cpuidle: change enter_s2idle() prototype

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.

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@mediatek.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Neal Liu

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,

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;
 }
 
 /*

drivers/idle/intel_idle.c

@@ -173,13 +173,15 @@ 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;
 }
 
 /*

include/linux/cpuidle.h

@@ -65,10 +65,13 @@ struct cpuidle_state {
 	 * CPUs execute ->enter_s2idle with the local tick or entire timekeeping
 	 * suspended, so it must not re-enable interrupts at any point (even
 	 * temporarily) or attempt to change states of clock event devices.
+	 *
+	 * This callback may point to the same function as ->enter if all of
+	 * the above requirements are met by it.
 	 */
-	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 */