1 /* 2 * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved. 3 * 4 * SPDX-License-Identifier: BSD-3-Clause 5 */ 6 7 #include <stdint.h> 8 9 #include <arch_helpers.h> 10 #include <arch_features.h> 11 #include <plat/common/platform.h> 12 13 #define RANDOM_CANARY_VALUE ((u_register_t) 3288484550995823360ULL) 14 plat_get_stack_protector_canary(void)15u_register_t plat_get_stack_protector_canary(void) 16 { 17 #if ENABLE_FEAT_RNG 18 /* Use the RNDR instruction if the CPU supports it */ 19 if (is_armv8_5_rng_present()) { 20 return read_rndr(); 21 } 22 #endif 23 24 /* 25 * Ideally, a random number should be returned above. If a random 26 * number generator is not supported, return instead a 27 * combination of a timer's value and a compile-time constant. 28 * This is better than nothing but not necessarily really secure. 29 */ 30 return RANDOM_CANARY_VALUE ^ read_cntpct_el0(); 31 } 32 33