[3.16.y-ckt stable] Patch "m68k: Define asmlinkage_protect" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    m68k: Define asmlinkage_protect

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 5ae1b59c00a80e8420f3bbe04fdf6f3ff93a01e1 Mon Sep 17 00:00:00 2001
From: Andreas Schwab <schwab at linux-m68k.org>
Date: Wed, 23 Sep 2015 23:12:09 +0200
Subject: m68k: Define asmlinkage_protect

commit 8474ba74193d302e8340dddd1e16c85cc4b98caf upstream.

Make sure the compiler does not modify arguments of syscall functions.
This can happen if the compiler generates a tailcall to another
function.  For example, without asmlinkage_protect sys_openat is compiled
into this function:

sys_openat:
	clr.l %d0
	move.w 18(%sp),%d0
	move.l %d0,16(%sp)
	jbra do_sys_open

Note how the fourth argument is modified in place, modifying the register
%d4 that gets restored from this stack slot when the function returns to
user-space.  The caller may expect the register to be unmodified across
system calls.

Signed-off-by: Andreas Schwab <schwab at linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert at linux-m68k.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/m68k/include/asm/linkage.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/m68k/include/asm/linkage.h b/arch/m68k/include/asm/linkage.h
index 5a822bb790f7..066e74f666ae 100644
--- a/arch/m68k/include/asm/linkage.h
+++ b/arch/m68k/include/asm/linkage.h
@@ -4,4 +4,34 @@
 #define __ALIGN .align 4
 #define __ALIGN_STR ".align 4"

+/*
+ * Make sure the compiler doesn't do anything stupid with the
+ * arguments on the stack - they are owned by the *caller*, not
+ * the callee. This just fools gcc into not spilling into them,
+ * and keeps it from doing tailcall recursion and/or using the
+ * stack slots for temporaries, since they are live and "used"
+ * all the way to the end of the function.
+ */
+#define asmlinkage_protect(n, ret, args...) \
+	__asmlinkage_protect##n(ret, ##args)
+#define __asmlinkage_protect_n(ret, args...) \
+	__asm__ __volatile__ ("" : "=r" (ret) : "0" (ret), ##args)
+#define __asmlinkage_protect0(ret) \
+	__asmlinkage_protect_n(ret)
+#define __asmlinkage_protect1(ret, arg1) \
+	__asmlinkage_protect_n(ret, "m" (arg1))
+#define __asmlinkage_protect2(ret, arg1, arg2) \
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
+#define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
+#define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4))
+#define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5))
+#define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5), "m" (arg6))
+
 #endif