No, this doesn't require access to internal documentation of anything, just googling a little. Like the sibling comment points out, the whole baseband thing is a bit of a messageboard trope and has been for about decade. This is one of these things you can sort of guess from first principles! I.e. how likely is it that this well-known problem (the potential security implications of DMA/memory mapped peripherals) has remained completely unmitigated and unaddressed by smartphone designers for 10+ years?