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1// SPDX-License-Identifier: GPL-2.02/*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 11typedef union efi_rng_protocol efi_rng_protocol_t;12 13union 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 bytes30 * @size: size of the buffer31 * @out: caller allocated buffer to receive the random bytes32 *33 * The call will fail if either the firmware does not implement the34 * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill35 * the buffer.36 *37 * Return: status code38 */39efi_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 table54 *55 * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are56 * saved as a configuration table which can be used as entropy by the kernel57 * 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 bytes60 * available, the configuration table will not be installed and an error code61 * will be returned.62 *63 * Return: status code64 */65efi_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 size81 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 that89 * case, instead of overwriting it, let's create a new buffer that can90 * hold both, and concatenate the existing and the new seeds.91 * Note that we should read the seed size with caution, in case the92 * 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 the102 * allocation will survive a kexec reboot (although we refresh the seed103 * 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 algorithm120 * 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 causes136 * EFI to also zero out its representation on disk.137 * This is somewhat idealistic, but overwriting the138 * variable with zeros is likely just as fraught too.139 * TODO: in the future, maybe we can hash it forward140 * 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 else148 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 171err_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");175err_warn:176 if (prev_seed)177 efi_warn("Retaining bootloader-supplied seed only");178 return status;179}180