Merge branch 'feature/secure_boot_esp32s2' into 'master'

Feature/secure boot esp32s2

See merge request espressif/esp-idf!8254

components/bootloader_support/src/esp32s2/secure_boot.c

@@ -11,43 +11,315 @@
 // 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 "esp_secure_boot.h"
+#include <string.h>
+
 #include "esp_log.h"
+#include "esp_secure_boot.h"
+#include "soc/efuse_reg.h"
+
+#include "bootloader_flash.h"
+#include "bootloader_sha.h"
+#include "bootloader_utility.h"
+
+#include "esp_rom_crc.h"
+#include "esp_efuse.h"
+#include "esp_efuse_table.h"
+
+#include "esp32s2/rom/efuse.h"
 #include "esp32s2/rom/secure_boot.h"
 
-static const char *TAG = "secure_boot";
+static const char *TAG = "secure_boot_v2";
+#define ALIGN_UP(num, align) (((num) + ((align) - 1)) & ~((align) - 1))
 
-esp_err_t esp_secure_boot_permanently_enable(void)
+#define SIG_BLOCK_MAGIC_BYTE 0xe7
+#define CRC_SIGN_BLOCK_LEN 1196
+#define SIG_BLOCK_PADDING 4096
+
+#define DIGEST_LEN 32
+
+/* A signature block is valid when it has correct magic byte, crc and image digest. */
+static esp_err_t validate_signature_block(const ets_secure_boot_sig_block_t *block, int block_num, const uint8_t *image_digest)
 {
-    uint8_t hash[32];
-
-    if (esp_rom_efuse_is_secure_boot_enabled())
-    {
-        ESP_LOGI(TAG, "secure boot is already enabled, continuing..");
+    uint32_t crc = esp_rom_crc32_le(0, (uint8_t *)block, CRC_SIGN_BLOCK_LEN);
+    if (block->magic_byte != SIG_BLOCK_MAGIC_BYTE) {
+        // All signature blocks have been parsed, no new signature block present.
+        ESP_LOGD(TAG, "Signature block(%d) invalid/absent.", block_num);
+        return ESP_FAIL;
+    }
+    if (block->block_crc != crc) {
+        ESP_LOGE(TAG, "Magic byte correct but incorrect crc.");
+        return ESP_FAIL;
+    }
+    if (memcmp(image_digest, block->image_digest, DIGEST_LEN)) {
+        ESP_LOGE(TAG, "Magic byte & CRC correct but incorrect image digest.");
+        return ESP_FAIL;
+    } else {
+        ESP_LOGD(TAG, "valid signature block(%d) found", block_num);
         return ESP_OK;
     }
 
-    ESP_LOGI(TAG, "Verifying bootloader signature...\n");
-    int r = ets_secure_boot_verify_bootloader(hash, false);
-    if (r != ESP_OK) {
-        ESP_LOGE(TAG, "Failed to verify bootloader signature");
-        return r;
+    return ESP_FAIL;
+}
+
+/* Structure to hold public key digests calculated from the signature blocks of a single image.
+
+   Each image can have one or more signature blocks (up to SECURE_BOOT_NUM_BLOCKS). Each signature block
+   includes a public key.
+
+   Different to the ROM ets_secure_boot_key_digests_t structure which holds pointers to eFuse data with digests,
+   in this data structure the digest data is included.
+*/
+typedef struct {
+    uint8_t key_digests[SECURE_BOOT_NUM_BLOCKS][DIGEST_LEN];
+    unsigned num_digests; /* Number of valid digests, starting at index 0 */
+} image_sig_public_key_digests_t;
+
+/* Generates the public key digests of the valid public keys in an image's
+   signature block, verifies each signature, and stores the key digests in the
+   public_key_digests structure.
+
+   @param flash_offset Image offset in flash
+   @param flash_size Image size in flash (not including signature block)
+   @param[out] public_key_digests Pointer to structure to hold the key digests for valid sig blocks
+
+
+   Note that this function doesn't read any eFuses, so it doesn't know if the
+   keys are ultimately trusted by the hardware or not
+
+   @return - ESP_OK if no signatures failed to verify, or if no valid signature blocks are found at all.
+           - ESP_FAIL if there's a valid signature block that doesn't verify using the included public key (unexpected!)
+*/
+static esp_err_t s_calculate_image_public_key_digests(uint32_t flash_offset, uint32_t flash_size, image_sig_public_key_digests_t *public_key_digests)
+{
+    esp_err_t ret;
+    uint8_t image_digest[DIGEST_LEN] = {0};
+    uint8_t __attribute__((aligned(4))) key_digest[DIGEST_LEN] = {0};
+    size_t sig_block_addr = flash_offset + ALIGN_UP(flash_size, FLASH_SECTOR_SIZE);
+
+    ESP_LOGD(TAG, "calculating public key digests for sig blocks of image offset 0x%x (sig block offset 0x%x)", flash_offset, sig_block_addr);
+
+    bzero(public_key_digests, sizeof(image_sig_public_key_digests_t));
+
+    ret = bootloader_sha256_flash_contents(flash_offset, sig_block_addr - flash_offset, image_digest);
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "error generating image digest, %d", ret);
+        return ret;
     }
 
