linux-kernel - Printk specifiers for _

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Message-ID: <20201120164412.GD619708@rowland.harvard.edu>
Date:   Fri, 20 Nov 2020 11:44:12 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Kernel development list <linux-kernel@...r.kernel.org>
Subject: Printk specifiers for __user pointers

To the VSPRINTF maintainers:

Documentation/core-api/printk-formats.rst lists a large number of format 
specifiers for pointers of various sorts.  Yet as far as I can see, 
there is no specifier meant for use with __user pointers.

The security implications of printing the true, unmangled value of a 
__user pointer are minimal, since doing so does not leak any kernel 
information.  So %px would work, but tools like checkpatch.pl don't like 
it.

Should a new specifier be added?  If not, should we simply use %px?

Alan Stern