4 ms·

And isn't the message encrypted before it gets to the baseband?

by nsxwolf 12y ago

nitrogen 12y ago
The baseband has direct access to the application processor's RAM in many (most?) mobile designs.
- nsxwolf 12y ago
  That's... horrible... why?!
  - JoshTriplett 12y ago
    Partly because, historically (e.g. on feature phones), the GSM baseband serves as the primary processor (with real-time responsiveness requirements), with "applications" as a subordinate function. The concept of GSM being "just" a modem peripheral is a more recent development, coming more from the laptop arena; pushing that model down into phones (especially cheap phones) will take work. Even on top of that, the concept of not trusting your peripherals is a recent one as well. Ideally, all hardware peripherals would have no more permissions than they need; for instance, no ability to DMA except to specific pre-arranged regions. In practice, most systems don't actually set up that level of security.
    - nsxwolf 12y ago
      Is this true of say, the iPhone? It seems like a wifi iPad or iPod Touch is exactly the same as an iPhone, but without the baseband. If the baseband were a peripheral of the A8 SoC, this would seem like a trivial difference. But it seems if that's not the case, the iPad A8 would have considerable architectural differences compared to the iPhone one.
      - JoshTriplett 12y ago
        It's less true in some modern smartphones (disclaimer: not an expert on the iOS/iDevice architecture in particular), but a shocking amount of code still ends up on the baseband, and the baseband still has as much trust as the kernel. For example, the baseband processor often serves as an offloading engine for power efficiency reasons, to avoid waking up the main processor; thus, the baseband processor might have direct access to the audio hardware, so that phonecall audio doesn't need to wake up the host CPU.
- edude03 12y ago
  @nsxwolf because surprisingly the baseband is actually the main processor in most modern designs, the application processor (your quad core snapdragon or whatever) is a slave to the baseband and receives events and data it

And isn't the message encrypted before it gets to the baseband?

by nsxwolf 12y ago

And isn't the message encrypted before it gets to the baseband?

nitrogen 12y ago

The baseband has direct access to the application processor's RAM in many (most?) mobile designs.

nsxwolf 12y ago
That's... horrible... why?!
- JoshTriplett 12y ago
  Partly because, historically (e.g. on feature phones), the GSM baseband serves as the primary processor (with real-time responsiveness requirements), with "applications" as a subordinate function. The concept of GSM being "just" a modem peripheral is a more recent development, coming more from the laptop arena; pushing that model down into phones (especially cheap phones) will take work. Even on top of that, the concept of not trusting your peripherals is a recent one as well. Ideally, all hardware peripherals would have no more permissions than they need; for instance, no ability to DMA except to specific pre-arranged regions. In practice, most systems don't actually set up that level of security.
  - nsxwolf 12y ago
    Is this true of say, the iPhone? It seems like a wifi iPad or iPod Touch is exactly the same as an iPhone, but without the baseband. If the baseband were a peripheral of the A8 SoC, this would seem like a trivial difference. But it seems if that's not the case, the iPad A8 would have considerable architectural differences compared to the iPhone one.
    - JoshTriplett 12y ago
      It's less true in some modern smartphones (disclaimer: not an expert on the iOS/iDevice architecture in particular), but a shocking amount of code still ends up on the baseband, and the baseband still has as much trust as the kernel. For example, the baseband processor often serves as an offloading engine for power efficiency reasons, to avoid waking up the main processor; thus, the baseband processor might have direct access to the audio hardware, so that phonecall audio doesn't need to wake up the host CPU.
edude03 12y ago
@nsxwolf because surprisingly the baseband is actually the main processor in most modern designs, the application processor (your quad core snapdragon or whatever) is a slave to the baseband and receives events and data it