Re: [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all addresses as unhashed

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>, Petr Mladek <pmladek@suse.com>,
	Marco Elver <elver@google.com>, Timur Tabi <timur@kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	roman.fietze@magna.com, Kees Cook <keescook@chromium.org>,
	John Ogness <john.ogness@linutronix.de>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Pavel Machek <pavel@ucw.cz>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all addresses as unhashed
Date: Tue, 2 Mar 2021 15:28:09 +0100	[thread overview]
Message-ID: <CAMuHMdVYJ0ydFEZ+xPLt27J9pBW+B8pJNPBDZ2Vw5g5k1atarg@mail.gmail.com> (raw)
In-Reply-To: <20210302090811.620ae7d0@gandalf.local.home>

Hi Steven,

On Tue, Mar 2, 2021 at 3:08 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> On Tue, 2 Mar 2021 14:49:42 +0100
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > So this is basically a kernel tinyfication issue, right? Is that still pursued
> > > today? Are there better config options suitable for this than CONFIG_DEBUG_KERNEL?
> >
> > As long as I hear about products running Linux on SoCs with 10 MiB of
> > SRAM, I think the answer is yes.
> > I'm not immediately aware of a better config option.  There are no more
> > TINY options left, and EXPERT selects DEBUG_KERNEL.
>
> Since the trace_printk() uses the same type of notice, I wonder if we could
> make this into a helper function and just pass in the top part.
>
> +       pr_warn("**********************************************************\n");
> +       pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
> +       pr_warn("**                                                      **\n");
>
>
> +       pr_warn("** This system shows unhashed kernel memory addresses   **\n");
> +       pr_warn("** via the console, logs, and other interfaces. This    **\n");
> +       pr_warn("** might reduce the security of your system.            **\n");
>
> Only the above section is really unique. The rest can be a boiler plate.

Good idea. drivers/iommu/iommu-debugfs.c has a third copy.

> +       pr_warn("**                                                      **\n");
> +       pr_warn("** If you see this message and you are not debugging    **\n");
> +       pr_warn("** the kernel, report this immediately to your system   **\n");
> +       pr_warn("** administrator!                                       **\n");
> +       pr_warn("**                                                      **\n");
> +       pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
> +       pr_warn("**********************************************************\n");

Fortunately gcc is already smart enough to deduplicate identical strings,
but only in the same source file.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds