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feat: Add API to verify the bootloader and app image

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Added an API to verify the bootloader and app image before revoking the key in Secure Boot V2.
This will help in preventing the device to be bricked if the bootloader/application cannot be
verified by any other keys in efuse
This commit is contained in:
Harshit Malpani
2023-07-04 10:18:47 +05:30
parent 2472c62fff
commit 1df186d4e1
5 changed files with 176 additions and 81 deletions
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components/app_update/esp_ota_ops.c
+58 -51
View File
@@ -1,5 +1,5 @@
/*
* SPDX-FileCopyrightText: 2015-2021 Espressif Systems (Shanghai) CO LTD
* SPDX-FileCopyrightText: 2015-2023 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
@@ -924,9 +924,27 @@ esp_err_t esp_ota_erase_last_boot_app_partition(void)
return ESP_OK;
}
#if SOC_EFUSE_SECURE_BOOT_KEY_DIGESTS > 1 && CONFIG_SECURE_BOOT_V2_ENABLED
esp_err_t esp_ota_revoke_secure_boot_public_key(esp_ota_secure_boot_public_key_index_t index) {
#if SOC_SUPPORT_SECURE_BOOT_REVOKE_KEY && CONFIG_SECURE_BOOT_V2_ENABLED
// Validates the image at "app_pos" with the secure boot digests other than "revoked_key_index"
static bool validate_img(esp_ota_secure_boot_public_key_index_t revoked_key_index, esp_partition_pos_t *app_pos)
{
bool verified = false;
for (int i = 0; i < SOC_EFUSE_SECURE_BOOT_KEY_DIGESTS; i++) {
if (i == revoked_key_index) {
continue;
}
if (esp_secure_boot_verify_with_efuse_digest_index(i, app_pos) == ESP_OK) {
verified = true;
ESP_LOGI(TAG, "Application successfully verified with public key digest %d", i);
break;
}
}
return verified;
}
esp_err_t esp_ota_revoke_secure_boot_public_key(esp_ota_secure_boot_public_key_index_t index)
{
if (!esp_secure_boot_enabled()) {
ESP_LOGE(TAG, "Secure boot v2 has not been enabled.");
return ESP_FAIL;
@@ -939,71 +957,60 @@ esp_err_t esp_ota_revoke_secure_boot_public_key(esp_ota_secure_boot_public_key_i
return ESP_ERR_INVALID_ARG;
}
esp_image_sig_public_key_digests_t app_digests = { 0 };
esp_err_t err = esp_secure_boot_get_signature_blocks_for_running_app(true, &app_digests);
if (err != ESP_OK || app_digests.num_digests == 0) {
ESP_LOGE(TAG, "This app is not signed, but check signature on update is enabled in config. It won't be possible to verify any update.");
const esp_partition_t *running_app_part = esp_ota_get_running_partition();
#ifdef CONFIG_BOOTLOADER_APP_ROLLBACK_ENABLE
esp_ota_img_states_t running_app_state;
ret = esp_ota_get_state_partition(running_app_part, &running_app_state);
if (ret != ESP_OK) {
ESP_LOGE(TAG, "esp_ota_get_state_partition returned: %s", esp_err_to_name(ret));
return ESP_FAIL;
}
if (running_app_state != ESP_OTA_IMG_VALID) {
ESP_LOGE(TAG, "The current running application is not marked as a valid image. Aborting..");
return ESP_FAIL;
}
#endif
esp_err_t ret;
esp_secure_boot_key_digests_t trusted_keys;
ret = esp_secure_boot_read_key_digests(&trusted_keys);
esp_err_t ret = esp_secure_boot_read_key_digests(&trusted_keys);
if (ret != ESP_OK) {
ESP_LOGE(TAG, "Could not read the secure boot key digests from efuse. Aborting..");
return ESP_FAIL;
}
if (trusted_keys.key_digests[index] == NULL) {
ESP_LOGI(TAG, "Trusted Key block(%d) already revoked.", index);
ESP_LOGI(TAG, "Given public key digest(%d) is already revoked.", index);
return ESP_OK;
}
