Re: [PATCH 07/31] kasan: only apply __GFP_ZEROTAGS when memory is zeroed

[Alexander Potapenko]

On Tue, Nov 30, 2021 at 10:41 PM <andrey.konovalov@xxxxxxxxx> wrote:
>
> From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> __GFP_ZEROTAGS should only be effective if memory is being zeroed.
> Currently, hardware tag-based KASAN violates this requirement.
>
> Fix by including an initialization check along with checking for
> __GFP_ZEROTAGS.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>

> ---
>  mm/kasan/hw_tags.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 0b8225add2e4..c643740b8599 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -199,11 +199,12 @@ void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
>          * page_alloc.c.
>          */
>         bool init = !want_init_on_free() && want_init_on_alloc(flags);
> +       bool init_tags = init && (flags & __GFP_ZEROTAGS);
>
>         if (flags & __GFP_SKIP_KASAN_POISON)
>                 SetPageSkipKASanPoison(page);
>
> -       if (flags & __GFP_ZEROTAGS) {
> +       if (init_tags) {
>                 int i;
>
>                 for (i = 0; i != 1 << order; ++i)
> --
> 2.25.1
>


-- 
Alexander Potapenko
Software Engineer

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