linux-kernel - Re: [PATCH v10 tip 5/9] tracing: allow BPF programs to call bpf_trace

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Message-ID: <20150323120753.GA22560@gmail.com>
Date:	Mon, 23 Mar 2015 13:07:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	'Alexei Starovoitov' <ast@...mgrid.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 tip 5/9] tracing: allow BPF programs to call
 bpf_trace_printk()


* David Laight <David.Laight@...LAB.COM> wrote:

> From: Alexei Starovoitov
> > Debugging of BPF programs needs some form of printk from the program,
> > so let programs call limited trace_printk() with %d %u %x %p modifiers only.
> 
> Should anyone be allowed to use BPF programs to determine the kernel
> addresses of any items?
> Looks as though it is leaking kernel addresses to userspace.
> Note that the problem is with the arguments, not the format string.

All of these are privileged operations - inherent if you are trying to 
debug the kernel.

Thanks,

	Ingo
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