linux-kernel - Re: [PATCH v2 1/6] driver core: Move the "authorized" attribute from USB/Thunderbolt to core

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Date:   Thu, 30 Sep 2021 08:25:35 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 S . Tsirkin" <mst@...hat.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 1/6] driver core: Move the "authorized" attribute from
 USB/Thunderbolt to core

On Thu, Sep 30, 2021 at 8:00 AM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Sep 29, 2021 at 06:55:12PM -0700, Dan Williams wrote:
> > On Wed, Sep 29, 2021 at 6:43 PM Alan Stern <stern@...land.harvard.edu> wrote:
> > >
> > > On Wed, Sep 29, 2021 at 06:05:06PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > > > Currently bus drivers like "USB" or "Thunderbolt" implement a custom
> > > > version of device authorization to selectively authorize the driver
> > > > probes. Since there is a common requirement, move the "authorized"
> > > > attribute support to the driver core in order to allow it to be used
> > > > by other subsystems / buses.
> > > >
> > > > Similar requirements have been discussed in the PCI [1] community for
> > > > PCI bus drivers as well.
> > > >
> > > > No functional changes are intended. It just converts authorized
> > > > attribute from int to bool and moves it to the driver core. There
> > > > should be no user-visible change in the location or semantics of
> > > > attributes for USB devices.
> > > >
> > > > Regarding thunderbolt driver, although it declares sw->authorized as
> > > > "int" and allows 0,1,2 as valid values for sw->authorized attribute,
> > > > but within the driver, in all authorized attribute related checks,
> > > > it is treated as bool value. So when converting the authorized
> > > > attribute from int to bool value, there should be no functional
> > > > changes other than value 2 being not visible to the user.
> > > >
> > > > [1]: https://lore.kernel.org/all/CACK8Z6E8pjVeC934oFgr=VB3pULx_GyT2NkzAogdRQJ9TKSX9A@mail.gmail.com/
> > > >
> > > > Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > >
> > > Since you're moving the authorized flag from the USB core to the
> > > driver core, the corresponding sysfs attribute functions should be
> > > moved as well.
> >
> > Unlike when 'removable' moved from USB to the driver core there isn't
> > a common definition for how the 'authorized' sysfs-attribute behaves
> > across buses. The only common piece is where this flag is stored in
> > the data structure, i.e. the 'authorized' sysfs interface is
> > purposefully left bus specific.
>
> How about implementing "library" versions of show_authorized() and
> store_authorized() that the bus-specific attribute routines can call?
> These library routines would handle parsing the input values, storing
> the new flag, and displaying the stored flag value.  That way at
> least the common parts of these APIs would be centralized in the
> driver core, and any additional functionality could easily be added
> by the bus-specific attribute routine.
>

While show_authorized() seems like it could be standardized, have a
look at what the different store_authorized() implementations do.
Thunderbolt wants "switch approval" vs "switch challenge" and USB has
a bunch of bus-specific work to do when the authorization state
changes. I don't see much room for a library to help there as more
buses add authorization support. That said I do think it would be
useful to have a common implementation available for generic probe
authorization to toggle the flag if the bus does not have any
authorization work to do, but that seems a follow-on once this core is
accepted.