linux-kernel - Re: [PATCH RFC 0/4] Add support to directly attach BPF program to ftrace

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Message-ID: <20190716235500.GA199237@google.com>
Date:   Tue, 16 Jul 2019 19:55:00 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
        Brendan Gregg <brendan.d.gregg@...il.com>, connoro@...gle.com,
        Daniel Borkmann <daniel@...earbox.net>,
        duyuchao <yuchao.du@...soc.com>, Ingo Molnar <mingo@...hat.com>,
        jeffv@...gle.com, Karim Yaghmour <karim.yaghmour@...rsys.com>,
        kernel-team@...roid.com, linux-kselftest@...r.kernel.org,
        Manali Shukla <manalishukla14@...il.com>,
        Manjo Raja Rao <linux@...ojrajarao.com>,
        Martin KaFai Lau <kafai@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Matt Mullins <mmullins@...com>,
        Michal Gregorczyk <michalgr@...com>,
        Michal Gregorczyk <michalgr@...e.com>,
        Mohammad Husain <russoue@...il.com>, namhyung@...gle.com,
        namhyung@...nel.org, netdev@...r.kernel.org,
        paul.chaignon@...il.com, primiano@...gle.com,
        Qais Yousef <qais.yousef@....com>,
        Shuah Khan <shuah@...nel.org>,
        Song Liu <songliubraving@...com>,
        Srinivas Ramana <sramana@...eaurora.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tamir Carmeli <carmeli.tamir@...il.com>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH RFC 0/4] Add support to directly attach BPF program to
 ftrace

On Tue, Jul 16, 2019 at 06:41:50PM -0400, Joel Fernandes wrote:
> On Tue, Jul 16, 2019 at 03:26:52PM -0700, Alexei Starovoitov wrote:
> > On Tue, Jul 16, 2019 at 05:30:50PM -0400, Joel Fernandes wrote:
> > > 
> > > I also thought about the pinning idea before, but we also want to add support
> > > for not just raw tracepoints, but also regular tracepoints (events if you
> > > will). I am hesitant to add a new BPF API just for creating regular
> > > tracepoints and then pinning those as well.
> > 
> > and they should be done through the pinning as well.
> 
> Hmm ok, I will give it some more thought.

I think I can make the new BPF API + pinning approach work, I will try to
work on something like this and post it soon.

Also, I had a question below if you don't mind taking a look:

thanks Alexei!

> > > I don't see why a new bpf node for a trace event is a bad idea, really.
> > 
> > See the patches for kprobe/uprobe FD-based api and the reasons behind it.
> > tldr: text is racy, doesn't scale, poor security, etc.
> 
> Is it possible to use perf without CAP_SYS_ADMIN and control security at the
> per-event level? We are selective about who can access which event, using
> selinux. That's how our ftrace-based tracers work. Its fine grained per-event
> control. That's where I was going with the tracefs approach since we get that
> granularity using the file system.
> 
> Thanks.
>