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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Max Gurtovoy <mgurtovoy@nvidia.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	virtualization <virtualization@lists.linux-foundation.org>,
	linux-block@vger.kernel.org, Yongji Xie <xieyongji@bytedance.com>,
	Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [PATCH v5] virtio-blk: Add validation for block size in config space
Date: Mon, 23 Aug 2021 08:13:34 -0400	[thread overview]
Message-ID: <20210823080952-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <7f0181d7-ff5c-0346-66ee-1de3ed23f5dd@nvidia.com>

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.

-- 
MST

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