From:   Kees Cook <keescook@chromium.org>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Kees Cook <keescook@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>, concord@gentoo.org,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Petr Mladek <pmladek@suse.com>, linux-mm@kvack.org,
        stable@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Christoph Lameter <cl@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Bart Van Assche <bvanassche@acm.org>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: [PATCH] Revert "slub: force on no_hash_pointers when slub_debug is enabled"
Date:   Wed,  8 Feb 2023 11:47:17 -0800
Message-Id: <20230208194712.never.999-kees@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

This reverts commit 792702911f581f7793962fbeb99d5c3a1b28f4c3.

Linking no_hash_pointers() to slub_debug has had a chilling effect
on using slub_debug features for security hardening, since system
builders are forced to choose between redzoning and heap address location
exposures. Instead, just require that the "no_hash_pointers" boot param
needs to be used to expose pointers during slub_debug reports.

Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: concord@gentoo.org
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/kernel.h | 2 --
 lib/vsprintf.c         | 2 +-
 mm/slub.c              | 4 ----
 3 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index fe6efb24d151..e3d9d3879495 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -229,8 +229,6 @@ int sscanf(const char *, const char *, ...);
 extern __scanf(2, 0)
 int vsscanf(const char *, const char *, va_list);
 
-extern int no_hash_pointers_enable(char *str);
-
 extern int get_option(char **str, int *pint);
 extern char *get_options(const char *str, int nints, int *ints);
 extern unsigned long long memparse(const char *ptr, char **retptr);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index be71a03c936a..410b4a80a58a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2222,7 +2222,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
 	return widen_string(buf, buf - buf_start, end, spec);
 }
 
-int __init no_hash_pointers_enable(char *str)
+static int __init no_hash_pointers_enable(char *str)
 {
 	if (no_hash_pointers)
 		return 0;
diff --git a/mm/slub.c b/mm/slub.c
index 13459c69095a..63f7337dd433 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5005,10 +5005,6 @@ void __init kmem_cache_init(void)
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
 
-	/* Print slub debugging pointers without hashing */
-	if (__slub_debug_enabled())
-		no_hash_pointers_enable(NULL);
-
 	kmem_cache_node = &boot_kmem_cache_node;
 	kmem_cache = &boot_kmem_cache;
 
-- 
2.34.1