trezor-firmware/embed/boardloader/lowlevel.c

#include STM32_HAL_H

#include "flash.h"
#include "lowlevel.h"

#pragma GCC optimize("no-stack-protector") // applies to all functions in this file

#if PRODUCTION
    #define WANT_RDP_LEVEL   (OB_RDP_LEVEL_2)
    #define WANT_WRP_SECTORS (OB_WRP_SECTOR_0 | OB_WRP_SECTOR_1 | OB_WRP_SECTOR_2)
#else
    #define WANT_RDP_LEVEL   (OB_RDP_LEVEL_0)
    #define WANT_WRP_SECTORS (0)
#endif

#define WANT_BOR_LEVEL (OB_BOR_LEVEL3)

// reference RM0090 section 3.9.10; SPRMOD is 0 meaning PCROP disabled.; DB1M is 0 because we use 2MB dual-bank; BFB2 is 0 allowing boot from flash;
#define FLASH_OPTCR_VALUE ( (((~WANT_WRP_SECTORS) << FLASH_OPTCR_nWRP_Pos) & FLASH_OPTCR_nWRP_Msk) | \
                            (WANT_RDP_LEVEL << FLASH_OPTCR_RDP_Pos) | FLASH_OPTCR_nRST_STDBY | FLASH_OPTCR_nRST_STOP | FLASH_OPTCR_WDG_SW | WANT_BOR_LEVEL )

// reference RM0090 section 3.7.1 table 16
#define OPTION_BYTES_RDP_USER_VALUE  ((uint16_t) ((WANT_RDP_LEVEL << FLASH_OPTCR_RDP_Pos) | FLASH_OPTCR_nRST_STDBY | FLASH_OPTCR_nRST_STOP | FLASH_OPTCR_WDG_SW | WANT_BOR_LEVEL))
#define OPTION_BYTES_BANK1_WRP_VALUE ((uint16_t) ((~WANT_WRP_SECTORS) & 0xFFFU))
#define OPTION_BYTES_BANK2_WRP_VALUE ((uint16_t) 0xFFFU)

// reference RM0090 section 3.7.1 table 16. use 16 bit pointers because the top 48 bits are all reserved.
#define OPTION_BYTES_RDP_USER  (*(volatile uint16_t * const) 0x1FFFC000U)
#define OPTION_BYTES_BANK1_WRP (*(volatile uint16_t * const) 0x1FFFC008U)
#define OPTION_BYTES_BANK2_WRP (*(volatile uint16_t * const) 0x1FFEC008U)

uint32_t flash_wait_and_clear_status_flags(void)
{
    while(FLASH->SR & FLASH_SR_BSY); // wait for all previous flash operations to complete
    const uint32_t result = FLASH->SR & FLASH_STATUS_ALL_FLAGS; // get the current status flags
    FLASH->SR |= FLASH_STATUS_ALL_FLAGS; // clear all status flags
    return result;
}

secbool flash_check_option_bytes(void)
{
    flash_wait_and_clear_status_flags();
    // check values stored in flash interface registers
    if ((FLASH->OPTCR & ~3) != FLASH_OPTCR_VALUE) { // ignore bits 0 and 1 because they are control bits
        return secfalse;
    }
    if (FLASH->OPTCR1 != FLASH_OPTCR1_nWRP) {
        return secfalse;
    }
    // check values stored in flash memory
    if ((OPTION_BYTES_RDP_USER & ~3) != OPTION_BYTES_RDP_USER_VALUE) { // bits 0 and 1 are unused
        return secfalse;
    }
    if ((OPTION_BYTES_BANK1_WRP & 0xCFFFU) != OPTION_BYTES_BANK1_WRP_VALUE) { // bits 12 and 13 are unused
        return secfalse;
    }
    if ((OPTION_BYTES_BANK2_WRP & 0xFFFU) != OPTION_BYTES_BANK2_WRP_VALUE) { // bits 12, 13, 14, and 15 are unused
        return secfalse;
    }
    return sectrue;
}

