futex: Mark get_robust_list as deprecated

Notify get_robust_list users that the syscall is going away.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: kernel-hardening@lists.openwall.com
Cc: spender@grsecurity.net
Link: http://lkml.kernel.org/r/20120323190855.GA27213@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/feature-removal-schedule.txt

@@ -529,3 +529,13 @@ When:	3.5
 Why:	The old kmap_atomic() with two arguments is deprecated, we only
 	keep it for backward compatibility for few cycles and then drop it.
 Who:	Cong Wang <amwang@redhat.com>
+
+----------------------------
+
+What:	get_robust_list syscall
+When:	2013
+Why:	There appear to be no production users of the get_robust_list syscall,
+	and it runs the risk of leaking address locations, allowing the bypass
+	of ASLR. It was only ever intended for debugging, so it should be
+	removed.
+Who:	Kees Cook <keescook@chromium.org>

kernel/futex.c

@@ -2449,6 +2449,8 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
 
+	WARN_ONCE(1, "deprecated: get_robust_list will be deleted in 2013.\n");
+
 	rcu_read_lock();
 
 	ret = -ESRCH;

kernel/futex_compat.c

@@ -142,6 +142,8 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
 
+	WARN_ONCE(1, "deprecated: get_robust_list will be deleted in 2013.\n");
+
 	rcu_read_lock();
 
 	ret = -ESRCH;