netdev - Re: [PATCH net-next 1/2] bpf: add support for sys_{enter|exit}

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Date:   Wed, 2 Aug 2017 14:07:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH net-next 1/2] bpf: add support for sys_{enter|exit}_*
 tracepoints

On Tue, Aug 01, 2017 at 11:30:04PM -0700, Yonghong Song wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 426c2ff..623c977 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8050,7 +8050,7 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
>  
>  static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
>  {
> -	bool is_kprobe, is_tracepoint;
> +	bool is_cap_any, is_kprobe, is_tracepoint;
>  	struct bpf_prog *prog;
>  
>  	if (event->attr.type != PERF_TYPE_TRACEPOINT)
> @@ -8059,9 +8059,11 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
>  	if (event->tp_event->prog)
>  		return -EEXIST;
>  
> +	/* currently, CAP_ANY only for sys_enter_* and sys_exit_* tracepoints */
> +	is_cap_any = event->tp_event->flags & TRACE_EVENT_FL_CAP_ANY;
>  	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;
>  	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;
> -	if (!is_kprobe && !is_tracepoint)
> +	if (!is_cap_any && !is_kprobe && !is_tracepoint)
>  		/* bpf programs can only be attached to u/kprobe or tracepoint */
>  		return -EINVAL;
>  
> @@ -8070,7 +8072,8 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
>  		return PTR_ERR(prog);
>  
>  	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
> -	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
> +	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT) ||
> +	    (is_cap_any && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
>  		/* valid fd, but invalid bpf program type */
>  		bpf_prog_put(prog);
>  		return -EINVAL;

This looks wrong. FL_CAP_ANY is a privilege thing, not something that
identifies syscall hooks (it just so happens only those now have the bit
set, but that's an accident more than anything else).