s390/kasan: enable stack and global variables access checks

By defining KASAN_SHADOW_OFFSET in Kconfig stack and global variables
memory access check instrumentation is enabled. gcc version 4.9.2 or
newer is also required.
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -56,6 +56,11 @@ config PCI_QUIRKS
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
 
+config KASAN_SHADOW_OFFSET
+	hex
+	depends on KASAN
+	default 0x30000000000
+
 config S390
 	def_bool y
 	select ARCH_BINFMT_ELF_STATE

arch/s390/include/asm/kasan.h

@@ -9,7 +9,7 @@
 #define KASAN_SHADOW_SCALE_SHIFT 3
 #define KASAN_SHADOW_SIZE						       \
 	(_AC(1, UL) << (_REGION2_SHIFT - KASAN_SHADOW_SCALE_SHIFT))
-#define KASAN_SHADOW_OFFSET	_AC(0x30000000000, UL)
+#define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
 #define KASAN_SHADOW_START	KASAN_SHADOW_OFFSET
 #define KASAN_SHADOW_END	(KASAN_SHADOW_START + KASAN_SHADOW_SIZE)