void flash_lock_option_bytes(void)
{
    FLASH->OPTCR |= FLASH_OPTCR_OPTLOCK; // lock the option bytes
}

void flash_unlock_option_bytes(void)
{
    if ((FLASH->OPTCR & FLASH_OPTCR_OPTLOCK) == 0) {
        return; // already unlocked
    }
    // reference RM0090 section 3.7.2
    // write the special sequence to unlock
    FLASH->OPTKEYR = FLASH_OPT_KEY1;
    FLASH->OPTKEYR = FLASH_OPT_KEY2;
    while (FLASH->OPTCR & FLASH_OPTCR_OPTLOCK); // wait until the flash option control register is unlocked
}

uint32_t flash_set_option_bytes(void)
{
    // reference RM0090 section 3.7.2
    flash_wait_and_clear_status_flags();
    flash_unlock_option_bytes();
    flash_wait_and_clear_status_flags();
    FLASH->OPTCR1 = FLASH_OPTCR1_nWRP; // no write protection on any sectors in bank 2
    FLASH->OPTCR = FLASH_OPTCR_VALUE; // WARNING: dev board safe unless you compile for PRODUCTION or change this value!!!
    FLASH->OPTCR |= FLASH_OPTCR_OPTSTRT; // begin committing changes to flash
    const uint32_t result = flash_wait_and_clear_status_flags(); // wait until changes are committed
    flash_lock_option_bytes();
    return result;
}

secbool flash_configure_option_bytes(void)
{
    if (sectrue == flash_check_option_bytes()) {
        return sectrue; // we DID NOT have to change the option bytes
    }

    do {
        flash_set_option_bytes();
    } while(sectrue != flash_check_option_bytes());

    return secfalse; // notify that we DID have to change the option bytes
}

void periph_init(void)
{
    // STM32F4xx HAL library initialization:
    //  - configure the Flash prefetch, instruction and data caches
    //  - configure the Systick to generate an interrupt each 1 msec
    //  - set NVIC Group Priority to 4
    //  - global MSP (MCU Support Package) initialization
    HAL_Init();

    // Enable GPIO clocks
    __HAL_RCC_GPIOA_CLK_ENABLE();
    __HAL_RCC_GPIOB_CLK_ENABLE();
    __HAL_RCC_GPIOC_CLK_ENABLE();
    __HAL_RCC_GPIOD_CLK_ENABLE();

    // enable the PVD (programmable voltage detector).
    // select the "2.7V" threshold (level 5).
    // this detector will be active regardless of the
    // flash option byte BOR setting.
    __HAL_RCC_PWR_CLK_ENABLE();
    PWR_PVDTypeDef pvd_config;
    pvd_config.PVDLevel = PWR_PVDLEVEL_5;
    pvd_config.Mode = PWR_PVD_MODE_IT_RISING_FALLING;
    HAL_PWR_ConfigPVD(&pvd_config);
    HAL_PWR_EnablePVD();
    NVIC_EnableIRQ(PVD_IRQn);
}

secbool reset_flags_check(void)
{
#if PRODUCTION
    // this is effective enough that it makes development painful, so only use it for production.
    // check the reset flags to assure that we arrive here due to a regular full power-on event,
    // and not as a result of a lesser reset.
    if ((RCC->CSR & (RCC_CSR_LPWRRSTF | RCC_CSR_WWDGRSTF | RCC_CSR_IWDGRSTF | RCC_CSR_SFTRSTF | RCC_CSR_PORRSTF | RCC_CSR_PINRSTF | RCC_CSR_BORRSTF)) != (RCC_CSR_PORRSTF | RCC_CSR_PINRSTF | RCC_CSR_BORRSTF)) {
        return secfalse;
    }
#endif

    RCC->CSR |= RCC_CSR_RMVF; // clear the reset flags

    return sectrue;
}