Fix race in GIC IPRIORITY and ITARGET accessors

GICD_IPRIORITYR and GICD_ITARGETSR specifically support byte addressing
so that individual interrupt priorities can be atomically updated by
issuing a single byte write. The previous implementation of
gicd_set_ipriority() and gicd_set_itargetsr() used 32-bit register
accesses, modifying values for 4 interrupts at a time, using a
read-modify-write approach. This potentially may cause concurrent changes
by other CPUs to the adjacent interrupts to be corrupted. This patch fixes
the issue by modifying these accessors to use byte addressing.

Fixes ARM-software/tf-issues#343

Change-Id: Iec28b5f5074045b00dfb8d5f5339b685f9425915

drivers/arm/gic/gic_v2.c

 /*
- * Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -261,10 +261,6 @@ void gicd_set_icactiver(uintptr_t base, unsigned int id)
  */
 void gicd_set_ipriorityr(uintptr_t base, unsigned int id, unsigned int pri)
 {
-	unsigned int reg = base + GICD_IPRIORITYR + (id & ~3);
-	unsigned int shift = (id & 3) << 3;
-	unsigned int reg_val = mmio_read_32(reg);
-
 	/*
 	 * Enforce ARM recommendation to manage priority values such
 	 * that group1 interrupts always have a lower priority than
@@ -278,17 +274,12 @@ void gicd_set_ipriorityr(uintptr_t base, unsigned int id, unsigned int pri)
 		pri >= GIC_HIGHEST_SEC_PRIORITY &&
 			pri <= GIC_LOWEST_SEC_PRIORITY);
 
-	reg_val &= ~(GIC_PRI_MASK << shift);
-	reg_val |= (pri & GIC_PRI_MASK) << shift;
-	mmio_write_32(reg, reg_val);
+	mmio_write_8(base + GICD_IPRIORITYR + id, pri & GIC_PRI_MASK);
 }
 
 void gicd_set_itargetsr(uintptr_t base, unsigned int id, unsigned int target)
 {
-	unsigned byte_off = id & ((1 << ITARGETSR_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_itargetsr(base, id);
-
-	gicd_write_itargetsr(base, id, reg_val | (target << (byte_off << 3)));
+	mmio_write_8(base + GICD_ITARGETSR + id, target & GIC_TARGET_CPU_MASK);
 }
 
 /*******************************************************************************

drivers/arm/gic/v2/gicv2_helpers.c

 /*
- * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2016, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -101,10 +101,7 @@ void gicd_write_spendsgir(uintptr_t base, unsigned int id, unsigned int val)
  */
 void gicd_set_itargetsr(uintptr_t base, unsigned int id, unsigned int target)
 {
-	unsigned byte_off = id & ((1 << ITARGETSR_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_itargetsr(base, id);
-
-	gicd_write_itargetsr(base, id, reg_val | (target << (byte_off << 3)));
+	mmio_write_8(base + GICD_ITARGETSR + id, target & GIC_TARGET_CPU_MASK);
 }
 
 /*******************************************************************************