[RFC] LSM deprecation / removal policies

[Song Liu]

On Sat, May 3, 2025 at 4:47 AM Tetsuo Handa
<penguin-kernel at i-love.sakura.ne.jp> wrote:
>
> On 2025/05/03 5:01, Paul Moore wrote:
> > ## Removing LSM Hooks
> >
> > If a LSM hook is no longer used by any in-kernel LSMs, there is no ongoing work
> > in progress involving the hook, and no expectation of future work that will use
> > the hook, the LSM community may consider removal of the LSM hook.  The decision
> > to ultimately remove the LSM hook should balance ongoing maintenance and
> > performance concerns with the social challenges of reintroducing the hook if
> > it is needed at a later date.
>
> What about BPF-based LSM users? Since BPF-based LSMs cannot be in-kernel LSMs,
> it will be difficult for users of BPF-based LSMs to respond (that someone wants
> some to-be-removed LSM hook) when removal of an LSM hook is proposed.

If a LSM hook is important for an out-of-tree BPF LSM solution, the owner can
add a BPF selftest for this specific hook. This does not guarantee the hook will
stay, but it can most likely detect unintentional removal of LSM hooks.

Thanks,
Song