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@@ -11,43 +11,311 @@
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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-#include "esp_secure_boot.h"
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+#include <string.h>
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+
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#include "esp_log.h"
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+#include "esp_secure_boot.h"
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+#include "soc/efuse_reg.h"
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+
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+#include "bootloader_flash.h"
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+#include "bootloader_sha.h"
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+#include "bootloader_utility.h"
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+
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+#include "esp_rom_crc.h"
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+#include "esp_efuse.h"
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+#include "esp_efuse_table.h"
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+
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#include "esp32s2/rom/secure_boot.h"
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-static const char *TAG = "secure_boot";
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+static const char *TAG = "secure_boot_v2";
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+#define ALIGN_UP(num, align) (((num) + ((align) - 1)) & ~((align) - 1))
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+
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+#define SIG_BLOCK_MAGIC_BYTE 0xe7
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+#define CRC_SIGN_BLOCK_LEN 1196
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+#define SIG_BLOCK_PADDING 4096
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+
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+#define DIGEST_LEN 32
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+
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+/* A signature block is valid when it has correct magic byte, crc and image digest. */
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+static esp_err_t validate_signature_block(int block_num, const ets_secure_boot_signature_t *sig_block, uint8_t *digest)
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+{
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+ uint32_t crc = esp_rom_crc32_le(0, (uint8_t *)&sig_block->block[block_num], CRC_SIGN_BLOCK_LEN);
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+ if (sig_block->block[block_num].magic_byte != SIG_BLOCK_MAGIC_BYTE) {
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+ // All signature blocks have been parsed, no new signature block present.
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+ ESP_LOGD(TAG, "Signature block(%d) invalid/absent.", block_num);
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+ return ESP_FAIL;
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+ }
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+ if (sig_block->block[block_num].block_crc != crc) {
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+ ESP_LOGE(TAG, "Magic byte correct but incorrect crc.");
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+ return ESP_FAIL;
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+ }
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+ if (memcmp(digest, sig_block->block[block_num].image_digest, DIGEST_LEN)) {
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+ ESP_LOGE(TAG, "Magic byte & CRC correct but incorrect image digest.");
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+ return ESP_FAIL;
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+ } else {
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+ ESP_LOGD(TAG, "valid signature block(%d) found", block_num);
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+ return ESP_OK;
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+ }
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+
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+ return ESP_FAIL;
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+}
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+
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+// Inputs the flash_offset and length of an image(app or bootloader), validates & verifies its secure boot v2 signature.
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+// Generates the public key digests of the valid public keys in a signature block and writes it into trusted_keys.
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+// The key_digests in trusted keys whose signature blocks are invalid will be set to NULL.
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+static esp_err_t secure_boot_v2_digest_generate(uint32_t flash_offset, uint32_t flash_size, ets_secure_boot_key_digests_t * const trusted_keys)
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+{
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+ int i = 0;
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+ esp_err_t ret = ESP_FAIL;
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+
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+ uint8_t image_digest[DIGEST_LEN] = {0};
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+ uint8_t public_key_digests[SECURE_BOOT_NUM_BLOCKS][DIGEST_LEN];
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+ size_t sig_block_addr = flash_offset + ALIGN_UP(flash_size, FLASH_SECTOR_SIZE);
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+ ret = bootloader_sha256_flash_contents(flash_offset, sig_block_addr - flash_offset, image_digest);
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+ if (ret != ESP_OK) {
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+ ESP_LOGE(TAG, "error generating image digest, %d", ret);
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+ return ret;
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+ }
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+
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+ ESP_LOGD(TAG, "reading signature block");
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+ const ets_secure_boot_signature_t *sig_block = bootloader_mmap(sig_block_addr, sizeof(ets_secure_boot_signature_t));
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+ if (sig_block == NULL) {
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+ ESP_LOGE(TAG, "bootloader_mmap(0x%x, 0x%x) failed", sig_block_addr, sizeof(ets_secure_boot_signature_t));
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+ return ESP_FAIL;
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+ }
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+
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+ for (i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
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+ ret = validate_signature_block(i, sig_block, image_digest);
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+ if (ret != ESP_OK) {
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+ break;
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+ }
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+
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+ /* Generating the SHA of the public key components in the signature block */
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+ bootloader_sha256_handle_t sig_block_sha;
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+ sig_block_sha = bootloader_sha256_start();
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+ bootloader_sha256_data(sig_block_sha, &sig_block->block[i].key, sizeof(sig_block->block[i].key));
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+ bootloader_sha256_finish(sig_block_sha, public_key_digests[i]);
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+
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+ memcpy((uint8_t *)trusted_keys->key_digests[0], public_key_digests[i], DIGEST_LEN); // Overwriting 0th index to verify each valid signature block
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+ /* A signature block is verified when it is valid and the signature in its signature block can be verified with a valid public key */
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+ uint8_t verified_digest[DIGEST_LEN] = {0};
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+ ets_secure_boot_status_t r = ets_secure_boot_verify_signature(sig_block, image_digest, trusted_keys, verified_digest);
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+ if (r != SB_SUCCESS) {
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+ ESP_LOGE(TAG, "Secure boot key (%d) verification failed.", i);
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+ ret = ESP_FAIL;
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+ goto exit;
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+ }
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+ }
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+
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+ // At least 1 verified signature block found.
