[PATCH 4.9 11/28] vfio/pci: Fix potential Spectre v1

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

commit 0e714d27786ce1fb3efa9aac58abc096e68b1c2a upstream.

info.index can be indirectly controlled by user-space, hence leading
to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/vfio/pci/vfio_pci.c:734 vfio_pci_ioctl()
warn: potential spectre issue 'vdev->region'

Fix this by sanitizing info.index before indirectly using it to index
vdev->region

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/vfio/pci/vfio_pci.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -28,6 +28,7 @@
 #include <linux/uaccess.h>
 #include <linux/vfio.h>
 #include <linux/vgaarb.h>
+#include <linux/nospec.h>
 
 #include "vfio_pci_private.h"
 
@@ -755,6 +756,9 @@ static long vfio_pci_ioctl(void *device_
 			if (info.index >=
 			    VFIO_PCI_NUM_REGIONS + vdev->num_regions)
 				return -EINVAL;
+			info.index = array_index_nospec(info.index,
+							VFIO_PCI_NUM_REGIONS +
+							vdev->num_regions);
 
 			i = info.index - VFIO_PCI_NUM_REGIONS;