netdev - Re: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE

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Message-ID: <CACycT3tL7URz3n-KhMAwYH+Sn1e1TSyfU+RKcc8jpPDJ7WcZ2w@mail.gmail.com>
Date:   Thu, 15 Apr 2021 19:17:08 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE

On Thu, Apr 15, 2021 at 5:05 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2021/4/15 下午4:36, Jason Wang 写道:
> >>>
> >> Please state this explicitly at the start of the document. Existing
> >> interfaces like FUSE are designed to avoid trusting userspace.
> >
> >
> > There're some subtle difference here. VDUSE present a device to kernel
> > which means IOMMU is probably the only thing to prevent a malicous
> > device.
> >
> >
> >> Therefore
> >> people might think the same is the case here. It's critical that people
> >> are aware of this before deploying VDUSE with virtio-vdpa.
> >>
> >> We should probably pause here and think about whether it's possible to
> >> avoid trusting userspace. Even if it takes some effort and costs some
> >> performance it would probably be worthwhile.
> >
> >
> > Since the bounce buffer is used the only attack surface is the
> > coherent area, if we want to enforce stronger isolation we need to use
> > shadow virtqueue (which is proposed in earlier version by me) in this
> > case. But I'm not sure it's worth to do that.
>
>
>
> So this reminds me the discussion in the end of last year. We need to
> make sure we don't suffer from the same issues for VDUSE at least
>
> https://yhbt.net/lore/all/c3629a27-3590-1d9f-211b-c0b7be152b32@redhat.com/T/#mc6b6e2343cbeffca68ca7a97e0f473aaa871c95b
>
> Or we can solve it at virtio level, e.g remember the dma address instead
> of depending on the addr in the descriptor ring
>

I might miss something. But VDUSE has recorded the dma address during
dma mapping, so we would not do bouncing if the addr/length is invalid
during dma unmapping. Is it enough?

Thanks,
Yongji