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

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