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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     "Enrico Weigelt, metux IT consult" <lkml@metux.net>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Alex Williamson <alex.williamson@redhat.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Robin Murphy <robin.murphy@arm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        David Gibson <david@gibson.dropbear.id.au>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Jason Wang <jasowang@redhat.com>
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <671efe89-2430-04fa-5f31-f52589276f01@redhat.com>
Date:   Wed, 9 Jun 2021 11:11:17 +0200
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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.

Paolo