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Date: Mon, 23 Mar 2015 13:07:53 +0100
From: Ingo Molnar <mingo@kernel.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "'Alexei Starovoitov'" <ast@plumgrid.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Namhyung Kim <namhyung@kernel.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v10 tip 5/9] tracing: allow BPF programs to call
 bpf_trace_printk()
Message-ID: <20150323120753.GA22560@gmail.com>
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* David Laight <David.Laight@ACULAB.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