2015-07-26 13:43:46

by Vasily Kulikov

Subject: [PATCH 1/3] fix LIST_POISON{1,2} offset

Poison pointer values should be small enough to find a room in
non-mmap'able/hardly-mmap'able space. E.g. on x86 "poison pointer
space" is located starting from 0x0. Given unprivileged users cannot
mmap anything below mmap_min_addr, it should be safe to use poison
pointers lower than mmap_min_addr.

The current poison pointer values of LIST_POISON{1,2} might be
too big for mmap_min_addr values equal or less than 1 MB (common case,
e.g. Ubuntu uses only 0x10000). There is little point to use such a big
value given the "poison pointer space" below 1 MB is not yet exhausted.
Changing it to a smaller value solves the problem for small
mmap_min_addr setups.

The values are suggested by Solar Designer:
http://www.openwall.com/lists/oss-security/2015/05/02/6

Signed-off-by: Vasily Kulikov <[email protected]>
---
include/linux/poison.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/poison.h b/include/linux/poison.h
index 7b2a7fc..ee697b9 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -19,8 +19,8 @@
* under normal circumstances, used to verify that nobody uses
* non-initialized list entries.
*/
-#define LIST_POISON1 ((void *) 0x00100100 + POISON_POINTER_DELTA)
-#define LIST_POISON2 ((void *) 0x00200200 + POISON_POINTER_DELTA)
+#define LIST_POISON1 ((void *) 0x100 + POISON_POINTER_DELTA)
+#define LIST_POISON2 ((void *) 0x200 + POISON_POINTER_DELTA)

/********** include/linux/timer.h **********/
/*
--
2.1.0

2015-07-26 13:45:43

by Vasily Kulikov

Subject: [PATCH 2/3] use POISON_POINTER_DELTA for poison pointers

TIMER_ENTRY_STATIC and TAIL_MAPPING are defined as poison pointers which
should point to nowhere. Redefine them using POISON_POINTER_DELTA arithmetics
to make sure they really point to non-mappable area declared by the
target architecture.

Signed-off-by: Vasily Kulikov <[email protected]>
---
include/linux/poison.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/poison.h b/include/linux/poison.h
index ee697b9..a721bcd 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -27,14 +27,14 @@
* Magic number "tsta" to indicate a static timer initializer
* for the object debugging code.
*/
-#define TIMER_ENTRY_STATIC ((void *) 0x74737461)
+#define TIMER_ENTRY_STATIC ((void *) 0x300 + POISON_POINTER_DELTA)

/********** mm/debug-pagealloc.c **********/
#define PAGE_POISON 0xaa

/********** mm/page_alloc.c ************/

-#define TAIL_MAPPING ((void *) 0x01014A11 + POISON_POINTER_DELTA)
+#define TAIL_MAPPING ((void *) 0x400 + POISON_POINTER_DELTA)

/********** mm/slab.c **********/
/*
--
2.1.0

2015-07-26 13:47:08

by Vasily Kulikov

Subject: [PATCH 3/3] remove not-used poison pointer macros

Signed-off-by: Vasily Kulikov <[email protected]>
---
include/linux/poison.h | 7 -------
1 file changed, 7 deletions(-)

diff --git a/include/linux/poison.h b/include/linux/poison.h
index a721bcd..4a27153 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -73,10 +73,6 @@
#define ATM_POISON_FREE 0x12
#define ATM_POISON 0xdeadbeef

-/********** net/ **********/
-#define NEIGHBOR_DEAD 0xdeadbeef
-#define NETFILTER_LINK_POISON 0xdead57ac
-
/********** kernel/mutexes **********/
#define MUTEX_DEBUG_INIT 0x11
#define MUTEX_DEBUG_FREE 0x22
@@ -87,7 +83,4 @@
/********** security/ **********/
#define KEY_DESTROY 0xbd

-/********** sound/oss/ **********/
-#define OSS_POISON_FREE 0xAB
-
#endif
--
2.1.0

2015-07-26 18:42:34

by Thomas Gleixner

Subject: Re: [PATCH 2/3] use POISON_POINTER_DELTA for poison pointers

On Sun, 26 Jul 2015, Vasily Kulikov wrote:
> TIMER_ENTRY_STATIC and TAIL_MAPPING are defined as poison pointers which
> should point to nowhere. Redefine them using POISON_POINTER_DELTA arithmetics
> to make sure they really point to non-mappable area declared by the
> target architecture.
>
> Signed-off-by: Vasily Kulikov <[email protected]>
> ---
> include/linux/poison.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index ee697b9..a721bcd 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -27,14 +27,14 @@
> * Magic number "tsta" to indicate a static timer initializer
> * for the object debugging code.
> */
> -#define TIMER_ENTRY_STATIC ((void *) 0x74737461)
> +#define TIMER_ENTRY_STATIC ((void *) 0x300 + POISON_POINTER_DELTA)

Acked-by: Thomas Gleixner <[email protected]>