[PATCH] mm/slub: Add slub_debug option to panic on memory corruption

[Georgi Djakov <georgi.djakov@linaro.org>]

Being able to stop the system immediately when a memory corruption
is detected is crucial to finding the source of it. This is very
useful when the memory can be inspected with kdump or other tools.

Let's add an option panic the kernel when slab debug catches an
object or list corruption.

This new option is not enabled by default (yet), so it needs to be
enabled explicitly (for example by adding "slub_debug=FZPUC" to
the kernel command line).

Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
---
 Documentation/vm/slub.rst | 1 +
 include/linux/slab.h      | 3 +++
 mm/slab.h                 | 2 +-
 mm/slub.c                 | 9 +++++++++
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 03f294a638bd..32878c44f3de 100644
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -53,6 +53,7 @@ Possible debug options are::
 	Z		Red zoning
 	P		Poisoning (object and padding)
 	U		User tracking (free and alloc)
+	C		Panic on object corruption (enables SLAB_CORRUPTION_PANIC)
 	T		Trace (please only use on single slabs)
 	A		Enable failslab filter mark for the cache
 	O		Switch debugging off for caches that would have
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 0c97d788762c..ebff5e704d08 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -39,6 +39,9 @@
 #define SLAB_STORE_USER		((slab_flags_t __force)0x00010000U)
 /* Panic if kmem_cache_create() fails */
 #define SLAB_PANIC		((slab_flags_t __force)0x00040000U)
+/* Panic if memory corruption is detected */
+#define SLAB_CORRUPTION_PANIC	((slab_flags_t __force)0x00080000U)
+
 /*
  * SLAB_TYPESAFE_BY_RCU - **WARNING** READ THIS!
  *
diff --git a/mm/slab.h b/mm/slab.h
index 120b1d0dfb6d..ae0079017fc6 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -134,7 +134,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
 #elif defined(CONFIG_SLUB_DEBUG)
 #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
-			  SLAB_TRACE | SLAB_CONSISTENCY_CHECKS)
+			  SLAB_TRACE | SLAB_CONSISTENCY_CHECKS | SLAB_CORRUPTION_PANIC)
 #else
 #define SLAB_DEBUG_FLAGS (0)
 #endif
diff --git a/mm/slub.c b/mm/slub.c
index 077a019e4d7a..49351427f701 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -741,6 +741,8 @@ void object_err(struct kmem_cache *s, struct page *page,
 {
 	slab_bug(s, "%s", reason);
 	print_trailer(s, page, object);
+	if (slub_debug & SLAB_CORRUPTION_PANIC)
+		panic(reason);
 }
 
 static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
@@ -755,6 +757,8 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
 	slab_bug(s, "%s", buf);
 	print_page_info(page);
 	dump_stack();
+	if (slub_debug & SLAB_CORRUPTION_PANIC)
+		panic("slab: slab error\n");
 }
 
 static void init_object(struct kmem_cache *s, void *object, u8 val)
@@ -776,6 +780,8 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
 static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
 						void *from, void *to)
 {
+	if (slub_debug & SLAB_CORRUPTION_PANIC)
+		panic("slab: object overwritten\n");
 	slab_fix(s, "Restoring 0x%p-0x%p=0x%x\n", from, to - 1, data);
 	memset(from, data, to - from);
 }
@@ -1319,6 +1325,9 @@ parse_slub_debug_flags(char *str, slab_flags_t *flags, char **slabs, bool init)
 		case 'a':
 			*flags |= SLAB_FAILSLAB;
 			break;
+		case 'c':
+			*flags |= SLAB_CORRUPTION_PANIC;
+			break;
 		case 'o':
 			/*
 			 * Avoid enabling debugging on caches if its minimum