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

From: Ingo Molnar
Date: Mon Mar 23 2015 - 08:08:11 EST

* David Laight <David.Laight@xxxxxxxxxx> 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.


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