s390/kasan: support memcpy_real with TRACE_IRQFLAGS

Currently if the kernel is built with CONFIG_TRACE_IRQFLAGS and KASAN
and used as crash kernel it crashes itself due to
trace_hardirqs_off/trace_hardirqs_on being called with DAT off. This
happens because trace_hardirqs_off/trace_hardirqs_on are instrumented and
kasan code tries to perform access to shadow memory to validate memory
accesses. Kasan shadow memory is populated with vmemmap, so all accesses
require DAT on.

memcpy_real could be called with DAT on or off (with kasan enabled DAT
is set even before early code is executed).

Make sure that trace_hardirqs_off/trace_hardirqs_on are called with DAT
on and only actual __memcpy_real is called with DAT off.

Also annotate __memcpy_real and _memcpy_real with __no_sanitize_address
to avoid further problems due to switching DAT off.

Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/mm/maccess.c

@@ -70,7 +70,7 @@ void notrace s390_kernel_write(void *dst, const void *src, size_t size)
 	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
 }
 
-static int __memcpy_real(void *dest, void *src, size_t count)
+static int __no_sanitize_address __memcpy_real(void *dest, void *src, size_t count)
 {
 	register unsigned long _dest asm("2") = (unsigned long) dest;
 	register unsigned long _len1 asm("3") = (unsigned long) count;
@@ -91,19 +91,23 @@ static int __memcpy_real(void *dest, void *src, size_t count)
 	return rc;
 }
 
-static unsigned long _memcpy_real(unsigned long dest, unsigned long src,
-				  unsigned long count)
+static unsigned long __no_sanitize_address _memcpy_real(unsigned long dest,
+							unsigned long src,
+							unsigned long count)
 {
 	int irqs_disabled, rc;
 	unsigned long flags;
 
 	if (!count)
 		return 0;
-	flags = __arch_local_irq_stnsm(0xf8UL);
+	flags = arch_local_irq_save();
 	irqs_disabled = arch_irqs_disabled_flags(flags);
 	if (!irqs_disabled)
 		trace_hardirqs_off();
+	__arch_local_irq_stnsm(0xf8); // disable DAT
 	rc = __memcpy_real((void *) dest, (void *) src, (size_t) count);
+	if (flags & PSW_MASK_DAT)
+		__arch_local_irq_stosm(0x04); // enable DAT
 	if (!irqs_disabled)
 		trace_hardirqs_on();
 	__arch_local_irq_ssm(flags);