lora-irrigation/strobe_rng_init.c

/*-
 * Copyright 2021 John-Mark Gurney.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <strobe.h>

#include <strobe_rng_init.h>

#include <stm32l1xx.h>
#include <stm32l1xx_hal_flash_ex.h>

#include <utilities.h>

#include <unistd.h>

#define nitems(x)	(sizeof(x) / sizeof *(x))
#define DEFINE_RNG_SAVE	1
#if DEFINE_RNG_SAVE
const rng_word_t rng_save[roundup(32, sizeof(rng_word_t)) / sizeof(rng_word_t)] __attribute__ ((section (".eeprom")));
#endif

void
strobe_rng_init(void)
{

	/*
	 * Seed RNG
	 * Seed w/ saved state.
	 */
	strobe_seed_prng((uint8_t *)rng_save, sizeof rng_save);

	/*
	 * On first boot, SRAM is uninitialized and randomness from
	 * it is used.
	 *
	 * Note: This depends upon sbrk pointing to uinitalized SRAM.
	 */
	strobe_seed_prng(sbrk(0), 2*1024);

}

void
strobe_rng_save(void)
{
	rng_word_t tmp[sizeof rng_save / sizeof(rng_word_t)];
	size_t i;
	int r;

	/*
	 * Save entropy for next reset.
	 */
	r = strobe_randomize((uint8_t *)tmp, sizeof tmp);
	(void)r;

	CRITICAL_SECTION_BEGIN();

	HAL_FLASHEx_DATAEEPROM_Unlock();

	for (i = 0; i < nitems(tmp); i++)
		HAL_FLASHEx_DATAEEPROM_Program(FLASH_TYPEPROGRAMDATA_WORD, (intptr_t)&rng_save[i], tmp[i]);

	HAL_FLASHEx_DATAEEPROM_Lock();

	CRITICAL_SECTION_END();
}