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@xxxxxxxxxxxx>
---
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;
--
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