Re: [PATCH v9 13/17] vdpa: factor out vhost_vdpa_pa_map() and vhost_vdpa_pa_unmap()

[Yongji Xie <xieyongji@bytedance.com>]

On Tue, Jul 13, 2021 at 7:31 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Tue, Jul 13, 2021 at 04:46:52PM +0800, Xie Yongji wrote:
> > @@ -613,37 +618,28 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v, u64 iova, u64 size)
> >       }
> >  }
> >
> > -static int vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
> > -                                        struct vhost_iotlb_msg *msg)
> > +static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
> > +                          u64 iova, u64 size, u64 uaddr, u32 perm)
> >  {
> >       struct vhost_dev *dev = &v->vdev;
> > -     struct vhost_iotlb *iotlb = dev->iotlb;
> >       struct page **page_list;
> >       unsigned long list_size = PAGE_SIZE / sizeof(struct page *);
> >       unsigned int gup_flags = FOLL_LONGTERM;
> >       unsigned long npages, cur_base, map_pfn, last_pfn = 0;
> >       unsigned long lock_limit, sz2pin, nchunks, i;
> > -     u64 iova = msg->iova;
> > +     u64 start = iova;
> >       long pinned;
> >       int ret = 0;
> >
> > -     if (msg->iova < v->range.first ||
> > -         msg->iova + msg->size - 1 > v->range.last)
> > -             return -EINVAL;
>
> This is not related to your patch, but can the "msg->iova + msg->size"
> addition can have an integer overflow.  From looking at the callers it
> seems like it can.  msg comes from:
>   vhost_chr_write_iter()
>   --> dev->msg_handler(dev, &msg);
>       --> vhost_vdpa_process_iotlb_msg()
>          --> vhost_vdpa_process_iotlb_update()
>
> If I'm thinking of the right thing then these are allowed to overflow to
> 0 because of the " - 1" but not further than that.  I believe the check
> needs to be something like:
>
>         if (msg->iova < v->range.first ||
>             msg->iova - 1 > U64_MAX - msg->size ||
>             msg->iova + msg->size - 1 > v->range.last)
>

Make sense.

> But writing integer overflow check correctly is notoriously difficult.
> Do you think you could send a fix for that which is separate from the
> patcheset?  We'd want to backport it to stable.
>

OK, I will send a patch to fix it.

Thanks,
Yongji