linux-kernel - Re: [PATCH 4/4] mm: kfence: Only load kfence

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Message-ID: <CAG_fn=X9oaw0zJrcmShNcvd3UsNSFKsH3kSdD5Yx=4Sk_WtNrQ@mail.gmail.com>
Date:   Wed, 25 Aug 2021 11:31:22 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/4] mm: kfence: Only load kfence_test when kfence is enabled

On Wed, Aug 25, 2021 at 11:17 AM Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
>
> Provide kfence_is_enabled() helper, only load kfence_test module
> when kfence is enabled.

What's wrong with the current behavior?
I think we need at least some way to tell the developer that KFENCE
does not work, and a failing test seems to be the perfect one.

> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>  include/linux/kfence.h  | 2 ++
>  mm/kfence/core.c        | 8 ++++++++
>  mm/kfence/kfence_test.c | 2 ++
>  3 files changed, 12 insertions(+)
>
> diff --git a/include/linux/kfence.h b/include/linux/kfence.h
> index 3fe6dd8a18c1..f08f24e8a726 100644
> --- a/include/linux/kfence.h
> +++ b/include/linux/kfence.h
> @@ -22,6 +22,8 @@
>  #define KFENCE_POOL_SIZE ((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 * PAGE_SIZE)
>  extern char *__kfence_pool;
>
> +bool kfence_is_enabled(void);
> +
>  #ifdef CONFIG_KFENCE_STATIC_KEYS
>  #include <linux/static_key.h>
>  DECLARE_STATIC_KEY_FALSE(kfence_allocation_key);
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 7a97db8bc8e7..f1aaa7ebdcad 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -51,6 +51,14 @@ static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE
>  #endif
>  #define MODULE_PARAM_PREFIX "kfence."
>
> +bool kfence_is_enabled(void)
> +{
> +       if (!kfence_sample_interval || !READ_ONCE(kfence_enabled))
> +               return false;
> +       return true;
> +}
> +EXPORT_SYMBOL_GPL(kfence_is_enabled);
> +
>  static int param_set_sample_interval(const char *val, const struct kernel_param *kp)
>  {
>         unsigned long num;
> diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
> index eb6307c199ea..4087f9f1497e 100644
> --- a/mm/kfence/kfence_test.c
> +++ b/mm/kfence/kfence_test.c
> @@ -847,6 +847,8 @@ static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
>   */
>  static int __init kfence_test_init(void)
>  {
> +       if (!kfence_is_enabled())
> +               return 0;
>         /*
>          * Because we want to be able to build the test as a module, we need to
>          * iterate through all known tracepoints, since the static registration
> --
> 2.26.2
>
> --
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-- 
Alexander Potapenko
Software Engineer

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