[PATCH mm v5 05/39] kasan, page_alloc: init memory of skipped pages on free

[andrey.konovalov at linux.dev]

From: Andrey Konovalov <andreyknvl at google.com>

Since commit 7a3b83537188 ("kasan: use separate (un)poison implementation
for integrated init"), when all init, kasan_has_integrated_init(), and
skip_kasan_poison are true, free_pages_prepare() doesn't initialize
the page. This is wrong.

Fix it by remembering whether kasan_poison_pages() performed
initialization, and call kernel_init_free_pages() if it didn't.

Reordering kasan_poison_pages() and kernel_init_free_pages() is OK,
since kernel_init_free_pages() can handle poisoned memory.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>

---

Changes v2->v3:
- Drop Fixes tag, as the patch won't cleanly apply to older kernels
  anyway. The commit is mentioned in the patch description.

Changes v1->v2:
- Reorder kasan_poison_pages() and free_pages_prepare() in this patch
  instead of doing it in the previous one.
---
 mm/page_alloc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f78058115288..37e121ff99b1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1375,11 +1375,16 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	 * With hardware tag-based KASAN, memory tags must be set before the
 	 * page becomes unavailable via debug_pagealloc or arch_free_page.
 	 */
-	if (init && !kasan_has_integrated_init())
-		kernel_init_free_pages(page, 1 << order);
-	if (!skip_kasan_poison)
+	if (!skip_kasan_poison) {
 		kasan_poison_pages(page, order, init);
 
+		/* Memory is already initialized if KASAN did it internally. */
+		if (kasan_has_integrated_init())
+			init = false;
+	}
+	if (init)
+		kernel_init_free_pages(page, 1 << order);
+
 	/*
 	 * arch_free_page() can make the page's contents inaccessible.  s390
 	 * does this.  So nothing which can access the page's contents should
-- 
2.25.1