esp_image_sig_public_key_digests_t trusted_digests = { 0 };
for (unsigned i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
if (i == index) {
continue; // omitting - to find if there is a valid key after revoking this digest
}
/* Check if the application can be verified with a key other than the one being revoked */
esp_partition_pos_t running_app_pos = {
.offset = running_app_part->address,
.size = running_app_part->size,
};
if (trusted_keys.key_digests[i] != NULL) {
bool all_zeroes = true;
for (unsigned j = 0; j < ESP_SECURE_BOOT_DIGEST_LEN; j++) {
all_zeroes = all_zeroes && (*(uint8_t *)(trusted_keys.key_digests[i] + j) == 0);
}
if (!all_zeroes) {
memcpy(trusted_digests.key_digests[trusted_digests.num_digests++], (uint8_t *)trusted_keys.key_digests[i], ESP_SECURE_BOOT_DIGEST_LEN);
} else {
ESP_LOGD(TAG, "Empty trusted key block (%d).", i);
}
}
}
bool match = false;
for (unsigned i = 0; i < trusted_digests.num_digests; i++) {
if (match == true) {
break;
}
for (unsigned j = 0; j < app_digests.num_digests; j++) {
if (memcmp(trusted_digests.key_digests[i], app_digests.key_digests[j], ESP_SECURE_BOOT_DIGEST_LEN) == 0) {
ESP_LOGI(TAG, "App key block(%d) matches Trusted key block(%d)[%d -> Next active trusted key block].", j, i, i);
esp_err_t err = esp_efuse_set_digest_revoke(index);
if (err != ESP_OK) {
ESP_LOGE(TAG, "Failed to revoke digest (0x%x).", err);
return ESP_FAIL;
}
ESP_LOGI(TAG, "Revoked signature block %d.", index);
match = true;
break;
}
}
}
if (match == false) {
ESP_LOGE(TAG, "Running app doesn't have another valid secure boot key. Cannot revoke current key(%d).", index);
if (!validate_img(index, &running_app_pos)) {
ESP_LOGE(TAG, "Application cannot be verified with any key other than the one being revoked");
return ESP_FAIL;
}
/* Check if bootloder can be verified with any key other than the one being revoked */
esp_partition_pos_t bootloader_pos = {
.offset = ESP_BOOTLOADER_OFFSET,
.size = (ESP_PARTITION_TABLE_OFFSET - ESP_BOOTLOADER_OFFSET),
};
if (!validate_img(index, &bootloader_pos)) {
ESP_LOGE(TAG, "Bootloader cannot be verified with any key other than the one being revoked");
return ESP_FAIL;
}
esp_err_t err = esp_efuse_set_digest_revoke(index);
if (err != ESP_OK) {
ESP_LOGE(TAG, "Failed to revoke digest (0x%x).", err);
return ESP_FAIL;
}
ESP_LOGI(TAG, "Revoked signature block %d.", index);
return ESP_OK;
}
#endif
components/app_update/include/esp_ota_ops.h
+2 -2
View File
@@ -350,10 +350,10 @@ typedef enum {
} esp_ota_secure_boot_public_key_index_t;
/**
* @brief Revokes the old signature digest. To be called in the application after the rollback logic.
* @brief Revokes the signature digest denoted by the given index. This should be called in the application only after the rollback logic otherwise the device may end up in unrecoverable state.
*
* Relevant for Secure boot v2 on ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6, ESP32-H2 where up to 3 key digests can be stored (Key \#N-1, Key \#N, Key \#N+1).
* When key \#N-1 used to sign an app is invalidated, an OTA update is to be sent with an app signed with key \#N-1 & Key \#N.
* When a key used to sign an app is invalidated, an OTA update is to be sent with an app signed with at least one of the other two keys which has not been revoked already.
* After successfully booting the OTA app should call this function to revoke Key \#N-1.
*
* @param index - The index of the signature block to be revoked