[RFC,01/13] Add architecture independent hardened atomic base

This series brings the PaX/Grsecurity PAX_REFCOUNT [1]
feature support to the upstream kernel. All credit for the
feature goes to the feature authors.

The name of the upstream feature is HARDENED_ATOMIC
and it is configured using CONFIG_HARDENED_ATOMIC and
HAVE_ARCH_HARDENED_ATOMIC.

This series only adds x86 support; other architectures are expected
to add similar support gradually.

Feature Summary
---------------
The primary goal of KSPP is to provide protection against classes
of vulnerabilities.  One such class of vulnerabilities, known as
use-after-free bugs, frequently results when reference counters
guarding shared kernel objects are overflowed.  The existence of
a kernel path in which a reference counter is incremented more
than it is decremented can lead to wrapping. This buggy path can be
executed until INT_MAX/LONG_MAX is reached, at which point further
increments will cause the counter to wrap to 0.  At this point, the
kernel will erroneously mark the object as not in use, resulting in
a multitude of undesirable cases: releasing the object to other users,
freeing the object while it still has legitimate users, or other
undefined conditions.  The above scenario is known as a use-after-free
bug.

HARDENED_ATOMIC provides mandatory protection against kernel
reference counter overflows.  In Linux, reference counters
are implemented using the atomic_t and atomic_long_t types.
HARDENED_ATOMIC modifies the functions dealing with these types
such that when INT_MAX/LONG_MAX is reached, the atomic variables
remain saturated at these maximum values, rather than wrapping.

There are several non-reference counter users of atomic_t and
atomic_long_t (the fact that these types are being so widely
misused is not addressed by this series).  These users, typically
statistical counters, are not concerned with whether the values of
these types wrap, and therefore can dispense with the added performance
penalty incurred from protecting against overflows. New types have
been introduced for these users: atomic_wrap_t and atomic_long_wrap_t.
Functions for manipulating these types have been added as well.

Note that the protection provided by HARDENED_ATOMIC is not "opt-in":
since atomic_t is so widely misused, it must be protected as-is.
HARDENED_ATOMIC protects all users of atomic_t and atomic_long_t
against overflow.  New users wishing to use atomic types, but not
needing protection against overflows, should use the new types
introduced by this series: atomic_wrap_t and atomic_long_wrap_t.

Bugs Prevented
--------------
HARDENED_ATOMIC would directly mitigate these Linux kernel bugs:

CVE-2016-3135 - Netfilter xt_alloc_table_info integer overflow
CVE-2016-0728 - Keyring refcount overflow
CVE-2014-2851 - Group_info refcount overflow
CVE-2010-2959 - CAN integer overflow vulnerability,
related post: https://jon.oberheide.org/blog/2010/09/10/linux-kernel-can-slub-overflow/

And a relatively fresh exploit example:
https://www.exploit-db.com/exploits/39773/

[1] https://forums.grsecurity.net/viewtopic.php?f=7&t=4173

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 include/asm-generic/atomic-long.h | 166 +++++++++++++++++++++++++++-----------
 include/asm-generic/atomic.h      |   9 +++
 include/asm-generic/atomic64.h    |  13 +++
 include/asm-generic/bug.h         |   4 +
 include/asm-generic/local.h       |  15 ++++
 include/linux/atomic.h            |  14 ++++
 include/linux/types.h             |  17 ++++
 kernel/panic.c                    |  12 +++
 security/Kconfig                  |  15 ++++
 9 files changed, 219 insertions(+), 46 deletions(-)

[RFC,01/13] Add architecture independent hardened atomic base

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