esp-idf/components/bootloader_support/src/esp_image_format.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 <sys/param.h>

#include <rom/rtc.h>
#include <soc/cpu.h>
#include <esp_image_format.h>
#include <esp_secure_boot.h>
#include <esp_log.h>
#include <bootloader_flash.h>
#include <bootloader_random.h>
#include <bootloader_sha.h>

static const char *TAG = "esp_image";

#define HASH_LEN 32 /* SHA-256 digest length */

#define SIXTEEN_MB 0x1000000
#define ESP_ROM_CHECKSUM_INITIAL 0xEF

/* Headroom to ensure between stack SP (at time of checking) and data loaded from flash */
#define STACK_LOAD_HEADROOM 32768

#ifdef BOOTLOADER_BUILD
/* 64 bits of random data to obfuscate loaded RAM with, until verification is complete
   (Means loaded code isn't executable until after the secure boot check.)
*/
static uint32_t ram_obfs_value[2];
#endif

/* Return true if load_addr is an address the bootloader should load into */
static bool should_load(uint32_t load_addr);
/* Return true if load_addr is an address the bootloader should map via flash cache */
static bool should_map(uint32_t load_addr);

/* Load or verify a segment */
static esp_err_t process_segment(int index, uint32_t flash_addr, esp_image_segment_header_t *header, bool silent, bool do_load, bootloader_sha256_handle_t sha_handle, uint32_t *checksum);

/* Verify the main image header */
static esp_err_t verify_image_header(uint32_t src_addr, const esp_image_header_t *image, bool silent);

/* Verify a segment header */
static esp_err_t verify_segment_header(int index, const esp_image_segment_header_t *segment, uint32_t segment_data_offs, bool silent);

/* Log-and-fail macro for use in esp_image_load */
#define FAIL_LOAD(...) do {                         \
        if (!silent) {                              \
            ESP_LOGE(TAG, __VA_ARGS__);             \
        }                                           \
        goto err;                                   \
    }                                               \
    while(0)

static esp_err_t verify_checksum(bootloader_sha256_handle_t sha_handle, uint32_t checksum_word, esp_image_metadata_t *data);

static esp_err_t __attribute__((unused)) verify_secure_boot_signature(bootloader_sha256_handle_t sha_handle, esp_image_metadata_t *data);
static esp_err_t __attribute__((unused)) verify_simple_hash(bootloader_sha256_handle_t sha_handle, esp_image_metadata_t *data);

esp_err_t esp_image_load(esp_image_load_mode_t mode, const esp_partition_pos_t *part, esp_image_metadata_t *data)
{
#ifdef BOOTLOADER_BUILD
    bool do_load = (mode == ESP_IMAGE_LOAD);
#else
    bool do_load = false; // Can't load the image in app mode
#endif
    bool silent = (mode == ESP_IMAGE_VERIFY_SILENT);
    esp_err_t err = ESP_OK;
    // checksum the image a word at a time. This shaves 30-40ms per MB of image size
    uint32_t checksum_word = ESP_ROM_CHECKSUM_INITIAL;
    bootloader_sha256_handle_t sha_handle = NULL;

    if (data == NULL || part == NULL) {
        return ESP_ERR_INVALID_ARG;
    }

    if (part->size > SIXTEEN_MB) {
        err = ESP_ERR_INVALID_ARG;
        FAIL_LOAD("partition size 0x%x invalid, larger than 16MB", part->size);
    }

    bzero(data, sizeof(esp_image_metadata_t));
    data->start_addr = part->offset;

    ESP_LOGD(TAG, "reading image header @ 0x%x", data->start_addr);
    err = bootloader_flash_read(data->start_addr, &data->image, sizeof(esp_image_header_t), true);
    if (err != ESP_OK) {
        goto err;
    }

    // Calculate SHA-256 of image if secure boot is on, or if image has a hash appended
#ifdef CONFIG_SECURE_BOOT_ENABLED
    if (1) {
#else
    if (data->image.hash_appended) {
#endif
        sha_handle = bootloader_sha256_start();
        if (sha_handle == NULL) {
            return ESP_ERR_NO_MEM;
        }
        bootloader_sha256_data(sha_handle, &data->image, sizeof(esp_image_header_t));
    }

