
>  struct vfio_device_file {
>  	struct vfio_device *device;
> +	struct vfio_group *group;
> +
>  	bool access_granted;
>  	spinlock_t kvm_ref_lock; /* protect kvm field */
>  	struct kvm *kvm;
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 6d5d3c2180c8..c8721d5d05fa 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -477,6 +477,13 @@ int vfio_device_open(struct vfio_device_file *df)
>  
>  	lockdep_assert_held(&device->dev_set->lock);
>  
> +	/*
> +	 * Only the group path allows the device opened multiple times.
> +	 * The device cdev path doesn't have a secure way for it.
> +	 */
> +	if (device->open_count != 0 && !df->group)
> +		return -EINVAL;
> +
>  	device->open_count++;
>  	if (device->open_count == 1) {
>  		ret = vfio_device_first_open(df);