From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932098AbbJUQ6I (ORCPT <rfc822;w@1wt.eu>);
	Wed, 21 Oct 2015 12:58:08 -0400
Received: from casper.infradead.org ([85.118.1.10]:34592 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753200AbbJUQ6F (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 21 Oct 2015 12:58:05 -0400
Date: Wed, 21 Oct 2015 18:57:58 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: pi3orama <pi3orama@163.com>
Cc: "Wangnan (F)" <wangnan0@huawei.com>, Alexei Starovoitov <ast@plumgrid.com>,
        xiakaixu <xiakaixu@huawei.com>, davem@davemloft.net, acme@kernel.org,
        mingo@redhat.com, masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org,
        daniel@iogearbox.net, linux-kernel@vger.kernel.org, hekuang@huawei.com,
        netdev@vger.kernel.org
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY
 maps trace data output when perf sampling
Message-ID: <20151021165758.GK3604@twins.programming.kicks-ass.net>
References: <20151021091254.GF2881@worktop.programming.kicks-ass.net>
 <56276968.6070604@huawei.com>
 <20151021113316.GM17308@twins.programming.kicks-ass.net>
 <56277BCE.6030400@huawei.com>
 <20151021121713.GC3604@twins.programming.kicks-ass.net>
 <56279634.5000606@huawei.com>
 <20151021134951.GH3604@twins.programming.kicks-ass.net>
 <1D2C9396-01CB-4981-B493-EA311F0457E7@163.com>
 <20151021140921.GI3604@twins.programming.kicks-ass.net>
 <586A5B33-C9C9-433D-B6E9-019264BF7DDB@163.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <586A5B33-C9C9-433D-B6E9-019264BF7DDB@163.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Oct 21, 2015 at 11:06:47PM +0800, pi3orama wrote:
> > So explain; how does this eBPF stuff work.
> 
> I think I get your point this time, and let me explain the eBPF stuff to you.
> 
> You are aware that BPF programmer can break the system in this way:
> 
> A=get_non_local_perf_event()
> perf_event_read_local(A)
> BOOM!
> 
> However the above logic is impossible because BPF program can't work this
> way.
> 
> First of all, it is impossible for a BPF program directly invoke a
> kernel function.  Doesn't like kernel module, BPF program can only
> invoke functions designed for them, like what this patch does. So the
> ability of BPF programs is strictly restricted by kernel. If we don't
> allow BPF program call perf_event_read_local() across core, we can
> check this and return error in function we provide for them.
> 
> Second: there's no way for a BPF program directly access a perf event.
> All perf events have to be wrapped by a map and be accessed by BPF
> functions described above. We don't allow BPF program fetch array
> element from that map. So pointers of perf event is safely protected
> from BPF program.
> 
> In summary, your either-or logic doesn't hold in BPF world. A BPF
> program can only access perf event in a highly restricted way. We
> don't allow it calling perf_event_read_local() across core, so it
> can't.

Urgh, that's still horridly inconsistent. Can we please come up with a
consistent interface to perf?