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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Sat, Mar 22, 2025 at 04:48:14PM -0400, Paul Moore wrote:
> 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? :)

No worries I was able to decipher this :-)

> 
> > 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

BR, Jarkko