From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Tue, 24 Oct 2017 11:22:47 +0100
Subject: [PATCH] locking/barriers: Add implicit smp_read_barrier_depends() to
 READ_ONCE()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

CVE-2017-5754

[ Note, this is a Git cherry-pick of the following commit:

    76ebbe78f739 ("locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()")

  ... for easier x86 PTI code testing and back-porting. ]

In preparation for the removal of lockless_dereference(), which is the
same as READ_ONCE() on all architectures other than Alpha, add an
implicit smp_read_barrier_depends() to READ_ONCE() so that it can be
used to head dependency chains on all architectures.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1508840570-22169-3-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit c2bc66082e1048c7573d72e62f597bdc5ce13fea)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit 6ef3d843f8f1a8b72ca83d4b1d457c2896278ccd)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 include/linux/compiler.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 043b60de041e..8af8814ebe7a 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -314,6 +314,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 		__read_once_size(&(x), __u.__c, sizeof(x));		\
 	else								\
 		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
 	__u.__val;							\
 })
 #define READ_ONCE(x) __READ_ONCE(x, 1)
-- 
2.14.2

