[patch 1/4] Add routine for generating an ID for kernel pointer

[Cyrill Gorcunov]

The routine XORs the given pointer with a random value
producing an ID (32 or 64 bit, depending on the arch).

Since it's a valuable information -- only CAP_SYS_ADMIN
is allowed to obtain it.

Based-on-patch-from: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
CC: Glauber Costa <glommer@xxxxxxxxxxxxx>
CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
CC: Matt Helsley <matthltc@xxxxxxxxxx>
CC: Pekka Enberg <penberg@xxxxxxxxxx>
CC: Eric Dumazet <eric.dumazet@xxxxxxxxx>
CC: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 include/linux/mm.h |   10 ++++++++++
 mm/Kconfig         |   16 ++++++++++++++++
 mm/util.c          |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)

Index: linux-2.6.git/include/linux/mm.h
===================================================================
--- linux-2.6.git.orig/include/linux/mm.h
+++ linux-2.6.git/include/linux/mm.h
@@ -1640,5 +1640,15 @@ extern void copy_user_huge_page(struct p
 				unsigned int pages_per_huge_page);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
+enum {
+	GEN_OBJ_ID_TYPES,
+};
+
+#ifdef CONFIG_GENERIC_OBJECT_IDS
+unsigned long gen_obj_id(void *ptr, int type);
+#else
+static inline unsigned long gen_obj_id(void *ptr, int type) { return 0; }
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */
Index: linux-2.6.git/mm/Kconfig
===================================================================
--- linux-2.6.git.orig/mm/Kconfig
+++ linux-2.6.git/mm/Kconfig
@@ -373,3 +373,19 @@ config CLEANCACHE
 	  in a negligible performance hit.
 
 	  If unsure, say Y to enable cleancache
+
+config GENERIC_OBJECT_IDS
+	bool "Enable generic object ids infrastructure"
+	depends on CHECKPOINT_RESTORE
+	default n
+	help
+	  Turn on the functionality that can generate IDs for kernel
+	  objects, which are exported to userspace via /proc filesystem.
+
+	  It is useful if you need to examinate kernel objects and test
+	  if they are shared between several tasks. These IDs should never
+	  be used for anything but the "sameness" test. Besides, the IDs are
+	  dynamic and valid only while object is alive, once it get freed or
+	  kernel is rebooted -- the IDs will be changed.
+
+	  If unsure, say N here.
Index: linux-2.6.git/mm/util.c
===================================================================
--- linux-2.6.git.orig/mm/util.c
+++ linux-2.6.git/mm/util.c
@@ -4,6 +4,8 @@
 #include <linux/export.h>
 #include <linux/err.h>
 #include <linux/sched.h>
+#include <linux/random.h>
+#include <linux/capability.h>
 #include <asm/uaccess.h>
 
 #include "internal.h"
@@ -307,3 +309,50 @@ EXPORT_TRACEPOINT_SYMBOL(kmalloc_node);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc_node);
 EXPORT_TRACEPOINT_SYMBOL(kfree);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_free);
+
+#ifdef CONFIG_GENERIC_OBJECT_IDS
+static unsigned long gen_obj_cookie[GEN_OBJ_ID_TYPES] __read_mostly;
+
+unsigned long gen_obj_id(void *ptr, int type)
+{
+	if (!capable(CAP_SYS_ADMIN) || !ptr)
+		return 0;
+
+	BUG_ON(type >= GEN_OBJ_ID_TYPES);
+
+	/*
+	 * Note the simple XOR is used here not in a sake
+	 * of security by any means, but rather to break
+	 * an "impression" that such IDs means something
+	 * other than a number which can be used for comparison
+	 * with another number generated by this helper only.
+	 */
+	return ((unsigned long)ptr) ^ gen_obj_cookie[type];
+}
+
+static __init int gen_obj_cookie_init(void)
+{
+#if BITS_PER_LONG == 64
+	const unsigned long emergency_cookie = 0xefcdab8967452301;
+#else
+	const unsigned long emergency_cookie = 0x98badcf9;
+#endif
+	int i;
+
+	for (i = 0; i < GEN_OBJ_ID_TYPES; i++) {
+		get_random_bytes(&gen_obj_cookie[i],
+				 sizeof(unsigned long));
+		/*
+		 * In 'impossible' case of random-bytes = 0
+		 * we still would have non-zero value.
+		 */
+		gen_obj_cookie[i] =
+			(gen_obj_cookie[i] & __PAGE_OFFSET) +
+			(emergency_cookie & ~__PAGE_OFFSET);
+	}
+
+	return 0;
+}
+
+late_initcall(gen_obj_cookie_init);
+#endif

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