psci: fix error due to a non zero context id

In the previous psci implementation, the psci_afflvl_power_on_finish()
function would run into an error condition if the value of the context
id parameter in the cpu_on and cpu_suspend psci calls was != 0. The
parameter was being restored as the return value of the affinity level
0 finisher function. A non zero context id would be treated as an
error condition. This would prevent successful wake up of the cpu from
a power down state. Also, the contents of the general purpose
registers were not being cleared upon return to the non-secure world
after a cpu power up. This could potentially allow the non-secure
world to view secure data.

This patch ensures that all general purpose registers are set to ~0
prior to the final eret that drops the execution to the non-secure
world. The context id is used to initialize the general purpose
register x0 prior to re-entry into the non-secure world and is no
longer restored as a function return value. A platform helper
(platform_get_stack()) has been introduced to facilitate this change.

Change-Id: I2454911ffd75705d6aa8609a5d250d9b26fa097c

1 files changed, 1 insertions, 0 deletions

diff --git a/plat/fvp/platform.h b/plat/fvp/platform.h
index 399a772..38bd558 100644
--- a/plat/fvp/platform.h
+++ b/plat/fvp/platform.h
@@ -331,6 +331,7 @@ extern unsigned long platform_get_cfgvar(unsigned int);
 extern int platform_config_setup(void);
 extern void plat_report_exception(unsigned long);
 extern unsigned long plat_get_ns_image_entrypoint(void);
+extern unsigned long platform_get_stack(unsigned long mpidr);
 
 /* Declarations for fvp_topology.c */
 extern int plat_setup_topology(void);