Subject: Re: [PATCH v10 tip 5/9] tracing: allow BPF programs to call bpf_trace_printk()

From: Ingo Molnar <[email-masked]>
Date: Mon, 23 Mar 2015 13:07:53 +0100

* David Laight <David.Laight-ZS65k/[email-masked]> 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