esp-idf/components/bootloader_support/src/esp32c3/flash_encrypt.c

// Copyright 2015-2020 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 <strings.h>

#include "bootloader_flash_priv.h"
#include "bootloader_random.h"
#include "bootloader_utility.h"
#include "esp_image_format.h"
#include "esp_flash_encrypt.h"
#include "esp_flash_partitions.h"
#include "esp_secure_boot.h"
#include "esp_log.h"
#include "esp32c3/rom/secure_boot.h"
#include "esp32c3/rom/cache.h"
#include "esp32c3/rom/efuse.h"

static const char *TAG = "flash_encrypt";

/* Static functions for stages of flash encryption */
static esp_err_t initialise_flash_encryption(void);
static esp_err_t encrypt_flash_contents(uint32_t flash_crypt_cnt, bool flash_crypt_wr_dis);
static esp_err_t encrypt_bootloader(void);
static esp_err_t encrypt_and_load_partition_table(esp_partition_info_t *partition_table, int *num_partitions);
static esp_err_t encrypt_partition(int index, const esp_partition_info_t *partition);

esp_err_t esp_flash_encrypt_check_and_update(void)
{
    // TODO ESP32-C3 IDF-2116
    uint32_t cnt = REG_GET_FIELD(EFUSE_RD_REPEAT_DATA1_REG, EFUSE_SPI_BOOT_CRYPT_CNT);
    ESP_LOGV(TAG, "SPI_BOOT_CRYPT_CNT 0x%x", cnt);

    bool flash_crypt_wr_dis = false; // TODO: check if CRYPT_CNT is write disabled

    _Static_assert(EFUSE_SPI_BOOT_CRYPT_CNT == 0x7, "assuming CRYPT_CNT is only 3 bits wide");

    if (cnt == 1 || cnt == 3 || cnt == 7) {
        /* Flash is already encrypted */
        int left;
        if (cnt == 7 /* || disabled */) {
            left = 0;
        } else if (cnt == 3) {
            left = 1;
        } else {
            left = 2;
        }
        ESP_LOGI(TAG, "flash encryption is enabled (%d plaintext flashes left)", left);
        return ESP_OK;
    } else {
        /* Flash is not encrypted, so encrypt it! */
        return encrypt_flash_contents(cnt, flash_crypt_wr_dis);
    }
}

static esp_err_t initialise_flash_encryption(void)
{
    /* Before first flash encryption pass, need to initialise key & crypto config */

    /* Find out if a key is already set */
    bool has_key = ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY, NULL);

    if (has_key) {
        ESP_LOGI(TAG, "Using pre-existing key in efuse");

        ESP_LOGE(TAG, "TODO: Check key is read & write protected"); // TODO
    } else {
        ESP_LOGI(TAG, "Generating new flash encryption key...");
        const unsigned BLOCKS_NEEDED = 1;
        const ets_efuse_purpose_t PURPOSE_START = ETS_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY;
        const ets_efuse_purpose_t PURPOSE_END = ETS_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY;

        if (ets_efuse_count_unused_key_blocks() < BLOCKS_NEEDED) {
            ESP_LOGE(TAG, "Not enough free efuse key blocks (need %d) to continue", BLOCKS_NEEDED);
            return ESP_ERR_INVALID_STATE;
        }

        for (ets_efuse_purpose_t purpose = PURPOSE_START; purpose <= PURPOSE_END; purpose++) {
            uint32_t buf[8] = {0};
            bootloader_fill_random(buf, sizeof(buf));
            ets_efuse_block_t block = ets_efuse_find_unused_key_block();
            ESP_LOGD(TAG, "Writing ETS_EFUSE_BLOCK_KEY%d with purpose %d",
                     block - ETS_EFUSE_BLOCK_KEY0, purpose);
            bootloader_debug_buffer(buf, sizeof(buf), "Key content");
            int r = ets_efuse_write_key(block, purpose, buf, sizeof(buf));
            bzero(buf, sizeof(buf));
            if (r != 0) {
                ESP_LOGE(TAG, "Failed to write efuse block %d with purpose %d. Can't continue.");
                return ESP_FAIL;
            }
        }
        ESP_LOGD(TAG, "Key generation complete");
    }

    ESP_LOGE(TAG, "TODO: burn remaining security protection bits");

    return ESP_OK;
}

/* Encrypt all flash data that should be encrypted */
static esp_err_t encrypt_flash_contents(uint32_t spi_boot_crypt_cnt, bool flash_crypt_wr_dis)
{
    esp_err_t err;
    esp_partition_info_t partition_table[ESP_PARTITION_TABLE_MAX_ENTRIES];
    int num_partitions;

    /* If the last spi_boot_crypt_cnt bit is burned or write-disabled, the
       device can't re-encrypt itself. */
    if (flash_crypt_wr_dis || spi_boot_crypt_cnt == EFUSE_SPI_BOOT_CRYPT_CNT) {
        ESP_LOGE(TAG, "Cannot re-encrypt data (SPI_BOOT_CRYPT_CNT 0x%02x write disabled %d", spi_boot_crypt_cnt, flash_crypt_wr_dis);
        return ESP_FAIL;
    }

    if (spi_boot_crypt_cnt == 0) {
        /* Very first flash of encrypted data: generate keys, etc. */
        err = initialise_flash_encryption();
        if (err != ESP_OK) {
            return err;
        }
    }

    err = encrypt_bootloader();
    if (err != ESP_OK) {
        return err;
    }

    err = encrypt_and_load_partition_table(partition_table, &num_partitions);
    if (err != ESP_OK) {
        return err;
    }

    /* Now iterate the just-loaded partition table, looking for entries to encrypt
     */

