linux-kernel - [PATCH] Revert "slub: force on no_hash_pointers when slub

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Date:   Wed,  8 Feb 2023 11:47:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Kees Cook <keescook@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>, concord@...too.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Petr Mladek <pmladek@...e.com>, linux-mm@...ck.org,
        stable@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] Revert "slub: force on no_hash_pointers when slub_debug is enabled"

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@...e.cz>
Cc: Stephen Boyd <swboyd@...omium.org>
Cc: concord@...too.org
Cc: Pekka Enberg <penberg@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Petr Mladek <pmladek@...e.com>
Cc: linux-mm@...ck.org
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
Signed-off-by: Kees Cook <keescook@...omium.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