Re: [PATCH v2] cpuidle: change enter_s2idle() prototype

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Jul 6, 2020 at 5:13 AM Neal Liu <neal.liu@mediatek.com> wrote:
>
> Control Flow Integrity(CFI) is a security mechanism that disallows
> changes to the original control flow graph of a compiled binary,
> making it significantly harder to perform such attacks.
>
> init_state_node() assign same function callback to different
> function pointer declarations.
>
> static int init_state_node(struct cpuidle_state *idle_state,
>                            const struct of_device_id *matches,
>                            struct device_node *state_node) { ...
>         idle_state->enter = match_id->data; ...
>         idle_state->enter_s2idle = match_id->data; }
>
> Function declarations:
>
> struct cpuidle_state { ...
>         int (*enter) (struct cpuidle_device *dev,
>                       struct cpuidle_driver *drv,
>                       int index);
>
>         void (*enter_s2idle) (struct cpuidle_device *dev,
>                               struct cpuidle_driver *drv,
>                               int index); };
>
> In this case, either enter() or enter_s2idle() would cause CFI check
> failed since they use same callee.

Can you please explain this in a bit more detail?

As it stands, I don't understand the problem statement enough to apply
the patch.

> Align function prototype of enter() since it needs return value for
> some use cases. The return value of enter_s2idle() is no
> need currently.

So last time I requested you to document why ->enter_s2idle needs to
return an int in the code, which has not been done.  Please do that.

> Signed-off-by: Neal Liu <neal.liu@mediatek.com>
> ---
>  drivers/acpi/processor_idle.c   |    6 ++++--
>  drivers/cpuidle/cpuidle-tegra.c |    8 +++++---
>  drivers/idle/intel_idle.c       |    6 ++++--
>  include/linux/cpuidle.h         |    6 +++---
>  4 files changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 75534c5..6ffb6c9 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -655,8 +655,8 @@ static int acpi_idle_enter(struct cpuidle_device *dev,
>         return index;
>  }
>
> -static void acpi_idle_enter_s2idle(struct cpuidle_device *dev,
> -                                  struct cpuidle_driver *drv, int index)
> +static int acpi_idle_enter_s2idle(struct cpuidle_device *dev,
> +                                 struct cpuidle_driver *drv, int index)
>  {
>         struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
>
> @@ -674,6 +674,8 @@ static void acpi_idle_enter_s2idle(struct cpuidle_device *dev,
>                 }
>         }
>         acpi_idle_do_entry(cx);
> +
> +       return 0;
>  }
>
>  static int acpi_processor_setup_cpuidle_cx(struct acpi_processor *pr,
> diff --git a/drivers/cpuidle/cpuidle-tegra.c b/drivers/cpuidle/cpuidle-tegra.c
> index 1500458..a12fb14 100644
> --- a/drivers/cpuidle/cpuidle-tegra.c
> +++ b/drivers/cpuidle/cpuidle-tegra.c
> @@ -253,11 +253,13 @@ static int tegra_cpuidle_enter(struct cpuidle_device *dev,
>         return err ? -1 : index;
>  }
>
> -static void tegra114_enter_s2idle(struct cpuidle_device *dev,
> -                                 struct cpuidle_driver *drv,
> -                                 int index)
> +static int tegra114_enter_s2idle(struct cpuidle_device *dev,
> +                                struct cpuidle_driver *drv,
> +                                int index)
>  {
>         tegra_cpuidle_enter(dev, drv, index);
> +
> +       return 0;
>  }
>
>  /*
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index f449584..b178da3 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -175,13 +175,15 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
>   * Invoked as a suspend-to-idle callback routine with frozen user space, frozen
>   * scheduler tick and suspended scheduler clock on the target CPU.
>   */
> -static __cpuidle void intel_idle_s2idle(struct cpuidle_device *dev,
> -                                       struct cpuidle_driver *drv, int index)
> +static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
> +                                      struct cpuidle_driver *drv, int index)
>  {
>         unsigned long eax = flg2MWAIT(drv->states[index].flags);
>         unsigned long ecx = 1; /* break on interrupt flag */
>
>         mwait_idle_with_hints(eax, ecx);
> +
> +       return 0;
>  }
>
>  /*
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index ec2ef63..bee10c0 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -66,9 +66,9 @@ struct cpuidle_state {
>          * suspended, so it must not re-enable interrupts at any point (even
>          * temporarily) or attempt to change states of clock event devices.
>          */
> -       void (*enter_s2idle) (struct cpuidle_device *dev,
> -                             struct cpuidle_driver *drv,
> -                             int index);
> +       int (*enter_s2idle)(struct cpuidle_device *dev,
> +                           struct cpuidle_driver *drv,
> +                           int index);
>  };
>
>  /* Idle State Flags */
> --
> 1.7.9.5