From: Vlastimil Babka <vbabka@suse.cz>
To: Petr Mladek <pmladek@suse.com>,
Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Marco Elver <elver@google.com>, Timur Tabi <timur@kernel.org>,
Steven Rostedt <rostedt@goodmis.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 14:37:19 +0100 [thread overview]
Message-ID: <8893ff08-1e50-316c-f632-cd37be1690d5@suse.cz> (raw)
In-Reply-To: <YD49x/UGUq6MSE39@alley>
On 3/2/21 2:29 PM, Petr Mladek wrote:
> On Tue 2021-03-02 13:51:35, Geert Uytterhoeven wrote:
>> > > > +
>> > > > + 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");
>> > > > + 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");
>> > > > +
>> > > > + return 0;
>> > > > +}
>> > > > +early_param("no_hash_pointers", no_hash_pointers_enable);
>> > >
>> > > While bloat-o-meter is not smart enough to notice the real size impact,
>> > > this does add more than 500 bytes of string data to the kernel.
>> > > Do we really need such a large message?
>> > > Perhaps the whole no_hash_pointers machinery should be protected by
>> > > "#ifdef CONFIG_DEBUG_KERNEL"?
>
> This was the deal. The configure option is a no-go, see below and also
> https://lore.kernel.org/r/CAHk-=wgaK4cz=K-JB4p-KPXBV73m9bja2w1W1Lr3iu8+NEPk7A@mail.gmail.com
I think it's a no-go only when enabling such option equals to "no_hash_pointers"
being always passed. What Geert suggests is that you need both
CONFIG_DEBUG_KERNEL *and* no_hash_pointers and that's different.
>> > We recently stumbled across this, and it appears an increasing number
>> > of production kernels enable CONFIG_DEBUG_KERNEL [1], so it likely
>> > isn't the solution (we tried to use CONFIG_DEBUG_KERNEL in similar
>>
>> I guess the people who do care about kernel size do know to disable
>> CONFIG_DEBUG_KERNEL, so it would help them.
>> The everything-but-the-kitchen-sink distro people don't care about kernel
>> size anyway.
>
> The problem with the configure option is not about size. The problem is
> that there would be many kernels in the wild with this option enabled.
> People would install them without knowing that they are less secure.
Same as above.
> Distros would need to provide both kernels. Well, they already do.
> But it might be worse. Some distros might even want to enable it
> by default.
>
> Also many bugs might be debugged without this option. Some bugs
> are hard to reproduce and might be visible only on production
> systems. It should be possible to enable this only when really
> needed and the user must be aware of the risk.
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?
>> > Would placing the strings into an __initconst array help?
>>
>> That would indeed help to reduce run-time memory consumption.
>
> Sure. We could do this. Do you want to send a patch, please?
>
>> It would not solve the raw kernel size increase.
>
> I see. Well, the compression should be pretty efficient
> for a text (with many spaces).
>
> Best Regards,
> Petr
>
next prev parent reply other threads:[~2021-03-02 16:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-14 16:13 [PATCH 0/3][v4] add support for never printing hashed addresses Timur Tabi
2021-02-14 16:13 ` [PATCH 1/3] [v4] lib: use KSTM_MODULE_GLOBALS macro in kselftest drivers Timur Tabi
2021-02-14 16:13 ` [PATCH 2/3] [v4] kselftest: add support for skipped tests Timur Tabi
2021-02-14 16:13 ` [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all addresses as unhashed Timur Tabi
2021-03-02 11:51 ` Geert Uytterhoeven
2021-03-02 12:45 ` Marco Elver
2021-03-02 12:51 ` Geert Uytterhoeven
2021-03-02 13:29 ` Petr Mladek
2021-03-02 13:37 ` Vlastimil Babka [this message]
2021-03-02 13:49 ` Geert Uytterhoeven
2021-03-02 14:08 ` Steven Rostedt
2021-03-02 14:26 ` Marco Elver
2021-03-02 14:35 ` Matthew Wilcox
2021-03-02 14:40 ` Marco Elver
2021-03-02 14:55 ` Geert Uytterhoeven
2021-03-02 14:57 ` Marco Elver
2021-03-02 14:28 ` Geert Uytterhoeven
2021-03-02 15:16 ` Rasmus Villemoes
2021-03-02 15:29 ` Andy Shevchenko
2021-03-02 17:53 ` Petr Mladek
2021-09-11 2:25 ` Xiaoming Ni
2021-09-11 2:39 ` Tetsuo Handa
2021-02-14 16:18 ` [PATCH 0/3][v4] add support for never printing hashed addresses Timur Tabi
2021-02-15 11:08 ` Petr Mladek
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