linux-kernel - Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user

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Date:   Tue, 28 Sep 2021 08:54:31 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "hch@....de" <hch@....de>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "corbet@....net" <corbet@....net>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>
Subject: Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma
 interfaces

On Tue, Sep 28, 2021 at 07:13:01AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Monday, September 27, 2021 10:40 PM
> > 
> > On Mon, Sep 27, 2021 at 01:32:34PM +0000, Tian, Kevin wrote:
> > 
> > > but I'm little worried that even vfio-pci itself cannot be bound now,
> > > which implies that all devices in a group which are intended to be
> > > used by the user must be bound to vfio-pci in a breath before the
> > > user attempts to open any of them, i.e. late-binding and device-
> > > hotplug is disallowed after the initial open. I'm not sure how
> > > important such an usage would be, but it does cause user-tangible
> > > semantics change.
> > 
> > Oh, that's bad..
> > 
> > I guess your approach is the only way forward, it will have to be
> > extensively justified in the commit message for Greg et al.
> > 
> 
> Just thought about another alternative. What about having driver
> core to call iommu after call_driver_probe()?

Then the kernel is now already exposed to an insecure scenario, we
must not do probe if any user device is attached at all.

Jason