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

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

[Gustavo A. R. Silva]

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

diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 4d2f53a..b703f20 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -43,6 +43,8 @@
 #include <linux/mdev.h>
 #include <linux/debugfs.h>
 
+#include <linux/nospec.h>
+
 #include "i915_drv.h"
 #include "gvt.h"
 
@@ -1139,7 +1141,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
 	} 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;
@@ -1224,6 +1227,10 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
 				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;
 
-- 
2.7.4

Re: [PATCH] drm/i915/kvmgt: Fix potential Spectre v1

[Zhenyu Wang]

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On 2018.08.02 22:40:19 -0500, Gustavo A. R. Silva wrote:
> 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

Thanks for catching this! Applied.

> 
> 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>
> ---
>  drivers/gpu/drm/i915/gvt/kvmgt.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 4d2f53a..b703f20 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -43,6 +43,8 @@
>  #include <linux/mdev.h>
>  #include <linux/debugfs.h>
>  
> +#include <linux/nospec.h>
> +
>  #include "i915_drv.h"
>  #include "gvt.h"
>  
> @@ -1139,7 +1141,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  	} 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;
> @@ -1224,6 +1227,10 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  				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;
>  
> -- 
> 2.7.4
> 
> _______________________________________________
> intel-gvt-dev mailing list
> intel-gvt-dev@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev

-- 
Open Source Technology Center, Intel ltd.

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Re: [PATCH] drm/i915/kvmgt: Fix potential Spectre v1

[Gustavo A. R. Silva]

Hi Zhenyu,

On 8/6/18 9:26 PM, Zhenyu Wang wrote:
> On 2018.08.02 22:40:19 -0500, Gustavo A. R. Silva wrote:
>> 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
> 
> Thanks for catching this! Applied.
> 

Glad to help. :)

Thanks
--
Gustavo