mm: use compare-exchange operation to set KASAN page tag

PATCH Superseded Peter Collingbourne 1 participant 1 message Jan 18, 2022

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Stable branch Memory management MM core

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Peter Collingbourne

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2022-01-18 22:52 UTC #0 lore raw

PATCH v2 1/1 mm: use compare-exchange operation to set KASAN page tag

It has been reported that the tag setting operation on newly-allocated pages can cause the page flags to be corrupted when performed concurrently with other flag updates as a result of the use of non-atomic operations. Fix the problem by using a compare-exchange loop to update the tag.

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/I456b24a2b9067d93968d43b4bb3351c0cec63101

Fixes 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc")

Cc [email protected]

---
v2:
- use READ_ONCE()

 include/linux/mm.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

include/linux/mm.h +11 -5

index c768a7c81b0b..37d1aa65f28c 100644
@@ -1531,11 +1531,17 @@ static inline u8 page_kasan_tag(const struct page *page)
 
 static inline void page_kasan_tag_set(struct page *page, u8 tag)
 {
-	if (kasan_enabled()) {
-		tag ^= 0xff;
-		page->flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
-		page->flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
-	}
+	unsigned long old_flags, flags;
+
+	if (!kasan_enabled())
+		return;
+
+	tag ^= 0xff;
+	do {
+		old_flags = flags = READ_ONCE(page->flags);
+		flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
+		flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
+	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
 }
 
 static inline void page_kasan_tag_reset(struct page *page)

Signature · 1 line

2.34.1.703.g22d0c6ccf7-goog