The patch titled Subject: mm: use compare-exchange operation to set KASAN page tag has been added to the -mm tree. Its filename is mm-use-compare-exchange-operation-to-set-kasan-page-tag.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-use-compare-exchange-operation-... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-use-compare-exchange-operation-...

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------------------------------------------------------ From: Peter Collingbourne pcc@google.com Subject: 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.

Link: https://lkml.kernel.org/r/20220113031434.464992-1-pcc@google.com Link: https://linux-review.googlesource.com/id/I456b24a2b9067d93968d43b4bb3351c0ce... Signed-off-by: Peter Collingbourne pcc@google.com Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc") Cc: Andrey Ryabinin ryabinin.a.a@gmail.com Cc: Alexander Potapenko glider@google.com Cc: Andrey Konovalov andreyknvl@gmail.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/include/linux/mm.h~mm-use-compare-exchange-operation-to-set-kasan-page-tag +++ a/include/linux/mm.h @@ -1524,11 +1524,17 @@ static inline u8 page_kasan_tag(const st

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 = 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) _

Patches currently in -mm which might be from pcc@google.com are

mm-use-compare-exchange-operation-to-set-kasan-page-tag.patch