Re: [RFC PATCH untested] vhost: block speculation of translated descriptors

[Jason Wang <jasowang@redhat.com>]

On 2019/9/8 下午7:05, 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 <mst@redhat.com>
> ---
>   drivers/vhost/vhost.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 5dc174ac8cac..0ee375fb7145 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2072,7 +2072,9 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
>   		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);
> +			(node->userspace_addr +
> +			 array_index_nospec(addr - node->start,
> +					    node->size));
>   		s += size;
>   		addr += size;
>   		++ret;


I've tried this on Kaby Lake smap off metadata acceleration off using 
testpmd (virtio-user) + vhost_net. I don't see obvious performance 
difference with TX PPS.

Thanks