Re: [PATCH v4] isa-applesmc: provide OSK forwarding on Apple hosts

[Alexander Graf]

On 25.10.21 16:22, Daniel P. Berrangé wrote:
> On Mon, Oct 25, 2021 at 12:13:32PM +0200, Alexander Graf wrote:
> > On 22.10.21 18:14, Vladislav Yaroshchuk wrote:
> > > On Apple hosts we can read AppleSMC OSK key directly from host's
> > > SMC and forward this value to QEMU Guest.
> > >
> > > Usage:
> > > `-device isa-applesmc,hostosk=on`
> > >
> > > Apple licence allows use and run up to two additional copies
> > > or instances of macOS operating within virtual operating system
> > > environments on each Apple-branded computer that is already running
> > > the Apple Software, for purposes of:
> > > - software development
> > > - testing during software development
> > > - using macOS Server
> > > - personal, non-commercial use
> > >
> > > Guest macOS requires AppleSMC with correct OSK. The most legal
> > > way to pass it to the Guest is to forward the key from host SMC
> > > without any value exposion.
> > >
> > > Based on 
> > > https://web.archive.org/web/20200103161737/osxbook.com/book/bonus/chapter7/tpmdrmmyth/
> > >
> > > Signed-off-by: Vladislav Yaroshchuk <yaroshchuk2000@gmail.com>
>
> > > @@ -331,6 +464,25 @@ static void applesmc_isa_realize(DeviceState *dev, Error 
> > > **errp)
> > >        isa_register_ioport(&s->parent_obj, &s->io_err,
> > >                            s->iobase + APPLESMC_ERR_PORT);
> > > +    if (s->hostosk_flag) {
> > > +        /*
> > > +         * Property 'hostosk' has higher priority than 'osk'
> > > +         * and shadows it.
> > > +         * Free user-provided 'osk' property value
> > > +         */
> > > +        if (s->osk) {
> > > +            warn_report("isa-applesmc.osk is shadowed "
> > > +                        "by isa-applesmc.hostosk");
> > > +            g_free(s->osk);
> > > +        }
> > > +
> > > +        if (!applesmc_read_host_osk(&s->osk, &err)) {
> > > +            /* On host OSK retrieval error report a warning */
> > > +            error_report_err(err);
> > > +            s->osk = default_osk;
> > > +        }
> > > +    }
> >
> > This part is yucky. A few things:
> >
> > 1) QEMU in general does not fail user requested operations silently. If the
> > user explicitly asked to read the host OSK and we couldn't, it must
> > propagate that error.
> > 2) In tandem to the above, I think the only consistent CX is to make both
> > options mutually exclusive. The easiest way to achieve that IMHO would be to
> > overload the "osk" property. If it is "host", then use the host one.
> > 3) Should we make "osk"="host" the default on macOS as well then? Of course,
> > that one should *not* fail hard when it can't read the key, because it's an
> > implicit request rather than an explicit one.
> The problem with using a magic string value for the existing "osk"
> parameter is that this is not introspectable by management apps.


What introspectability would you like to have?


> IMHO, using an explicit separate parameter is the right approach.
>
> We just need to make sure we report an error properly via the
> 'Error **errp' parameter to this method instead of warn_report
> or error_report_err, when the user gives a non-sensible combination,
> or if reading the host value fails.


How about we change the default behavior altogether? Either you pass osk 
as argument, then that takes precedence. Or you don't, then we'll try to 
grab it from the host. If that fails, we error out (instead of the warn 
today).

That's a slight behavioral change, but I don't think anyone really wants 
to run the applesmc device without OSK in the first place. And at least 
we wouldn't break users that have working osk= configs.


Alex