linux-kernel - Re: [PATCH v3] virtio: pci: check bar values read from virtio config space

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Date:   Wed, 30 Mar 2022 02:35:55 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Keir Fraser <keirf@...gle.com>, kernel-team@...roid.com,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] virtio: pci: check bar values read from virtio config
 space

On Wed, Mar 30, 2022 at 10:43:40AM +0800, Jason Wang wrote:
> On Wed, Mar 23, 2022 at 10:07 PM Keir Fraser <keirf@...gle.com> wrote:
> >
> > virtio pci config structures may in future have non-standard bar
> > values in the bar field. We should anticipate this by skipping any
> > structures containing such a reserved value.
> >
> > The bar value should never change: check for harmful modified values
> > we re-read it from the config space in vp_modern_map_capability().
> >
> > Also clean up an existing check to consistently use PCI_STD_NUM_BARS.
> >
> > Signed-off-by: Keir Fraser <keirf@...gle.com>
> 
> Acked-by: Jason Wang <jasowang@...hat.com>
> 


Thanks! I don't want to rebase anymore though so not adding this ack.
Sorry!

> >  drivers/virtio/virtio_pci_modern.c     | 12 +++++++++---
> >  drivers/virtio/virtio_pci_modern_dev.c |  9 ++++++++-
> >  2 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > index 5455bc041fb6..6adfcd0297a7 100644
> > --- a/drivers/virtio/virtio_pci_modern.c
> > +++ b/drivers/virtio/virtio_pci_modern.c
> > @@ -293,7 +293,7 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
> >
> >         for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR); pos > 0;
> >              pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
> > -               u8 type, cap_len, id;
> > +               u8 type, cap_len, id, res_bar;
> >                 u32 tmp32;
> >                 u64 res_offset, res_length;
> >
> > @@ -315,9 +315,14 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
> >                 if (id != required_id)
> >                         continue;
> >
> > -               /* Type, and ID match, looks good */
> >                 pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap,
> > -                                                        bar), bar);
> > +                                                        bar), &res_bar);
> > +               if (res_bar >= PCI_STD_NUM_BARS)
> > +                       continue;
> > +
> > +               /* Type and ID match, and the BAR value isn't reserved.
> > +                * Looks good.
> > +                */
> >
> >                 /* Read the lower 32bit of length and offset */
> >                 pci_read_config_dword(dev, pos + offsetof(struct virtio_pci_cap,
> > @@ -337,6 +342,7 @@ static int virtio_pci_find_shm_cap(struct pci_dev *dev, u8 required_id,
> >                                                      length_hi), &tmp32);
> >                 res_length |= ((u64)tmp32) << 32;
> >
> > +               *bar = res_bar;
> >                 *offset = res_offset;
> >                 *len = res_length;
> >
> > diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> > index e8b3ff2b9fbc..591738ad3d56 100644
> > --- a/drivers/virtio/virtio_pci_modern_dev.c
> > +++ b/drivers/virtio/virtio_pci_modern_dev.c
> > @@ -35,6 +35,13 @@ vp_modern_map_capability(struct virtio_pci_modern_device *mdev, int off,
> >         pci_read_config_dword(dev, off + offsetof(struct virtio_pci_cap, length),
> >                               &length);
> >
> > +       /* Check if the BAR may have changed since we requested the region. */
> > +       if (bar >= PCI_STD_NUM_BARS || !(mdev->modern_bars & (1 << bar))) {
> > +               dev_err(&dev->dev,
> > +                       "virtio_pci: bar unexpectedly changed to %u\n", bar);
> > +               return NULL;
> > +       }
> > +
> >         if (length <= start) {
> >                 dev_err(&dev->dev,
> >                         "virtio_pci: bad capability len %u (>%u expected)\n",
> > @@ -120,7 +127,7 @@ static inline int virtio_pci_find_capability(struct pci_dev *dev, u8 cfg_type,
> >                                      &bar);
> >
> >                 /* Ignore structures with reserved BAR values */
> > -               if (bar > 0x5)
> > +               if (bar >= PCI_STD_NUM_BARS)
> >                         continue;
> >
> >                 if (type == cfg_type) {
> > --
> > 2.35.1.894.gb6a874cedc-goog
> >