linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Message-ID: <20210609115445.GX1002214@nvidia.com>
Date:   Wed, 9 Jun 2021 08:54:45 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Robin Murphy <robin.murphy@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Wed, Jun 09, 2021 at 11:11:17AM +0200, Paolo Bonzini wrote:
> On 09/06/21 10:51, Enrico Weigelt, metux IT consult wrote:
> > On 08.06.21 21:00, Jason Gunthorpe wrote:
> > 
> > > Eg I can do open() on a file and I get to keep that FD. I get to keep
> > > that FD even if someone later does chmod() on that file so I can't
> > > open it again.
> > > 
> > > There are lots of examples where a one time access control check
> > > provides continuing access to a resource. I feel the ongoing proof is
> > > the rarity in Unix.. 'revoke' is an uncommon concept in Unix..
> > 
> > Yes, it's even possible that somebody w/ privileges opens an fd and
> > hands it over to somebody unprivileged (eg. via unix socket). This is
> > a very basic unix concept. If some (already opened) fd now suddenly
> > behaves differently based on the current caller, that would be a break
> > with traditional unix semantics.
> 
> That's already more or less meaningless for both KVM and VFIO, since they
> are tied to an mm.

vfio isn't supposed to be tied to a mm.

Jason