Subject: Re: [PATCH v14 30/42] virtio_pci: introduce helper to get/set queue reset

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 22 Sep 2023 06:46:39 -0400

On Fri, Sep 22, 2023 at 09:49:18AM +0800, Xuan Zhuo wrote:
> On Thu, 21 Sep 2023 10:02:53 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > On Mon, Aug 01, 2022 at 02:38:50PM +0800, Xuan Zhuo wrote:
> > > Introduce new helpers to implement queue reset and get queue reset
> > > status.
> > >
> > >  https://github.com/oasis-tcs/virtio-spec/issues/124
> > >  https://github.com/oasis-tcs/virtio-spec/issues/139
> > >
> > > Signed-off-by: Xuan Zhuo <[email-masked]>
> > > Acked-by: Jason Wang <[email-masked]>
> > > ---
> > >  drivers/virtio/virtio_pci_modern_dev.c | 39 ++++++++++++++++++++++++++
> > >  include/linux/virtio_pci_modern.h      |  2 ++
> > >  2 files changed, 41 insertions(+)
> > >
> > > diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> > > index fa2a9445bb18..869cb46bef96 100644
> > > --- a/drivers/virtio/virtio_pci_modern_dev.c
> > > +++ b/drivers/virtio/virtio_pci_modern_dev.c
> > > @@ -3,6 +3,7 @@
> > >  #include <linux/virtio_pci_modern.h>
> > >  #include <linux/module.h>
> > >  #include <linux/pci.h>
> > > +#include <linux/delay.h>
> > >
> > >  /*
> > >   * vp_modern_map_capability - map a part of virtio pci capability
> > > @@ -474,6 +475,44 @@ void vp_modern_set_status(struct virtio_pci_modern_device *mdev,
> > >  }
> > >  EXPORT_SYMBOL_GPL(vp_modern_set_status);
> > >
> > > +/*
> > > + * vp_modern_get_queue_reset - get the queue reset status
> > > + * @mdev: the modern virtio-pci device
> > > + * @index: queue index
> > > + */
> > > +int vp_modern_get_queue_reset(struct virtio_pci_modern_device *mdev, u16 index)
> > > +{
> > > +	struct virtio_pci_modern_common_cfg __iomem *cfg;
> > > +
> > > +	cfg = (struct virtio_pci_modern_common_cfg __iomem *)mdev->common;
> > > +
> > > +	vp_iowrite16(index, &cfg->cfg.queue_select);
> > > +	return vp_ioread16(&cfg->queue_reset);
> > > +}
> > > +EXPORT_SYMBOL_GPL(vp_modern_get_queue_reset);
> > > +
> >
> > Actually, this does not validate that the config structure is big
> > enough. So it can access some unrelated memory. Don't know whether
> > that's exploitable e.g. for CoCo but not nice, anyway.
> > Need to validate the size and disable reset if it's too small.
> 
> 
> static int vp_modern_disable_vq_and_reset(struct virtqueue *vq)
> {
> 	struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
> 	struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
> 	struct virtio_pci_vq_info *info;
> 	unsigned long flags;
> 
> ->	if (!virtio_has_feature(vq->vdev, VIRTIO_F_RING_RESET))
> 		return -ENOENT;
> 
> 	vp_modern_set_queue_reset(mdev, vq->index);
> 
> 
> I checked VIRTIO_F_RING_RESET before call this.

Yes but the point is that virtio is used with untrusted devices
(e.g. for SEV/TDX), so you can't really assume config structures
are in sync with feature bits.

> Do you mean, we should put the check to this function.
> 
> 
> Thanks.
> 
> 
> 
> >
> >
> > > +/*
> > > + * vp_modern_set_queue_reset - reset the queue
> > > + * @mdev: the modern virtio-pci device
> > > + * @index: queue index
> > > + */
> > > +void vp_modern_set_queue_reset(struct virtio_pci_modern_device *mdev, u16 index)
> > > +{
> > > +	struct virtio_pci_modern_common_cfg __iomem *cfg;
> > > +
> > > +	cfg = (struct virtio_pci_modern_common_cfg __iomem *)mdev->common;
> > > +
> > > +	vp_iowrite16(index, &cfg->cfg.queue_select);
> > > +	vp_iowrite16(1, &cfg->queue_reset);
> > > +
> > > +	while (vp_ioread16(&cfg->queue_reset))
> > > +		msleep(1);
> > > +
> > > +	while (vp_ioread16(&cfg->cfg.queue_enable))
> > > +		msleep(1);
> > > +}
> > > +EXPORT_SYMBOL_GPL(vp_modern_set_queue_reset);
> > > +
> > >  /*
> > >   * vp_modern_queue_vector - set the MSIX vector for a specific virtqueue
> > >   * @mdev: the modern virtio-pci device
> > > diff --git a/include/linux/virtio_pci_modern.h b/include/linux/virtio_pci_modern.h
> > > index 05123b9a606f..c4eeb79b0139 100644
> > > --- a/include/linux/virtio_pci_modern.h
> > > +++ b/include/linux/virtio_pci_modern.h
> > > @@ -113,4 +113,6 @@ void __iomem * vp_modern_map_vq_notify(struct virtio_pci_modern_device *mdev,
> > >  				       u16 index, resource_size_t *pa);
> > >  int vp_modern_probe(struct virtio_pci_modern_device *mdev);
> > >  void vp_modern_remove(struct virtio_pci_modern_device *mdev);
> > > +int vp_modern_get_queue_reset(struct virtio_pci_modern_device *mdev, u16 index);
> > > +void vp_modern_set_queue_reset(struct virtio_pci_modern_device *mdev, u16 index);
> > >  #endif
> > > --
> > > 2.31.0
> >