lib/efi_loader/efi_rng_sw.c

/*
 * Copyright (c) 2026 The Fuchsia Authors
 *
 * SPDX-License-Identifier:	BSD-3-Clause
 */

/*
 * WARNING: This is a software-based pseudo-random number generator (PRNG)
 * intended ONLY for development and debugging. It uses U-Boot's native
 * rand() which is NOT cryptographically secure.
 *
 * DO NOT use this implementation in production environments or for security-
 * sensitive applications (e.g. key generation, cryptography).
 */

#include <common.h>
#include <efi_loader.h>
#include <efi_rng.h>

static const efi_guid_t rng_raw_guid = EFI_RNG_ALGORITHM_RAW;

static efi_status_t EFIAPI rng_getinfo(struct efi_rng_protocol *this,
				       efi_uintn_t *rng_algorithm_list_size,
				       efi_guid_t *rng_algorithm_list)
{
	EFI_ENTRY("%p, %p, %p", this, rng_algorithm_list_size,
		  rng_algorithm_list);

	if (!this || !rng_algorithm_list_size)
		return EFI_EXIT(EFI_INVALID_PARAMETER);

	if (!rng_algorithm_list ||
	    *rng_algorithm_list_size < sizeof(*rng_algorithm_list)) {
		*rng_algorithm_list_size = sizeof(*rng_algorithm_list);
		return EFI_EXIT(EFI_BUFFER_TOO_SMALL);
	}

	*rng_algorithm_list_size = sizeof(*rng_algorithm_list);
	guidcpy(rng_algorithm_list, &rng_raw_guid);

	return EFI_EXIT(EFI_SUCCESS);
}

/*
 * WARNING: U-Boot's rand() is a simple LCG and is NOT cryptographically
 * secure. This is strictly for development and debugging.
 *
 * DO NOT use this implementation in production environments or for security-
 * sensitive applications.
 */
static efi_status_t EFIAPI getrng(struct efi_rng_protocol *this,
				  efi_guid_t *rng_algorithm,
				  efi_uintn_t rng_value_length,
				  uint8_t *rng_value)
{
	EFI_ENTRY("%p, %p, %zu, %p", this, rng_algorithm, rng_value_length,
		  rng_value);

	if (!this || !rng_value || !rng_value_length)
		return EFI_EXIT(EFI_INVALID_PARAMETER);

	if (rng_algorithm) {
		if (guidcmp(rng_algorithm, &rng_raw_guid))
			return EFI_EXIT(EFI_UNSUPPORTED);
	}

	for (efi_uintn_t i = 0; i < rng_value_length; i++) {
		rng_value[i] = rand() & 0xff;
	}

	return EFI_EXIT(EFI_SUCCESS);
}

static const struct efi_rng_protocol efi_rng_protocol = {
	.get_info = rng_getinfo,
	.get_rng = getrng,
};

const efi_guid_t efi_guid_rng_protocol = EFI_RNG_PROTOCOL_GUID;

efi_status_t efi_rng_sw_register(void)
{
	efi_status_t ret;

	printf("\n*****************************************************************\n");
	printf("WARNING: Registering a SOFTWARE-BASED (INSECURE) EFI RNG Protocol!\n");
	printf("This is ONLY for development and debugging. DO NOT use in production!\n");
	printf("*****************************************************************\n\n");

	srand(timer_get_us());

	ret = efi_add_protocol(efi_root, &efi_guid_rng_protocol,
			       (void *)&efi_rng_protocol);
	if (ret != EFI_SUCCESS)
		printf("Cannot install software EFI_RNG_PROTOCOL\n");

	return ret;
}