// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
 */

#include <linux/efi.h>
#include <asm/efi.h>

#include "efistub.h"

typedef union efi_rng_protocol efi_rng_protocol_t;

union efi_rng_protocol {
        struct {
                efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
                                                  unsigned long *,
                                                  efi_guid_t *);
                efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
                                                 efi_guid_t *, unsigned long,
                                                 u8 *out);
        };
        struct {
                u32 get_info;
                u32 get_rng;
        } mixed_mode;
};

/**
 * efi_get_random_bytes() - fill a buffer with random bytes
 * @size:       size of the buffer
 * @out:        caller allocated buffer to receive the random bytes
 *
 * The call will fail if either the firmware does not implement the
 * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
 * the buffer.
 *
 * Return:      status code
 */
efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
{
        efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
        efi_status_t status;
        efi_rng_protocol_t *rng = NULL;

        status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
        if (status != EFI_SUCCESS)
                return status;

        return efi_call_proto(rng, get_rng, NULL, size, out);
}

/**
 * efi_random_get_seed() - provide random seed as configuration table
 *
 * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
 * saved as a configuration table which can be used as entropy by the kernel
 * for the initialization of its pseudo random number generator.
 *
 * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
 * available, the configuration table will not be installed and an error code
 * will be returned.
 *
 * Return:      status code
 */
efi_status_t efi_random_get_seed(void)
{
        efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
        efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
        efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
        struct linux_efi_random_seed *prev_seed, *seed = NULL;
        int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
        unsigned long nv_seed_size = 0, offset = 0;
        efi_rng_protocol_t *rng = NULL;
        efi_status_t status;

        status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
        if (status != EFI_SUCCESS)
                seed_size = 0;

        // Call GetVariable() with a zero length buffer to obtain the size
        get_efi_var(L"RandomSeed", &rng_table_guid, NULL, &nv_seed_size, NULL);
        if (!seed_size && !nv_seed_size)
                return status;

        seed_size += nv_seed_size;

        /*
         * Check whether a seed was provided by a prior boot stage. In that
         * case, instead of overwriting it, let's create a new buffer that can
         * hold both, and concatenate the existing and the new seeds.
         * Note that we should read the seed size with caution, in case the
         * table got corrupted in memory somehow.
         */
        prev_seed = get_efi_config_table(rng_table_guid);
        if (prev_seed && prev_seed->size <= 512U) {
                prev_seed_size = prev_seed->size;
                seed_size += prev_seed_size;
        }

        /*
         * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
         * allocation will survive a kexec reboot (although we refresh the seed
         * beforehand)
         */
        status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
                             struct_size(seed, bits, seed_size),
                             (void **)&seed);
        if (status != EFI_SUCCESS) {
                efi_warn("Failed to allocate memory for RNG seed.\n");
                goto err_warn;
        }

        if (rng) {
                status = efi_call_proto(rng, get_rng, &rng_algo_raw,
                                        EFI_RANDOM_SEED_SIZE, seed->bits);

                if (status == EFI_UNSUPPORTED)
                        /*
                         * Use whatever algorithm we have available if the raw algorithm
                         * is not implemented.
                         */
                        status = efi_call_proto(rng, get_rng, NULL,
                                                EFI_RANDOM_SEED_SIZE, seed->bits);

                if (status == EFI_SUCCESS)
                        offset = EFI_RANDOM_SEED_SIZE;
        }

        if (nv_seed_size) {
                status = get_efi_var(L"RandomSeed", &rng_table_guid, NULL,
                                     &nv_seed_size, seed->bits + offset);

                if (status == EFI_SUCCESS)
                        /*
                         * We delete the seed here, and /hope/ that this causes
                         * EFI to also zero out its representation on disk.
                         * This is somewhat idealistic, but overwriting the
                         * variable with zeros is likely just as fraught too.
                         * TODO: in the future, maybe we can hash it forward
                         * instead, and write a new seed.
                         */
                        status = set_efi_var(L"RandomSeed", &rng_table_guid, 0,
                                             0, NULL);

                if (status == EFI_SUCCESS)
                        offset += nv_seed_size;
                else
                        memzero_explicit(seed->bits + offset, nv_seed_size);
        }

        if (!offset)
                goto err_freepool;

        if (prev_seed_size) {
                memcpy(seed->bits + offset, prev_seed->bits, prev_seed_size);
                offset += prev_seed_size;
        }

        seed->size = offset;
        status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
        if (status != EFI_SUCCESS)
                goto err_freepool;

        if (prev_seed_size) {
                /* wipe and free the old seed if we managed to install the new one */
                memzero_explicit(prev_seed->bits, prev_seed_size);
                efi_bs_call(free_pool, prev_seed);
        }
        return EFI_SUCCESS;

err_freepool:
        memzero_explicit(seed, struct_size(seed, bits, seed_size));
        efi_bs_call(free_pool, seed);
        efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL or EFI variable\n");
err_warn:
        if (prev_seed)
                efi_warn("Retaining bootloader-supplied seed only");
        return status;
}