    /* Go through each partition and encrypt if necessary */
    for (int i = 0; i < num_partitions; i++) {
        err = encrypt_partition(i, &partition_table[i]);
        if (err != ESP_OK) {
            return err;
        }
    }

    ESP_LOGD(TAG, "All flash regions checked for encryption pass");

    /* Set least significant 0-bit in spi_boot_crypt_cnt */
    int ffs_inv = __builtin_ffs((~spi_boot_crypt_cnt) & 0x7);
    /* ffs_inv shouldn't be zero, as zero implies spi_boot_crypt_cnt == 0xFF */
    uint32_t new_spi_boot_crypt_cnt = spi_boot_crypt_cnt + (1 << (ffs_inv - 1));
    ESP_LOGD(TAG, "SPI_BOOT_CRYPT_CNT 0x%x -> 0x%x", spi_boot_crypt_cnt, new_spi_boot_crypt_cnt);

    ets_efuse_clear_program_registers();
    REG_SET_FIELD(EFUSE_PGM_DATA2_REG, EFUSE_SPI_BOOT_CRYPT_CNT, new_spi_boot_crypt_cnt);
    ets_efuse_program(ETS_EFUSE_BLOCK0);

    ESP_LOGI(TAG, "Flash encryption completed");

    return ESP_OK;
}

static esp_err_t encrypt_bootloader(void)
{
    esp_err_t err;
    uint32_t image_length;
    /* Check for plaintext bootloader (verification will fail if it's already encrypted) */
    if (esp_image_verify_bootloader(&image_length) == ESP_OK) {
        ESP_LOGD(TAG, "bootloader is plaintext. Encrypting...");
        err = esp_flash_encrypt_region(ESP_BOOTLOADER_OFFSET, image_length);
        if (err != ESP_OK) {
            ESP_LOGE(TAG, "Failed to encrypt bootloader in place: 0x%x", err);
            return err;
        }

        if (esp_secure_boot_enabled()) {
            // TODO: anything different for secure boot?
        }
    } else {
        ESP_LOGW(TAG, "no valid bootloader was found");
    }

    return ESP_OK;
}

static esp_err_t encrypt_and_load_partition_table(esp_partition_info_t *partition_table, int *num_partitions)
{
    esp_err_t err;
    /* Check for plaintext partition table */
    err = bootloader_flash_read(ESP_PARTITION_TABLE_OFFSET, partition_table, ESP_PARTITION_TABLE_MAX_LEN, false);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "Failed to read partition table data");
        return err;
    }
    if (esp_partition_table_verify(partition_table, false, num_partitions) == ESP_OK) {
        ESP_LOGD(TAG, "partition table is plaintext. Encrypting...");
        esp_err_t err = esp_flash_encrypt_region(ESP_PARTITION_TABLE_OFFSET,
                        FLASH_SECTOR_SIZE);
        if (err != ESP_OK) {
            ESP_LOGE(TAG, "Failed to encrypt partition table in place. %x", err);
            return err;
        }
    } else {
        ESP_LOGE(TAG, "Failed to read partition table data - not plaintext?");
        return ESP_ERR_INVALID_STATE;
    }

    /* Valid partition table loaded */
    return ESP_OK;
}

static esp_err_t encrypt_partition(int index, const esp_partition_info_t *partition)
{
    esp_err_t err;
    bool should_encrypt = (partition->flags & PART_FLAG_ENCRYPTED);

    if (partition->type == PART_TYPE_APP) {
        /* check if the partition holds a valid unencrypted app */
        esp_image_metadata_t data_ignored;
        err = esp_image_verify(ESP_IMAGE_VERIFY,
                               &partition->pos,
                               &data_ignored);
        should_encrypt = (err == ESP_OK);
    } else if (partition->type == PART_TYPE_DATA && partition->subtype == PART_SUBTYPE_DATA_OTA) {
        /* check if we have ota data partition and the partition should be encrypted unconditionally */
        should_encrypt = true;
    }

    if (!should_encrypt) {
        return ESP_OK;
    } else {
        /* should_encrypt */
        ESP_LOGI(TAG, "Encrypting partition %d at offset 0x%x (length 0x%x)...", index, partition->pos.offset, partition->pos.size);

        err = esp_flash_encrypt_region(partition->pos.offset, partition->pos.size);
        ESP_LOGI(TAG, "Done encrypting");
        if (err != ESP_OK) {
            ESP_LOGE(TAG, "Failed to encrypt partition %d", index);
        }
        return err;
    }
}

esp_err_t esp_flash_encrypt_region(uint32_t src_addr, size_t data_length)
{
    esp_err_t err;
    uint32_t buf[FLASH_SECTOR_SIZE / sizeof(uint32_t)];

    if (src_addr % FLASH_SECTOR_SIZE != 0) {
        ESP_LOGE(TAG, "esp_flash_encrypt_region bad src_addr 0x%x", src_addr);
        return ESP_FAIL;
    }

    for (size_t i = 0; i < data_length; i += FLASH_SECTOR_SIZE) {
        uint32_t sec_start = i + src_addr;
        err = bootloader_flash_read(sec_start, buf, FLASH_SECTOR_SIZE, false);
        if (err != ESP_OK) {
            goto flash_failed;
        }
        err = bootloader_flash_erase_sector(sec_start / FLASH_SECTOR_SIZE);
        if (err != ESP_OK) {
            goto flash_failed;
        }
        err = bootloader_flash_write(sec_start, buf, FLASH_SECTOR_SIZE, true);
        if (err != ESP_OK) {
            goto flash_failed;
        }
    }
    return ESP_OK;

flash_failed:
    ESP_LOGE(TAG, "flash operation failed: 0x%x", err);
    return err;
}