Re: [PATCH v4 bpf 0/4] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP

Linus Torvalds
2022-04-16T20:31:16Z

On Sat, Apr 16, 2022 at 12:55 PM Song Liu <songliubraving@fb.com> wrote:
>
> Based on this analysis, I think we should either
> 1) ship the whole set with 5.18; or
> 2) ship 1/4, 3/4, and 4/4 with 5.18, and 2/4 with 5.19.

Honestly, I think the proper thing to do is

- apply #1, because yes, that "use huge pages" should be an opt-in.

- but just disable hugepages for now.

I think those games with set_memory_nx() and friends just show how
rough this all is right now.

In fact, I personally think that the whole bpf 'prog_pack' stuff
should probably be disabled. It looks incredible broken to me right
now.

Unless I mis-read it, it does a "module_alloc()" to allocate the vmap
area, and then just marks it executable without having even
initialized the pages. Am I missing something? So now we have random
kernel memory that is marked executable.

Sure, it's also marked RO, but who cares? It's random data that is now
executable.

Maybe I am missing something, but I really don't think this is ready
for prime-time. We should effectively disable it all, and have people
think through it a lot more.

Linus