linux-kernel - Re: [PATCH v4 3/9] vsprintf: Do not check address of well-known strings

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Message-ID: <0ff89c4e-e20d-467e-de36-61e3a5557c7d@rasmusvillemoes.dk>
Date:   Thu, 5 Apr 2018 15:30:51 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/9] vsprintf: Do not check address of well-known
 strings

On 2018-04-04 10:58, Petr Mladek wrote:
> We are going to check the address using probe_kernel_address(). It will
> be more expensive and it does not make sense for well known address.
> 
> This patch splits the string() function. The variant without the check
> is then used on locations that handle string constants or strings defined
> as local variables.
> 
> This patch does not change the existing behavior.

Please leave string() alone, except for moving the < PAGE_SIZE check to
a new helper checked_string (feel free to find a better name), and use
checked_string for handling %s and possibly the few other cases where
we're passing a user-supplied pointer. That avoids cluttering the entire
file with double-underscore calls, and e.g. in the %pO case, it's easier
to understand why one uses two different *string() helpers if the name
of one somehow conveys how it is different from the other.

Rasmus