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

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

[akpm]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Peter Collingbourne <pcc@google.com>
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@google.com
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@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@google.com are

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

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

[akpm]

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-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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
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/I456b24a2b9067d93968d43b4bb3351c0cec63101
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