On Thu, Dec 22, 2022 at 6:20 PM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Thu, Dec 22, 2022 at 02:03:41PM -0500, Paul Moore wrote:
> > On Thu, Dec 22, 2022 at 12:19 PM <sdf@xxxxxxxxxx> wrote:
> > > On 12/21, Paul Moore wrote:
> > > > When changing the ebpf program put() routines to support being called
> > > > from within IRQ context the program ID was reset to zero prior to
> > > > generating the audit UNLOAD record, which obviously rendered the ID
> > > > field bogus (always zero). This patch resolves this by adding a new
> > > > field, bpf_prog_aux::id_audit, which is set when the ebpf program is
> > > > allocated an ID and never reset, ensuring a valid ID field,
> > > > regardless of the state of the original ID field, bpf_prox_aud::id.
> > >
> > > > I also modified the bpf_audit_prog() logic used to associate the
> > > > AUDIT_BPF record with other associated records, e.g. @ctx != NULL.
> > > > Instead of keying off the operation, it now keys off the execution
> > > > context, e.g. '!in_irg && !irqs_disabled()', which is much more
> > > > appropriate and should help better connect the UNLOAD operations with
> > > > the associated audit state (other audit records).
> > >
> > > [..]
> > >
> > > > As an note to future bug hunters, I did briefly consider removing the
> > > > ID reset in bpf_prog_free_id(), as it would seem that once the
> > > > program is removed from the idr pool it can no longer be found by its
> > > > ID value, but commit ad8ad79f4f60 ("bpf: offload: free program id
> > > > when device disappears") seems to imply that it is beneficial to
> > > > reset the ID value. Perhaps as a secondary indicator that the ebpf
> > > > program is unbound/orphaned.
> > >
> > > That seems like the way to go imho. Can we have some extra 'invalid_id'
> > > bitfield in the bpf_prog so we can set it in bpf_prog_free_id and
> > > check in bpf_prog_free_id (for this offloaded use-case)? Because
> > > having two ids and then keeping track about which one to use, depending
> > > on the context, seems more fragile?
> >
> > I would definitely prefer to keep just a single ID value, and that was
> > the first approach I took when drafting this patch, but when looking
> > through the git log it looked like there was some desire to reset the
> > ID to zero on free. Not being an expert on the ebpf kernel code I
> > figured I would just write the patch up this way and make a comment
> > about not zero'ing out the ID in the commit description so we could
> > have a discussion about it.
> >
> > I'm not seeing any other comments, so I'll go ahead with putting
> > together a v2 that sets an invalid flag/bit and I'll post that for
> > further discussion/review.
>
> great, perf suffers the same issue:
> https://lore.kernel.org/bpf/Y3SRWVoycV290S16@krava/
>
> any chance you could include it as well? I can send a patch
> later if needed
Hi Jiri,
I'm pretty sure the current approach recommended by Stanislav, to
never reset/zero the ID and instead mark it as invalid via a flag in
the bpf_prog struct, should resolve the perf problem as well. My time
is a little short at the moment due to the holidays, but perhaps with
a little luck I'll get a new revision of the patch posted soon
(today?) and you can take a look and give it a test. Are you
subscribed to the linux-audit and/or bpf mailing lists? If not I can
CC you directly on the next revision.
--
paul-moore.com
