Ask the least smart LLM you have access to (I tried gemini lite flash) to make a list of ways for processes in microVMs to use a sidechannel attack to talk to each other and you'll get quite a list (including obviously cache hits/misses). Heck a smart CS junior would come up with it. It's well studied!

The microVMs probably don't have "two co-operating workloads are able to communicate" in their threat model. The main concern would be if a malicious payload was able to affect or extract data from any other VM.

Both workloads being malicious and trying to establish a hidden data channel between them probably makes this attack a lot easier than conventional spectre/meltdown where it's trying to target ordinary processes that are not intentionally trying to be loud.

Hidden data channel between cooperating processes is not quite as alarming, but it may have some implications for malware command and control.

Seems like a win to me. Their microvms can now be hardened in the lab, not in an emergency :)

Makes sense when you think about it- CPU cache would be a layer / vulnerability level up from the microVM layer

Also a somewhat common exploit pattern for low level stuff (along with dram and cpu cache is not all that different)

properly implementing things like iommu, amd-vi, svm/hvms and such things more granularly can easily avoid this kind of crap. it costs a lot of processing and performance which is why people skip over it or dont do it.. or maybe they dont read CPU manuals anymore. idk..

its relatively easy to reset caches etc. between contexts. so them it becomes the game of what a context is.

I’m not sure I see a real threat here.

If you’re running an untrusted workload, you’re already running it.

Whether it can communicate with another untrusted workload, even though it should be separated, meh.

Unexpected? Probably. but I’m not sure it’s a security risk.