[sounds]

TL;DR yes, the BB cpu has full access to everything, including the "main" cpu and all running processes. Why not, right? :)

It is important to note that all smartphone chips are optimized first for low cost and low power usage.

To actually isolate the baseband processor+GPS+Cell radio+Mic+Speaker would require a second high-speed bus.

Most cell phone processor designs put both the baseband and application processor in the same package both for cost and power saving reasons. Since both processors are typically ARM cores they will easily interface to the same bus for memory and peripherals. Only having one external bus means fewer external components, which is typically the strongest factor relative to the total power and cost.

There is also the legacy element. The article notes that most of the BB code is at least a decade old by now. Unless that code got a major rewrite, it would not run on a new, isolated architecture.

Specific processor block diagrams:

Samsung - https://memorylink.samsung.com/ecomobile/mem/ecomobile/appli...

Qualcomm (page 4) - https://developer.qualcomm.com/download/qusnapdragons4whitep...

[jwise0]

That's not always the case. For instance, on Galaxy Nexus (CDMA), the radio is split from the AP, and are in fact manufactured by two completely different folks (the AP is TI OMAP, and the radio is VIA Telecom). I'd imagine the same thing with Mediatek, who is a large and growing player. You are right that Qualcomm does fuse their radio with their AP, though, and they do control quite a lot of the US market.

[sounds]

Well, good, if the radio and baseband do not live on-die with the AP. Market forces are pushing for a completely integrated design, but it's interesting from a security perspective.

The baseband is still considered the master CPU during boot - at least on the CDMA Nexus. So although there are some corner cases in terms of architecture, the security model is still completely broken. Send a payload to the baseband over the air, compromise it, and the entire phone is yours.

[akgerber]

Qualcomm mostly has the modem on the same chip as the apps processor, but not always: the recently-popular APQ8064[0] (used in the Nexus 4) had a separate modem.

[0]http://en.wikipedia.org/wiki/Snapdragon_%28system_on_chip%29