esp-idf/components/bootloader_support/src/secure_boot.c

// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <string.h>

#include "esp_attr.h"
#include "esp_types.h"
#include "esp_log.h"

#include "rom/cache.h"
#include "rom/ets_sys.h"
#include "rom/secure_boot.h"

#include "soc/dport_reg.h"
#include "soc/io_mux_reg.h"
#include "soc/efuse_reg.h"
#include "soc/rtc_cntl_reg.h"

#include "sdkconfig.h"

#include "bootloader_flash.h"
#include "bootloader_random.h"
#include "esp_image_format.h"
#include "esp_secure_boot.h"
#include "esp_flash_encrypt.h"
#include "esp_efuse.h"

static const char* TAG = "secure_boot";

/**
 *  @function :     secure_boot_generate
 *  @description:   generate boot digest (aka "abstract") & iv
 *
 *  @inputs:        image_len - length of image to calculate digest for
 */
static bool secure_boot_generate(uint32_t image_len){
    esp_err_t err;
    esp_secure_boot_iv_digest_t digest;
    const uint32_t *image;

    /* hardware secure boot engine only takes full blocks, so round up the
       image length. The additional data should all be 0xFF.
    */
    if (image_len % sizeof(digest.iv) != 0) {
        image_len = (image_len / sizeof(digest.iv) + 1) * sizeof(digest.iv);
    }
    ets_secure_boot_start();
    ets_secure_boot_rd_iv((uint32_t *)digest.iv);
    ets_secure_boot_hash(NULL);
    /* iv stored in sec 0 */
    err = bootloader_flash_erase_sector(0);
    if (err != ESP_OK)
    {
        ESP_LOGE(TAG, "SPI erase failed: 0x%x", err);
        return false;
    }

    /* generate digest from image contents */
    image = bootloader_mmap(0x1000, image_len);
    if (!image) {
        ESP_LOGE(TAG, "bootloader_mmap(0x1000, 0x%x) failed", image_len);
        return false;
    }
    for (int i = 0; i < image_len; i+= sizeof(digest.iv)) {
        ets_secure_boot_hash(&image[i/sizeof(uint32_t)]);
    }
    bootloader_munmap(image);

    ets_secure_boot_obtain();
    ets_secure_boot_rd_abstract((uint32_t *)digest.digest);
    ets_secure_boot_finish();

    ESP_LOGD(TAG, "write iv+digest to flash");
    err = bootloader_flash_write(FLASH_OFFS_SECURE_BOOT_IV_DIGEST, &digest,
                           sizeof(digest), esp_flash_encryption_enabled());
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "SPI write failed: 0x%x", err);
        return false;
    }
    Cache_Read_Enable(0);
    return true;
}

/* Burn values written to the efuse write registers */
static inline void burn_efuses()
{
#ifdef CONFIG_SECURE_BOOT_TEST_MODE
    ESP_LOGE(TAG, "SECURE BOOT TEST MODE. Not really burning any efuses! NOT SECURE");
#else
    esp_efuse_burn_new_values();
#endif
}

esp_err_t esp_secure_boot_permanently_enable(void) {
    esp_err_t err;
    uint32_t image_len = 0;
    if (esp_secure_boot_enabled())
    {
        ESP_LOGI(TAG, "bootloader secure boot is already enabled, continuing..");
        return ESP_OK;
    }

    err = esp_image_basic_verify(0x1000, true, &image_len);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "bootloader image appears invalid! error %d", err);
        return err;
    }

    uint32_t dis_reg = REG_READ(EFUSE_BLK0_RDATA0_REG);
    bool efuse_key_read_protected = dis_reg & EFUSE_RD_DIS_BLK2;
    bool efuse_key_write_protected = dis_reg & EFUSE_WR_DIS_BLK2;
    if (efuse_key_read_protected == false
        && efuse_key_write_protected == false
        && REG_READ(EFUSE_BLK2_RDATA0_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA1_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA2_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA3_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA4_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA5_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA6_REG) == 0
        && REG_READ(EFUSE_BLK2_RDATA7_REG) == 0) {

        /* On-device key generation is temporarily disabled, until
         * RNG operation during bootloader is qualified.
         * See docs/security/secure-boot.rst for details. */
        ESP_LOGE(TAG, "On-device key generation is not yet available.");
        return ESP_ERR_NOT_SUPPORTED;
    } else {
        ESP_LOGW(TAG, "Using pre-loaded secure boot key in EFUSE block 2");
    }

    ESP_LOGI(TAG, "Generating secure boot digest...");
    if (false == secure_boot_generate(image_len)){
        ESP_LOGE(TAG, "secure boot generation failed");
        return ESP_FAIL;
    }
    ESP_LOGI(TAG, "Digest generation complete.");

#ifndef CONFIG_SECURE_BOOT_TEST_MODE
    if (!efuse_key_read_protected) {
        ESP_LOGE(TAG, "Pre-loaded key is not read protected. Refusing to blow secure boot efuse.");
        return ESP_ERR_INVALID_STATE;
    }
    if (!efuse_key_write_protected) {
        ESP_LOGE(TAG, "Pre-loaded key is not write protected. Refusing to blow secure boot efuse.");
        return ESP_ERR_INVALID_STATE;
    }
#endif

    ESP_LOGI(TAG, "blowing secure boot efuse...");
    ESP_LOGD(TAG, "before updating, EFUSE_BLK0_RDATA6 %x", REG_READ(EFUSE_BLK0_RDATA6_REG));

    uint32_t new_wdata6 = EFUSE_RD_ABS_DONE_0;

#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
    ESP_LOGI(TAG, "Disable JTAG...");
    new_wdata6 |= EFUSE_RD_DISABLE_JTAG;
#else
    ESP_LOGW(TAG, "Not disabling JTAG - SECURITY COMPROMISED");
#endif

#ifndef CONFIG_SECURE_BOOT_ALLOW_ROM_BASIC
    ESP_LOGI(TAG, "Disable ROM BASIC interpreter fallback...");
    new_wdata6 |= EFUSE_RD_CONSOLE_DEBUG_DISABLE;
#else
    ESP_LOGW(TAG, "Not disabling ROM BASIC fallback - SECURITY COMPROMISED");
#endif

    REG_WRITE(EFUSE_BLK0_WDATA6_REG, new_wdata6);
    burn_efuses();
    uint32_t after = REG_READ(EFUSE_BLK0_RDATA6_REG);
    ESP_LOGD(TAG, "after updating, EFUSE_BLK0_RDATA6 %x", after);
    if (after & EFUSE_RD_ABS_DONE_0) {
        ESP_LOGI(TAG, "secure boot is now enabled for bootloader image");
        return ESP_OK;
    } else {
#ifdef CONFIG_SECURE_BOOT_TEST_MODE
        ESP_LOGE(TAG, "secure boot not enabled due to test mode");
#else
        ESP_LOGE(TAG, "secure boot not enabled for bootloader image, EFUSE_RD_ABS_DONE_0 is probably write protected!");
#endif
        return ESP_ERR_INVALID_STATE;
    }
}