[dapper CVE 1/1] x86: replace LOCK_PREFIX in futex.h

[Andy Whitcroft]

From: Thomas Gleixner <tglx at linutronix.de>

The exception fixup for the futex macros __futex_atomic_op1/2 and
futex_atomic_cmpxchg_inatomic() is missing an entry when the lock
prefix is replaced by a NOP via SMP alternatives.

Chuck Ebert tracked this down from the information provided in:
https://bugzilla.redhat.com/show_bug.cgi?id=429412

A possible solution would be to add another fixup after the
LOCK_PREFIX, so both the LOCK and NOP case have their own entry in the
exception table, but it's not really worth the trouble.

Simply replace LOCK_PREFIX with lock and keep those untouched by SMP
alternatives.

Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Ingo Molnar <mingo at elte.hu>
[cebbert at redhat.com: backport to 2.6.24]
Signed-off-by: Chris Wright <chrisw at sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>

CVE-2010-3086
BugLink: http://bugs.launchpad.net/bugs/706060
(backported from commit 9d55b9923a1b7ea8193b8875c57ec940dc2ff027 upstream)
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 include/asm-i386/futex.h   |    4 ++--
 include/asm-x86_64/futex.h |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/asm-i386/futex.h b/include/asm-i386/futex.h
index e7a271d..33b574d 100644
--- a/include/asm-i386/futex.h
+++ b/include/asm-i386/futex.h
@@ -28,7 +28,7 @@
 "1:	movl	%2, %0\n\
 	movl	%0, %3\n"					\
 	insn "\n"						\
-"2:	" LOCK_PREFIX "cmpxchgl %3, %2\n\
+"2:	lock ; cmpxchgl %3, %2\n\
 	jnz	1b\n\
 3:	.section .fixup,\"ax\"\n\
 4:	mov	%5, %1\n\
@@ -68,7 +68,7 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
 #endif
 		switch (op) {
 		case FUTEX_OP_ADD:
-			__futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret,
+			__futex_atomic_op1("lock ; xaddl %0, %2", ret,
 					   oldval, uaddr, oparg);
 			break;
 		case FUTEX_OP_OR:
diff --git a/include/asm-x86_64/futex.h b/include/asm-x86_64/futex.h
index 8602c09..d74be2a 100644
--- a/include/asm-x86_64/futex.h
+++ b/include/asm-x86_64/futex.h
@@ -27,7 +27,7 @@
 "1:	movl	%2, %0\n\
 	movl	%0, %3\n"					\
 	insn "\n"						\
-"2:	" LOCK_PREFIX "cmpxchgl %3, %2\n\
+"2:	lock ; cmpxchgl %3, %2\n\
 	jnz	1b\n\
 3:	.section .fixup,\"ax\"\n\
 4:	mov	%5, %1\n\
@@ -62,7 +62,7 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
 		__futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg);
 		break;
 	case FUTEX_OP_ADD:
-		__futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval,
+		__futex_atomic_op1("lock ; xaddl %0, %2", ret, oldval,
 				   uaddr, oparg);
 		break;
 	case FUTEX_OP_OR:
-- 
1.7.1