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In-Reply-To: <938a827f9927ee2112d98e2053ad7764aae9d8f8.1638308023.git.andreyknvl@google.com>
From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 2 Dec 2021 16:40:21 +0100
Message-ID: <CAG_fn=WRKRUskUrN1wb20gv2nLF-DOPBF5aDAg+q+sFKczDw1Q@mail.gmail.com>
Subject: Re: [PATCH 07/31] kasan: only apply __GFP_ZEROTAGS when memory is zeroed
To:     andrey.konovalov@linux.dev
Cc:     Marco Elver <elver@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Peter Collingbourne <pcc@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
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On Tue, Nov 30, 2021 at 10:41 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> __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@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
>  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 =3D !want_init_on_free() && want_init_on_alloc(flags);
> +       bool init_tags =3D init && (flags & __GFP_ZEROTAGS);
>
>         if (flags & __GFP_SKIP_KASAN_POISON)
>                 SetPageSkipKASanPoison(page);
>
> -       if (flags & __GFP_ZEROTAGS) {
> +       if (init_tags) {
>                 int i;
>
>                 for (i =3D 0; i !=3D 1 << order; ++i)
> --
> 2.25.1
>


--=20
Alexander Potapenko
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