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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251016235332.GA265079@nvidia.com>
Date: Thu, 16 Oct 2025 20:53:32 -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 int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
> +				   struct dma_buf_attachment *attachment)
> +{
> +	struct vfio_pci_dma_buf *priv = dmabuf->priv;
> +
> +	if (!attachment->peer2peer)
> +		return -EOPNOTSUPP;
> +
> +	if (priv->revoked)
> +		return -ENODEV;
> +
> +	switch (pci_p2pdma_map_type(priv->provider, attachment->dev)) {
> +	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +		break;
> +	case PCI_P2PDMA_MAP_BUS_ADDR:
> +		/*
> +		 * There is no need in IOVA at all for this flow.
> +		 * We rely on attachment->priv == NULL as a marker
> +		 * for this mode.
> +		 */
> +		return 0;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	attachment->priv = kzalloc(sizeof(struct dma_iova_state), GFP_KERNEL);
> +	if (!attachment->priv)
> +		return -ENOMEM;
> +
> +	dma_iova_try_alloc(attachment->dev, attachment->priv, 0, priv->size);

The lifetime of this isn't good..

> +	return 0;
> +}
> +
> +static void vfio_pci_dma_buf_detach(struct dma_buf *dmabuf,
> +				    struct dma_buf_attachment *attachment)
> +{
> +	kfree(attachment->priv);
> +}

If the caller fails to call map then it leaks the iova.

> +static struct sg_table *
> +vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,
> +		     enum dma_data_direction dir)
> +{
[..]


> +err_unmap_dma:
> +	if (!i || !state)
> +		; /* Do nothing */
> +	else if (dma_use_iova(state))
> +		dma_iova_destroy(attachment->dev, state, mapped_len, dir,
> +				 attrs);

If we hit this error path then it is freed..

> +static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment,
> +				   struct sg_table *sgt,
> +				   enum dma_data_direction dir)
> +{
> +	struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
> +	struct dma_iova_state *state = attachment->priv;
> +	unsigned long attrs = DMA_ATTR_MMIO;
> +	struct scatterlist *sgl;
> +	int i;
> +
> +	if (!state)
> +		; /* Do nothing */
> +	else if (dma_use_iova(state))
> +		dma_iova_destroy(attachment->dev, state, priv->size, dir,
> +				 attrs);

It is freed here too, but we can call map multiple times. Every time a
move_notify happens can trigger another call to map.

I think just call unlink in those two and put dma_iova_free in detach

Jason