Re: [PATCH v2] bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD

[Paul Moore <paul@paul-moore.com>]

On Fri, Dec 23, 2022 at 1:55 PM Paul Moore <paul@paul-moore.com> 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
> calling the perf event and audit UNLOAD record generators, which
> resulted in problems as the ebpf program ID was bogus (always zero).
> This patch resolves this by adding a new flag, bpf_prog::valid_id, to
> indicate when the bpf_prog_aux ID field is valid; it is set to true/1
> in bpf_prog_alloc_id() and set to false/0 in bpf_prog_free_id().  In
> order to help ensure that access to the bpf_prog_aux ID field takes
> into account the new valid_id flag, the bpf_prog_aux ID field is
> renamed to bpf_prog_aux::__id and a getter function,
> bpf_prog_get_id(), was created and all users of bpf_prog_aux::id were
> converted to the new caller.  Exceptions to this include some of the
> internal ebpf functions and the xdp trace points, although the latter
> still take into account the valid_id flag.
>
> 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).
>
> Fixes: d809e134be7a ("bpf: Prepare bpf_prog_put() to be called from irq context.")
> Reported-by: Burn Alting <burn.alting@iinet.net.au>
> Reported-by: Jiri Olsa <olsajiri@gmail.com>
> Signed-off-by: Paul Moore <paul@paul-moore.com>
>
> --
> * v2
>   - change subj
>   - add mention of the perf regression
>   - drop the dedicated program audit ID
>   - add the bpf_prog::valid_id flag, bpf_prog_get_id() getter
>   - convert prog ID users to new ID getter
> * v1
>   - subj was: "bpf: restore the ebpf audit UNLOAD id field"
>   - initial draft
> ---
>  drivers/net/netdevsim/bpf.c  |  6 ++++--
>  include/linux/bpf.h          | 11 +++++++++--
>  include/linux/bpf_verifier.h |  2 +-
>  include/trace/events/xdp.h   |  4 ++--
>  kernel/bpf/arraymap.c        |  2 +-
>  kernel/bpf/bpf_struct_ops.c  |  2 +-
>  kernel/bpf/cgroup.c          |  2 +-
>  kernel/bpf/core.c            |  2 +-
>  kernel/bpf/cpumap.c          |  2 +-
>  kernel/bpf/devmap.c          |  2 +-
>  kernel/bpf/syscall.c         | 27 +++++++++++++++------------
>  kernel/events/core.c         |  6 +++++-
>  kernel/trace/bpf_trace.c     |  2 +-
>  net/core/dev.c               |  2 +-
>  net/core/filter.c            |  3 ++-
>  net/core/rtnetlink.c         |  2 +-
>  net/core/sock_map.c          |  2 +-
>  net/ipv6/seg6_local.c        |  3 ++-
>  net/sched/act_bpf.c          |  2 +-
>  net/sched/cls_bpf.c          |  2 +-
>  20 files changed, 52 insertions(+), 34 deletions(-)

...

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 9e7d46d16032..18e965bd7db9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1688,6 +1689,12 @@ void bpf_prog_inc(struct bpf_prog *prog);
>  struct bpf_prog * __must_check bpf_prog_inc_not_zero(struct bpf_prog *prog);
>  void bpf_prog_put(struct bpf_prog *prog);
>
> +static inline u32 bpf_prog_get_id(const struct bpf_prog *prog)
> +{
> +       if (WARN(!prog->valid_id, "Attempting to use an invalid eBPF program"))
> +               return 0;
> +       return prog->aux->__id;
> +}
>  void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock);
>  void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock);

The bpf_prog_get_id() either needs to be moved outside the `#ifdef
CONFIG_BPF_SYSCALL` block, or a dummy function needs to be added when
CONFIG_BPF_SYSCALL is undefined.  I can fix that up easily enough, but
given the time of year I'll wait a bit to see if there are any other
comments before posting another revision.

-- 
paul-moore.com