    ESP_LOGD(TAG, "image header: 0x%02x 0x%02x 0x%02x 0x%02x %08x",
             data->image.magic,
             data->image.segment_count,
             data->image.spi_mode,
             data->image.spi_size,
             data->image.entry_addr);

    err = verify_image_header(data->start_addr, &data->image, silent);
    if (err != ESP_OK) {
goto err;
    }

    if (data->image.segment_count > ESP_IMAGE_MAX_SEGMENTS) {
        FAIL_LOAD("image at 0x%x segment count %d exceeds max %d",
                  data->start_addr, data->image.segment_count, ESP_IMAGE_MAX_SEGMENTS);
    }

    uint32_t next_addr = data->start_addr + sizeof(esp_image_header_t);
    for(int i = 0; i < data->image.segment_count; i++) {
        esp_image_segment_header_t *header = &data->segments[i];
        ESP_LOGV(TAG, "loading segment header %d at offset 0x%x", i, next_addr);
        err = process_segment(i, next_addr, header, silent, do_load, sha_handle, &checksum_word);
        if (err != ESP_OK) {
            goto err;
        }
        next_addr += sizeof(esp_image_segment_header_t);
        data->segment_data[i] = next_addr;
        next_addr += header->data_len;
    }

    // Segments all loaded, verify length
    uint32_t end_addr = next_addr;
    if (end_addr < data->start_addr) {
        FAIL_LOAD("image offset has wrapped");
    }

    data->image_len = end_addr - data->start_addr;
    ESP_LOGV(TAG, "image start 0x%08x end of last section 0x%08x", data->start_addr, end_addr);
    err = verify_checksum(sha_handle, checksum_word, data);
    if (err != ESP_OK) {
        goto err;
    }

    if (data->image_len > part->size) {
        FAIL_LOAD("Image length %d doesn't fit in partition length %d", data->image_len, part->size);
    }

    bool is_bootloader = (data->start_addr == ESP_BOOTLOADER_OFFSET);
    /* For secure boot, we don't verify signature on bootloaders.

       For non-secure boot, we don't verify any SHA-256 hash appended to the bootloader because esptool.py may have
       rewritten the header - rely on esptool.py having verified the bootloader at flashing time, instead.
    */
    if (!is_bootloader) {
#ifdef CONFIG_SECURE_BOOT_ENABLED
        // secure boot images have a signature appended
        err = verify_secure_boot_signature(sha_handle, data);
#else
        // No secure boot, but SHA-256 can be appended for basic corruption detection
        if (sha_handle != NULL) {
            err = verify_simple_hash(sha_handle, data);
        }
#endif // CONFIG_SECURE_BOOT_ENABLED
    } else { // is_bootloader
        // bootloader may still have a sha256 digest handle open
        if (sha_handle != NULL) {
            bootloader_sha256_finish(sha_handle, NULL);
        }
    }
    sha_handle = NULL;
    if (err != ESP_OK) {
        goto err;
    }

#ifdef BOOTLOADER_BUILD
    if (do_load) { // Need to deobfuscate RAM
        for (int i = 0; i < data->image.segment_count; i++) {
            uint32_t load_addr = data->segments[i].load_addr;
            if (should_load(load_addr)) {
                uint32_t *loaded = (uint32_t *)load_addr;
                for (int j = 0; j < data->segments[i].data_len/sizeof(uint32_t); j++) {
                    loaded[j] ^= (j & 1) ? ram_obfs_value[0] : ram_obfs_value[1];
                }
            }
        }
    }
#endif

    // Success!
    return ESP_OK;

 err:
    if (err == ESP_OK) {
      err = ESP_ERR_IMAGE_INVALID;
    }
    if (sha_handle != NULL) {
        // Need to finish the hash process to free the handle
        bootloader_sha256_finish(sha_handle, NULL);
    }
    // Prevent invalid/incomplete data leaking out
    bzero(data, sizeof(esp_image_metadata_t));
    return err;
}

static esp_err_t verify_image_header(uint32_t src_addr, const esp_image_header_t *image, bool silent)
{
    esp_err_t err = ESP_OK;

