1 /* 2 * Copyright (c) 2017, ARM Limited and Contributors. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are met: 6 * 7 * Redistributions of source code must retain the above copyright notice, this 8 * list of conditions and the following disclaimer. 9 * 10 * Redistributions in binary form must reproduce the above copyright notice, 11 * this list of conditions and the following disclaimer in the documentation 12 * and/or other materials provided with the distribution. 13 * 14 * Neither the name of ARM nor the names of its contributors may be used 15 * to endorse or promote products derived from this software without specific 16 * prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 19 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE 22 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28 * POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #include <assert.h> 32 #include <mmio.h> 33 #include <string.h> 34 #include <utils.h> 35 #include "juno_def.h" 36 37 #define NSAMPLE_CLOCKS 1 /* min 1 cycle, max 231 cycles */ 38 #define NRETRIES 5 39 40 static inline int output_valid(void) 41 { 42 int i; 43 44 for (i = 0; i < NRETRIES; i++) { 45 uint32_t val; 46 47 val = mmio_read_32(TRNG_BASE + TRNG_STATUS); 48 if (val & 1U) 49 break; 50 } 51 if (i >= NRETRIES) 52 return 0; /* No output data available. */ 53 return 1; 54 } 55 56 /* 57 * This function fills `buf` with `len` bytes of entropy. 58 * It uses the Trusted Entropy Source peripheral on Juno. 59 * Returns 0 when the buffer has been filled with entropy 60 * successfully and -1 otherwise. 61 */ 62 int juno_getentropy(void *buf, size_t len) 63 { 64 uint8_t *bp = buf; 65 66 assert(buf); 67 assert(len); 68 assert(!check_uptr_overflow((uintptr_t)bp, len)); 69 70 /* Disable interrupt mode. */ 71 mmio_write_32(TRNG_BASE + TRNG_INTMASK, 0); 72 /* Program TRNG to sample for `NSAMPLE_CLOCKS`. */ 73 mmio_write_32(TRNG_BASE + TRNG_CONFIG, NSAMPLE_CLOCKS); 74 75 while (len > 0) { 76 int i; 77 78 /* Start TRNG. */ 79 mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1); 80 81 /* Check if output is valid. */ 82 if (!output_valid()) 83 return -1; 84 85 /* Fill entropy buffer. */ 86 for (i = 0; i < TRNG_NOUTPUTS; i++) { 87 size_t n; 88 uint32_t val; 89 90 val = mmio_read_32(TRNG_BASE + i * sizeof(uint32_t)); 91 n = MIN(len, sizeof(uint32_t)); 92 memcpy(bp, &val, n); 93 bp += n; 94 len -= n; 95 if (len == 0) 96 break; 97 } 98 99 /* Reset TRNG outputs. */ 100 mmio_write_32(TRNG_BASE + TRNG_STATUS, 1); 101 } 102 103 return 0; 104 } 105