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bootloader/esp32c3: Adds secure boot (not yet supported)

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This commit is contained in:
KonstantinKondrashov
2020-12-28 21:53:02 +08:00
parent f45c881f82
commit 98f726fa4b
14 changed files with 446 additions and 127 deletions
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303
components/bootloader_support/src/esp32c3/secure_boot.c
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@@ -11,32 +11,303 @@
// 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_priv.h"
#include "bootloader_sha.h"
#include "bootloader_utility.h"
#include "esp_rom_crc.h"
#include "esp_efuse.h"
#include "esp_efuse_table.h"
#include "esp32c3/rom/efuse.h"
#include "esp32c3/rom/secure_boot.h"
#include "esp_rom_efuse.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;
}
ets_efuse_clear_program_registers();
REG_SET_BIT(EFUSE_PGM_DATA3_REG, EFUSE_SECURE_BOOT_EN);
ets_efuse_program(ETS_EFUSE_BLOCK0);
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;
}
static esp_err_t check_and_generate_secure_boot_keys(const esp_image_metadata_t *image_data)
{
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 = esp_efuse_find_purpose(ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0, NULL);
has_secure_boot_digest |= esp_efuse_find_purpose(ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1, NULL);
has_secure_boot_digest |= esp_efuse_find_purpose(ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2, NULL);
ESP_LOGI(TAG, "Secure boot digests %s", has_secure_boot_digest ? "already present":"absent, generating..");
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);
esp_efuse_purpose_t secure_boot_key_purpose[SECURE_BOOT_NUM_BLOCKS] = {
ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0,
ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1,
ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2,
};
ret = esp_efuse_write_keys(secure_boot_key_purpose, boot_key_digests.key_digests, boot_key_digests.num_digests);
if (ret) {
if (ret == ESP_ERR_NOT_ENOUGH_UNUSED_KEY_BLOCKS) {
ESP_LOGE(TAG, "Bootloader signatures(%d) more than available key slots.", boot_key_digests.num_digests);
} else {
ESP_LOGE(TAG, "Failed to write efuse block with purpose (err=0x%x). Can't continue.", ret);
}
return ret;
}
/* 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;
for (int i = 0; i < boot_key_digests.num_digests; i++) {
if (esp_efuse_get_digest_revoke(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);
esp_efuse_set_digest_revoke(i);
}
}
}
return ESP_OK;
}
esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *image_data)
{
ESP_LOGI(TAG, "enabling secure boot v2...");
if (esp_secure_boot_enabled()) {
ESP_LOGI(TAG, "secure boot v2 is already enabled, continuing..");
return ESP_OK;
}
esp_efuse_batch_write_begin(); /* Batch all efuse writes at the end of this function */
esp_err_t key_state = check_and_generate_secure_boot_keys(image_data);
if (key_state != ESP_OK) {
esp_efuse_batch_write_cancel();
return key_state;
}
esp_efuse_write_field_bit(ESP_EFUSE_DIS_LEGACY_SPI_BOOT);
#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
#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
ESP_LOGI(TAG, "Disable hardware & software JTAG...");
esp_efuse_write_field_bit(ESP_EFUSE_DIS_PAD_JTAG);
esp_efuse_write_field_bit(ESP_EFUSE_DIS_USB_JTAG);
esp_efuse_write_field_bit(ESP_EFUSE_SOFT_DIS_JTAG);
#else
ESP_LOGW(TAG, "Not disabling JTAG - SECURITY COMPROMISED");
#endif
#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);
esp_err_t err = esp_efuse_batch_write_commit();
if (err != ESP_OK) {
ESP_LOGE(TAG, "Error programming security eFuses (err=0x%x).", err);
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");

81
components/bootloader_support/src/esp32c3/secure_boot_signatures.c
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@@ -14,80 +14,81 @@
#include "sdkconfig.h"
#include "bootloader_flash.h"
#include <string.h>
#include "esp_fault.h"
#include "bootloader_flash_priv.h"
#include "bootloader_sha.h"
#include "bootloader_utility.h"
#include "esp_log.h"
#include "esp_image_format.h"
#include "esp_secure_boot.h"
#include "esp32c3/rom/secure_boot.h"
static const char *TAG = "secure_boot";
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) {
ESP_LOGE(TAG, "bootloader_mmap(0x%x, 0x%x) failed", src_addr, length + sizeof(ets_secure_boot_signature_t));
ESP_LOGE(TAG, "bootloader_mmap(0x%x, 0x%x) failed", src_addr, length+sizeof(ets_secure_boot_signature_t));
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);
/* 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;
}
esp_err_t esp_secure_boot_verify_signature_block(uint32_t sig_block_flash_offs, const uint8_t *image_digest)
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;
assert(sig_block_flash_offs % 4096 == 0); // TODO: enforce this in a better way
memset(&trusted_keys, 0, sizeof(ets_secure_boot_key_digests_t));
memset(trusted_key_copies, 0, 2 * sizeof(ets_secure_boot_key_digests_t));
const ets_secure_boot_signature_t *sig = bootloader_mmap(sig_block_flash_offs, sizeof(ets_secure_boot_signature_t));
if (!esp_secure_boot_enabled()) {
return ESP_OK;
}
if (sig == NULL) {
ESP_LOGE(TAG, "Failed to mmap data at offset 0x%x", sig_block_flash_offs);
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;
}
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, image_digest, &trusted_keys);
}
// 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);
bootloader_munmap(sig);
return (r == 0) ? ESP_OK : ESP_ERR_IMAGE_INVALID;
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;
}