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

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Date:   Wed, 30 Mar 2022 10:43:40 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Keir Fraser <keirf@...gle.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.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 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>

> ---
>  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
>