virtio: pci: check bar values read from virtio config space

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@google.com>
Link: https://lore.kernel.org/r/20220323140727.3499235-1-keirf@google.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 30654d3a0b41ed6fca1a46f9dac6ac01d925da53..a2671a20ef779f9cec805ae53438890911c4dea1 100644 (file)
--- 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 e8b3ff2b9fbc223af9cf0a8607d364a2fb9a44f4..591738ad3d565bc4d26b053d7cc2b42b70eff0cb 100644 (file)
--- 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) {