linux-kernel - Re: [PATCH v2] applesmc: add sysfs file to report OSK

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Message-ID: <20121213190742.GQ2097@hedwig.ini.cmu.edu>
Date:	Thu, 13 Dec 2012 14:07:42 -0500
From:	"Gabriel L. Somlo" <somlo@....edu>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Guenter Roeck <groeck-dsl@...global.net>, khali@...ux-fr.org,
	linux@...ck-us.net, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org, agraf@...e.de, rene@...ctcode.com
Subject: Re: [PATCH v2] applesmc: add sysfs file to report OSK

On Thu, Dec 13, 2012 at 08:20:11AM +0100, Henrik Rydberg wrote:
> > The only viable (from a legal CYA standpoint) thing I can think of is
> > to make it easy to acquire the OSK automatically, on demand, directly
> > from the hardware. Right now, the logical place for that is applesmc.ko.
> > It already controls access to the SMC, and already reports values for
> > various keys.
> 
> How about encrypting the string with a key only found on an Apple
> computer? There are strings available in both ACPI and EFI that could
> serve such a purpose.

I'd still be distributing the copyrighted string. I don't expect
encryption to placate the proverbial lawyers, nor the project/distro
maintainers who want to avoid them :)

Plus, now I'd also be taking on the responsibility of deciding when
it's (legally) OK to let QEMU boot OS X and when it isn't.

Besides, the most obvious Apple-only key that fits your description
is the OSK itself ! :)

> Regarding the patch, I agree with Guenter that putting more unrelated
> things into the hwmon subsystem makes no sense. Most of the
> information in applesmc should go into the hwmon, thermal, backlight
> and input subsystems, but some strings should go somewhere else (maybe
> /sys/firmware/smc/?). The reluctance you experience here is a
> technical one; someone will need to make an effort to create a good
> place for your string, and it does not help that the string is, in
> fact, a constant. :-)
> 
> So, don't give up hope, but please do not expect an immediate solution.

OK, so if we agree that for legal-CYA reasons we must pretend to
ignore the constant-ness of the key value, are we now talking about
simply where in the sysfs hierarchy to place the node that will
spit it out ?

Right now it's under /sys/devices/platform/applesmc.768/
(i.e., it's a device, it's platform specific, and it's name is
applesmc-something).

The only ties to "hwmon" are that:
	- there's a "/sys/class/hwmon/hwmonX" symlink to the above
	  directory (among others, such as the graphics card and two
	  instances of "coretemp", at least on my MacPro5,1);
	- *most* of the files in it are indeed reporting sensor
	  readings;
	- the applesmc.c device driver source file itself lives under
	  drivers/hwmon/ in the kernel source tree.

Is it common practice to split off a subset of the values reported
by such a chip and make them show up elsehere (i.e. besides the
/sys/devices/platform/<chipname> folder) ? Does the relative size
of the subsets involved count as input into that decision proces ? :)

I personally don't know enough to have an opinion on where the best
place for this might be. You suggested "/sys/firmware/smc/", and I'd
be perfectly happy with that one too. Do you know who would decide
whether that's an acceptable alternative to /sys/devices/platform/applesmc ?

Thanks again,
--Gabriel
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