s390/traps: unpoison the kernel_stack_overflow()'s pt_regs

This is normally done by the generic entry code, but the
kernel_stack_overflow() flow bypasses it.

Link: https://lkml.kernel.org/r/20240621113706.315500-34-iii@linux.ibm.comSigned-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/s390/kernel/traps.c

@@ -27,6 +27,7 @@
 #include <linux/uaccess.h>
 #include <linux/cpu.h>
 #include <linux/entry-common.h>
+#include <linux/kmsan.h>
 #include <asm/asm-extable.h>
 #include <asm/vtime.h>
 #include <asm/fpu.h>
@@ -262,6 +263,11 @@ static void monitor_event_exception(struct pt_regs *regs)
 
 void kernel_stack_overflow(struct pt_regs *regs)
 {
+	/*
+	 * Normally regs are unpoisoned by the generic entry code, but
+	 * kernel_stack_overflow() is a rare case that is called bypassing it.
+	 */
+	kmsan_unpoison_entry_regs(regs);
 	bust_spinlocks(1);
 	printk("Kernel stack overflow.\n");
 	show_regs(regs);