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)15 u_register_t plat_get_stack_protector_canary(void)
16 {
17 	/* Use the RNDR instruction if the CPU supports it */
18 	if (is_feat_rng_supported()) {
19 		return read_rndr();
20 	}
21 
22 	/*
23 	 * Ideally, a random number should be returned above. If a random
24 	 * number generator is not supported, return instead a
25 	 * combination of a timer's value and a compile-time constant.
26 	 * This is better than nothing but not necessarily really secure.
27 	 */
28 	return RANDOM_CANARY_VALUE ^ read_cntpct_el0();
29 }
30 
31