linux-kernel - Re: [PATCH] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed

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Date:   Thu, 4 Feb 2021 22:49:44 +0100
From:   Pavel Machek <pavel@....cz>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Timur Tabi <timur@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        willy@...radead.org, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, roman.fietze@...na.com,
        keescook@...omium.org, john.ogness@...utronix.de,
        akinobu.mita@...il.com
Subject: Re: [PATCH] lib/vsprintf: make-printk-non-secret printks all
 addresses as unhashed

Hi!

> Pavel Machek <pavel@....cz> wrote:
> 
> > > +	pr_warn("** Kernel memory addresses are exposed, which may       **\n");
> > > +	pr_warn("** compromise security on your system.                  **\n");  
> > 
> > This is lies, right? And way too verbose.
> 
> Not really. More of an exaggeration than a lie. And the verbosity is
> to

Well... security is _not_ compromised but robustness against kernel
bugs is reduced. It should not exaggerate.

> make sure it's noticed by those that shouldn't have it set. This works well
> for keeping trace_printk() out of production kernels. Why do you
> care

So if we want people to see it, we up the severity, right? Like
pr_err()... Distro kernels have quiet, anyway...

Lets take a look for what we say for _real_ problems:

[    0.544757] Spectre V1 : Mitigation: usercopy/swapgs barriers and
__user pointer sanitiza
tion
[    0.544876] Spectre V2 : Mitigation: Full generic retpoline
[    0.544961] Spectre V2 : Spectre v2 / SpectreRSB mitigation:
Filling RSB on context switc
h
[    0.545064] L1TF: System has more than MAX_PA/2 memory. L1TF
mitigation not effective.
[    0.545163] L1TF: You may make it effective by booting the kernel
with mem=2147483648 par
ameter.
[    0.545281] L1TF: However, doing so will make a part of your RAM
unusable.
[    0.545374] L1TF: Reading
https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html
might help you decide.

This machine is insecure. Yet I don't see ascii-art *** all around..

"Kernel memory addresses are exposed, which is bad for security."
would be quite enough, I'd say...

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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