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

[Neal Liu <neal.liu@mediatek.com>]

Gentle ping on this patch.


On Fri, 2020-07-10 at 11:08 +0800, Neal Liu wrote:
> On Thu, 2020-07-09 at 14:18 +0200, Rafael J. Wysocki wrote:
> > 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.
> > 
> 
> Okay, Let's me try to explain more details.
> 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.
> 
> There are multiple control flow instructions that could be manipulated
> by the attacker and subvert control flow. The target instructions that
> use data to determine the actual destination.
> - indirect jump
> - indirect call
> - return
> 
> In this case, function prototype between caller and callee are mismatch.
> Caller: (type A)funcA
> Callee: (type A)funcB
> Callee: (type C)funcC
> 
> funcA calls funcB -> no problem
> funcA calls funcC -> CFI check failed
> 
> That's why we try to align function prototype.
> Please feel free to feedback if you have any questions.
> 
> > > 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
> 
>