linux-kernel - Re: [PATCH 1/3] lib/test_printf: Clean up test of hashed pointers

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Date:   Thu, 27 Feb 2020 15:30:51 +0100
From:   Uwe Kleine-König <uwe@...ine-koenig.org>
To:     Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, Ilya Dryomov <idryomov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        "Tobin C . Harding" <me@...in.cc>
Subject: Re: [PATCH 1/3] lib/test_printf: Clean up test of hashed pointers

Hello Petr,

On 2/27/20 2:01 PM, Petr Mladek wrote:
> The commit ad67b74d2469d9b82a ("printk: hash addresses printed with %p")
> helps to prevent leaking kernel addresses.
> 
> The testing of this functionality is a bit problematic because the output
> depends on a random key that is generated during boot. Though, it is
> still possible to check some aspects:
> 
>   + output string length
>   + hash differs from the original pointer value
>   + top half bits are zeroed on 64-bit systems

Is "hash differs from the original pointer value" a valid check?
Depending on the random value and the actual pointer I can imagine a
valid match. Such a match is unlikely but not necessarily bogus, is it?

Best regards
Uwe



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