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

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Message-ID: <YkLHbkQ/JlNGwoTa@google.com>
Date:   Tue, 29 Mar 2022 08:46:38 +0000
From:   Keir Fraser <keirf@...gle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     kernel-team@...roid.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] virtio: pci: check bar values read from virtio config
 space


Ping.

If you prefer I could read the capability offset and length in
virtio_pci_find_capability() and communicate them to
vp_modern_map_capability(), perhaps via a new struct virtio_pci_cap
used for only this purpose?


On Wed, Mar 23, 2022 at 02:07:27PM +0000, Keir Fraser 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>
> ---
>  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
>