On Thu, Jan 20, 2022 at 3:02 AM Peter Collingbourne <pcc@xxxxxxxxxx> wrote: > > 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 <pcc@xxxxxxxxxx> > Link: https://linux-review.googlesource.com/id/I456b24a2b9067d93968d43b4bb3351c0cec63101 > Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc") > Cc: stable@xxxxxxxxxxxxxxx > --- > v3: > - use try_cmpxchg() as suggested by Peter Zijlstra on another > patch > > v2: > - use READ_ONCE() > > include/linux/mm.h | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index c768a7c81b0b..87473fe52c3f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1531,11 +1531,18 @@ 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; > + 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) > -- > 2.34.1.703.g22d0c6ccf7-goog > Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> FWIW, try_cmpxchg() doesn't seem to be doing annotated atomic accesses when accessing old_flags, so using READ_ONCE() in page_kasan_tag_set() seems pointless after all.
