1301d27d9SRadoslaw Biernacki /* 2*83683dddSTomas Pilar * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved. 3301d27d9SRadoslaw Biernacki * 4301d27d9SRadoslaw Biernacki * SPDX-License-Identifier: BSD-3-Clause 5301d27d9SRadoslaw Biernacki */ 6301d27d9SRadoslaw Biernacki 7301d27d9SRadoslaw Biernacki #include <stdint.h> 8301d27d9SRadoslaw Biernacki 9301d27d9SRadoslaw Biernacki #include <arch_helpers.h> 10*83683dddSTomas Pilar #include <arch_features.h> 11301d27d9SRadoslaw Biernacki #include <plat/common/platform.h> 12301d27d9SRadoslaw Biernacki 13301d27d9SRadoslaw Biernacki #define RANDOM_CANARY_VALUE ((u_register_t) 3288484550995823360ULL) 14301d27d9SRadoslaw Biernacki 15301d27d9SRadoslaw Biernacki u_register_t plat_get_stack_protector_canary(void) 16301d27d9SRadoslaw Biernacki { 17*83683dddSTomas Pilar #if ENABLE_FEAT_RNG 18*83683dddSTomas Pilar /* Use the RNDR instruction if the CPU supports it */ 19*83683dddSTomas Pilar if (is_armv8_5_rng_present()) { 20*83683dddSTomas Pilar return read_rndr(); 21*83683dddSTomas Pilar } 22*83683dddSTomas Pilar #endif 23*83683dddSTomas Pilar 24301d27d9SRadoslaw Biernacki /* 25*83683dddSTomas Pilar * Ideally, a random number should be returned above. If a random 26*83683dddSTomas Pilar * number generator is not supported, return instead a 27301d27d9SRadoslaw Biernacki * combination of a timer's value and a compile-time constant. 28*83683dddSTomas Pilar * This is better than nothing but not necessarily really secure. 29301d27d9SRadoslaw Biernacki */ 30301d27d9SRadoslaw Biernacki return RANDOM_CANARY_VALUE ^ read_cntpct_el0(); 31301d27d9SRadoslaw Biernacki } 32301d27d9SRadoslaw Biernacki 33