Re: [RFC PATCH 06/20] bpf: lsm: Add Landlock kfuncs

[Justin Suess]

On Wed, Jul 01, 2026 at 09:28:22AM -0400, Paul Moore wrote:
> On Wed, Jul 1, 2026 at 8:52 AM Justin Suess <utilityemal77@xxxxxxxxx> wrote:
> > On Wed, Jul 01, 2026 at 08:12:34AM -0400, Paul Moore wrote:
> > > On Wed, Jul 1, 2026 at 6:59 AM Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
> > > > On Tue, Apr 07, 2026 at 04:01:28PM -0400, Justin Suess wrote:
> > > > > Create 2 kfuncs exposing control over Landlock functionality to BPF
> > > > > callers. Export an opaque struct bpf_landlock_ruleset preventing callers
> > > > > from accessing unstable internal Landlock fields.
> > >
> > > Generally speaking we don't want to provide APIs, either in-kernel or
> > > at the userspace/kernel boundary, that are specific to a single LSM,
> > > see the LSM syscalls or the security_current_getlsmprop_subj()
> > > function as examples.
> >
> > I would raise bpf_ima_file_hash, bpf_ima_inode_hash, as examples of
> > clear precedence for this. (BPF calling into specific LSM)
> 
> The BPF IMA helpers were merged back in the v5.18 timeframe when IMA
> was still standalone, it wasn't until v6.9 that IMA and EVM became
> proper LSMs.
> 
> > Kfuncs are explicitly marked as not being an ABI, and are more
> > flexible for later changes / deprecation etc. [1]
> 
> The issue isn't so much the kfunc itself, it is what the kfunc
> *calls*.  From what I saw in the proposed patch, the kfunc calls
> directly into Landlock instead of passing through the LSM framework,
> e.g. a function wrapper in security/security.c.
> 
> > LSM framework API can mean a lot of things. I assume you are meaning
> > like a pseudo-filesystem mounted interface that controls LSM?
> > Correct me if I'm wrong.
> 
> My apologies, I should have been more clear.  When I speak about the
> "LSM framework", I'm talking about the abstraction layer that provides
> the interface that the kernel and userspace uses to talk to individual
> LSMs.  The LSM framework is analogous to the VFS layer/framework in
> that it provides a single API for a variety of underlying subsystems.
> While not 100% correct, you can think of it the LSM framework as being
> the functions/hooks defined in security/security.c.
> 
> Does that help?
>
That does. security/security.c seems like a good place to enumerate the enabled
LSMs and to check to make sure that Landlock is actually enabled both in the kernel
build and that the Landlock LSM is up and running.

The above patch only checked if Landlock was compiled, when it should
actually be checking if Landlock is actively enabled.

So I will probably make a shim for it there that gates calls to
Landlock.
> -- 
> paul-moore.com