lkml.org 
[lkml]   [2011]   [Dec]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch 1/4] Add routine for generating an ID for kernel pointer
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.

- Tejun worried about the single poison value was a weak side -
leaking one makes all the IDs vulnerable. To address this
several poison values - one per object type - are introduced.
They are stored in a plain array.
- Pekka proposed to initialized poison values in the late_initcall callback
- ... and move the code to mm/util.c

Based-on-patch-from: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Glauber Costa <glommer@parallels.com>
CC: Andi Kleen <andi@firstfloor.org>
CC: Tejun Heo <tj@kernel.org>
CC: Matt Helsley <matthltc@us.ibm.com>
CC: Pekka Enberg <penberg@kernel.org>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Vasiliy Kulikov <segoon@openwall.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Alexey Dobriyan <adobriyan@gmail.com>
---
include/linux/gen_obj_id.h | 20 +++++++++++++++++
mm/Kconfig | 16 ++++++++++++++
mm/Makefile | 1
mm/gen_obj_id.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 88 insertions(+)

Index: linux-2.6.git/include/linux/gen_obj_id.h
===================================================================
--- /dev/null
+++ linux-2.6.git/include/linux/gen_obj_id.h
@@ -0,0 +1,20 @@
+#ifndef _LINUX_GEN_OBJ_ID_H
+#define _LINUX_GEN_OBJ_ID_H
+
+#ifdef __KERNEL__
+
+enum {
+ GEN_OBJ_ID_TYPES,
+};
+
+#ifdef CONFIG_GENERIC_OBJECT_ID
+extern 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_GEN_OBJ_ID_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_ID
+ bool "Enable generic object ID 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/Makefile
===================================================================
--- linux-2.6.git.orig/mm/Makefile
+++ linux-2.6.git/mm/Makefile
@@ -51,3 +51,4 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoiso
obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
obj-$(CONFIG_CLEANCACHE) += cleancache.o
+obj-$(CONFIG_GENERIC_OBJECT_ID) += gen_obj_id.o
Index: linux-2.6.git/mm/gen_obj_id.c
===================================================================
--- /dev/null
+++ linux-2.6.git/mm/gen_obj_id.c
@@ -0,0 +1,51 @@
+#include <linux/kernel.h>
+#include <linux/capability.h>
+#include <linux/random.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/gen_obj_id.h>
+
+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);


\
 
 \ /
  Last update: 2011-12-23 13:53    [W:0.138 / U:0.044 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site