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> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx> 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);