Re: Too many PMC implementations

[Alexander Nasonov <alnsn%yandex.ru@localhost>]

David Holland wrote:
> On Sat, Aug 25, 2018 at 11:26:07AM +0100, Alexander Nasonov wrote:
>  > 1. It's not standartised and it will very likely change in future versions
> 
> That doesn't really matter as long as you're only using one version at
> a time...

If bytecode is generated from a valid Lua program, it's indeed takes
very little effort to update to a new version. But updating handcrafted
bytecode may take a bit of time.

>  > 2. There is no bpf_validate for Lua bytecode. In fact, Lua team abandoned
>  >    an idea of bytecode validation few years ago. From Lua 5.3 manual:
>  > 
>  >    Lua does not check the consistency of binary chunks. Maliciously
>  >    crafted binary chunks can crash the interpreter.
> 
> Are we talking about installing untrusted/unprivileged kernel trace
> logic? Because that seems like a bad idea, or at least a very hard
> thing to get right... and if not, it doesn't matter if there's a
> validator.

Lua bytecode is turing complete and not validatable but I'm pretty sure
some subset of it (e.g. no loops, no strings, etc) can be validated.

> (Also, isn't EBPF not really validatable either, or am I mixing it
> up with something else?)

Last I checked, the author(s) of eBPF claimed that it can be validated.

-- 
Alex