linux-kernel - Re: [PATCH v5] virtio-blk: Add validation for block size in config space

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Message-ID: <CACycT3v83sVvUWxZ-+SDyeXMPiYd0zi5mtmg8AkXYgVLxVpTvA@mail.gmail.com>
Date:   Mon, 23 Aug 2021 16:35:17 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Max Gurtovoy <mgurtovoy@...dia.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-block@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] virtio-blk: Add validation for block size in config space

On Mon, Aug 23, 2021 at 4:07 PM Max Gurtovoy <mgurtovoy@...dia.com> wrote:
>
>
> On 8/23/2021 7:31 AM, Yongji Xie wrote:
> > On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy <mgurtovoy@...dia.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.

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

Thanks,
Yongji