Re: [PATCH v2] hw/virtio: reject inverted virtio-iommu IOVA ranges

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 29, 2026 at 06:52:47PM +0800, Jia Jia wrote:
> Guest MAP and UNMAP requests can set virt_end below virt_start. Since
> virt_end is inclusive, this is not a valid interval. MAP nevertheless
> stores it in domain->mappings, but interval_cmp() assumes low <= high.
> For an inverted key, interval_cmp(key, key) returns -1. A covering UNMAP
> can therefore find the key but fail to remove it and repeat forever while
> holding s->mutex.
> 
> Reject inverted request ranges with VIRTIO_IOMMU_S_INVAL and make the
> notifier range decomposition skip invalid ranges. Keep the existing
> notifier-before-remove ordering, but return VIRTIO_IOMMU_S_DEVERR if
> g_tree_remove() fails.
> 
> Fixes: fe2cacae2438 ("virtio-iommu: Implement map/unmap")
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4104
> Signed-off-by: Jia Jia <physicalmtea@gmail.com>
> ---
> v2:
> - Drop migration-state validation and keep the existing post-load callback.
> 
>  hw/virtio/virtio-iommu.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> index 533bd5073f..b7145c8277 100644
> --- a/hw/virtio/virtio-iommu.c
> +++ b/hw/virtio/virtio-iommu.c
> @@ -210,7 +210,13 @@ static void virtio_iommu_notify_map_unmap(IOMMUMemoryRegion *mr,
>                                            IOMMUTLBEvent *event,
>                                            hwaddr virt_start, hwaddr virt_end)
>  {
> -    uint64_t delta = virt_end - virt_start;
> +    uint64_t delta;
> +
> +    if (virt_end < virt_start) {
> +        return;
> +    }
> +
> +    delta = virt_end - virt_start;


you do not need to move the delta assignment.


>      event->entry.iova = virt_start;
>      event->entry.addr_mask = delta;
> @@ -807,6 +813,10 @@ static int virtio_iommu_map(VirtIOIOMMU *s,
>          return VIRTIO_IOMMU_S_INVAL;
>      }
>  
> +    if (virt_end < virt_start) {
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
> +
>      domain = g_tree_lookup(s->domains, GUINT_TO_POINTER(domain_id));
>      if (!domain) {
>          return VIRTIO_IOMMU_S_NOENT;
> @@ -857,6 +867,10 @@ static int virtio_iommu_unmap(VirtIOIOMMU *s,
>  
>      trace_virtio_iommu_unmap(domain_id, virt_start, virt_end);
>  
> +    if (virt_end < virt_start) {
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
> +
>      domain = g_tree_lookup(s->domains, GUINT_TO_POINTER(domain_id));
>      if (!domain) {
>          return VIRTIO_IOMMU_S_NOENT;
> @@ -879,7 +893,10 @@ static int virtio_iommu_unmap(VirtIOIOMMU *s,
>                  virtio_iommu_notify_unmap(ep->iommu_mr, current_low,
>                                            current_high);
>              }
> -            g_tree_remove(domain->mappings, iter_key);
> +            if (!g_tree_remove(domain->mappings, iter_key)) {
> +                ret = VIRTIO_IOMMU_S_DEVERR;
> +                break;
> +            }
>              trace_virtio_iommu_unmap_done(domain_id, current_low, current_high);
>          } else {
>              ret = VIRTIO_IOMMU_S_RANGE;
> -- 
> 2.34.1