plat/arm: Add support for SEPARATE_NOBITS_REGION

In order to support SEPARATE_NOBITS_REGION for Arm platforms, we need to load
BL31 PROGBITS into secure DRAM space and BL31 NOBITS into SRAM. Hence mandate
the build to require that ARM_BL31_IN_DRAM is enabled as well.

Naturally with SEPARATE_NOBITS_REGION enabled, the BL31 initialization code
cannot be reclaimed to be used for runtime data such as secondary cpu stacks.

Memory map for BL31 NOBITS region also has to be created.

Change-Id: Ibbc8c9499a32e63fd0957a6e254608fbf6fa90c9
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

include/plat/arm/common/arm_def.h

 /*
- * Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -395,13 +395,21 @@
 /*******************************************************************************
  * BL31 specific defines.
  ******************************************************************************/
-#if ARM_BL31_IN_DRAM
+#if ARM_BL31_IN_DRAM || SEPARATE_NOBITS_REGION
 /*
  * Put BL31 at the bottom of TZC secured DRAM
  */
 #define BL31_BASE			ARM_AP_TZC_DRAM1_BASE
 #define BL31_LIMIT			(ARM_AP_TZC_DRAM1_BASE +	\
 						PLAT_ARM_MAX_BL31_SIZE)
+/*
+ * For SEPARATE_NOBITS_REGION, BL31 PROGBITS are loaded in TZC secured DRAM.
+ * And BL31 NOBITS are loaded in Trusted SRAM such that BL2 is overwritten.
+ */
+#if SEPARATE_NOBITS_REGION
+#define BL31_NOBITS_BASE		BL2_BASE
+#define BL31_NOBITS_LIMIT		BL2_LIMIT
+#endif /* SEPARATE_NOBITS_REGION */
 #elif (RESET_TO_BL31)
 /* Ensure Position Independent support (PIE) is enabled for this config.*/
 # if !ENABLE_PIE

plat/arm/common/arm_bl31_setup.c

 /*
- * Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -56,6 +56,14 @@ IMPORT_SYM(unsigned long, __INIT_CODE_END__, BL_INIT_CODE_END);
 					MT_CODE | MT_SECURE)
 #endif
 
+#if SEPARATE_NOBITS_REGION
+#define MAP_BL31_NOBITS		MAP_REGION_FLAT(			\
+					BL31_NOBITS_BASE,		\
+					BL31_NOBITS_LIMIT 		\
+						- BL31_NOBITS_BASE,	\
+					MT_MEMORY | MT_RW | MT_SECURE)
+
+#endif
 /*******************************************************************************
  * Return a pointer to the 'entry_point_info' structure of the next image for the
  * security state specified. BL33 corresponds to the non-secure image type
@@ -294,6 +302,9 @@ void __init arm_bl31_plat_arch_setup(void)
 		MAP_BL31_TOTAL,
 #if RECLAIM_INIT_CODE
 		MAP_BL_INIT_CODE,
+#endif
+#if SEPARATE_NOBITS_REGION
+		MAP_BL31_NOBITS,
 #endif
 		ARM_MAP_BL_RO,
 #if USE_ROMLIB

plat/arm/common/arm_common.mk

 #
-# Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2020, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -125,6 +125,23 @@ ENABLE_PMF			:=	1
 # mapping the former as executable and the latter as execute-never.
 SEPARATE_CODE_AND_RODATA	:=	1
 
+# On ARM platforms, disable SEPARATE_NOBITS_REGION by default. Both PROGBITS
+# and NOBITS sections of BL31 image are adjacent to each other and loaded
+# into Trusted SRAM.
+SEPARATE_NOBITS_REGION		:=	0
+
+# In order to support SEPARATE_NOBITS_REGION for Arm platforms, we need to load
+# BL31 PROGBITS into secure DRAM space and BL31 NOBITS into SRAM. Hence mandate
+# the build to require that ARM_BL31_IN_DRAM is enabled as well.
+ifeq ($(SEPARATE_NOBITS_REGION),1)
+    ifneq ($(ARM_BL31_IN_DRAM),1)
+         $(error For SEPARATE_NOBITS_REGION, ARM_BL31_IN_DRAM must be enabled)
+    endif
+    ifneq ($(RECLAIM_INIT_CODE),0)
+          $(error For SEPARATE_NOBITS_REGION, RECLAIM_INIT_CODE cannot be supported)
+    endif
+endif
+
 # Disable ARM Cryptocell by default
 ARM_CRYPTOCELL_INTEG		:=	0
 $(eval $(call assert_boolean,ARM_CRYPTOCELL_INTEG))