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+ if (i > 0) {
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+ // validate_signature_block returns ESP_FAIL when a sig block is absent, which isn't an error.
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+ while (--i) {
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+ trusted_keys->key_digests[i] = public_key_digests[i];
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+ }
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+ ret = ESP_OK;
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+ }
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+
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+exit:
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+ /* Set the pointer to an invalid/absent block to NULL */
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+ while (i < SECURE_BOOT_NUM_BLOCKS) {
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+ trusted_keys->key_digests[i] = NULL;
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+ i++;
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+ }
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+ ESP_LOGI(TAG, "Secure boot verification success.");
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+ bootloader_munmap(sig_block);
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+ return ret;
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+}
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+
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+/* Traverses ets_secure_boot_key_digests_t to find the number of non-null key_digests */
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+static uint8_t get_signature_block_count(ets_secure_boot_key_digests_t * const trusted_keys) {
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+ uint8_t bootloader_sig_block_count = 0;
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+ for (uint8_t i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
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+ if (trusted_keys->key_digests[i] != NULL) {
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+ bootloader_sig_block_count++;
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-esp_err_t esp_secure_boot_permanently_enable(void)
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+ for (uint8_t j = 0; j < DIGEST_LEN ; j++) {
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+ ESP_LOGD(TAG, "Secure Boot Digest %d: 0x%x", i, *(((uint8_t *)trusted_keys->key_digests[i]) + j));
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+ }
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+ }
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+ }
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+ return bootloader_sig_block_count;
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+}
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+
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+esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *image_data)
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{
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- uint8_t hash[32];
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+ ESP_LOGI(TAG, "enabling secure boot v2 - ESP32-S2...");
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- if (esp_rom_efuse_is_secure_boot_enabled())
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- {
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- ESP_LOGI(TAG, "secure boot is already enabled, continuing..");
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+ if (esp_secure_boot_enabled()) {
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+ ESP_LOGI(TAG, "secure boot v2 is already enabled, continuing..");
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return ESP_OK;
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}
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- ESP_LOGI(TAG, "Verifying bootloader signature...\n");
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- int r = ets_secure_boot_verify_bootloader(hash, false);
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- if (r != ESP_OK) {
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- ESP_LOGE(TAG, "Failed to verify bootloader signature");
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- return r;
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+ esp_err_t ret;
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+ /* Verify the bootloader */
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+ esp_image_metadata_t bootloader_data = { 0 };
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+ ret = esp_image_verify_bootloader_data(&bootloader_data);
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+ if (ret != ESP_OK) {
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+ ESP_LOGE(TAG, "bootloader image appears invalid! error %d", ret);
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+ return ret;
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}
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- esp_efuse_batch_write_begin(); /* Batch all efuse writes at the end of this function */
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+ /* Check if secure boot digests are present */
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+ bool has_secure_boot_digest = ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0, NULL);
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+ has_secure_boot_digest |= ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1, NULL);
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+ has_secure_boot_digest |= ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2, NULL);
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+ ESP_LOGI(TAG, "Secure boot digests %s", has_secure_boot_digest ? "already present":"absent, generating..");
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+
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+
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+ ets_efuse_clear_program_registers();
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+ uint8_t i, j, bootloader_sig_block_count = 0;
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+ if (!has_secure_boot_digest) {
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+ ets_secure_boot_key_digests_t boot_trusted_keys, app_trusted_keys;
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+ uint8_t boot_trusted_key_data[SECURE_BOOT_NUM_BLOCKS][DIGEST_LEN] = {0}, app_trusted_key_data[SECURE_BOOT_NUM_BLOCKS][DIGEST_LEN] = {0};
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+
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+ for(i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
