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

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Date:   Fri, 12 Feb 2021 12:52:01 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Timur Tabi <timur@...nel.org>
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

Hi,

I have realized that I did not comment the two ideas.

On Wed 2021-02-10 11:27:45, Timur Tabi wrote:
> 
> 
> 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?

seq_buf is a handy API that might be used for different purpose.
For example, it seems to be used ftrace where people might want
to see real pointers when debugging.

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

I am not sure if there is an easy and reliable way how to detect the
user-space context. On some architectures, it might be possible to
guess it by the address of the buffer. But it will not work when
the message is temporary printed into a local buffer and copied
later.

Let's keep it simple. Heuristics often become very complex over time.

Best Regards,
Petr