s390/cpcmd: fix inline assembly register clobbering

[ Upstream commit 7a2f914 ]

Register variables initialized using arithmetic. That leads to
kasan instrumentaton code corrupting the registers contents.
Follow GCC guidlines and use temporary variables for assigning
init values to register variables.

Fixes: 94c12cc ("[S390] Inline assembly cleanup.")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Local-Register-Variables.html
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/s390/kernel/cpcmd.c

@@ -37,10 +37,12 @@ static int diag8_noresponse(int cmdlen)
 
 static int diag8_response(int cmdlen, char *response, int *rlen)
 {
+	unsigned long _cmdlen = cmdlen | 0x40000000L;
+	unsigned long _rlen = *rlen;
 	register unsigned long reg2 asm ("2") = (addr_t) cpcmd_buf;
 	register unsigned long reg3 asm ("3") = (addr_t) response;
-	register unsigned long reg4 asm ("4") = cmdlen | 0x40000000L;
-	register unsigned long reg5 asm ("5") = *rlen;
+	register unsigned long reg4 asm ("4") = _cmdlen;
+	register unsigned long reg5 asm ("5") = _rlen;
 
 	asm volatile(
 		"	diag	%2,%0,0x8\n"