1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org> 4 */ 5 6 #include <linux/efi.h> 7 #include <asm/efi.h> 8 9 #include "efistub.h" 10 11 typedef union efi_rng_protocol efi_rng_protocol_t; 12 13 union efi_rng_protocol { 14 struct { 15 efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *, 16 unsigned long *, 17 efi_guid_t *); 18 efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *, 19 efi_guid_t *, unsigned long, 20 u8 *out); 21 }; 22 struct { 23 u32 get_info; 24 u32 get_rng; 25 } mixed_mode; 26 }; 27 28 /** 29 * efi_get_random_bytes() - fill a buffer with random bytes 30 * @size: size of the buffer 31 * @out: caller allocated buffer to receive the random bytes 32 * 33 * The call will fail if either the firmware does not implement the 34 * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill 35 * the buffer. 36 * 37 * Return: status code 38 */ 39 efi_status_t efi_get_random_bytes(unsigned long size, u8 *out) 40 { 41 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; 42 efi_status_t status; 43 efi_rng_protocol_t *rng = NULL; 44 45 status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng); 46 if (status != EFI_SUCCESS) 47 return status; 48 49 return efi_call_proto(rng, get_rng, NULL, size, out); 50 } 51 52 /** 53 * efi_random_get_seed() - provide random seed as configuration table 54 * 55 * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are 56 * saved as a configuration table which can be used as entropy by the kernel 57 * for the initialization of its pseudo random number generator. 58 * 59 * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes 60 * available, the configuration table will not be installed and an error code 61 * will be returned. 62 * 63 * Return: status code 64 */ 65 efi_status_t efi_random_get_seed(void) 66 { 67 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; 68 efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW; 69 efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID; 70 struct linux_efi_random_seed *prev_seed, *seed = NULL; 71 int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE; 72 unsigned long nv_seed_size = 0, offset = 0; 73 efi_rng_protocol_t *rng = NULL; 74 efi_status_t status; 75 76 status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng); 77 if (status != EFI_SUCCESS) 78 seed_size = 0; 79 80 // Call GetVariable() with a zero length buffer to obtain the size 81 get_efi_var(L"RandomSeed", &rng_table_guid, NULL, &nv_seed_size, NULL); 82 if (!seed_size && !nv_seed_size) 83 return status; 84 85 seed_size += nv_seed_size; 86 87 /* 88 * Check whether a seed was provided by a prior boot stage. In that 89 * case, instead of overwriting it, let's create a new buffer that can 90 * hold both, and concatenate the existing and the new seeds. 91 * Note that we should read the seed size with caution, in case the 92 * table got corrupted in memory somehow. 93 */ 94 prev_seed = get_efi_config_table(rng_table_guid); 95 if (prev_seed && prev_seed->size <= 512U) { 96 prev_seed_size = prev_seed->size; 97 seed_size += prev_seed_size; 98 } 99 100 /* 101 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the 102 * allocation will survive a kexec reboot (although we refresh the seed 103 * beforehand) 104 */ 105 status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY, 106 struct_size(seed, bits, seed_size), 107 (void **)&seed); 108 if (status != EFI_SUCCESS) { 109 efi_warn("Failed to allocate memory for RNG seed.\n"); 110 goto err_warn; 111 } 112 113 if (rng) { 114 status = efi_call_proto(rng, get_rng, &rng_algo_raw, 115 EFI_RANDOM_SEED_SIZE, seed->bits); 116 117 if (status == EFI_UNSUPPORTED) 118 /* 119 * Use whatever algorithm we have available if the raw algorithm 120 * is not implemented. 121 */ 122 status = efi_call_proto(rng, get_rng, NULL, 123 EFI_RANDOM_SEED_SIZE, seed->bits); 124 125 if (status == EFI_SUCCESS) 126 offset = EFI_RANDOM_SEED_SIZE; 127 } 128 129 if (nv_seed_size) { 130 status = get_efi_var(L"RandomSeed", &rng_table_guid, NULL, 131 &nv_seed_size, seed->bits + offset); 132 133 if (status == EFI_SUCCESS) 134 /* 135 * We delete the seed here, and /hope/ that this causes 136 * EFI to also zero out its representation on disk. 137 * This is somewhat idealistic, but overwriting the 138 * variable with zeros is likely just as fraught too. 139 * TODO: in the future, maybe we can hash it forward 140 * instead, and write a new seed. 141 */ 142 status = set_efi_var(L"RandomSeed", &rng_table_guid, 0, 143 0, NULL); 144 145 if (status == EFI_SUCCESS) 146 offset += nv_seed_size; 147 else 148 memzero_explicit(seed->bits + offset, nv_seed_size); 149 } 150 151 if (!offset) 152 goto err_freepool; 153 154 if (prev_seed_size) { 155 memcpy(seed->bits + offset, prev_seed->bits, prev_seed_size); 156 offset += prev_seed_size; 157 } 158 159 seed->size = offset; 160 status = efi_bs_call(install_configuration_table, &rng_table_guid, seed); 161 if (status != EFI_SUCCESS) 162 goto err_freepool; 163 164 if (prev_seed_size) { 165 /* wipe and free the old seed if we managed to install the new one */ 166 memzero_explicit(prev_seed->bits, prev_seed_size); 167 efi_bs_call(free_pool, prev_seed); 168 } 169 return EFI_SUCCESS; 170 171 err_freepool: 172 memzero_explicit(seed, struct_size(seed, bits, seed_size)); 173 efi_bs_call(free_pool, seed); 174 efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL or EFI variable\n"); 175 err_warn: 176 if (prev_seed) 177 efi_warn("Retaining bootloader-supplied seed only"); 178 return status; 179 } 180