Commit 79270291 authored by Stephen Boyd's avatar Stephen Boyd Committed by Linus Torvalds
Browse files

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.

[akpm@linux-foundation.org: fix build with CONFIG_SLUB_DEBUG=n]

Link: https://lkml.kernel.org/r/20210601182202.3011020-5-swboyd@chromium.org


Signed-off-by: default avatarStephen Boyd <swboyd@chromium.org>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarPetr Mladek <pmladek@suse.com>
Cc: Joe Perches <joe@perches.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 582d1212

include/linux/kernel.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

lib/vsprintf.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

mm/slub.c

+19 −1
Original line number Diff line number Diff line
@@ -118,12 +118,26 @@ 
 */



#ifdef CONFIG_SLUB_DEBUG



#ifdef CONFIG_SLUB_DEBUG_ON

DEFINE_STATIC_KEY_TRUE(slub_debug_enabled);

#else

DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);

#endif

#endif



static inline bool __slub_debug_enabled(void)

{

	return static_branch_unlikely(&slub_debug_enabled);

}



#else		/* CONFIG_SLUB_DEBUG */



static inline bool __slub_debug_enabled(void)

{

	return false;

}



#endif		/* CONFIG_SLUB_DEBUG */



static inline bool kmem_cache_debug(struct kmem_cache *s)

{
@@ -4487,6 +4501,10 @@ 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;