From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: "Jens Axboe" <axboe@kernel.dk>,
"Jonathan Corbet" <corbet@lwn.net>,
kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
netdev@vger.kernel.org, "Randy Dunlap" <rdunlap@infradead.org>,
"Matthew Wilcox" <willy@infradead.org>,
virtualization@lists.linux-foundation.org,
"Christoph Hellwig" <hch@infradead.org>,
"Christian Brauner" <christian.brauner@canonical.com>,
bcrl@kvack.org, viro@zeniv.linux.org.uk,
"Stefan Hajnoczi" <stefanha@redhat.com>,
linux-fsdevel@vger.kernel.org,
"Dan Carpenter" <dan.carpenter@oracle.com>,
"Mika Penttilä" <mika.penttila@nextfour.com>
Subject: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE
Date: Fri, 16 Apr 2021 11:02:57 +0800 [thread overview]
Message-ID: <17e3312e-686b-c5dd-852d-e9ffb7f4c707@redhat.com> (raw)
In-Reply-To: <CACycT3tyksBYxgbQLFJ-mFCKkaWotucM5_ho_K3q4wMpR0P=gw@mail.gmail.com>
在 2021/4/16 上午10:58, Yongji Xie 写道:
> On Fri, Apr 16, 2021 at 10:20 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> 在 2021/4/15 下午7:17, Yongji Xie 写道:
>>> On Thu, Apr 15, 2021 at 5:05 PM Jason Wang <jasowang@redhat.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?
>>
>> E.g malicous device write a buggy dma address in the descriptor ring, so
>> we had:
>>
>> vring_unmap_one_split(desc->addr, desc->len)
>> dma_unmap_single()
>> vduse_dev_unmap_page()
>> vduse_domain_bounce()
>>
>> And in vduse_domain_bounce() we had:
>>
>> while (size) {
>> map = &domain->bounce_maps[iova >> PAGE_SHIFT];
>> offset = offset_in_page(iova);
>> sz = min_t(size_t, PAGE_SIZE - offset, size);
>>
>> This means we trust the iova which is dangerous and exacly the issue
>> mentioned in the above link.
>>
>> From VDUSE level need to make sure iova is legal.
>>
> I think we already do that in vduse_domain_bounce():
>
> while (size) {
> map = &domain->bounce_maps[iova >> PAGE_SHIFT];
>
> if (WARN_ON(!map->bounce_page ||
> map->orig_phys == INVALID_PHYS_ADDR))
> return;
So you don't check whether iova is legal before using it, so it's at
least a possible out of bound access of the bounce_maps[] isn't it? (e.g
what happens if iova is ULLONG_MAX).
>
>
>> From virtio level, we should not truse desc->addr.
>>
> We would not touch desc->addr after vring_unmap_one_split(). So I'm
> not sure what we need to do at the virtio level.
I think the point is to record the dma addres/len somewhere instead of
reading them from descriptor ring.
Thanks
>
> Thanks,
> Yongji
>
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next prev parent reply other threads:[~2021-04-16 3:03 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210331080519.172-1-xieyongji@bytedance.com>
[not found] ` <20210331080519.172-2-xieyongji@bytedance.com>
[not found] ` <20210331091545.lr572rwpyvrnji3w@wittgenstein>
2021-03-31 9:26 ` [PATCH v6 01/10] file: Export receive_fd() to modules Dan Carpenter
[not found] ` <20210331080519.172-8-xieyongji@bytedance.com>
2021-04-08 2:36 ` [PATCH v6 07/10] vdpa: Support transferring virtual addressing during DMA mapping Jason Wang
[not found] ` <20210331080519.172-9-xieyongji@bytedance.com>
2021-04-08 3:25 ` [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver Jason Wang
[not found] ` <20210331080519.172-10-xieyongji@bytedance.com>
2021-04-08 6:57 ` [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace Jason Wang
[not found] ` <CACycT3v_KFQXoxRbEj8c0Ve6iKn9RbibtBDgBFs=rf0ZOmTBBQ@mail.gmail.com>
2021-04-09 5:36 ` Jason Wang
[not found] ` <CACycT3vwATp4+Ao0fjuyeeLQN+xHH=dXF+JUyuitkn4k8hELnA@mail.gmail.com>
2021-04-12 7:16 ` Jason Wang
[not found] ` <CACycT3vxO21Yt6+px2c2Q8DONNUNehdo2Vez_RKQCKe76CM2TA@mail.gmail.com>
2021-04-12 9:37 ` Jason Wang
[not found] ` <CACycT3vbDhUKM0OX-zo02go09gh2+EEdyZ_YQuz8PXzo3EngXw@mail.gmail.com>
2021-04-13 3:35 ` Jason Wang
[not found] ` <CACycT3tHxtfgQhQgv0VyF_U523qASEv1Ydc4XuX43MFRzGVbfw@mail.gmail.com>
2021-04-14 8:18 ` Jason Wang
2021-04-16 3:24 ` Jason Wang
[not found] ` <20210331080519.172-4-xieyongji@bytedance.com>
2021-04-09 16:15 ` [PATCH v6 03/10] vhost-vdpa: protect concurrent access to vhost device iotlb Michael S. Tsirkin
[not found] ` <CACycT3tPWwpGBNEqiL4NPrwGZhmUtAVHUZMOdbSHzjhN-ytg_A@mail.gmail.com>
2021-04-11 20:48 ` Michael S. Tsirkin
[not found] ` <CACycT3v5Z8s9_pL79m0FY5jxx3fTRHHbtARfg0On3xTnNCOdkg@mail.gmail.com>
2021-04-12 9:00 ` Michael S. Tsirkin
2021-04-14 7:34 ` [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace Michael S. Tsirkin
2021-04-14 7:49 ` Jason Wang
[not found] ` <20210331080519.172-11-xieyongji@bytedance.com>
2021-04-08 7:18 ` [PATCH v6 10/10] Documentation: Add documentation for VDUSE Jason Wang
2021-04-14 14:14 ` Stefan Hajnoczi
[not found] ` <CACycT3uNR+nZY5gY0UhPkeOyi7Za6XkX4b=hasuDcgqdc7fqfg@mail.gmail.com>
2021-04-15 7:19 ` Stefan Hajnoczi
2021-04-15 8:36 ` Jason Wang
2021-04-15 9:04 ` Jason Wang
[not found] ` <CACycT3tL7URz3n-KhMAwYH+Sn1e1TSyfU+RKcc8jpPDJ7WcZ2w@mail.gmail.com>
2021-04-16 2:20 ` Jason Wang
[not found] ` <CACycT3tyksBYxgbQLFJ-mFCKkaWotucM5_ho_K3q4wMpR0P=gw@mail.gmail.com>
2021-04-16 3:02 ` Jason Wang [this message]
2021-04-15 14:38 ` Stefan Hajnoczi
2021-04-16 2:23 ` Jason Wang
[not found] ` <CACycT3u_qAE=D_ezLPU9SpXPMACErmpqpH5pMg0TZAb3CZVGdg@mail.gmail.com>
2021-04-16 5:39 ` Jason Wang
[not found] ` <CACycT3tRN1n_PJm1mu3=s1dK941Pac15cpaysqZZKLR6xKaXSg@mail.gmail.com>
2021-04-15 14:17 ` Re: " Stefan Hajnoczi
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