Re: [Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone

[Pavel Machek <pavel@ucw.cz>]

On Sat 2015-08-01 11:55:23, Mark Brown wrote:
> On Sat, Aug 01, 2015 at 12:03:06AM +0200, Pavel Machek wrote:
> > On Fri 2015-07-31 18:52:15, Mark Brown wrote:
> 
> > > Given that the baseband is a key part of the data path it's not like
> > > you're gaining anything there as far as I can see?   I suppose you could
> > > argue that the AP is actually an additional attack surface here.
> 
> > Actually yes, I believe I'm gaining a lot.
> 
> > If baseband is directly connected to the microphone, it can eavesdrop
> > on me while the phone appears to be idle.
> 
> Oh, right.  That's not an issue since there's generally routing control
> in the rest of the system (within the CODEC and sometimes elsewhere
> also) so you can isolate the baseband from the local audio sources and
> only connect it in call.  When not in use the CODEC will be powered down
> and even when in use by the AP you'd usually not route to the baseband.
> 
> The baseband normally doesn't have sufficient physical access to
> relevant control interfaces to get any input.

Ok, on many systems you are right, I guess.

That still leaves these reasons to route it though the CPU:

* ability to record calls

* ability to do signal processing on the data, like echo cancel for
  speakerphone (or perhaps changing your voice to female one)

* ability to do advanced stuff like GSM-to-VOIP gateway.

But yes, connecting baseband directly to audio is simpler...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html