[PATCH mm v10 31/42] kasan, mm: untag page address in free_reserved_area

[Andrey Konovalov]

From: Vincenzo Frascino <vincenzo.frascino at arm.com>

free_reserved_area() memsets the pages belonging to a given memory area.
As that memory hasn't been allocated via page_alloc, the KASAN tags that
those pages have are 0x00. As the result the memset might result in a tag
mismatch.

Untag the address to avoid spurious faults.

Cc: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
---
Change-Id: If12b4944383575b8bbd7d971decbd7f04be6748b
---
 mm/page_alloc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 855627e52f81..4a69fef13ac7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7653,6 +7653,11 @@ unsigned long free_reserved_area(void *start, void *end, int poison, const char
 		 * alias for the memset().
 		 */
 		direct_map_addr = page_address(page);
+		/*
+		 * Perform a kasan-unchecked memset() since this memory
+		 * has not been initialized.
+		 */
+		direct_map_addr = kasan_reset_tag(direct_map_addr);
 		if ((unsigned int)poison <= 0xFF)
 			memset(direct_map_addr, poison, PAGE_SIZE);
 
-- 
2.29.2.299.gdc1121823c-goog