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@xxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Tested-by: Terrence Xu <terrence.xu@xxxxxxxxx>
> Tested-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Tested-by: Yanting Jiang <yanting.jiang@xxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
> 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;
> +
in previous patches df fields were protected with various locks. I refer
to vfio_device_group_open() implementation. No need here?
By the way since the group is set here, wrt [PATCH v9 06/25] kvm/vfio:
Accept vfio device file from userspace you have a way to determine if a
device was opened in the legacy way, no?
> 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.
allows the device to be 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);
Thanks
Eric
