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

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Message-ID: <CAMuHMdVYJ0ydFEZ+xPLt27J9pBW+B8pJNPBDZ2Vw5g5k1atarg@mail.gmail.com>
Date:   Tue, 2 Mar 2021 15:28:09 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, Petr Mladek <pmladek@...e.com>,
        Marco Elver <elver@...gle.com>, Timur Tabi <timur@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        roman.fietze@...na.com, Kees Cook <keescook@...omium.org>,
        John Ogness <john.ogness@...utronix.de>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Pavel Machek <pavel@....cz>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all
 addresses as unhashed

Hi Steven,

On Tue, Mar 2, 2021 at 3:08 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 2 Mar 2021 14:49:42 +0100
> Geert Uytterhoeven <geert@...ux-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@...ux-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