[1/1] include/linux/poison.h: fix LIST_POISON{1,2} offset

From: Vasily Kulikov <segoon@openwall.com>

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 <segoon@openwall.com>
Cc: Solar Designer <solar@openwall.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 8a5e5e02fc83aaf67053ab53b359af08c6c49aaf)
CVE-2016-0821
BugLink: https://bugs.launchpad.net/bugs/1561389
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 include/linux/poison.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Clean cherry-pick, fixes CVE, no newer upstream patches that change this.
--chris

On Mon, Apr 18, 2016 at 03:04:43PM +0100, Luis Henriques wrote:
> From: Vasily Kulikov <segoon@openwall.com>
> 
> 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 <segoon@openwall.com>
> Cc: Solar Designer <solar@openwall.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> (cherry picked from commit 8a5e5e02fc83aaf67053ab53b359af08c6c49aaf)
> CVE-2016-0821
> BugLink: https://bugs.launchpad.net/bugs/1561389
> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
> ---
>  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 2110a81c5e2a..253c9b4198ef 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 **********/
>  /*
> 
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