On Fri, Jun 10, 2022 at 04:21:38PM +0100, Catalin Marinas wrote: > __kasan_unpoison_pages() colours the memory with a random tag and stores > it in page->flags in order to re-create the tagged pointer via > page_to_virt() later. When the tag from the page->flags is read, ensure > that the in-memory tags are already visible by re-ordering the > page_kasan_tag_set() after kasan_unpoison(). The former already has > barriers in place through try_cmpxchg(). On the reader side, the order > is ensured by the address dependency between page->flags and the memory > access. > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> > Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> > Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > --- > mm/kasan/common.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index c40c0e7b3b5f..78be2beb7453 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -108,9 +108,10 @@ void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init) > return; > > tag = kasan_random_tag(); > + kasan_unpoison(set_tag(page_address(page), tag), > + PAGE_SIZE << order, init); > for (i = 0; i < (1 << order); i++) > page_kasan_tag_set(page + i, tag); > - kasan_unpoison(page_address(page), PAGE_SIZE << order, init); This looks good to me, but after reading the cover letter I'm wondering whether the try_cmpxchg() in page_kasan_tag_set() could be relaxed to try_cmpxchg_release() as a separate optimisation? Will
