bpf helper functions from kernel module

bpf helper functions from kernel module

[Kenny Ho]

Hi,

From https://www.collabora.com/news-and-blog/blog/2019/04/15/an-ebpf-overview-part-2-machine-and-bytecode/
"The BPF-accesible kernel "helper" functions are defined by the kernel
core (not extensible through modules) via an API similar to defining
syscalls"

Has there been interest/discussion around having helper functions from
kernel modules?  Going through the code, I am guessing one of the
obstacles is to have the verifier checking against helper functions
that may or may not be available but I am not an expert of the
subsystem.  What are the current opinions on having helper functions
from kernel modules?

Regards,
Kenny Ho

Re: bpf helper functions from kernel module

[Toke Høiland-Jørgensen]

Kenny Ho <y2kenny@gmail.com> writes:

> Hi,
>
> From https://www.collabora.com/news-and-blog/blog/2019/04/15/an-ebpf-overview-part-2-machine-and-bytecode/
> "The BPF-accesible kernel "helper" functions are defined by the kernel
> core (not extensible through modules) via an API similar to defining
> syscalls"
>
> Has there been interest/discussion around having helper functions from
> kernel modules?  Going through the code, I am guessing one of the
> obstacles is to have the verifier checking against helper functions
> that may or may not be available but I am not an expert of the
> subsystem.  What are the current opinions on having helper functions
> from kernel modules?

The support for calling kernel functions directly (AKA "unstable
helpers") will likely be the way this will be achievable. See the
comment in brackets half-way down in the description here:

https://lore.kernel.org/bpf/20210325015142.1544736-1-kafai@fb.com/

-Toke

Re: bpf helper functions from kernel module

[Kenny Ho]

On Thu, Apr 22, 2021 at 12:43 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> The support for calling kernel functions directly (AKA "unstable
> helpers") will likely be the way this will be achievable. See the
> comment in brackets half-way down in the description here:
>
> https://lore.kernel.org/bpf/20210325015142.1544736-1-kafai@fb.com/

Oh this is very cool, I will look into it.  Thanks for the pointer.

Regards,
Kenny