linux-kernel - Re: [PATCH] vfio/pci: Fix potential Spectre v1

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Date:   Wed, 18 Jul 2018 14:33:36 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio/pci: Fix potential Spectre v1

On Tue, 17 Jul 2018 12:39:00 -0500
"Gustavo A. R. Silva" <gustavo@...eddedor.com> 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/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@...r.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 4 ++++
>  1 file changed, 4 insertions(+)

Applied to vfio for-linus branch for v4.18.  Thanks!

Alex


> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index b423a30..125b58e 100644
> --- 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"
>  
> @@ -727,6 +728,9 @@ static long vfio_pci_ioctl(void *device_data,
>  			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;
>