| Message ID | 20230213151348.56451-13-yi.l.liu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add vfio_device cdev for iommufd support | expand |
> From: Liu, Yi L <yi.l.liu@intel.com> > Sent: Monday, February 13, 2023 11:14 PM > > With the introduction of vfio device cdev, userspace can get device > access by either the legacy group path or the cdev path. For VFIO devices, > it can only be opened by one of the group path and the cdev path at one > time. e.g. when the device is opened via cdev path, the group path should > be failed. Both paths will call into vfio_device_open(), so the exclusion > is done in it. the exclusive part between two paths is handled by the last patch. this patch should stay with explaining single-open facet in cdev path. > > + /* > + * Device cdev path cannot support multiple device open since > + * it doesn't have a secure way for it. So a second device > + * open attempt should be failed if the caller is from a cdev > + * path. > + */ remove the last sentence. > + if (device->open_count != 0 && df->is_cdev_device) > + return -EINVAL; > + > device->open_count++; > if (device->open_count == 1) { > ret = vfio_device_first_open(df, dev_id, pt_id); > @@ -543,7 +552,12 @@ static int vfio_device_fops_release(struct inode > *inode, struct file *filep) > struct vfio_device_file *df = filep->private_data; > struct vfio_device *device = df->device; > > - vfio_device_group_close(df); > + /* > + * group path supports multiple device open, while cdev doesn't. > + * So use vfio_device_group_close() for !is_cdev_device case. > + */ I don't say why multi-open is the reason to call group_close(). Isn't it straightforward to do so in the group path? I'd just remove the comment. > + if (!df->is_cdev_device) > + vfio_device_group_close(df); > > vfio_device_put_registration(device); > > -- > 2.34.1
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h index 7a77fb12bd2c..620ebcf966fc 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; + bool is_cdev_device; + 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 05dd4b89e9d1..c0be4b27f96c 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -472,6 +472,15 @@ int vfio_device_open(struct vfio_device_file *df, lockdep_assert_held(&device->dev_set->lock); + /* + * Device cdev path cannot support multiple device open since + * it doesn't have a secure way for it. So a second device + * open attempt should be failed if the caller is from a cdev + * path. + */ + if (device->open_count != 0 && df->is_cdev_device) + return -EINVAL; + device->open_count++; if (device->open_count == 1) { ret = vfio_device_first_open(df, dev_id, pt_id); @@ -543,7 +552,12 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep) struct vfio_device_file *df = filep->private_data; struct vfio_device *device = df->device; - vfio_device_group_close(df); + /* + * group path supports multiple device open, while cdev doesn't. + * So use vfio_device_group_close() for !is_cdev_device case. + */ + if (!df->is_cdev_device) + vfio_device_group_close(df); vfio_device_put_registration(device);
With the introduction of vfio device cdev, userspace can get device access by either the legacy group path or the cdev path. For VFIO devices, it can only be opened by one of the group path and the cdev path at one time. e.g. when the device is opened via cdev path, the group path should be failed. Both paths will call into vfio_device_open(), so the exclusion is done in it. 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@intel.com> --- drivers/vfio/vfio.h | 2 ++ drivers/vfio/vfio_main.c | 16 +++++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-)