Re: [RFC v2 2/4] hisi_acc_vfio_pci: Override ioctl method to limit BAR2 region size

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2 Jul 2021 10:58:47 +0100
Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> wrote:

> HiSilicon ACC VF device BAR2 region consists of both functional register
> space and migration control register space. From a security point of
> view, it's not advisable to export the migration control region to Guest.
> 
> Hence, hide the migration region and report only the functional register
> space.
> 
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
>  drivers/vfio/pci/hisi_acc_vfio_pci.c | 42 +++++++++++++++++++++++++++-
>  1 file changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisi_acc_vfio_pci.c
> index a9e173098ab5..d57cf6d7adaf 100644
> --- a/drivers/vfio/pci/hisi_acc_vfio_pci.c
> +++ b/drivers/vfio/pci/hisi_acc_vfio_pci.c
> @@ -12,6 +12,46 @@
>  #include <linux/vfio.h>
>  #include <linux/vfio_pci_core.h>
>  
> +static long hisi_acc_vfio_pci_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
> +				    unsigned long arg)
> +{
> +	struct vfio_pci_core_device *vdev =
> +		container_of(core_vdev, struct vfio_pci_core_device, vdev);
> +
> +	if (cmd == VFIO_DEVICE_GET_REGION_INFO) {
> +		struct pci_dev *pdev = vdev->pdev;
> +		struct vfio_region_info info;
> +		unsigned long minsz;
> +
> +		minsz = offsetofend(struct vfio_region_info, offset);
> +
> +		if (copy_from_user(&info, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (info.argsz < minsz)
> +			return -EINVAL;
> +
> +		if (info.index == VFIO_PCI_BAR2_REGION_INDEX) {
> +			info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
> +
> +			/*
> +			 * ACC VF dev BAR2 region(64K) consists of both functional
> +			 * register space and migration control register space.
> +			 * Report only the first 32K(functional region) to Guest.
> +			 */
> +			info.size = pci_resource_len(pdev, info.index) / 2;
> +

Great, but what actually prevents the user from accessing the full
extent of the BAR since you're re-using core code for read/write/mmap,
which are all basing access on pci_resource_len()?  Thanks,

Alex

> +			info.flags = VFIO_REGION_INFO_FLAG_READ |
> +					VFIO_REGION_INFO_FLAG_WRITE |
> +					VFIO_REGION_INFO_FLAG_MMAP;
> +
> +			return copy_to_user((void __user *)arg, &info, minsz) ?
> +					    -EFAULT : 0;
> +		}
> +	}
> +	return vfio_pci_core_ioctl(core_vdev, cmd, arg);
> +}
> +
>  static int hisi_acc_vfio_pci_open(struct vfio_device *core_vdev)
>  {
>  	struct vfio_pci_core_device *vdev =
> @@ -33,7 +73,7 @@ static const struct vfio_device_ops hisi_acc_vfio_pci_ops = {
>  	.name		= "hisi-acc-vfio-pci",
>  	.open		= hisi_acc_vfio_pci_open,
>  	.release	= vfio_pci_core_release,
> -	.ioctl		= vfio_pci_core_ioctl,
> +	.ioctl		= hisi_acc_vfio_pci_ioctl,
>  	.read		= vfio_pci_core_read,
>  	.write		= vfio_pci_core_write,
>  	.mmap		= vfio_pci_core_mmap,