# Re: \[PATCH V33 24/30\] bpf: Restrict bpf when kernel lockdown is in confidentiality mode

- From: Matthew Garrett \<hidden\>
- Date: 2019-06-21 20:06:00 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2019/06/5636494
- Thread: https://ratatoskr.run/linux-api/2019/06/5635618/t.md

```text
On Thu, Jun 20, 2019 at 10:22 PM Andy Lutomirski [ref] wrote:
> On Thu, Jun 20, 2019 at 6:21 PM Matthew Garrett
> [ref] wrote:
> > --- a/security/lockdown/lockdown.c
> > +++ b/security/lockdown/lockdown.c
> > @@ -33,6 +33,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> >         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
> >         [LOCKDOWN_KCORE] = "/proc/kcore access",
> >         [LOCKDOWN_KPROBES] = "use of kprobes",
> > +       [LOCKDOWN_BPF] = "use of bpf",
> >         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
>
> The text here says "use of bpf", but what this patch is *really* doing
> is locking down use of BPF to read kernel memory.  If the details
> change, then every LSM needs to get updated, and we risk breaking user
> policies that are based on LSMs that offer excessively fine
> granularity.

The text is descriptive rather than normative, and no changes should
be made that alter the semantics of a reason - it makes more sense to
just add another reason.

> I'd be more comfortable if the LSM only got to see "confidentiality"
> or "integrity".

If LSM authors can be trusted to do the right thing here, then I see
no problem in providing additional data. I'm happy to defer to James
on that.
```