Re: [PATCH bpf-next] bpf: Make trampolines W^X

From: Alexei Starovoitov
Date: Mon Jan 06 2020 - 17:13:32 EST

On Sun, Jan 05, 2020 at 10:33:54AM +0900, Andy Lutomirski wrote:
> >> On Jan 4, 2020, at 8:03 PM, Justin Capella <justincapella@xxxxxxxxx> wrote:
> > ï
> > I'm rather ignorant about this topic but it would make sense to check prior to making executable from a security standpoint wouldn't it? (In support of the (set_memory_ro + set_memory_x)
> >
> Maybe, depends if itâs structured in a way thatâs actually helpful from a security perspective.
> It doesnât help that set_memory_x and friends are not optimized at all. These functions are very, very, very slow and adversely affect all CPUs.

That was one of the reason it wasn't done in the first.
Also ftrace trampoline break w^x as well.
Not sure what is the plan for ftrace, but for bpf trampoline I'm going to switch
to text_poke (without _bp) once tip bits get merged during next merge window.
Then bpf trampoline will be allocated as ro+x and text_poke will be used instead of memcpy.