Re: FAILED: patch "[PATCH] s390/stack: fix possible register corruption with stack" failed to apply to 5.4-stable tree

[Heiko Carstens <hca@linux.ibm.com>]

On Sun, Jun 27, 2021 at 04:20:36PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> thanks,
> 
> greg k-h

Please find below the backported patch which applies to 5.4-stable:

From 1a124d1b216ddf165ce0635ef77878c83731c3dc Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Fri, 18 Jun 2021 16:58:47 +0200
Subject: [PATCH] s390/stack: fix possible register corruption with stack
 switch helper

[ Upstream commit 67147e96a332b56c7206238162771d82467f86c0 ]

The CALL_ON_STACK macro is used to call a C function from inline
assembly, and therefore must consider the C ABI, which says that only
registers 6-13, and 15 are non-volatile (restored by the called
function).

The inline assembly incorrectly marks all registers used to pass
parameters to the called function as read-only input operands, instead
of operands that are read and written to. This might result in
register corruption depending on usage, compiler, and compile options.

Fix this by marking all operands used to pass parameters as read/write
operands. To keep the code simple even register 6, if used, is marked
as read-write operand.

Fixes: ff340d2472ec ("s390: add stack switch helper")
Cc: <stable@kernel.org> # 4.20
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
 arch/s390/include/asm/stacktrace.h | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
index 3679d224fd3c..6836532f8d1a 100644
--- a/arch/s390/include/asm/stacktrace.h
+++ b/arch/s390/include/asm/stacktrace.h
@@ -79,12 +79,16 @@ struct stack_frame {
 	CALL_ARGS_4(arg1, arg2, arg3, arg4);				\
 	register unsigned long r4 asm("6") = (unsigned long)(arg5)
 
-#define CALL_FMT_0 "=&d" (r2) :
-#define CALL_FMT_1 "+&d" (r2) :
-#define CALL_FMT_2 CALL_FMT_1 "d" (r3),
-#define CALL_FMT_3 CALL_FMT_2 "d" (r4),
-#define CALL_FMT_4 CALL_FMT_3 "d" (r5),
-#define CALL_FMT_5 CALL_FMT_4 "d" (r6),
+/*
+ * To keep this simple mark register 2-6 as being changed (volatile)
+ * by the called function, even though register 6 is saved/nonvolatile.
+ */
+#define CALL_FMT_0 "=&d" (r2)
+#define CALL_FMT_1 "+&d" (r2)
+#define CALL_FMT_2 CALL_FMT_1, "+&d" (r3)
+#define CALL_FMT_3 CALL_FMT_2, "+&d" (r4)
+#define CALL_FMT_4 CALL_FMT_3, "+&d" (r5)
+#define CALL_FMT_5 CALL_FMT_4, "+&d" (r6)
 
 #define CALL_CLOBBER_5 "0", "1", "14", "cc", "memory"
 #define CALL_CLOBBER_4 CALL_CLOBBER_5
@@ -105,7 +109,7 @@ struct stack_frame {
 		"	brasl	14,%[_fn]\n"				\
 		"	la	15,0(%[_prev])\n"			\
 		: [_prev] "=&a" (prev), CALL_FMT_##nr			\
-		  [_stack] "a" (stack),					\
+		: [_stack] "a" (stack),					\
 		  [_bc] "i" (offsetof(struct stack_frame, back_chain)),	\
 		  [_fn] "X" (fn) : CALL_CLOBBER_##nr);			\
 	r2;								\
-- 
2.25.1