While we don’t usually want to disparage the efforts of amateur chipmakers, in this case the M-Series has been hyped to hell and so this side channel attack deserves a bit more publicity than it is getting from the Tame Apple Press.

The problem can only be mitigated by building defenses into third-party cryptographic software that could drastically degrade M-series performance when executing cryptographic operations, particularly on the earlier M1 and M2 generations. This means that any speed advantage Apple might claim for its M-Series would disappear overnight. 

According to Ars Technica a team of boffins has found something rotten in the way that Job’s Mob chips handle cryptography.

The risk lies in the chip's data memory-dependent prefetcher, a hardware tweak that forecasts the memory addresses that active code will likely need shortly. By popping the data into the CPU cache ahead of time, the DMP – that's short for this feature – cuts down the delay between the main memory and the CPU, a typical snag in today's computing. These DMPs are fresh on the scene, found only in M-series chips and Intel's latest Raptor Lake microarchitecture, though their older cousins, the prefetchers, have been around for donkey's years.

The fresh study reveals a hitherto ignored quirk of DMPs in Apple's silicon: Occasionally, it muddles up memory content with the pointer value that's meant for fetching different data. Consequently, the DMP frequently reads the data and tries to use it as an address for memory access. This 'dereferencing' of 'pointers'—that is, accessing data and spilling it via a side channel—blatantly breaches the constant-time principle.

With this new blunder, it's Jobs' Mob has left the back door wide open.