144 lines
4.1 KiB
C
144 lines
4.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
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*/
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#include <linux/efi.h>
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#include <asm/efi.h>
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#include "efistub.h"
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typedef union efi_rng_protocol efi_rng_protocol_t;
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union efi_rng_protocol {
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struct {
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efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
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unsigned long *,
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efi_guid_t *);
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efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
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efi_guid_t *, unsigned long,
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u8 *out);
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};
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struct {
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u32 get_info;
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u32 get_rng;
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} mixed_mode;
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};
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/**
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* efi_get_random_bytes() - fill a buffer with random bytes
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* @size: size of the buffer
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* @out: caller allocated buffer to receive the random bytes
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*
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* The call will fail if either the firmware does not implement the
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* EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
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* the buffer.
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*
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* Return: status code
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*/
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efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
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{
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efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
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efi_status_t status;
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efi_rng_protocol_t *rng = NULL;
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status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
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if (status != EFI_SUCCESS)
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return status;
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return efi_call_proto(rng, get_rng, NULL, size, out);
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}
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/**
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* efi_random_get_seed() - provide random seed as configuration table
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*
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* The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
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* saved as a configuration table which can be used as entropy by the kernel
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* for the initialization of its pseudo random number generator.
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*
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* If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
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* available, the configuration table will not be installed and an error code
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* will be returned.
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*
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* Return: status code
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*/
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efi_status_t efi_random_get_seed(void)
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{
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efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
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efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
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efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
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struct linux_efi_random_seed *prev_seed, *seed = NULL;
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int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
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efi_rng_protocol_t *rng = NULL;
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efi_status_t status;
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status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
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if (status != EFI_SUCCESS)
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return status;
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/*
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* Check whether a seed was provided by a prior boot stage. In that
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* case, instead of overwriting it, let's create a new buffer that can
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* hold both, and concatenate the existing and the new seeds.
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* Note that we should read the seed size with caution, in case the
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* table got corrupted in memory somehow.
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*/
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prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID);
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if (prev_seed && prev_seed->size <= 512U) {
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prev_seed_size = prev_seed->size;
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seed_size += prev_seed_size;
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}
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/*
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* Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
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* allocation will survive a kexec reboot (although we refresh the seed
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* beforehand)
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*/
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status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
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struct_size(seed, bits, seed_size),
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(void **)&seed);
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if (status != EFI_SUCCESS) {
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efi_warn("Failed to allocate memory for RNG seed.\n");
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goto err_warn;
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}
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status = efi_call_proto(rng, get_rng, &rng_algo_raw,
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EFI_RANDOM_SEED_SIZE, seed->bits);
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if (status == EFI_UNSUPPORTED)
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/*
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* Use whatever algorithm we have available if the raw algorithm
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* is not implemented.
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*/
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status = efi_call_proto(rng, get_rng, NULL,
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EFI_RANDOM_SEED_SIZE, seed->bits);
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if (status != EFI_SUCCESS)
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goto err_freepool;
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seed->size = seed_size;
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if (prev_seed_size)
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memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
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prev_seed_size);
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status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
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if (status != EFI_SUCCESS)
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goto err_freepool;
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if (prev_seed_size) {
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/* wipe and free the old seed if we managed to install the new one */
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memzero_explicit(prev_seed->bits, prev_seed_size);
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efi_bs_call(free_pool, prev_seed);
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}
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return EFI_SUCCESS;
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err_freepool:
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memzero_explicit(seed, struct_size(seed, bits, seed_size));
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efi_bs_call(free_pool, seed);
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efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n");
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err_warn:
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if (prev_seed)
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efi_warn("Retaining bootloader-supplied seed only");
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return status;
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}
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