Comment by iamnothere
13 hours ago
> Regulations say the baseband MUST control: all wireless signals (including wifi and GPS), all microphones and speakers, and it must be able to disable the camera electrically. It must have a tamper-resistant identifier (IMEI number ... kind of).
This is simply not true.
Source: I own a phone where this is not the case. Many Linux phones internally attach their wireless devices via USB, so there is good separation.
Also many upscale phones have decoupled the baseband from things that were once connected to it, as an attempt to improve security. (On iOS for instance the main CPU controls wifi.)
Connecting a cellular radio via USB provides far less isolation than the approach of a tiny kernel driver connected to an IOMMU isolated cellular radio on mainstream devices. USB has immense complexity and attack surface, especially with a standard Linux kernel configuration. Forensic data extraction companies mostly haven't bothered using attack vectors other than USB due to it being such a weak point. Many of the things people claim about cellular radios in mainstream smartphones are largely not true and they're missing that other radios are implemented in a very comparable way.
Cellular, Wi-Fi, Bluetooth, GNSS NFC, UWB, etc. do get implemented on secondary processors running their own OS but on mainstream smartphones those are typically well isolated and don't have privileged access to other components. The cellular radio in an iPhone or Pixel is on a separate chip but that's a separate thing from it being isolated. Snapdragon devices with cellular implemented by the main SoC still have an isolated radio. Snapdragon implements multiple radios via isolated processes in a microkernel-based RTOS where the overall baseband is also isolated from the rest of the device. There are a lot of lower quality implementations than iPhones, Pixels and Snapdragon devices but the intention is still generally to have the radios isolated even if they don't do it as well as those.
The Linux USB stack improves over time, and besides, implementing it with USB makes it easier to implement hardware toggle switches. (Cutting power pins to the USB modem is like unplugging it.)
Edit: I’ll add that I think smartphone “security” is almost impossible to achieve, given the complexity of everything and the opacity of modem vendor stacks, which is why I just assume endpoint compromise. I use my phone rarely and with toggle switches normally “off”, and I don’t consider it a secure device or use it very often. If you believe that a secure phone is possible, however, then Graphene is definitely a better fit than a Linux phone.
Just FYI the person you're replying to is intimately familiar with GrapheneOS
(Founder/lead dev/ex lead dev, can't recall exactly)
1 reply →
> cellular radio via USB provides far less isolation
Really? Does the radio somehow become the USB Host in this equation and magically start driving the conversation? How?