From: "Michael S. Tsirkin" <mst@redhat.com>
To: Eric Auger <eric.auger@redhat.com>
Cc: jasowang@redhat.com, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
iommu@lists.linux-foundation.org, eric.auger.pro@gmail.com,
robin.murphy@arm.com, hch@lst.de
Subject: Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call
Date: Mon, 22 Jul 2019 11:33:35 -0400 [thread overview]
Message-ID: <20190722112704-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20190722145509.1284-3-eric.auger@redhat.com>
On Mon, Jul 22, 2019 at 04:55:09PM +0200, Eric Auger wrote:
> Do not call dma_max_mapping_size for devices that have no DMA
> mask set, otherwise we can hit a NULL pointer dereference.
>
> This occurs when a virtio-blk-pci device is protected with
> a virtual IOMMU.
>
> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Suggested-by: Christoph Hellwig <hch@lst.de>
Christoph, I wonder why did you suggest this?
The connection between dma_mask and dma_max_mapping_size
is far from obvious. The documentation doesn't exist.
Do we really have to teach all users about this hack?
Why not just make dma_max_mapping_size DTRT?
> ---
> drivers/virtio/virtio_ring.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c8be1c4f5b55..37c143971211 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -262,7 +262,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
> {
> size_t max_segment_size = SIZE_MAX;
>
> - if (vring_use_dma_api(vdev))
> + if (vring_use_dma_api(vdev) && vdev->dev.dma_mask)
> max_segment_size = dma_max_mapping_size(&vdev->dev);
>
> return max_segment_size;
> --
> 2.20.1
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next prev parent reply other threads:[~2019-07-22 15:34 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-22 14:55 [PATCH 0/2] Fix NULL pointer dereference with virtio-blk-pci and virtual IOMMU Eric Auger
2019-07-22 14:55 ` [PATCH 1/2] dma-mapping: Protect dma_addressing_limited against NULL dma_mask Eric Auger
2019-07-22 15:26 ` Christoph Hellwig
2019-07-22 15:46 ` Auger Eric
2019-07-22 14:55 ` [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call Eric Auger
2019-07-22 15:27 ` Christoph Hellwig
2019-07-22 15:39 ` Michael S. Tsirkin
2019-07-22 15:33 ` Michael S. Tsirkin [this message]
2019-07-23 15:38 ` Christoph Hellwig
2019-07-23 15:47 ` Michael S. Tsirkin
2019-07-22 15:36 ` Robin Murphy
2019-07-22 15:45 ` Michael S. Tsirkin
2019-07-23 15:38 ` Christoph Hellwig
2019-07-24 22:10 ` Michael S. Tsirkin
2019-07-25 5:25 ` Christoph Hellwig
2019-07-25 11:53 ` Auger Eric
2019-07-25 13:04 ` Christoph Hellwig
2019-07-25 16:32 ` Auger Eric
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