The patch titled
Subject: mm, kasan: 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-to-set-kasan-page-tag.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-use-compare-exchange-operation-to-set-kasan-page-tag.patch
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------------------------------------------------------
From: Peter Collingbourne <pcc@xxxxxxxxxx>
Subject: mm, kasan: 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/20220120020148.1632253-1-pcc@xxxxxxxxxx
Link: https://linux-review.googlesource.com/id/I456b24a2b9067d93968d43b4bb3351c0cec63101
Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc")
Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
--- a/include/linux/mm.h~mm-use-compare-exchange-operation-to-set-kasan-page-tag
+++ a/include/linux/mm.h
@@ -1506,11 +1506,18 @@ 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;
+ old_flags = READ_ONCE(page->flags);
+ do {
+ flags = old_flags;
+ flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
+ flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
+ } while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
}
static inline void page_kasan_tag_reset(struct page *page)
_
Patches currently in -mm which might be from pcc@xxxxxxxxxx are
mm-use-compare-exchange-operation-to-set-kasan-page-tag.patch
