kmsan: expose kmsan_get_metadata()

Each s390 CPU has lowcore pages associated with it.  Each CPU sees its own
lowcore at virtual address 0 through a hardware mechanism called
prefixing.  Additionally, all lowcores are mapped to non-0 virtual
addresses stored in the lowcore_ptr[] array.

When lowcore is accessed through virtual address 0, one needs to resolve
metadata for lowcore_ptr[raw_smp_processor_id()].

Expose kmsan_get_metadata() to make it possible to do this from the arch
code.

Link: https://lkml.kernel.org/r/20240621113706.315500-10-iii@linux.ibm.comSigned-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.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: Heiko Carstens <hca@linux.ibm.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>

include/linux/kmsan.h

@@ -230,6 +230,15 @@ void kmsan_handle_urb(const struct urb *urb, bool is_out);
  */
 void kmsan_unpoison_entry_regs(const struct pt_regs *regs);
 
+/**
+ * kmsan_get_metadata() - Return a pointer to KMSAN shadow or origins.
+ * @addr:      kernel address.
+ * @is_origin: whether to return origins or shadow.
+ *
+ * Return NULL if metadata cannot be found.
+ */
+void *kmsan_get_metadata(void *addr, bool is_origin);
+
 #else
 
 static inline void kmsan_init_shadow(void)

mm/kmsan/instrumentation.c

@@ -14,6 +14,7 @@
 
 #include "kmsan.h"
 #include <linux/gfp.h>
+#include <linux/kmsan.h>
 #include <linux/kmsan_string.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>

mm/kmsan/kmsan.h

@@ -66,7 +66,6 @@ struct shadow_origin_ptr {
 
 struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *addr, u64 size,
 						     bool store);
-void *kmsan_get_metadata(void *addr, bool is_origin);
 void __init kmsan_init_alloc_meta_for_range(void *start, void *end);
 
 enum kmsan_bug_reason {