Re: [PATCH v2 4/7] vfio: Introduce VFIO_DEVICE_FEATURE ioctl and first user

[Cornelia Huck]

On Wed, 19 Feb 2020 11:54:18 -0700
Alex Williamson <alex.williamson@xxxxxxxxxx> wrote:

> The VFIO_DEVICE_FEATURE ioctl is meant to be a general purpose, device
> agnostic ioctl for setting, retrieving, and probing device features.
> This implementation provides a 16-bit field for specifying a feature
> index, where the data porition of the ioctl is determined by the
> semantics for the given feature.  Additional flag bits indicate the
> direction and nature of the operation; SET indicates user data is
> provided into the device feature, GET indicates the device feature is
> written out into user data.  The PROBE flag augments determining
> whether the given feature is supported, and if provided, whether the
> given operation on the feature is supported.
> 
> The first user of this ioctl is for setting the vfio-pci VF token,
> where the user provides a shared secret key (UUID) on a SR-IOV PF
> device, which users must provide when opening associated VF devices.
> 
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>  drivers/vfio/pci/vfio_pci.c |   52 +++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/vfio.h   |   37 +++++++++++++++++++++++++++++++
>  2 files changed, 89 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 8dd6ef9543ca..e4d5d26e5e71 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -1180,6 +1180,58 @@ static long vfio_pci_ioctl(void *device_data,
>  
>  		return vfio_pci_ioeventfd(vdev, ioeventfd.offset,
>  					  ioeventfd.data, count, ioeventfd.fd);
> +	} else if (cmd == VFIO_DEVICE_FEATURE) {
> +		struct vfio_device_feature feature;
> +		uuid_t uuid;
> +
> +		minsz = offsetofend(struct vfio_device_feature, flags);
> +
> +		if (copy_from_user(&feature, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (feature.argsz < minsz)
> +			return -EINVAL;
> +
> +		if (feature.flags & ~(VFIO_DEVICE_FEATURE_MASK |
> +				      VFIO_DEVICE_FEATURE_SET |
> +				      VFIO_DEVICE_FEATURE_GET |
> +				      VFIO_DEVICE_FEATURE_PROBE))
> +			return -EINVAL;

GET|SET|PROBE is well-defined, but what about GET|SET without PROBE? Do
we want to fence this in the generic ioctl handler part? Or is there
any sane way to implement that (read and then write back something?)

> +
> +		switch (feature.flags & VFIO_DEVICE_FEATURE_MASK) {
> +		case VFIO_DEVICE_FEATURE_PCI_VF_TOKEN:
> +			if (!vdev->vf_token)
> +				return -ENOTTY;
> +
> +			/*
> +			 * We do not support GET of the VF Token UUID as this
> +			 * could expose the token of the previous device user.
> +			 */
> +			if (feature.flags & VFIO_DEVICE_FEATURE_GET)
> +				return -EINVAL;
> +
> +			if (feature.flags & VFIO_DEVICE_FEATURE_PROBE)
> +				return 0;
> +
> +			/* Don't SET unless told to do so */
> +			if (!(feature.flags & VFIO_DEVICE_FEATURE_SET))
> +				return -EINVAL;
> +
> +			if (feature.argsz < minsz + sizeof(uuid))
> +				return -EINVAL;
> +
> +			if (copy_from_user(&uuid, (void __user *)(arg + minsz),
> +					   sizeof(uuid)))
> +				return -EFAULT;
> +
> +			mutex_lock(&vdev->vf_token->lock);
> +			uuid_copy(&vdev->vf_token->uuid, &uuid);
> +			mutex_unlock(&vdev->vf_token->lock);
> +
> +			return 0;
> +		default:
> +			return -ENOTTY;
> +		}
>  	}
>  
>  	return -ENOTTY;
(...)