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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 9 Sep 2019 10:45:10 -0400

On Mon, Sep 09, 2019 at 03:19:55PM +0800, Jason Wang wrote:
> 
> 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 <[email-masked]>
> > ---
> >   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

Should I push this to Linus right now then? It's a security thing so
maybe we better do it ASAP ... what's your opinion?

-- 
MST