Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <cover.1605305705.git.andreyknvl@google.com> <b167fd21b86e7d728ba3a8e20be4f7e8373bc22c.1605305705.git.andreyknvl@google.com>
In-Reply-To: <b167fd21b86e7d728ba3a8e20be4f7e8373bc22c.1605305705.git.andreyknvl@google.com>
From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 18 Nov 2020 17:07:45 +0100
Message-ID: <CAG_fn=Xc_OOtqE5Q-fFejBBCfLGtc_kOmZAuE1wdTsjCOmpQ4Q@mail.gmail.com>
Subject: Re: [PATCH mm v10 31/42] kasan, mm: untag page address in free_reserved_area
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Nov 13, 2020 at 11:17 PM Andrey Konovalov <andreyknvl@google.com> w=
rote:
>
> From: Vincenzo Frascino <vincenzo.frascino@arm.com>
>
> free_reserved_area() memsets the pages belonging to a given memory area.
> As that memory hasn't been allocated via page_alloc, the KASAN tags that
> those pages have are 0x00. As the result the memset might result in a tag
> mismatch.
>
> Untag the address to avoid spurious faults.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
> Change-Id: If12b4944383575b8bbd7d971decbd7f04be6748b
> ---
>  mm/page_alloc.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 855627e52f81..4a69fef13ac7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7653,6 +7653,11 @@ unsigned long free_reserved_area(void *start, void=
 *end, int poison, const char
>                  * alias for the memset().
>                  */
>                 direct_map_addr =3D page_address(page);
> +               /*
> +                * Perform a kasan-unchecked memset() since this memory
> +                * has not been initialized.
> +                */
> +               direct_map_addr =3D kasan_reset_tag(direct_map_addr);
>                 if ((unsigned int)poison <=3D 0xFF)
>                         memset(direct_map_addr, poison, PAGE_SIZE);
>
> --
> 2.29.2.299.gdc1121823c-goog
>


--=20
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Stra=C3=9Fe, 33
80636 M=C3=BCnchen

Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg