Thread (107 messages) 107 messages, 6 authors, 2020-11-13
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[PATCH v9 33/44] kasan, mm: untag page address in free_reserved_area

From: Andrey Konovalov <hidden>
Date: 2020-11-10 22:12:30
Also in: linux-mm, lkml
Subsystem: memory management, memory management - page allocator, the rest · Maintainers: Andrew Morton, Vlastimil Babka, Linus Torvalds

From: Vincenzo Frascino <vincenzo.frascino@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@linux-foundation.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <redacted>
---
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 23f5066bd4a5..24b45261e2bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7593,6 +7593,11 @@ 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);
 
-- 
2.29.2.222.g5d2a92d10f8-goog


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