linux-kernel - Re: [PATCH 3/6] x86/dumpstack: make printk_stack

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Date:   Thu, 25 Aug 2016 22:19:51 -0400
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Nilay Vaish <nilayvaish@...il.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 3/6] x86/dumpstack: make printk_stack_address() more
 generally useful

On Thu, Aug 25, 2016 at 5:23 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Aug 25, 2016 2:08 PM, "Josh Poimboeuf" <jpoimboe@...hat.com> wrote:
>>
>> Ah, the plot thickens.  I didn't know about 'dmesg_restrict'.  So I
>> guess we don't have to restrict the stack dump addresses after all,
>> since the entire dmesg buffer is protected by syslog()?
>
> No.
>
> Guys, the whole dmesg_restrict thing is a joke. You can't restrict access to
> system messages in general. It's just a stupid idea.

I'm not advocating that it's a globally useful protection, I was just
trying to point out that so much stuff is already exposed in the
system log that it's likely not a great use of time to think about
censoring things there right now. Obviously if it both improves
debuggability _and_ removes raw addresses from the log, I'm all for
it. :)

-Kees

-- 
Kees Cook
Nexus Security