Is it reliably exploitable from JS, or is it again a theoretical thing nobody has ever bothered to implement in practice? Is there a web page that would show me some of my kernel memory?
https://leaky.page/ will show you browser memory. Kernel memory is not vulnerable with browser sandboxing and current mitigations.
The two tests do work for me, but the actual leaking doesn't. No matter how I tweak the parameters, it fails with "error: too many wrong false negatives in leak test (> 20%)". I guess my CPU might just be too old ¯\_(ツ)_/¯
What browser/CPU? I only get "error: could not infer memory layout" on Firefox and Brave with a Zen 3 CPU