On Wed, Sep 11, 2019 at 02:16:28PM +0200, Michal Hocko wrote: > On Wed 11-09-19 08:10:00, 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@xxxxxxxxxx> > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx> > > Tested-by: Jason Wang <jasowang@xxxxxxxxxx> > > no need to mark fo stable? Other spectre fixes tend to be backported > even when the security implications are not really clear. The risk > should be low and better to be covered in case. This is not really a fix - more a defence in depth thing, quite similar to e.g. commit b3bbfb3fb5d25776b8e3f361d2eedaabb0b496cd x86: Introduce __uaccess_begin_nospec() and uaccess_try_nospec in scope. That one doesn't seem to be tagged for stable. Was it queued there in practice? > > --- > > > > 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 > > -- > Michal Hocko > SUSE Labs
