Re: [PATCH 1/3] mm: kasan: Ensure the tags are visible before the tag in page->flags

[Andrey Konovalov <andreyknvl@gmail.com>]

On Tue, May 17, 2022 at 8:09 PM Catalin Marinas <catalin.marinas@arm.com> 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@arm.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
>  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 d9079ec11f31..f6b8dc4f354b 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);
>  }
>
>  void __kasan_poison_pages(struct page *page, unsigned int order, bool init)

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>