    if (image->magic != ESP_IMAGE_HEADER_MAGIC) {
        if (!silent) {
            ESP_LOGE(TAG, "image at 0x%x has invalid magic byte", src_addr);
        }
        err = ESP_ERR_IMAGE_INVALID;
    }
    if (!silent) {
        if (image->spi_mode > ESP_IMAGE_SPI_MODE_SLOW_READ) {
            ESP_LOGW(TAG, "image at 0x%x has invalid SPI mode %d", src_addr, image->spi_mode);
        }
        if (image->spi_speed > ESP_IMAGE_SPI_SPEED_80M) {
            ESP_LOGW(TAG, "image at 0x%x has invalid SPI speed %d", src_addr, image->spi_speed);
        }
        if (image->spi_size > ESP_IMAGE_FLASH_SIZE_MAX) {
            ESP_LOGW(TAG, "image at 0x%x has invalid SPI size %d", src_addr, image->spi_size);
        }
    }
    return err;
}

static esp_err_t process_segment(int index, uint32_t flash_addr, esp_image_segment_header_t *header, bool silent, bool do_load, bootloader_sha256_handle_t sha_handle, uint32_t *checksum)
{
    esp_err_t err;

    /* read segment header */
    err = bootloader_flash_read(flash_addr, header, sizeof(esp_image_segment_header_t), true);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "bootloader_flash_read failed at 0x%08x", flash_addr);
        return err;
    }
    if (sha_handle != NULL) {
        bootloader_sha256_data(sha_handle, header, sizeof(esp_image_segment_header_t));
    }

    intptr_t load_addr = header->load_addr;
    uint32_t data_len = header->data_len;
    uint32_t data_addr = flash_addr + sizeof(esp_image_segment_header_t);

    ESP_LOGV(TAG, "segment data length 0x%x data starts 0x%x", data_len, data_addr);

    err = verify_segment_header(index, header, data_addr, silent);
    if (err != ESP_OK) {
        return err;
    }

    if (data_len % 4 != 0) {
        FAIL_LOAD("unaligned segment length 0x%x", data_len);
    }

    bool is_mapping = should_map(load_addr);
    do_load = do_load && should_load(load_addr);

    if (!silent) {
        ESP_LOGI(TAG, "segment %d: paddr=0x%08x vaddr=0x%08x size=0x%05x (%6d) %s",
                 index, data_addr, load_addr,
                 data_len, data_len,
                 (do_load)?"load":(is_mapping)?"map":"");
    }

    if (do_load) {
        /* Before loading segment, check it doesn't clobber bootloader RAM... */
        uint32_t end_addr = load_addr + data_len;
        if (end_addr < 0x40000000) {
            intptr_t sp = (intptr_t)get_sp();
            if (end_addr > sp - STACK_LOAD_HEADROOM) {
                ESP_LOGE(TAG, "Segment %d end address 0x%08x too high (bootloader stack 0x%08x liimit 0x%08x)",
                         index, end_addr, sp, sp - STACK_LOAD_HEADROOM);
                return ESP_ERR_IMAGE_INVALID;
            }
        }
    }

    const uint32_t *data = (const uint32_t *)bootloader_mmap(data_addr, data_len);
    if(!data) {
        ESP_LOGE(TAG, "bootloader_mmap(0x%x, 0x%x) failed",
                 data_addr, data_len);
        return ESP_FAIL;
    }

#ifdef BOOTLOADER_BUILD
    // Set up the obfuscation value to use for loading
    while (ram_obfs_value[0] == 0 || ram_obfs_value[1] == 0) {
        bootloader_fill_random(ram_obfs_value, sizeof(ram_obfs_value));
    }
    uint32_t *dest = (uint32_t *)load_addr;
#endif

    const uint32_t *src = data;

    for (int i = 0; i < data_len; i += 4) {
        int w_i = i/4; // Word index
        uint32_t w = src[w_i];
        *checksum ^= w;
#ifdef BOOTLOADER_BUILD
        if (do_load) {
            dest[w_i] = w ^ ((w_i & 1) ? ram_obfs_value[0] : ram_obfs_value[1]);
        }
#endif
        // SHA_CHUNK determined experimentally as the optimum size
        // to call bootloader_sha256_data() with. This is a bit
        // counter-intuitive, but it's ~3ms better than using the
        // SHA256 block size.
        const size_t SHA_CHUNK = 1024;
        if (sha_handle != NULL && i % SHA_CHUNK == 0) {
            bootloader_sha256_data(sha_handle, &src[w_i],
                                   MIN(SHA_CHUNK, data_len - i));
        }
    }

