1 /* 2 * Copyright (c) 2019, Arm Limited. All rights reserved. 3 * 4 * SPDX-License-Identifier: BSD-3-Clause 5 */ 6 7 #include <cdefs.h> 8 #include <stdint.h> 9 10 /* 11 * Instruction pointer authentication key A. The low 64-bit are at [0], and the 12 * high bits at [1]. They are run-time constants so they are placed in the 13 * rodata section. They are written before MMU is turned on and the permissions 14 * are effective. 15 */ 16 uint64_t plat_apiakey[2] __section("rodata.apiakey"); 17 18 /* 19 * This is only a toy implementation to generate a seemingly random 128-bit key 20 * from sp and x30 values. A production system must re-implement this function 21 * to generate keys from a reliable randomness source. 22 */ 23 uint64_t *plat_init_apiakey(void) 24 { 25 uintptr_t return_addr = (uintptr_t)__builtin_return_address(0U); 26 uintptr_t frame_addr = (uintptr_t)__builtin_frame_address(0U); 27 28 plat_apiakey[0] = (return_addr << 13) ^ frame_addr; 29 plat_apiakey[1] = (frame_addr << 15) ^ return_addr; 30 31 return plat_apiakey; 32 } 33