linux-kernel - Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO regions

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Message-ID: <20251017130249.GA309181@nvidia.com>
Date: Fri, 17 Oct 2025 10:02:49 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	kvm@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linux-pci@...r.kernel.org, Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO
 regions

On Mon, Oct 13, 2025 at 06:26:11PM +0300, Leon Romanovsky wrote:
> +static void dma_ranges_to_p2p_phys(struct vfio_pci_dma_buf *priv,
> +				   struct vfio_device_feature_dma_buf *dma_buf,
> +				   struct vfio_region_dma_range *dma_ranges,
> +				   struct p2pdma_provider *provider)
> +{
> +	struct pci_dev *pdev = priv->vdev->pdev;
> +	phys_addr_t pci_start;
> +	u32 i;
> +
> +	pci_start = pci_resource_start(pdev, dma_buf->region_index);
> +	for (i = 0; i < dma_buf->nr_ranges; i++) {
> +		priv->phys_vec[i].len = dma_ranges[i].length;
> +		priv->phys_vec[i].paddr = pci_start + dma_ranges[i].offset;
> +		priv->size += priv->phys_vec[i].len;
> +	}

This is missing validation, the userspace can pass in any
length/offset but the resource is of limited size. Like this:

static int dma_ranges_to_p2p_phys(struct vfio_pci_dma_buf *priv,
				  struct vfio_device_feature_dma_buf *dma_buf,
				  struct vfio_region_dma_range *dma_ranges,
				  struct p2pdma_provider *provider)
{
	struct pci_dev *pdev = priv->vdev->pdev;
	phys_addr_t len = pci_resource_len(pdev, dma_buf->region_index);
	phys_addr_t pci_start;
	phys_addr_t pci_last;
	u32 i;

	if (!len)
		return -EINVAL;
	pci_start = pci_resource_start(pdev, dma_buf->region_index);
	pci_last = pci_start + len - 1;
	for (i = 0; i < dma_buf->nr_ranges; i++) {
		phys_addr_t last;

		if (!dma_ranges[i].length)
			return -EINVAL;

		if (check_add_overflow(pci_start, dma_ranges[i].offset,
				       &priv->phys_vec[i].paddr) ||
		    check_add_overflow(priv->phys_vec[i].paddr,
				       dma_ranges[i].length - 1, &last))
			return -EOVERFLOW;
		if (last > pci_last)
			return -EINVAL;

		priv->phys_vec[i].len = dma_ranges[i].length;
		priv->size += priv->phys_vec[i].len;
	}
	priv->nr_ranges = dma_buf->nr_ranges;
	priv->provider = provider;
	return 0;
}

Jason