[Piskvorrr]

If it were a feature phone, this would be an accurate summary. For a smartphone, calling is a minority usage (an actual issue with the modem, sure) and network access is assumed over a hostile link anyway; does it matter if it's hostile at hop 1 or hop 2, if the modem is not a privileged part of the system?

[RL_Quine]

Right. We're just moving the DMZ, and that's for a lot of cases totally fine. Rather than how people would assume it works like this.

    CPU -> LTE Modem || DMZ || Cellphone Provider

We have this for the Pinephone.

    CPU || DMZ || LTE Modem -> Cellphone Provider

This is fine.

Remember that in the first model, and in most typical phones, the LTE Modem have above root access to the CPU through DMA. The exception is some more modern devices like the iPhone, which give the modem a specific sandbox device to DMA into that's not the actual processor.

[my123]

On the iPhone, the modem has always been on a separate chip.

[detaro]

separate chip doesn't tell you anything about the security model.

[my123]

It was USB/HSIC and then switched over to PCIe with IOMMU.

[mirimir]

Right, regardless of chip configuration, modern phones use IOMMU for isolation. Arguably the main advantage of the PinePhone and Librem 5 is the kill switches.

[numpad0]

An FBI tracker under your car is not a privileged part of your car

[throwaway41597]

Could it be made less bad if you could turn the tracker off (switch to airplane mode by physically removing power from the modem) any time you want?

It'd be nice if the PinePhone supported this.

[mirimir]

Both the PinePhone and Librem 5 have physical kill switches for the modems.

[Piskvorrr]

I do not follow the car analogy, please explain.

[lvh]

Not GP: but I assume the answer is "because GPS is in the modem, the closed source untrusted part could still be actively disclosing your location".

[lallysingh]

.. But the modem itself is broadcasting it's identity to multiple radio receivers. Is there enough of a difference wrt GPS positioning for the distinction to matter?

[lvh]

Sure, I agree it’s subtle. But it is: a) much higher resolution b) potentially to a specific third party who may not have access to cell network data. Like, say, an angry ex-spouse.

[Piskvorrr]

Aha! That is a valid concern indeed. Lesser than the usual "baseband has full access to whole system", but still significant.