PM: hibernate: fix crashes with init_on_free=1

Upon resuming from hibernation, free pages may contain stale data from
the kernel that initiated the resume. This breaks the invariant
inflicted by init_on_free=1 that freed pages must be zeroed.

To deal with this problem, make clear_free_pages() also clear the free
pages when init_on_free is enabled.

Fixes: 6471384 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
Reported-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: 5.3+ <stable@vger.kernel.org> # 5.3+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

kernel/power/snapshot.c

@@ -1147,24 +1147,24 @@ void free_basic_memory_bitmaps(void)
 
 void clear_free_pages(void)
 {
-#ifdef CONFIG_PAGE_POISONING_ZERO
 	struct memory_bitmap *bm = free_pages_map;
 	unsigned long pfn;
 
 	if (WARN_ON(!(free_pages_map)))
 		return;
 
-	memory_bm_position_reset(bm);
-	pfn = memory_bm_next_pfn(bm);
-	while (pfn != BM_END_OF_MAP) {
-		if (pfn_valid(pfn))
-			clear_highpage(pfn_to_page(pfn));
-
+	if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
+		memory_bm_position_reset(bm);
 		pfn = memory_bm_next_pfn(bm);
+		while (pfn != BM_END_OF_MAP) {
+			if (pfn_valid(pfn))
+				clear_highpage(pfn_to_page(pfn));
+
+			pfn = memory_bm_next_pfn(bm);
+		}
+		memory_bm_position_reset(bm);
+		pr_info("free pages cleared after restore\n");
 	}
-	memory_bm_position_reset(bm);
-	pr_info("free pages cleared after restore\n");
-#endif /* PAGE_POISONING_ZERO */
 }
 
 /**