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+ boot_trusted_keys.key_digests[i] = boot_trusted_key_data[i];
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+ app_trusted_keys.key_digests[i] = app_trusted_key_data[i];
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+ }
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+
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+ /* Generate the bootloader public key digests */
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+ ret = secure_boot_v2_digest_generate(bootloader_data.start_addr, bootloader_data.image_len - SIG_BLOCK_PADDING, &boot_trusted_keys);
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+ if (ret != ESP_OK) {
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+ ESP_LOGE(TAG, "Public key digest generation failed.");
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+ return ret;
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+ }
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+
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+ bootloader_sig_block_count = get_signature_block_count(&boot_trusted_keys);
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+ if (bootloader_sig_block_count <= 0) {
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+ ESP_LOGI(TAG, "No valid signature blocks found. %d signature block(s) found.", bootloader_sig_block_count);
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+ return ESP_FAIL;
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+ }
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+ ESP_LOGI(TAG, "%d signature block(s) found appended to the bootloader.", bootloader_sig_block_count);
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+
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+ int unused_key_slots = ets_efuse_count_unused_key_blocks();
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+ if (bootloader_sig_block_count > unused_key_slots) {
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+ ESP_LOGE(TAG, "Bootloader signatures(%d) more than available key slots(%d).", bootloader_sig_block_count, unused_key_slots);
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+ return ESP_FAIL;
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+ }
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+
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+ for (i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
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+ if (boot_trusted_keys.key_digests[i] == NULL) {
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+ break;
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+ }
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+
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+ const uint32_t secure_boot_key_purpose[SECURE_BOOT_NUM_BLOCKS] = { ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0,
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+ ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1, ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2 };
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+
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+ ets_efuse_block_t block = ets_efuse_find_unused_key_block();
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+ if (block == ETS_EFUSE_BLOCK_MAX) {
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+ ESP_LOGE(TAG, "Key blocks not available.");
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+ return ESP_FAIL;
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+ }
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+
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+ int r = ets_efuse_write_key(block, secure_boot_key_purpose[i], boot_trusted_keys.key_digests[i], DIGEST_LEN);
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+ if (r != 0) {
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+ ESP_LOGE(TAG, "Failed to write efuse block %d with purpose %d. Can't continue.", block, secure_boot_key_purpose[i]);
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+ return ESP_FAIL;
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+ }
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+
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+ r = esp_efuse_set_write_protect(block);
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+ if (r != 0) {
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+ ESP_LOGE(TAG, "Failed to write protect efuse block %d. Can't continue.", block);
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+ return ESP_FAIL;
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+ }
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+ }
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+
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+ /* Generate the application public key digests */
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+ ret = secure_boot_v2_digest_generate(image_data->start_addr, image_data->image_len - SIG_BLOCK_PADDING, &app_trusted_keys);
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+ if (ret != ESP_OK) {
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+ ESP_LOGE(TAG, "Application signature block is invalid.");
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+ return ret;
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+ }
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+
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+ int app_sig_block_count = get_signature_block_count(&app_trusted_keys);
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+ ESP_LOGI(TAG, "%d signature block(s) found appended to the application.", app_sig_block_count);
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+
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+ /* Confirm if atleast one the public key from the application matches a public key in the bootloader
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+ (Also, ensure if that public revoke bit is not set for the matched key) */
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+ bool match = false;
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+ const uint32_t revoke_bits[SECURE_BOOT_NUM_BLOCKS] = { EFUSE_SECURE_BOOT_KEY_REVOKE0,
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+ EFUSE_SECURE_BOOT_KEY_REVOKE1, EFUSE_SECURE_BOOT_KEY_REVOKE2 };
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+
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+ for (i = 0; i < SECURE_BOOT_NUM_BLOCKS && match == false; i++) {
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+
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+ if (REG_GET_BIT(EFUSE_RD_REPEAT_DATA1_REG, revoke_bits[i])) {