    bootloader_munmap(data);

    return ESP_OK;

 err:
    if (err == ESP_OK) {
        err = ESP_ERR_IMAGE_INVALID;
    }
    return err;
}

static esp_err_t verify_segment_header(int index, const esp_image_segment_header_t *segment, uint32_t segment_data_offs, bool silent)
{
    if ((segment->data_len & 3) != 0
        || segment->data_len >= SIXTEEN_MB) {
        if (!silent) {
            ESP_LOGE(TAG, "invalid segment length 0x%x", segment->data_len);
        }
        return ESP_ERR_IMAGE_INVALID;
    }

    uint32_t load_addr = segment->load_addr;
    bool map_segment = should_map(load_addr);

    /* Check that flash cache mapped segment aligns correctly from flash to its mapped address,
       relative to the 64KB page mapping size.
    */
    ESP_LOGV(TAG, "segment %d map_segment %d segment_data_offs 0x%x load_addr 0x%x",
             index, map_segment, segment_data_offs, load_addr);
    if (map_segment
        && ((segment_data_offs % SPI_FLASH_MMU_PAGE_SIZE) != (load_addr % SPI_FLASH_MMU_PAGE_SIZE))) {
        if (!silent) {
            ESP_LOGE(TAG, "Segment %d load address 0x%08x, doesn't match data 0x%08x",
                     index, load_addr, segment_data_offs);
        }
        return ESP_ERR_IMAGE_INVALID;
    }

    return ESP_OK;
}

static bool should_map(uint32_t load_addr)
{
    return (load_addr >= SOC_IROM_LOW && load_addr < SOC_IROM_HIGH)
        || (load_addr >= SOC_DROM_LOW && load_addr < SOC_DROM_HIGH);
}

static bool should_load(uint32_t load_addr)
{
    /* Reload the RTC memory segments whenever a non-deepsleep reset
       is occurring */
    bool load_rtc_memory = rtc_get_reset_reason(0) != DEEPSLEEP_RESET;

    if (should_map(load_addr)) {
        return false;
    }

    if (load_addr < 0x10000000) {
        // Reserved for non-loaded addresses.
        // Current reserved values are
        // 0x0 (padding block)
        // 0x4 (unused, but reserved for an MD5 block)
        return false;
    }

    if (!load_rtc_memory) {
        if (load_addr >= SOC_RTC_IRAM_LOW && load_addr < SOC_RTC_IRAM_HIGH) {
            ESP_LOGD(TAG, "Skipping RTC code segment at 0x%08x\n", load_addr);
            return false;
        }
        if (load_addr >= SOC_RTC_DATA_LOW && load_addr < SOC_RTC_DATA_HIGH) {
            ESP_LOGD(TAG, "Skipping RTC data segment at 0x%08x\n", load_addr);
            return false;
        }
    }

    return true;
}

esp_err_t esp_image_verify_bootloader(uint32_t *length)
{
    esp_image_metadata_t data;
    const esp_partition_pos_t bootloader_part = {
        .offset = ESP_BOOTLOADER_OFFSET,
        .size = ESP_PARTITION_TABLE_OFFSET - ESP_BOOTLOADER_OFFSET,
    };
    esp_err_t err = esp_image_load(ESP_IMAGE_VERIFY,
                                   &bootloader_part,
                                   &data);
    if (length != NULL) {
        *length = (err == ESP_OK) ? data.image_len : 0;
    }
    return err;
}

static esp_err_t verify_checksum(bootloader_sha256_handle_t sha_handle, uint32_t checksum_word, esp_image_metadata_t *data)
{
    uint32_t unpadded_length = data->image_len;
    uint32_t length = unpadded_length + 1; // Add a byte for the checksum
    length = (length + 15) & ~15; // Pad to next full 16 byte block

