linux-kernel - [PATCH v3 4/4] slub: Force on no_hash_pointers when slub

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue,  1 Jun 2021 11:22:02 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>
Subject: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled

Obscuring the pointers that slub shows when debugging makes for some
confusing slub debug messages:

 Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17

Those addresses are hashed for kernel security reasons. If we're trying
to be secure with slub_debug on the commandline we have some big
problems given that we dump whole chunks of kernel memory to the kernel
logs. Let's force on the no_hash_pointers commandline flag when
slub_debug is on the commandline. This makes slub debug messages more
meaningful and if by chance a kernel address is in some slub debug
object dump we will have a better chance of figuring out what went
wrong.

Note that we don't use %px in the slub code because we want to reduce
the number of places that %px is used in the kernel. This also nicely
prints a big fat warning at kernel boot if slub_debug is on the
commandline so that we know that this kernel shouldn't be used on
production systems.

Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 include/linux/kernel.h | 2 ++
 lib/vsprintf.c         | 2 +-
 mm/slub.c              | 4 ++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 15d8bad3d2f2..bf950621febf 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -357,6 +357,8 @@ 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 f0c35d9b65bf..cc281f5895f9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2186,7 +2186,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
 bool no_hash_pointers __ro_after_init;
 EXPORT_SYMBOL_GPL(no_hash_pointers);
 
-static int __init no_hash_pointers_enable(char *str)
+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 bf4949115412..a722794f1dbd 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4460,6 +4460,10 @@ void __init kmem_cache_init(void)
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
 
+	/* Print slub debugging pointers without hashing */
+	if (static_branch_unlikely(&slub_debug_enabled))
+		no_hash_pointers_enable(NULL);
+
 	kmem_cache_node = &boot_kmem_cache_node;
 	kmem_cache = &boot_kmem_cache;
 
-- 
https://chromeos.dev