A pair of Rust kernel modules

No, but the problem was the *verifier*, not the input language. The same sort of thing written in raw eBPF was also rejected. (It worked if the loop bound was < 4. How... useful.)

Figuring out why required diving into the verifier source code, because there is of course nothing like a spec, and the verifier's verification contains enough holes where obviously valid code is rejected out of hand because nobody's written code to verify it (if you're lucky, there are comments noting the lack of said verification) that it frankly should be called a collection of holes with a little fabric connecting them :)