linux-kernel - Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest

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Message-ID: <20211001190048.GA512418@rowland.harvard.edu>
Date:   Fri, 1 Oct 2021 15:00:48 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Jason Wang <jasowang@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for
 confidential guest

On Fri, Oct 01, 2021 at 11:09:52AM -0700, Dan Williams wrote:
> On Fri, Oct 1, 2021 at 9:47 AM Alan Stern <stern@...land.harvard.edu> wrote:
> >
> > On Fri, Oct 01, 2021 at 09:13:54AM -0700, Dan Williams wrote:
> > > Bear with me, and perhaps it's a lack of imagination on my part, but I
> > > don't see how to get to a globally generic "authorized" sysfs ABI
> > > given that USB and Thunderbolt want to do bus specific actions on
> > > authorization toggle events. Certainly a default generic authorized
> > > attribute can be defined for all the other buses that don't have
> > > legacy here, but Thunderbolt will still require support for '2' as an
> > > authorized value, and USB will still want to base probe decisions on
> > > the authorization state of both the usb_device and the usb_interface.
> >
> > The USB part isn't really accurate (I can't speak for Thunderbolt).
> > When a usb_device is deauthorized, the device will be unconfigured,
> > deleting all its interfaces and removing the need for any probe
> > decisions about them.  In other words, the probe decision for a
> > usb_device or usb_interface depends only on the device's/interface's
> > own authorization state.
> >
> > True, the interface binding code does contain a test of the device's
> > authorization setting.  That test is redundant and can be removed.
> >
> > The actions that USB wants to take on authorization toggle events for
> > usb_devices are: for authorize, select and install a configuration;
> > for deauthorize, unconfigure the device.  Each of these could be
> > handled simply enough just by binding/unbinding the device.  (There
> > is some special code for handling wireless USB devices, but wireless
> > USB is now defunct.)
> 
> Ah, so are you saying that it would be sufficient for USB if the
> generic authorized implementation did something like:
> 
> dev->authorized = 1;
> device_attach(dev);
> 
> ...for the authorize case, and:
> 
> dev->authorize = 0;
> device_release_driver(dev);
> 
> ...for the deauthorize case?

Yes, I think so.  But I haven't tried making this change to test and 
see what really happens.

Alan Stern