Re: [Qemu-devel] [PATCH v3 01/20] virtio: mmio-v1: Validate queue PFN

[Michael S. Tsirkin]

On Fri, Jun 29, 2018 at 12:15:21PM +0100, Suzuki K Poulose wrote:
> virtio-mmio with virtio-v1 uses a 32bit PFN for the queue.
> If the queue pfn is too large to fit in 32bits, which
> we could hit on arm64 systems with 52bit physical addresses
> (even with 64K page size), we simply miss out a proper link
> to the other side of the queue.
> 
> Add a check to validate the PFN, rather than silently breaking
> the devices.
> 
> Cc: "Michael S. Tsirkin" <address@hidden>
> Cc: Jason Wang <address@hidden>
> Cc: Marc Zyngier <address@hidden>
> Cc: Christoffer Dall <address@hidden>
> Cc: Peter Maydel <address@hidden>
> Cc: Jean-Philippe Brucker <address@hidden>
> Signed-off-by: Suzuki K Poulose <address@hidden>
> ---
> Changes since v2:
>  - Change errno to -E2BIG
> ---
>  drivers/virtio/virtio_mmio.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 67763d3..82cedc8 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -397,9 +397,21 @@ static struct virtqueue *vm_setup_vq(struct 
> virtio_device *vdev, unsigned index,
>       /* Activate the queue */
>       writel(virtqueue_get_vring_size(vq), vm_dev->base + 
> VIRTIO_MMIO_QUEUE_NUM);
>       if (vm_dev->version == 1) {
> +             u64 q_pfn = virtqueue_get_desc_addr(vq) >> PAGE_SHIFT;
> +
> +             /*
> +              * virtio-mmio v1 uses a 32bit QUEUE PFN. If we have something
> +              * that doesn't fit in 32bit, fail the setup rather than
> +              * pretending to be successful.
> +              */
> +             if (q_pfn >> 32) {
> +                     dev_err(&vdev->dev, "virtio-mmio: queue address too 
> large\n");

How about:
        "hypervisor bug: legacy virtio-mmio must not be used with more than 
0x%llx Gigabytes of memory",
        0x1ULL << (32 - 30) << PAGE_SHIFT

> +                     err = -E2BIG;
> +                     goto error_bad_pfn;
> +             }
> +
>               writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_QUEUE_ALIGN);
> -             writel(virtqueue_get_desc_addr(vq) >> PAGE_SHIFT,
> -                             vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
> +             writel(q_pfn, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
>       } else {
>               u64 addr;
>  
> @@ -430,6 +442,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device 
> *vdev, unsigned index,
>  
>       return vq;
>  
> +error_bad_pfn:
> +     vring_del_virtqueue(vq);
>  error_new_virtqueue:
>       if (vm_dev->version == 1) {
>               writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
> -- 
> 2.7.4