-    esp_efuse_batch_write_begin(); /* Batch all efuse writes at the end of this function */
+    ESP_LOGD(TAG, "reading signatures");
+    const ets_secure_boot_signature_t *signatures = bootloader_mmap(sig_block_addr, sizeof(ets_secure_boot_signature_t));
+    if (signatures == NULL) {
+        ESP_LOGE(TAG, "bootloader_mmap(0x%x, 0x%x) failed", sig_block_addr, sizeof(ets_secure_boot_signature_t));
+        return ESP_FAIL;
+    }
+
+    for (int i = 0; i < SECURE_BOOT_NUM_BLOCKS; i++) {
+        const ets_secure_boot_sig_block_t *block = &signatures->block[i];
+
+        ret = validate_signature_block(block, i, image_digest);
+        if (ret != ESP_OK) {
+            ret = ESP_OK;  // past the last valid signature block
+            break;
+        }
+
+        /* Generating the SHA of the public key components in the signature block */
+        bootloader_sha256_handle_t sig_block_sha;
+        sig_block_sha = bootloader_sha256_start();
+        bootloader_sha256_data(sig_block_sha, &block->key, sizeof(block->key));
+        bootloader_sha256_finish(sig_block_sha, key_digest);
+
+        // Check we can verify the image using this signature and this key
+        uint8_t temp_verified_digest[DIGEST_LEN];
+        bool verified = ets_rsa_pss_verify(&block->key, block->signature, image_digest, temp_verified_digest);
+
+        if (!verified) {
+            /* We don't expect this: the signature blocks before we enable secure boot should all be verifiable or invalid,
+               so this is a fatal error
+            */
+            ret = ESP_FAIL;
+            ESP_LOGE(TAG, "Secure boot key (%d) verification failed.", i);
+            break;
+        }
+        ESP_LOGD(TAG, "Signature block (%d) is verified", i);
+        /* Copy the key digest to the buffer provided by the caller */
+        memcpy((void *)public_key_digests->key_digests[i], key_digest, DIGEST_LEN);
+        public_key_digests->num_digests++;
+    }
+
+    if (ret == ESP_OK && public_key_digests->num_digests > 0) {
+        ESP_LOGI(TAG, "Digests successfully calculated, %d valid signatures (image offset 0x%x)",
+                 public_key_digests->num_digests, flash_offset);
+    }
+
+    bootloader_munmap(signatures);
+    return ret;
+}
+
+esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *image_data)
+{
+    ESP_LOGI(TAG, "enabling secure boot v2 - ESP32-S2...");
+
+    if (esp_secure_boot_enabled()) {
+        ESP_LOGI(TAG, "secure boot v2 is already enabled, continuing..");
+        return ESP_OK;
+    }
+
+    esp_err_t ret;
+    /* Verify the bootloader */
+    esp_image_metadata_t bootloader_data = { 0 };
+    ret = esp_image_verify_bootloader_data(&bootloader_data);
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "bootloader image appears invalid! error %d", ret);
+        return ret;
+    }
+
+    /* Check if secure boot digests are present */
+    bool has_secure_boot_digest = ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0, NULL);
+    has_secure_boot_digest |= ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1, NULL);
+    has_secure_boot_digest |= ets_efuse_find_purpose(ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2, NULL);
+    ESP_LOGI(TAG, "Secure boot digests %s", has_secure_boot_digest ? "already present":"absent, generating..");
+
+    ets_efuse_clear_program_registers();
+    if (!has_secure_boot_digest) {
+        image_sig_public_key_digests_t boot_key_digests = {0};
+        image_sig_public_key_digests_t app_key_digests = {0};
+
+        /* Generate the bootloader public key digests */
+        ret = s_calculate_image_public_key_digests(bootloader_data.start_addr, bootloader_data.image_len - SIG_BLOCK_PADDING, &boot_key_digests);
+        if (ret != ESP_OK) {
+            ESP_LOGE(TAG, "Bootloader signature block is invalid");
+            return ret;
+        }
+
+        if (boot_key_digests.num_digests == 0) {
+            ESP_LOGE(TAG, "No valid bootloader signature blocks found.");
+            return ESP_FAIL;
+        }
+        ESP_LOGI(TAG, "%d signature block(s) found appended to the bootloader.", boot_key_digests.num_digests);
