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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Sat, 3 Apr 2021 16:05:30 +0200
Message-ID: <CA+fCnZc+-csYZ+4ao1Y4gmjhej9Rtt9WRzHhEvCee3ePHoydRg@mail.gmail.com>
Subject: Re: [PATCH] kfence: unpoison pool region before use
To:     Peter Collingbourne <pcc@google.com>
Cc:     Marco Elver <elver@google.com>, Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sat, Apr 3, 2021 at 7:13 AM Peter Collingbourne <pcc@google.com> wrote:
>
> If the memory region allocated by KFENCE had previously been poisoned,
> any validity checks done using kasan_byte_accessible() will fail. Fix
> it by unpoisoning the memory before using it as the pool region.

Which kasan_byte_accessible() call fails?

KASAN checks shouldn't be performed for KFENCE objects. We have a
number of is_kfence_address() checks in KASAN runtime, but maybe we're
missing some. Perhaps, we should even move those checks into the
high-level wrappers in include/linux/kasan.h.

> Link: https://linux-review.googlesource.com/id/I0af99e9f1c25eaf7e1ec295836b5d148d76940c5
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> ---
>  mm/kfence/core.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index d53c91f881a4..bb22b0cf77aa 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -633,13 +633,19 @@ static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
>
>  void __init kfence_alloc_pool(void)
>  {
> +       void *pool;
> +
>         if (!kfence_sample_interval)
>                 return;
>
> -       __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
> -
> -       if (!__kfence_pool)
> +       pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
> +       if (!pool) {
>                 pr_err("failed to allocate pool\n");
> +               return;
> +       }
> +
> +       kasan_unpoison_range(pool, KFENCE_POOL_SIZE);
> +       __kfence_pool = pool;
>  }
>
>  void __init kfence_init(void)
> --
> 2.31.0.208.g409f899ff0-goog
>