I was under the impression that most modern (past few years) SoCs like Exynos, Qualcomm, Apple silicon all had IOMMU support. Sometimes it’s misconfigured to be too permissive but that’s getting better.
Why's IOMMU thrown around so casually in this forum as if it's a silver-bullet explosive reactive armors? They'd be running something like 30 years old giant main loop with "// don't remove this line, build breaks" comments everywhere, not like Rust microservices on formally verified microkernel.
The main CPU/application processor/main CPU might be running better secured Unix/Linux and might be able to protect itself from peripheral CPUs, but that's not the point; a phone had always been a pair (minimum) of computers, traditionally referred to as Application Processor(AP) and Baseband Processor(BP), of only the slightly faster one is exposed to the user, and it's unclear what is going on inside the other one or how to handle it. That's the problem.
Do you know what other hardware your baseband processor has the ability to inspect?