+
+        int unused_key_slots = ets_efuse_count_unused_key_blocks();
+        if (boot_key_digests.num_digests > unused_key_slots) {
+            ESP_LOGE(TAG, "Bootloader signatures(%d) more than available key slots(%d).", boot_key_digests.num_digests, unused_key_slots);
+            return ESP_FAIL;
+        }
+
+        for (int i = 0; i < boot_key_digests.num_digests; i++) {
+            ets_efuse_block_t block;
+            const uint32_t secure_boot_key_purpose[SECURE_BOOT_NUM_BLOCKS] = { ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0,
+                                ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1, ETS_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2 };
+
+            block = ets_efuse_find_unused_key_block();
+            if (block == ETS_EFUSE_BLOCK_MAX) {
+                ESP_LOGE(TAG, "No more unused key blocks available.");
+                return ESP_FAIL;
+            }
+
+            int r = ets_efuse_write_key(block, secure_boot_key_purpose[i], boot_key_digests.key_digests[i], DIGEST_LEN);
+            if (r != 0) {
+                ESP_LOGE(TAG, "Failed to write efuse block %d with purpose %d. Can't continue.", block, secure_boot_key_purpose[i]);
+                return ESP_FAIL;
+            }
+
+            // Note: write key will write protect both the block and the purpose eFuse, always
+        }
+
+        /* Generate the application public key digests */
+        ret = s_calculate_image_public_key_digests(image_data->start_addr, image_data->image_len - SIG_BLOCK_PADDING, &app_key_digests);
+        if (ret != ESP_OK) {
+            ESP_LOGE(TAG, "App signature block is invalid.");
+            return ret;
+        }
+
+        if (app_key_digests.num_digests == 0) {
+            ESP_LOGE(TAG, "No valid applications signature blocks found.");
+            return ESP_FAIL;
+        }
+
+        ESP_LOGI(TAG, "%d signature block(s) found appended to the app.", app_key_digests.num_digests);
+        if (app_key_digests.num_digests > boot_key_digests.num_digests) {
+            ESP_LOGW(TAG, "App has %d signature blocks but bootloader only has %d. Some keys missing from bootloader?");
+        }
+
+        /* Confirm if at least one public key from the application matches a public key in the bootloader
+           (Also, ensure if that public revoke bit is not set for the matched key) */
+        bool match = false;
+        const uint32_t revoke_bits[SECURE_BOOT_NUM_BLOCKS] = { EFUSE_SECURE_BOOT_KEY_REVOKE0,
+                                EFUSE_SECURE_BOOT_KEY_REVOKE1, EFUSE_SECURE_BOOT_KEY_REVOKE2 };
+
+        for (int i = 0; i < boot_key_digests.num_digests; i++) {
+
+            if (REG_GET_BIT(EFUSE_RD_REPEAT_DATA1_REG, revoke_bits[i])) {
+                ESP_LOGI(TAG, "Key block(%d) has been revoked.", i);
+                continue; // skip if the key block is revoked
+            }
+
+            for (int j = 0; j < app_key_digests.num_digests; j++) {
+                if (!memcmp(boot_key_digests.key_digests[i], app_key_digests.key_digests[j], DIGEST_LEN)) {
+                    ESP_LOGI(TAG, "Application key(%d) matches with bootloader key(%d).", j, i);
+                    match = true;
+                }
+            }
+        }
+
+        if (match == false) {
+            ESP_LOGE(TAG, "No application key digest matches the bootloader key digest.");
+            return ESP_FAIL;
+        }
+
+        /* Revoke the empty signature blocks */
+        if (boot_key_digests.num_digests < SECURE_BOOT_NUM_BLOCKS) {
+            /* The revocation index can be 0, 1, 2. Bootloader count can be 1,2,3. */
+            for (uint8_t i = boot_key_digests.num_digests; i < SECURE_BOOT_NUM_BLOCKS; i++) {
+                ESP_LOGI(TAG, "Revoking empty key digest slot (%d)...", i);
+                ets_secure_boot_revoke_public_key_digest(i);
+            }
+        }
+    }
+
+    esp_err_t err = esp_efuse_batch_write_begin();
+    if (err != ESP_OK) {
+        ESP_LOGI(TAG, "Error batch programming security eFuses.");
+        return err;
+    }
+
+    __attribute__((unused)) static const uint8_t enable = 1;
 
