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

Michael S. Tsirkin
2019-09-11T13:52:36Z

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 <mst@redhat.com>
> Acked-by: Jason Wang <jasowang@redhat.com>
> Tested-by: Jason Wang <jasowang@redhat.com>
> ---

Cc: security@kernel.org

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