On Fri, Jun 10, 2022 at 5:21 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> Commit c275c5c6d50a ("kasan: disable freed user page poisoning with HW
> tags") added __GFP_SKIP_KASAN_POISON to GFP_HIGHUSER_MOVABLE. A similar
> argument can be made about unpoisoning, so also add
> __GFP_SKIP_KASAN_UNPOISON to user pages. To ensure the user page is
> still accessible via page_address() without a kasan fault, reset the
> page->flags tag.
>
> With the above changes, there is no need for the arm64
> tag_clear_highpage() to reset the page->flags tag.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> ---
> arch/arm64/mm/fault.c | 1 -
> include/linux/gfp.h | 2 +-
> mm/page_alloc.c | 7 +++++--
> 3 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index c5e11768e5c1..cdf3ffa0c223 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -927,6 +927,5 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
> void tag_clear_highpage(struct page *page)
> {
> mte_zero_clear_page_tags(page_address(page));
> - page_kasan_tag_reset(page);
> set_bit(PG_mte_tagged, &page->flags);
> }
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 2d2ccae933c2..0ace7759acd2 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -348,7 +348,7 @@ struct vm_area_struct;
> #define GFP_DMA32 __GFP_DMA32
> #define GFP_HIGHUSER (GFP_USER | __GFP_HIGHMEM)
> #define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE | \
> - __GFP_SKIP_KASAN_POISON)
> + __GFP_SKIP_KASAN_POISON | __GFP_SKIP_KASAN_UNPOISON)
> #define GFP_TRANSHUGE_LIGHT ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
> __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
> #define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e008a3df0485..f6ed240870bc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2397,6 +2397,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
> !should_skip_init(gfp_flags);
> bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS);
> + int i;
>
> set_page_private(page, 0);
> set_page_refcounted(page);
> @@ -2422,8 +2423,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> * should be initialized as well).
> */
> if (init_tags) {
> - int i;
> -
> /* Initialize both memory and tags. */
> for (i = 0; i != 1 << order; ++i)
> tag_clear_highpage(page + i);
> @@ -2438,6 +2437,10 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> /* Note that memory is already initialized by KASAN. */
> if (kasan_has_integrated_init())
> init = false;
> + } else {
> + /* Ensure page_address() dereferencing does not fault. */
> + for (i = 0; i != 1 << order; ++i)
> + page_kasan_tag_reset(page + i);
> }
> /* If memory is still not initialized, do it now. */
> if (init)
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