-    esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_EN);
     esp_efuse_write_field_bit(ESP_EFUSE_DIS_BOOT_REMAP);
     esp_efuse_write_field_bit(ESP_EFUSE_DIS_LEGACY_SPI_BOOT);
 
-    // TODO: also disable JTAG here, etc
+#ifdef CONFIG_SECURE_ENABLE_SECURE_ROM_DL_MODE
+    ESP_LOGI(TAG, "Enabling Security download mode...");
+    esp_efuse_write_field_bit(ESP_EFUSE_ENABLE_SECURITY_DOWNLOAD);
+#else
+    ESP_LOGW(TAG, "Not enabling Security download mode - SECURITY COMPROMISED");
+#endif
 
-    esp_err_t err = esp_efuse_batch_write_commit();
+#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
+    ESP_LOGI(TAG, "Disable hardware & software JTAG...");
+    esp_efuse_write_field_bit(ESP_EFUSE_HARD_DIS_JTAG);
+    esp_efuse_write_field_bit(ESP_EFUSE_SOFT_DIS_JTAG);
+#else
+    ESP_LOGW(TAG, "Not disabling JTAG - SECURITY COMPROMISED");
+#endif
 
-    if (err == ESP_OK) {
-        assert(esp_rom_efuse_is_secure_boot_enabled());
-        ESP_LOGI(TAG, "Secure boot permanently enabled");
+#ifdef CONFIG_SECURE_BOOT_ENABLE_AGGRESSIVE_KEY_REVOKE
+    esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_AGGRESSIVE_REVOKE);
+#endif
+
+    esp_efuse_write_field_bit(ESP_EFUSE_SECURE_BOOT_EN);
+
+    err = esp_efuse_batch_write_commit();
+    if (err != ESP_OK) {
+        ESP_LOGI(TAG, "Error programming security eFuses.");
+        return err;
     }
 
+#ifdef CONFIG_SECURE_BOOT_ENABLE_AGGRESSIVE_KEY_REVOKE
+    assert(ets_efuse_secure_boot_aggressive_revoke_enabled());
+#endif
+
+    assert(esp_rom_efuse_is_secure_boot_enabled());
+    ESP_LOGI(TAG, "Secure boot permanently enabled");
+
     return ESP_OK;
 }

components/bootloader_support/src/esp32s2/secure_boot_signatures.c

@@ -13,29 +13,32 @@
 // limitations under the License.
 #include "sdkconfig.h"
 
+#include <string.h>
+#include "esp_fault.h"
 #include "bootloader_flash.h"
 #include "bootloader_sha.h"
+#include "bootloader_utility.h"
 #include "esp_log.h"
 #include "esp_image_format.h"
+#include "esp_secure_boot.h"
 #include "esp32s2/rom/secure_boot.h"
 
 static const char* TAG = "secure_boot";
 
 #define DIGEST_LEN 32
+#define ALIGN_UP(num, align) (((num) + ((align) - 1)) & ~((align) - 1))
 
 esp_err_t esp_secure_boot_verify_signature(uint32_t src_addr, uint32_t length)
 {
-    ets_secure_boot_key_digests_t trusted_keys = { 0 };
     uint8_t digest[DIGEST_LEN];
     uint8_t verified_digest[DIGEST_LEN] = { 0 }; /* Note: this function doesn't do any anti-FI checks on this buffer */
     const uint8_t *data;
 
     ESP_LOGD(TAG, "verifying signature src_addr 0x%x length 0x%x", src_addr, length);
 
