linux-kernel - Re: [PATCH 0/4] Fix probe failed when modprobe modules

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Date:   Tue, 20 Dec 2022 14:44:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Li Zetao <lizetao1@...wei.com>, pbonzini@...hat.com,
        stefanha@...hat.com, axboe@...nel.dk, kraxel@...hat.com,
        david@...hat.com, ericvh@...il.com, lucho@...kov.net,
        asmadeus@...ewreck.org, linux_oss@...debyte.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, rusty@...tcorp.com.au,
        virtualization@...ts.linux-foundation.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH 0/4] Fix probe failed when modprobe modules

On Mon, Dec 19, 2022 at 6:15 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Tue, Nov 29, 2022 at 11:37:09AM +0800, Jason Wang wrote:
> > >
> > >
> > > Quite a lot of core work here. Jason are you still looking into
> > > hardening?
> >
> > Yes, last time we've discussed a solution that depends on the first
> > kick to enable the interrupt handler. But after some thought, it seems
> > risky since there's no guarantee that the device work in this way.
> >
> > One example is the current vhost_net, it doesn't wait for the kick to
> > process the rx packets. Any more thought on this?
> >
> > Thanks
>
> Specifically virtio net is careful to call virtio_device_ready
> under rtnl lock so buffers are only added after DRIVER_OK.

Right but it only got fixed this year after some code audit.

>
> However we do not need to tie this to kick, this is what I wrote:
>
> > BTW Jason, I had the idea to disable callbacks until driver uses the
> > virtio core for the first time (e.g. by calling virtqueue_add* family of
> > APIs). Less aggressive than your ideas but I feel it will add security
> > to the init path at least.
>
> So not necessarily kick, we can make adding buffers allow the
> interrupt.

Some questions:

1) It introduces a code defined behaviour other than depending on the
spec defined behavior like DRIVER_OK, this will lead extra complexity
in auditing
2) there's no guarantee that the interrupt handler is ready before
virtqueue_add(), or it requires barriers before virtqueue_add() to
make sure the handler is commit

So it looks to me the virtio_device_ready() should be still the
correct way to go:

1) it depends on spec defined behaviour like DRIVER_OK, and it then
can comply with possible future security requirement of drivers
defined in the spec
2) choose to use a new boolean instead of reusing vq->broken
3) enable the harden in driver one by one

Does it make sense?

Thanks

>
>
>
> --
> MST
>