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Subject: Re: [PATCH v5] virtio-blk: Add validation for block size in config
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To:     Yongji Xie <xieyongji@bytedance.com>
CC:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
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From:   Max Gurtovoy <mgurtovoy@nvidia.com>
Message-ID: <06af4897-7339-fca7-bdd9-e0f9c2c6195b@nvidia.com>
Date:   Mon, 23 Aug 2021 12:04:35 +0300
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On 8/23/2021 11:35 AM, Yongji Xie wrote:
> On Mon, Aug 23, 2021 at 4:07 PM Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
>>
>> On 8/23/2021 7:31 AM, Yongji Xie wrote:
>>> On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
>>>> On 8/9/2021 1:16 PM, Xie Yongji wrote:
>>>>> An untrusted device might presents an invalid block size
>>>>> in configuration space. This tries to add validation for it
>>>>> in the validate callback and clear the VIRTIO_BLK_F_BLK_SIZE
>>>>> feature bit if the value is out of the supported range.
>>>> This is not clear to me. What is untrusted device ? is it a buggy device ?
>>>>
>>> A buggy device, the devices in an encrypted VM, or a userspace device
>>> created by VDUSE [1].
>>>
>>> [1] https://lore.kernel.org/kvm/20210818120642.165-1-xieyongji@bytedance.com/
>> if it's a userspace device, why don't you fix its control path code
>> instead of adding workarounds in the kernel driver ?
>>
> VDUSE kernel module would not touch (be aware of) the device specific
> configuration space. It should be more reasonable to fix it in the
> device driver. There is also some existing interface (.validate()) for
> doing that.

who is emulating the device configuration space ?

> And regardless of userspace device, we still need to fix it for other cases.

which cases ? Do you know that there is a buggy HW we need to workaround ?


> Thanks,
> Yongji