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

[Neal Liu]

On Mon, 2020-06-29 at 17:17 +0200, Rafael J. Wysocki wrote:
> On Monday, June 29, 2020 11:05:40 AM CEST Neal Liu 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() assigns same function pointer to idle_state->enter
> > and idle_state->enter_s2idle. This definitely causes CFI failure
> > when calling either enter() or enter_s2idle().
> > 
> > Align enter_s2idle() with enter() function prototype to fix CFI
> > failure.
> 
> That needs to be documented somewhere close to the definition of the
> callbacks in question.
> 
> Otherwise it is completely unclear why this is a good idea.
> 

The problem is, init_state_mode() 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.

We try to align function prototype of enter() since it needs return
value for some use cases. The return value of enter_s2idle() is no need
currently.


> > Signed-off-by: Neal Liu <neal.liu@xxxxxxxxxxxx>
> > ---
> >  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
> > 
> 
> 
> 
>