linux-kernel - Re: [PATCH 3/3] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed

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Date:   Wed, 10 Feb 2021 11:27:45 -0600
From:   Timur Tabi <timur@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        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@...il.com, glider@...gle.com,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 3/3] lib/vsprintf: make-printk-non-secret printks all
 addresses as unhashed



On 2/10/21 7:41 AM, Petr Mladek wrote:
> 
> The option causes that vsprintf() will not hash pointers. Yes, it is
> primary used by printk(). But it is used also in some other
> interfaces, especially trace_printk(), seq_buf() API. The naked
> pointers might appear more or less anywhere, including procfs,
> sysfs, debugfs.

Fair point.  Shouldn't calls to seq_buf_printf() (and any printk usage 
that always exists in the context of a user-space process) use %pK anyway?

Hmmm.... maybe vsprintf() should automatically replace %p with %pK if it 
detects a user-space context?

> IMHO, we should fix this. The long discussion was about how to make
> this option safe. Users should be aware that it is not only about
> the kernel log.

Agreed.

> I suggest to rename the parameter "debug_never_hash_pointer" and use
> the same name for the parameter and the variable.

Will do.

> We also should make the warning more generic. I suggest to replace the
> first paragraph with something like:
> 
> 	pr_warn("** The hashing of printed pointers has been disabled   **\n");
> 	pr_warn("** for debugging purposes.                             **\n");
> 
> Feel free to use a better wording. I am not a native speaker.

You could have fooled me.

> Of course, also kernel-parameters.txt has to be updated accordingly.

Ok.