From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Kees Cook <keescook@chromium.org>,
LSM List <linux-security-module@vger.kernel.org>,
James Morris <jmorris@namei.org>, Jann Horn <jannh@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
Network Development <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, kernel-team <kernel-team@fb.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf, capabilities: introduce CAP_BPF
Date: Thu, 29 Aug 2019 09:34:34 -0400 [thread overview]
Message-ID: <20190829093434.36540972@gandalf.local.home> (raw)
In-Reply-To: <20190828220826.nlkpp632rsomocve@ast-mbp.dhcp.thefacebook.com>
On Wed, 28 Aug 2019 15:08:28 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> On Wed, Aug 28, 2019 at 09:14:21AM +0200, Peter Zijlstra wrote:
> > On Tue, Aug 27, 2019 at 04:01:08PM -0700, Andy Lutomirski wrote:
> >
> > > > Tracing:
> > > >
> > > > CAP_BPF and perf_paranoid_tracepoint_raw() (which is kernel.perf_event_paranoid == -1)
> > > > are necessary to:
> >
> > That's not tracing, that's perf.
> >
> re: your first comment above.
> I'm not sure what difference you see in words 'tracing' and 'perf'.
> I really hope we don't partition the overall tracing category
> into CAP_PERF and CAP_FTRACE only because these pieces are maintained
> by different people.
I think Peter meant: It's not tracing, it's profiling.
And there is a bit of separation between the two, although there is an
overlap.
Yes, perf can do tracing but it's designed more for profiling.
> On one side perf_event_open() isn't really doing tracing (as step by
> step ftracing of function sequences), but perf_event_open() opens
> an event and the sequence of events (may include IP) becomes a trace.
> imo CAP_TRACING is the best name to descibe the privileged space
> of operations possible via perf_event_open, ftrace, kprobe, stack traces, etc.
I have no issue with what you suggest. I guess it comes down to how
fine grain people want to go. Do we want it to be all or nothing?
Should CAP_TRACING allow for write access to tracefs? Or should we go
with needing both CAP_TRACING and permissions in that directory
(like changing the group ownership of the files at every boot).
Perhaps we should have a CAP_TRACING_RO, that gives read access to
tracefs (and write if the users have permissions). And have CAP_TRACING
to allow full write access as well (allowing for users to add kprobe
events and enabling tracers like the function tracer).
>
> Another reason are kuprobes. They can be crated via perf_event_open
> and via tracefs. Are they in CAP_PERF or in CAP_FTRACE ? In both, right?
> Should then CAP_KPROBE be used ? that would be an overkill.
> It would partition the space even further without obvious need.
>
> Looking from BPF angle... BPF doesn't have integration with ftrace yet.
> bpf_trace_printk is using ftrace mechanism, but that's 1% of ftrace.
> In the long run I really like to see bpf using all of ftrace.
> Whereas bpf is using a lot of 'perf'.
> And extending some perf things in bpf specific way.
> Take a look at how BPF_F_STACK_BUILD_ID. It's clearly perf/stack_tracing
> feature that generic perf can use one day.
> Currently it sits in bpf land and accessible via bpf only.
> Though its bpf only today I categorize it under CAP_TRACING.
>
> I think CAP_TRACING privilege should allow task to do all of perf_event_open,
> kuprobe, stack trace, ftrace, and kallsyms.
> We can think of some exceptions that should stay under CAP_SYS_ADMIN,
> but most of the functionality available by 'perf' binary should be
> usable with CAP_TRACING. 'perf' can do bpf too.
> With CAP_BPF it would be all set.
As the above seems to favor the idea of CAP_TRACING allowing write
access to tracefs, should we have a CAP_TRACING_RO for just read access
and limited perf abilities?
-- Steve
next prev parent reply other threads:[~2019-08-29 13:34 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190827205213.456318-1-ast@kernel.org>
2019-08-27 23:01 ` [PATCH bpf-next] bpf, capabilities: introduce CAP_BPF Andy Lutomirski
2019-08-27 23:21 ` Steven Rostedt
2019-08-27 23:34 ` Andy Lutomirski
2019-08-28 0:44 ` Steven Rostedt
2019-08-28 1:12 ` Andy Lutomirski
2019-08-28 2:22 ` Steven Rostedt
2019-08-28 0:38 ` Alexei Starovoitov
2019-08-28 3:30 ` Masami Hiramatsu
2019-08-28 4:47 ` Alexei Starovoitov
2019-08-28 0:34 ` Alexei Starovoitov
2019-08-28 0:55 ` Andy Lutomirski
2019-08-28 2:00 ` Andy Lutomirski
2019-08-28 4:49 ` Alexei Starovoitov
2019-08-28 6:20 ` Andy Lutomirski
2019-08-28 23:38 ` Alexei Starovoitov
2019-08-29 0:58 ` Andy Lutomirski
2019-08-28 4:43 ` Alexei Starovoitov
2019-08-28 6:12 ` Andy Lutomirski
2019-08-28 22:55 ` Alexei Starovoitov
2019-08-29 0:45 ` Andy Lutomirski
2019-08-29 0:53 ` Andy Lutomirski
2019-08-29 4:07 ` Alexei Starovoitov
2019-09-28 23:37 ` Steven Rostedt
2019-09-30 18:31 ` Kees Cook
2019-10-01 1:22 ` Alexei Starovoitov
2019-10-01 22:10 ` Steven Rostedt
2019-10-01 22:18 ` Alexei Starovoitov
2019-10-01 22:47 ` Steven Rostedt
2019-10-02 17:18 ` Alexei Starovoitov
2019-10-02 23:00 ` Steven Rostedt
2019-10-03 16:18 ` trace_printk issue. Was: " Alexei Starovoitov
2019-10-03 16:41 ` Steven Rostedt
2019-10-04 19:56 ` Alexei Starovoitov
2019-10-03 6:12 ` Masami Hiramatsu
2019-10-03 16:20 ` Alexei Starovoitov
2019-08-28 7:14 ` Peter Zijlstra
2019-08-28 22:08 ` Alexei Starovoitov
2019-08-29 13:34 ` Steven Rostedt [this message]
2019-08-29 15:43 ` Andy Lutomirski
2019-08-29 17:23 ` Alexei Starovoitov
2019-08-29 17:36 ` Andy Lutomirski
2019-08-29 17:49 ` Steven Rostedt
2019-08-29 17:19 ` Alexei Starovoitov
2019-08-29 17:47 ` Steven Rostedt
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