linux-kernel - Re: [PATCH 0/2] introduce DUMP_PREFIX

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Date:   Tue, 26 Jan 2021 12:14:04 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Timur Tabi <timur@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        Petr Mladek <pmladek@...e.com>, roman.fietze@...na.com,
        keescook@...omium.org, John Ogness <john.ogness@...utronix.de>,
        linux-mm@...ck.org, Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH 0/2] introduce DUMP_PREFIX_UNHASHED for hex dumps

On Tue, 26 Jan 2021 10:59:12 -0600
Timur Tabi <timur@...nel.org> wrote:

> The only drawback to this idea is: what happens if distros start 
> enabling CONFIG_PRINTK_NEVER_HASH by default, just because it makes 
> debugging easier?

I do believe distros should be more concerned about security than using
this for making debugging easier.

Perhaps we should add the same banner print if that config is set as
trace_printk() has if it is detected in the kernel or a module:

 **********************************************************
 **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
 **                                                      **
 ** trace_printk() being used. Allocating extra memory.  **
 **                                                      **
 ** This means that this is a DEBUG kernel and it is     **
 ** unsafe for production use.                           **
 **                                                      **
 ** If you see this message and you are not debugging    **
 ** the kernel, report this immediately to your vendor!  **
 **                                                      **
 **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
 **********************************************************

But have:

 **********************************************************
 **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
 **                                                      **
 ** CONFIG_PRINTK_NEVER_HASH enabled                     **
 **                                                      **
 ** This means that this is a DEBUG kernel and it is     **
 ** unsafe for production use.                           **
 **                                                      **
 ** If you see this message and you are not debugging    **
 ** the kernel, report this immediately to your vendor!  **
 **                                                      **
 **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
 **********************************************************

The above appears to keep people from using trace_printk(), I don't see why
it wouldn't work for this config ;-)

-- Steve