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Subject: Re: [PATCH 1/3] lib/test_printf: Clean up test of hashed pointers
To:     Petr Mladek <pmladek@suse.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        linux-kernel@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        "Tobin C . Harding" <me@tobin.cc>
References: <20200227130123.32442-1-pmladek@suse.com>
 <20200227130123.32442-2-pmladek@suse.com>
From:   =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
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Message-ID: <bdb7d995-f16f-335c-c06a-b6732dcbbfa2@kleine-koenig.org>
Date:   Thu, 27 Feb 2020 15:30:51 +0100
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From: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
To: Petr Mladek <pmladek@suse.com>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
 Steven Rostedt <rostedt@goodmis.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
 linux-kernel@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
 Kees Cook <keescook@chromium.org>, "Tobin C . Harding" <me@tobin.cc>
Message-ID: <bdb7d995-f16f-335c-c06a-b6732dcbbfa2@kleine-koenig.org>
Subject: Re: [PATCH 1/3] lib/test_printf: Clean up test of hashed pointers
References: <20200227130123.32442-1-pmladek@suse.com>
 <20200227130123.32442-2-pmladek@suse.com>
In-Reply-To: <20200227130123.32442-2-pmladek@suse.com>

--I0VyUx4H1cFryB8nUb4I59EwMx3eAsZbz
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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.
>=20
> The testing of this functionality is a bit problematic because the outp=
ut
> depends on a random key that is generated during boot. Though, it is
> still possible to check some aspects:
>=20
>   + 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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