Re: [PATCH v3 1/2] kfence: Allow re-enabling KFENCE after system startup

[Marco Elver]

On Mon, 7 Mar 2022 at 08:45, Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx> wrote:
>
> If once KFENCE is disabled by:
> echo 0 > /sys/module/kfence/parameters/sample_interval
> KFENCE could never be re-enabled until next rebooting.
>
> Allow re-enabling it by writing a positive num to sample_interval.
>
> Signed-off-by: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>


> ---
>  mm/kfence/core.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 13128fa13062..caa4e84c8b79 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -38,14 +38,17 @@
>  #define KFENCE_WARN_ON(cond)                                                   \
>         ({                                                                     \
>                 const bool __cond = WARN_ON(cond);                             \
> -               if (unlikely(__cond))                                          \
> +               if (unlikely(__cond)) {                                        \
>                         WRITE_ONCE(kfence_enabled, false);                     \
> +                       disabled_by_warn = true;                               \
> +               }                                                              \
>                 __cond;                                                        \
>         })
>
>  /* === Data ================================================================= */
>
>  static bool kfence_enabled __read_mostly;
> +static bool disabled_by_warn __read_mostly;
>
>  unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
>  EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */
> @@ -55,6 +58,7 @@ EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */
>  #endif
>  #define MODULE_PARAM_PREFIX "kfence."
>
> +static int kfence_enable_late(void);
>  static int param_set_sample_interval(const char *val, const struct kernel_param *kp)
>  {
>         unsigned long num;
> @@ -65,10 +69,11 @@ static int param_set_sample_interval(const char *val, const struct kernel_param
>
>         if (!num) /* Using 0 to indicate KFENCE is disabled. */
>                 WRITE_ONCE(kfence_enabled, false);
> -       else if (!READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)
> -               return -EINVAL; /* Cannot (re-)enable KFENCE on-the-fly. */
>
>         *((unsigned long *)kp->arg) = num;
> +
> +       if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)
> +               return disabled_by_warn ? -EINVAL : kfence_enable_late();
>         return 0;
>  }
>
> @@ -787,6 +792,16 @@ void __init kfence_init(void)
>                 (void *)(__kfence_pool + KFENCE_POOL_SIZE));
>  }
>
> +static int kfence_enable_late(void)
> +{
> +       if (!__kfence_pool)
> +               return -EINVAL;
> +
> +       WRITE_ONCE(kfence_enabled, true);
> +       queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
> +       return 0;
> +}
> +
>  void kfence_shutdown_cache(struct kmem_cache *s)
>  {
>         unsigned long flags;
> --
> 2.27.0
>