[PATCH] 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().

Besides fixing the crash, this also makes the annotation order consistent
with debug_pagealloc_map_pages() preceding kasan_alloc_pages().

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 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 c89e7b107514..54bc237fd319 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1311,10 +1311,14 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	 */
 	arch_free_page(page, order);
 
-	debug_pagealloc_unmap_pages(page, 1 << order);
-
+	/*
+	 * With hardware tag-based KASAN, memory tags must be set
+	 * before unmapping the page with debug_pagealloc.
+	 */
 	kasan_free_nondeferred_pages(page, order, fpi_flags);
 
+	debug_pagealloc_unmap_pages(page, 1 << order);
+
 	return true;
 }
 
-- 
2.30.1.766.gb4fecdf3b7-goog