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+ ESP_LOGI(TAG, "Key block(%d) has been revoked.", i);
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+ continue; // skip if the key block is revoked
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+ }
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+
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+ for (j = 0; j < SECURE_BOOT_NUM_BLOCKS; j++) {
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+ if (!memcmp(boot_trusted_key_data[i], app_trusted_key_data[j], DIGEST_LEN)) {
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+ ESP_LOGI(TAG, "Application key(%d) matches with bootloader key(%d).", j, i);
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+ match = true;
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+ break;
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+ }
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+ }
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+ }
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+
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+ if (match == false) {
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+ ESP_LOGE(TAG, "No application key digest matches the bootloader key digest.");
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+ return ESP_FAIL;
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+ }
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+
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+ /* Revoke the empty signature blocks */
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+ if (bootloader_sig_block_count < SECURE_BOOT_NUM_BLOCKS) {
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+ /* The revocation index can be 0, 1, 2. Bootloader count can be 1,2,3. */
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+ for (uint8_t i = bootloader_sig_block_count; i < SECURE_BOOT_NUM_BLOCKS; i++) {
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+ ESP_LOGI(TAG, "Revoking empty key digest slot (%d)...", i);
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+ ets_secure_boot_revoke_public_key_digest(i);
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+ }
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+ }
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+ }
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+
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+ esp_err_t err = esp_efuse_batch_write_begin();
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+ if (err != ESP_OK) {
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+ ESP_LOGI(TAG, "Error batch programming security eFuses.");
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+ return err;
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+ }
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+
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+ __attribute__((unused)) static const uint8_t enable = 1;
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- esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_EN);
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esp_efuse_write_field_bit(ESP_EFUSE_DIS_BOOT_REMAP);
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esp_efuse_write_field_bit(ESP_EFUSE_DIS_LEGACY_SPI_BOOT);
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- // TODO: also disable JTAG here, etc
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+#ifdef CONFIG_SECURE_ENABLE_SECURE_ROM_DL_MODE
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+ ESP_LOGI(TAG, "Enabling Security download mode...");
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+ esp_efuse_write_field_bit(ESP_EFUSE_ENABLE_SECURITY_DOWNLOAD);
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+#else
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+ ESP_LOGW(TAG, "Not enabling Security download mode - SECURITY COMPROMISED");
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+#endif
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+
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+#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
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+ ESP_LOGI(TAG, "Disable hardware & software JTAG...");
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+ esp_efuse_write_field_bit(ESP_EFUSE_HARD_DIS_JTAG);
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+ esp_efuse_write_field_bit(ESP_EFUSE_SOFT_DIS_JTAG);
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+#else
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+ ESP_LOGW(TAG, "Not disabling JTAG - SECURITY COMPROMISED");
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+#endif
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- esp_err_t err = esp_efuse_batch_write_commit();
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+#ifdef CONFIG_SECURE_BOOT_ENABLE_AGGRESSIVE_KEY_REVOKE
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+ esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_AGGRESSIVE_REVOKE);
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+#endif
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- if (err == ESP_OK) {
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- assert(esp_rom_efuse_is_secure_boot_enabled());
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- ESP_LOGI(TAG, "Secure boot permanently enabled");
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+ esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_EN);
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+
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+ err = esp_efuse_batch_write_commit();
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+ if (err != ESP_OK) {
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+ ESP_LOGI(TAG, "Error programming security eFuses.");
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+ return err;
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}
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+#ifdef CONFIG_SECURE_BOOT_ENABLE_AGGRESSIVE_KEY_REVOKE
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+ assert(ets_efuse_secure_boot_aggressive_revoke_enabled());
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+#endif
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+
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+ assert(esp_rom_efuse_is_secure_boot_enabled());
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+ ESP_LOGI(TAG, "Secure boot permanently enabled");
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+
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return ESP_OK;
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}
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Supreet Deshpande