[PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrey Konovalov]

Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
after debug_pagealloc_unmap_pages(). This causes a crash when
debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
unmapped page.

This patch puts kasan_free_nondeferred_pages() before
debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
the page unavailable.

Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>

---

Changes v1->v2:
- Move kasan_free_nondeferred_pages() before arch_free_page().

---
 mm/page_alloc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 969e7012fce0..0efb07b5907c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
 
 	kernel_poison_pages(page, 1 << order);
 
+	/*
+	 * With hardware tag-based KASAN, memory tags must be set before the
+	 * page becomes unavailable via debug_pagealloc or arch_free_page.
+	 */
+	kasan_free_nondeferred_pages(page, order, fpi_flags);
+
 	/*
 	 * arch_free_page() can make the page's contents inaccessible.  s390
 	 * does this.  So nothing which can access the page's contents should
@@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
 
 	debug_pagealloc_unmap_pages(page, 1 << order);
 
-	kasan_free_nondeferred_pages(page, order, fpi_flags);
-
 	return true;
 }
 
-- 
2.30.1.766.gb4fecdf3b7-goog