plat/arm: Implement ARMv8.3-PAuth interfaces

This feature is only supported on FVP.

Change-Id: I4e265610211d92a84bd2773c34acfbe02a1a1826
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

plat/arm/common/aarch64/arm_pauth.c

+/*
+ * Copyright (c) 2019, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <cdefs.h>
+#include <stdint.h>
+
+/*
+ * Instruction pointer authentication key A. The low 64-bit are at [0], and the
+ * high bits at [1]. They are run-time constants so they are placed in the
+ * rodata section. They are written before MMU is turned on and the permissions
+ * are effective.
+ */
+uint64_t plat_apiakey[2] __section("rodata.apiakey");
+
+/*
+ * This is only a toy implementation to generate a seemingly random 128-bit key
+ * from sp and x30 values. A production system must re-implement this function
+ * to generate keys from a reliable randomness source.
+ */
+uint64_t *plat_init_apiakey(void)
+{
+	uintptr_t return_addr = (uintptr_t)__builtin_return_address(0U);
+	uintptr_t frame_addr = (uintptr_t)__builtin_frame_address(0U);
+
+	plat_apiakey[0] = (return_addr << 13) ^ frame_addr;
+	plat_apiakey[1] = (frame_addr << 15) ^ return_addr;
+
+	return plat_apiakey;
+}

plat/arm/common/arm_common.mk

@@ -236,6 +236,11 @@ BL31_SOURCES		+=	lib/extensions/ras/std_err_record.c		\
 				lib/extensions/ras/ras_common.c
 endif
 
+# Pointer Authentication sources
+ifeq (${ENABLE_PAUTH}, 1)
+PLAT_BL_COMMON_SOURCES	+=	plat/arm/common/aarch64/arm_pauth.c
+endif
+
 # SPM uses libfdt in Arm platforms
 ifeq (${SPM_MM},0)
 ifeq (${ENABLE_SPM},1)