-    if ((src_addr + length) % 4096 != 0) {
-        ESP_LOGE(TAG, "addr 0x%x length 0x%x doesn't end on a sector boundary", src_addr, length);
-        return ESP_ERR_INVALID_ARG;
-    }
+    /* Padding to round off the input to the nearest 4k boundary */
+    int padded_length = ALIGN_UP(length, FLASH_SECTOR_SIZE);
+    ESP_LOGD(TAG, "verifying src_addr 0x%x length", src_addr, padded_length);
 
     data = bootloader_mmap(src_addr, length + sizeof(struct ets_secure_boot_sig_block));
     if (data == NULL) {
@@ -43,23 +46,16 @@ esp_err_t esp_secure_boot_verify_signature(uint32_t src_addr, uint32_t length)
         return ESP_FAIL;
     }
 
-    // Calculate digest of main image
-#ifdef BOOTLOADER_BUILD
-    bootloader_sha256_handle_t handle = bootloader_sha256_start();
-    bootloader_sha256_data(handle, data, length);
-    bootloader_sha256_finish(handle, digest);
-#else
-    /* Use thread-safe esp-idf SHA function */
-    esp_sha(SHA2_256, data, length, digest);
-#endif
-
-    int r = ets_secure_boot_read_key_digests(&trusted_keys);
-
-    if (r == ETS_OK) {
-        const ets_secure_boot_signature_t *sig = (const ets_secure_boot_signature_t *)(data + length);
-        // TODO: calling this function in IDF app context is unsafe
-        r = ets_secure_boot_verify_signature(sig, digest, &trusted_keys, verified_digest);
+    /* Calculate digest of main image */
+    esp_err_t err = bootloader_sha256_flash_contents(src_addr, padded_length, digest);
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "Digest calculation failed 0x%x, 0x%x", src_addr, padded_length);
+        bootloader_munmap(data);
+        return err;
     }
+
+    const ets_secure_boot_signature_t *sig = (const ets_secure_boot_signature_t *)(data + length);
+    int r = esp_secure_boot_verify_rsa_signature_block(sig, digest, verified_digest);
     bootloader_munmap(data);
 
     return (r == ETS_OK) ? ESP_OK : ESP_FAIL;
@@ -68,15 +64,30 @@ esp_err_t esp_secure_boot_verify_signature(uint32_t src_addr, uint32_t length)
 esp_err_t esp_secure_boot_verify_rsa_signature_block(const ets_secure_boot_signature_t *sig_block, const uint8_t *image_digest, uint8_t *verified_digest)
 {
     ets_secure_boot_key_digests_t trusted_keys;
+    ets_secure_boot_key_digests_t trusted_key_copies[2];
+    ETS_STATUS r;
+    ets_secure_boot_status_t sb_result;
 
-    int r = ets_secure_boot_read_key_digests(&trusted_keys);
-    if (r != 0) {
-        ESP_LOGE(TAG, "No trusted key digests were found in efuse!");
-    } else {
-        ESP_LOGD(TAG, "Verifying with RSA-PSS...");
-        // TODO: calling this function in IDF app context is unsafe
-        r = ets_secure_boot_verify_signature(sig_block, image_digest, &trusted_keys, verified_digest);
+    memset(&trusted_keys, 0, sizeof(ets_secure_boot_key_digests_t));
+    memset(trusted_key_copies, 0, 2 * sizeof(ets_secure_boot_key_digests_t));
+
+    if (!esp_secure_boot_enabled()) {
+        return ESP_OK;
     }
 
-    return (r == 0) ? ESP_OK : ESP_ERR_IMAGE_INVALID;
+    r = ets_secure_boot_read_key_digests(&trusted_keys);
+    if (r != ETS_OK) {
+        ESP_LOGI(TAG, "Could not read secure boot digests!");
+        return ESP_FAIL;
+    }
+
+    // Create the copies for FI checks (assuming result is ETS_OK, if it's not then it'll fail the fault check anyhow)
+    ets_secure_boot_read_key_digests(&trusted_key_copies[0]);
+    ets_secure_boot_read_key_digests(&trusted_key_copies[1]);
+    ESP_FAULT_ASSERT(memcmp(&trusted_keys, &trusted_key_copies[0], sizeof(ets_secure_boot_key_digests_t)) == 0);
+    ESP_FAULT_ASSERT(memcmp(&trusted_keys, &trusted_key_copies[1], sizeof(ets_secure_boot_key_digests_t)) == 0);
+
+    ESP_LOGI(TAG, "Verifying with RSA-PSS boot...");
+    sb_result = ets_secure_boot_verify_signature(sig_block, image_digest, &trusted_keys, verified_digest);
+    return (sb_result == SB_SUCCESS) ? ESP_OK : ESP_FAIL;
 }