Re: [RFC PATCH security-next 0/4] Introducing Hornet LSM

Paul Moore
2025-03-22T20:48:25Z

On Sat, Mar 22, 2025 at 4:44 PM Paul Moore <paul@paul-moore.com> wrote:
>
> On Sat, Mar 22, 2025 at 1:22 PM Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > On Fri, Mar 21, 2025 at 09:45:02AM -0700, Blaise Boscaccy wrote:
> > > This patch series introduces the Hornet LSM.
> > >
> > > Hornet takes a simple approach to light-skeleton-based eBPF signature
> >
> > Can you define "light-skeleton-based" before using the term.
> >
> > This is the first time in my life when I hear about it.
>
> I was in the same situation a few months ago when I first heard about it :)
>
> Blaise can surely provide a much better answer that what I'm about to
> write, but since Blaise is going to be at LSFMMBPF this coming week I
> suspect he might not have a lot of time to respond to email in the
> next few days so I thought I would do my best to try and answer :)
>
> An eBPF "light skeleton" is basically a BPF loader program and while
> I'm sure there are several uses for a light skeleton, or lskel for
> brevity, the single use case that we are interested in here, and the
> one that Hornet deals with, is the idea of using a lskel to enable
> signature verification of BPF programs as it seems to be the one way
> that has been deemed acceptable by the BPF maintainers.
>
> Once again, skipping over a lot of details, the basic idea is that you
> take your original BPF program (A), feed it into a BPF userspace tool
> to encapsulate the original program A into a BPF map and generate a
> corresponding light skeleton BPF program (B), and then finally sign
> the resulting binary containing the lskel program (B) and map
> corresponding to the original program A.

Forgive me, I mixed up my "A" and "B" above :/

> At runtime, the lskel binary
> is loaded into the kernel, and if Hornet is enabled, the signature of
> both the lskel program A and original program B is verified.

... and I did again here

> If the
> signature verification passes, lskel program A performs the necessary
> BPF CO-RE transforms on BPF program A stored in the BPF map and then
> attempts to load the original BPF program B, all from within the
> kernel, and with the map frozen to prevent tampering from userspace.

... and once more here because why not? :)

> Hopefully that helps fill in some gaps until someone more
> knowledgeable can provide a better answer and/or correct any mistakes
> in my explanation above ;)

--
paul-moore.com