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

[Michael S. Tsirkin]

On Mon, Aug 23, 2021 at 08:40:30PM +0800, Yongji Xie wrote:
> On Mon, Aug 23, 2021 at 8:13 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >
> > On Mon, Aug 23, 2021 at 01:45:31PM +0300, Max Gurtovoy wrote:
> > > It helpful if there is a justification for this.
> > >
> > > In this case, no such HW device exist and the only device that can cause
> > > this trouble today is user space VDUSE device that must be validated by the
> > > emulation VDUSE kernel driver.
> > >
> > > Otherwise, will can create 1000 commit like this in the virtio level (for
> > > example for each feature for each virtio device).
> >
> > Yea, it's a lot of work but I don't think it's avoidable.
> >
> > > >
> > > > > > > > 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 ?
> > > > > > >
> > > > > > No, there isn't now. But this could be a potential attack surface if
> > > > > > the host doesn't trust the device.
> > > > > If the host doesn't trust a device, why it continues using it ?
> > > > >
> > > > IIUC this is the case for the encrypted VMs.
> > >
> > > what do you mean encrypted VM ?
> > >
> > > And how this small patch causes a VM to be 100% encryption supported ?
> > >
> > > > > Do you suggest we do these workarounds in all device drivers in the kernel ?
> > > > >
> > > > Isn't it the driver's job to validate some unreasonable configuration?
> > >
> > > The check should be in different layer.
> > >
> > > Virtio blk driver should not cover on some strange VDUSE stuff.
> >
> > Yes I'm not convinced VDUSE is a valid use-case. I think that for
> > security and robustness it should validate data it gets from userspace
> > right there after reading it.
> > But I think this is useful for the virtio hardening thing.
> > https://lwn.net/Articles/865216/
> >
> > Yongji - I think the commit log should be much more explicit that
> > this is hardening. Otherwise people get confused and think this
> > needs a CVE or a backport for security.
> >
> 
> OK, do I need to send a v6? This patch seems to be already merged into
> Linus's tree.
> 
> Thanks,
> Yongji

No, it's a comment for the future - I assume you will keep adding this
kind of validation in other places.

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MST