Re: [PATCH] perf lock contention: Add a missing NULL check

[Ian Rogers]

On Tue, Apr 2, 2024 at 11:45 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> I got a report for a failure in BPF verifier on a recent kernel with
> perf lock contention command.  It checks task->sighand->siglock without
> checking if sighand is NULL or not.  Let's add one.
>
>   ; if (&curr->sighand->siglock == (void *)lock)
>   265: (79) r1 = *(u64 *)(r0 +2624)     ; frame1: R0_w=trusted_ptr_task_struct(off=0,imm=0) R1_w=rcu_ptr_or_null_sighand_struct(off=0,imm=0)
>   266: (b7) r2 = 0                      ; frame1: R2_w=0
>   267: (0f) r1 += r2
>   R1 pointer arithmetic on rcu_ptr_or_null_ prohibited, null-check it first
>   processed 164 insns (limit 1000000) max_states_per_insn 1 total_states 15 peak_states 15 mark_read 5
>   -- END PROG LOAD LOG --
>   libbpf: prog 'contention_end': failed to load: -13
>   libbpf: failed to load object 'lock_contention_bpf'
>   libbpf: failed to load BPF skeleton 'lock_contention_bpf': -13
>   Failed to load lock-contention BPF skeleton
>   lock contention BPF setup failed
>   lock contention did not detect any lock contention
>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
>  tools/perf/util/bpf_skel/lock_contention.bpf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index fb54bd38e7d0..4e5914d7eeaa 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -305,7 +305,7 @@ static inline __u32 check_lock_type(__u64 lock, __u32 flags)
>                 break;
>         case LCB_F_SPIN:  /* spinlock */
>                 curr = bpf_get_current_task_btf();
> -               if (&curr->sighand->siglock == (void *)lock)
> +               if (curr->sighand && &curr->sighand->siglock == (void *)lock)
>                         return LCD_F_SIGHAND_LOCK;
>                 break;
>         default:
> --
> 2.44.0.478.gd926399ef9-goog
>