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Subject: Re: [PATCH 0/3][RESEND] add support for never printing hashed
 addresses
To:     Timur Tabi <timur@kernel.org>
References: <20210210051814.845713-1-timur@kernel.org>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        akpm@linux-foundation.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        roman.fietze@magna.com, Kees Cook <keescook@chromium.org>,
        John Ogness <john.ogness@linutronix.de>,
        akinobu.mita@gmail.com, glider@google.com,
        Andrey Konovalov <andreyknvl@google.com>,
        Marco Elver <elver@google.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Message-ID: <6da0be5a-7cb0-4943-e61f-7c3275e60cb6@i-love.sakura.ne.jp>
Date:   Thu, 11 Feb 2021 00:46:15 +0900
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On 2021/02/10 14:18, Timur Tabi wrote:
> [accidentally sent from the wrong email address, so resending]
> 
> [The list of email addresses on CC: is getting quite lengthy,
> so I hope I've included everyone.]
> 
> Although hashing addresses printed via printk does make the
> kernel more secure, it interferes with debugging, especially
> with some functions like print_hex_dump() which always uses
> hashed addresses.

Oh, I was wishing

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3b53c73580c5..34c7e145ac3c 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -802,7 +802,7 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
 	 * Print the real pointer value for NULL and error pointers,
 	 * as they are not actual addresses.
 	 */
-	if (IS_ERR_OR_NULL(ptr))
+	if (IS_ERR_OR_NULL(ptr) || IS_ENABLED(CONFIG_DEBUG_DONT_HASH_POINTERS))
 		return pointer_string(buf, end, ptr, spec);
 
 	/* When debugging early boot use non-cryptographically secure hash. */

change as a kernel config option, for more we try to switch using kernel command line options,
more we likely make errors with sharing appropriate kernel command line options
(e.g. https://github.com/google/syzkaller/commit/99c64d5c672700d6c0de63d11db25a0678e47a75 ).