Re: [PATCH v3 3/3] vfio/pci: Check BAR resources before exporting a DMABUF

[Alex Williamson <alex@shazbot.org>]

On Thu, 30 Apr 2026 03:03:22 -0700
Matt Evans <mattev@meta.com> wrote:

> A DMABUF exports access to BAR resources and, although they are
> requested at startup time, we need to ensure they really were reserved
> before exporting.  Otherwise, it's possible to access unreserved
> resources through the export.
> 
> Add a check to the DMABUF-creation path.
> 
> Fixes: 5d74781ebc86c ("vfio/pci: Add dma-buf export support for MMIO regions")
> Signed-off-by: Matt Evans <mattev@meta.com>
> ---
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index f87fd32e4a01..3bc7d850e258 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -244,9 +244,11 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
>  		return -EINVAL;
>  
>  	/*
> -	 * For PCI the region_index is the BAR number like everything else.
> +	 * For PCI the region_index is the BAR number like everything
> +	 * else.  Check that PCI resources have been claimed for it.
>  	 */
> -	if (get_dma_buf.region_index >= VFIO_PCI_ROM_REGION_INDEX)
> +	if (get_dma_buf.region_index >= VFIO_PCI_ROM_REGION_INDEX ||
> +	    !IS_ERR(vfio_pci_core_get_iomap(vdev, get_dma_buf.region_index)))

Polarity of the test is wrong, should just be IS_ERR().

It would be good practice here to front-load the Fixes: patches in your
series.  I'd suggest making this patch #2, using the existing
setup_barmap API, then include it in the conversion to iomap in patch
#3.  Thanks,

Alex