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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: Stephen Boyd <swboyd@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Petr 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Stephen Boyd 2021-06-28 19:34:52 -07:00 committed by Linus Torvalds
parent 582d1212ed
commit 792702911f
3 changed files with 22 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/kernel.h
View File

@ -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);

2
lib/vsprintf.c
View File

@ -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;

20
mm/slub.c
View File

@ -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;