Subject: Re: [PATCH v2] vhost: block speculation of translated descriptors

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 11 Sep 2019 09:52:25 -0400

On Wed, Sep 11, 2019 at 08:10:00AM -0400, Michael S. Tsirkin wrote:
> iovec addresses coming from vhost are assumed to be
> pre-validated, but in fact can be speculated to a value
> out of range.
> 
> Userspace address are later validated with array_index_nospec so we can
> be sure kernel info does not leak through these addresses, but vhost
> must also not leak userspace info outside the allowed memory table to
> guests.
> 
> Following the defence in depth principle, make sure
> the address is not validated out of node range.
> 
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
> Acked-by: Jason Wang <[email-masked]>
> Tested-by: Jason Wang <[email-masked]>
> ---

Cc: [email-masked]

Pls advise on whether you'd like me to merge this directly,
Cc stable, or handle it in some other way.

> changes from v1: fix build on 32 bit
> 
>  drivers/vhost/vhost.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 5dc174ac8cac..34ea219936e3 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2071,8 +2071,10 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
>  		_iov = iov + ret;
>  		size = node->size - addr + node->start;
>  		_iov->iov_len = min((u64)len - s, size);
> -		_iov->iov_base = (void __user *)(unsigned long)
> -			(node->userspace_addr + addr - node->start);
> +		_iov->iov_base = (void __user *)
> +			((unsigned long)node->userspace_addr +
> +			 array_index_nospec((unsigned long)(addr - node->start),
> +					    node->size));
>  		s += size;
>  		addr += size;
>  		++ret;
> -- 
> MST