    // Verify checksum
    uint8_t buf[16];
    esp_err_t err = bootloader_flash_read(data->start_addr + unpadded_length, buf, length - unpadded_length, true);
    uint8_t calc = buf[length - unpadded_length - 1];
    uint8_t checksum = (checksum_word >> 24)
        ^ (checksum_word >> 16)
        ^ (checksum_word >> 8)
        ^ (checksum_word >> 0);
    if (err != ESP_OK || checksum != calc) {
        ESP_LOGE(TAG, "Checksum failed. Calculated 0x%x read 0x%x", checksum, calc);
        return ESP_ERR_IMAGE_INVALID;
    }
    if (sha_handle != NULL) {
        bootloader_sha256_data(sha_handle, buf, length - unpadded_length);
    }

    if (data->image.hash_appended) {
        // Account for the hash in the total image length
        length += HASH_LEN;
    }
    data->image_len = length;

    return ESP_OK;
}

static void debug_log_hash(const uint8_t *image_hash, const char *caption);

static esp_err_t verify_secure_boot_signature(bootloader_sha256_handle_t sha_handle, esp_image_metadata_t *data)
{
    uint8_t image_hash[HASH_LEN] = { 0 };

    // For secure boot, we calculate the signature hash over the whole file, which includes any "simple" hash
    // appended to the image for corruption detection
    if (data->image.hash_appended) {
        const void *simple_hash = bootloader_mmap(data->start_addr + data->image_len - HASH_LEN, HASH_LEN);
        bootloader_sha256_data(sha_handle, simple_hash, HASH_LEN);
        bootloader_munmap(simple_hash);
    }

    bootloader_sha256_finish(sha_handle, image_hash);

    // Log the hash for debugging
    debug_log_hash(image_hash, "Calculated secure boot hash");

    // Use hash to verify signature block
    const esp_secure_boot_sig_block_t *sig_block = bootloader_mmap(data->start_addr + data->image_len, sizeof(esp_secure_boot_sig_block_t));
    esp_err_t err = esp_secure_boot_verify_signature_block(sig_block, image_hash);
    bootloader_munmap(sig_block);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "Secure boot signature verification failed");

        // Go back and check if the simple hash matches or not (we're off the fast path so we can re-hash the whole image now)
        ESP_LOGI(TAG, "Calculating simple hash to check for corruption...");
        const void *whole_image = bootloader_mmap(data->start_addr, data->image_len - HASH_LEN);
        if (whole_image != NULL) {
            sha_handle = bootloader_sha256_start();
            bootloader_sha256_data(sha_handle, whole_image, data->image_len - HASH_LEN);
            bootloader_munmap(whole_image);
            if (verify_simple_hash(sha_handle, data) != ESP_OK) {
                ESP_LOGW(TAG, "image corrupted on flash");
            } else {
                ESP_LOGW(TAG, "image valid, signature bad");
            }
        }
        return ESP_ERR_IMAGE_INVALID;
    }

    return ESP_OK;
}

static esp_err_t verify_simple_hash(bootloader_sha256_handle_t sha_handle, esp_image_metadata_t *data)
{
    uint8_t image_hash[HASH_LEN] = { 0 };
    bootloader_sha256_finish(sha_handle, image_hash);

    // Log the hash for debugging
    debug_log_hash(image_hash, "Calculated hash");

    // Simple hash for verification only
    const void *hash = bootloader_mmap(data->start_addr + data->image_len - HASH_LEN, HASH_LEN);
    if (memcmp(hash, image_hash, HASH_LEN) != 0) {
        ESP_LOGE(TAG, "Image hash failed - image is corrupt");
        debug_log_hash(hash, "Expected hash");
        bootloader_munmap(hash);
        return ESP_ERR_IMAGE_INVALID;
    }

    bootloader_munmap(hash);
    return ESP_OK;
}

// Log a hash as a hex string
static void debug_log_hash(const uint8_t *image_hash, const char *label)
{
#if BOOT_LOG_LEVEL >= LOG_LEVEL_DEBUG
        char hash_print[sizeof(image_hash)*2 + 1];
        hash_print[sizeof(image_hash)*2] = 0;
        for (int i = 0; i < sizeof(image_hash); i++) {
            for (int shift = 0; shift < 2; shift++) {
                uint8_t nibble = (image_hash[i] >> (shift ? 0 : 4)) & 0x0F;
                if (nibble < 10) {
                    hash_print[i*2+shift] = '0' + nibble;
                } else {
                    hash_print[i*2+shift] = 'a' + nibble - 10;
                }
            }
        }
        ESP_LOGD(TAG, "%s: %s", label, hash_print);
#endif
}