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Re: [Qemu-devel] [PATCH] virtio: guard against negative vq notifies
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] virtio: guard against negative vq notifies |
Date: |
Thu, 19 May 2011 17:25:15 +0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Sun, May 08, 2011 at 10:29:07PM +0100, Stefan Hajnoczi wrote:
> The virtio_queue_notify() function checks that the virtqueue number is
> less than the maximum number of virtqueues. A signed comparison is used
> but the virtqueue number could be negative if a buggy or malicious guest
> is run. This results in memory accesses outside of the virtqueue array.
>
> It is risky doing input validation in common code instead of at the
> guest<->host boundary. Note that virtio_queue_set_addr(),
> virtio_queue_get_addr(), virtio_queue_get_num(), and many other virtio
> functions do *not* validate the virtqueue number argument.
>
> Instead of fixing the comparison in virtio_queue_notify(), move the
> comparison to the virtio bindings (just like VIRTIO_PCI_QUEUE_SEL) where
> we have a uint32_t value and can avoid ever calling into common virtio
> code if the virtqueue number is invalid.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
Looks good to me. Didn't test but
Acked-by: Michael S. Tsirkin <address@hidden>
Anthony, you are going to merge that? stable trees need that too,
probably very far back ...
> ---
> hw/syborg_virtio.c | 4 +++-
> hw/virtio-pci.c | 4 +++-
> hw/virtio.c | 4 +---
> 3 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/hw/syborg_virtio.c b/hw/syborg_virtio.c
> index 2f3e6da..00c7be8 100644
> --- a/hw/syborg_virtio.c
> +++ b/hw/syborg_virtio.c
> @@ -146,7 +146,9 @@ static void syborg_virtio_writel(void *opaque,
> target_phys_addr_t offset,
> vdev->queue_sel = value;
> break;
> case SYBORG_VIRTIO_QUEUE_NOTIFY:
> - virtio_queue_notify(vdev, value);
> + if (value < VIRTIO_PCI_QUEUE_MAX) {
> + virtio_queue_notify(vdev, value);
> + }
> break;
> case SYBORG_VIRTIO_STATUS:
> virtio_set_status(vdev, value & 0xFF);
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index c19629d..6862aa7 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -348,7 +348,9 @@ static void virtio_ioport_write(void *opaque, uint32_t
> addr, uint32_t val)
> vdev->queue_sel = val;
> break;
> case VIRTIO_PCI_QUEUE_NOTIFY:
> - virtio_queue_notify(vdev, val);
> + if (val < VIRTIO_PCI_QUEUE_MAX) {
> + virtio_queue_notify(vdev, val);
> + }
> break;
> case VIRTIO_PCI_STATUS:
> if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) {
> diff --git a/hw/virtio.c b/hw/virtio.c
> index 6e8814c..a651860 100644
> --- a/hw/virtio.c
> +++ b/hw/virtio.c
> @@ -585,9 +585,7 @@ void virtio_queue_notify_vq(VirtQueue *vq)
>
> void virtio_queue_notify(VirtIODevice *vdev, int n)
> {
> - if (n < VIRTIO_PCI_QUEUE_MAX) {
> - virtio_queue_notify_vq(&vdev->vq[n]);
> - }
> + virtio_queue_notify_vq(&vdev->vq[n]);
> }
>
> uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)
> --
> 1.7.4.4