For instance, you could just write your kernel module in a sufficiently safe language, like Rust, and have the same benefits. You could even pre-compile eBPF for the exact same level of safety. Still no need for the bpf() system call or the eBPF VM or JIT in the kernel.
* Strictly typed -- registers, and memory are type checked at compilation time. If you use something like Rust, you'd have to bring rustc into the kernel
* Guaranteed to terminate -- you cannot jump backwards, and there is an upper bound on the instruction count
* Bounded memory -- The registers, and accessible memory via maps are a fixed size. We don't have a stack per se.
Compiling Rust to this is possible, but it'd require quite a bit of infrastructure in the kernel to verify that the code is safe, versus the simplicity of eBPF. Early attempts at a general purpose in-kernel VM included passing an AST in, and then doing safety checking on the AST, but they proved too complicated to do safely.
I'm arguing against the in-kernel eBPF infrastructure: bpf system call, the JIT and the VM.
I think it makes more sense to just compile eBPF (or rust or whatever safe language you want) to a kernel module.
Accepting compiled stuff in the form of a kernel module requires root privileges and requires that the kernel essentially have complete trust in the code being loaded.
Loading eBPF eliminates the need to trust the process/user doing the loading to that level.