[PATCH 4.14 002/217] drm/i915/kvmgt: Fix potential Spectre v1

Greg Kroah-Hartman
2018-08-23T08:18:11Z

From: Gustavo A. R. Silva <gustavo@embeddedor.com>

commit de5372da605d3bca46e3102bab51b7e1c0e0a6f6 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/gpu/drm/i915/gvt/kvmgt.c:1232 intel_vgpu_ioctl() warn:
potential spectre issue 'vgpu->vdev.region' [r]

Fix this by sanitizing info.index before indirectly using it to index
vgpu->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@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/i915/gvt/kvmgt.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -42,6 +42,8 @@
#include <linux/vfio.h>
#include <linux/mdev.h>

+#include <linux/nospec.h>
+
#include "i915_drv.h"
#include "gvt.h"

@@ -953,7 +955,8 @@ static long intel_vgpu_ioctl(struct mdev
} else if (cmd == VFIO_DEVICE_GET_REGION_INFO) {
struct vfio_region_info info;
struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
- int i, ret;
+ unsigned int i;
+ int ret;
struct vfio_region_info_cap_sparse_mmap *sparse = NULL;
size_t size;
int nr_areas = 1;
@@ -1030,6 +1033,10 @@ static long intel_vgpu_ioctl(struct mdev
if (info.index >= VFIO_PCI_NUM_REGIONS +
vgpu->vdev.num_regions)
return -EINVAL;
+ info.index =
+ array_index_nospec(info.index,
+ VFIO_PCI_NUM_REGIONS +
+ vgpu->vdev.num_regions);

i = info.index - VFIO_PCI_NUM_REGIONS;