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points by jrexilius 2 days ago | 0 comments
It concerns me as well as the user-land OS isn't really where control of the RF happens. The OS running in their baseband chip is where the backdoors would best be placed from their perspective. But I'm happy that there are some additional options to run Graphene on the market.
[–] aseipp 2 days ago
The OS absolutely controls functionality of the baseband, it would be a legal nightmare if it just didn't actually respect proper radio settings. But from a design perspective, it doesn't actually matter that much at all I feel. Any practical and secure design for a cellular phone has to assume the network is totally compromised and hostile, and so it can never be in the trusted base. From this perspective, adding the radio chip and its software to that category is not actually a huge leap. Even today vendors who own all the IP on a bus will still insert IOMMUs, etc inbetween components. It isn't dissimilar to game consoles; they assume that anything outside their die is compromised and hostile, and if you start from that premise, you can still make it very secure even when your threat model includes hostile components on the PCB.

Radio firmware is probably somewhat broken in practice (what isn't these days) but ultimately the openness stuff is a red herring IMO as far as security is concerned, you either assume it's compromised or not.

[–] ysnp 2 days ago
The userspace OS needs to be where control of any radio (bluetooth, wi-fi, cellular, nfc, uwb etc.) components happens, otherwise it would be difficult to be compliant in terms of regulatory requirements like a working Flight Mode.

Baseband firmware/processors are still making strides in terms of defending against attacks so I don't think we are at the point where backdoors are needed. More likely that undocumented AT commands, plausibly deniable bugdoors and existing memory corruption vulnerabilities are already convenient reality. However, part of that reality is also that once the cellular modem is exploited OTA it is still a massive task to traverse IOMMU restrictions and get device owner data/secrets from the userspace OS. It doesn't even grant visibility into application traffic which has been aggressively TLS encrypted since the mid 2010s.

[–] abdullahkhalids 2 days ago
> The userspace OS needs to be where control of any radio (bluetooth, wi-fi, cellular, nfc, uwb etc.) components happens, otherwise it would be difficult to be compliant in terms of regulatory requirements like a working Flight Mode.

The entities that are putting in backdoors don't respect the law, and obviously will do what they can to obfuscate the backdoor enough to pass regulatory reviews.

My threat model is precisely entities that don't respect law or are unethical. So, the question then boils down to whether current regulatory review processes can catch such backdoors and the people running these processes cannot be bribed or otherwise forced to skip proper review?

[–] ysnp 2 days ago
It's my understanding that you cannot really defend against backdoors. You can somewhat mitigate their impact through good security/privacy design. Your energies may be better invested in a position that assumes any and all of the radios have been compromised or exploited and work from there (this is what mainstream flagship smartphone SoC/OS designers already do).
[–] cowlevel 2 days ago
Graphene doesn't expect to have control of the RF. It makes all the RF stuff happen on the other side of a firewall.
[–] abdullahkhalids 2 days ago
In modern phones, doesn't the main chip control the baseband chip rather than the other way? What is the threat model?

Obviously since phone calls and text messages are unencrypted the baseband chip could send them elsewhere. But your internet communication should already be encrypted before it hits the baseband chip. So is the threat model Motorola has intentionally introduced a backdoor to leak data from the main chip to the baseband chip?

[–] jrexilius 2 days ago
"control" is mostly a gentlemans agreement. It sends commands. The OS running in the baseband can decide how to handle the commands. Assuming a malicious vendor, motivated by its host nation, that would be where they could place the most effective backdoors.
[–] inkyoto 2 days ago
Vendors with nefarious intentions or operating on directives from a state agency are a real and valid concern, but the handset under consideration makes use of a Qualcomm baseband chipset, so the OS it runs on is supplied by Qualcomm, not the manufacturer.

If I understand it correctly (but please do correct me if I am wrong), Qualcomm supplies the baseband OS as a signed binary blob.

[–] jrexilius 2 days ago
My knowledge is third-hand as I haven't worked at Motorola for over 20 years (and back then I worked on "server" side, not device side), but I think you are correct. What I'm unclear on is how it differs from the chips (and associated blobs) sold for use in China, where the legal requirements differ, and how reliable the "signing" really is. I do know that some groups get special permission from Qualcomm to load other firmware and expose certain features to the user-land OS. My threat analysis is mostly theoretical and I can't really say that Qualcomms control is lacking or co-opted.