netdev - Re: [kernel-hardening] Re: [RFC 0/3] kallsyms: don't leak address when printing symbol

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Date:   Thu, 30 Nov 2017 10:58:34 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Kaiwan N Billimoria <kaiwan@...wantech.com>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel-hardening@...ts.openwall.com,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tycho Andersen <tycho@...ho.ws>
Subject: Re: [kernel-hardening] Re: [RFC 0/3] kallsyms: don't leak address
 when printing symbol

On Tue, Nov 28, 2017 at 08:58:44AM +0530, Kaiwan N Billimoria wrote:
> On Tue, Nov 28, 2017 at 7:20 AM, Tobin C. Harding <me@...in.cc> wrote:
> >
> > Noob question: how do we _know_ this. In other words how do we know no
> > userland tools rely on the current behaviour? No stress to answer Kees,
> > this is a pretty general kernel dev question.
> 
> Perhaps I'm reading this wrong, but anyway: besides ftrace, kprobes
> will require a
> symbol-to-address lookup. Specifically, in the function
> kprobe_lookup_name() which
> in turn invokes kallsyms_lookup_name().

We should be right for this call chain because the patch doesn't touch
kallsyms_lookup_name().

> AFAIK, SystemTap (userland) is built on top of the kprobes infrastructure..

This actually indirectly answers the concern. Since no userland tool
should be looking up a kernel address the only code we can break is
kernel code.


thanks,
Tobin