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secure boot v2: esp32: Prevent read disabling additional efuses

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Also reduce the number of eFuse write cycles during first boot when
Secure Boot and/or Flash Encryption are enabled.
This commit is contained in:
Angus Gratton
2020-03-20 13:55:15 +11:00
committed by Angus Gratton
parent 82e2b4a0d4
commit 142f69448f
4 changed files with 73 additions and 25 deletions
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31
components/bootloader_support/src/esp32/flash_encrypt.c
View File

@@ -73,6 +73,10 @@ esp_err_t esp_flash_encrypt_check_and_update(void)
static esp_err_t initialise_flash_encryption(void)
{
uint32_t new_wdata0 = 0;
uint32_t new_wdata5 = 0;
uint32_t new_wdata6 = 0;
uint32_t coding_scheme = REG_GET_FIELD(EFUSE_BLK0_RDATA6_REG, EFUSE_CODING_SCHEME);
if (coding_scheme != EFUSE_CODING_SCHEME_VAL_NONE && coding_scheme != EFUSE_CODING_SCHEME_VAL_34) {
ESP_LOGE(TAG, "Unknown/unsupported CODING_SCHEME value 0x%x", coding_scheme);
@@ -97,11 +101,10 @@ static esp_err_t initialise_flash_encryption(void)
&& REG_READ(EFUSE_BLK1_RDATA7_REG) == 0) {
ESP_LOGI(TAG, "Generating new flash encryption key...");
esp_efuse_write_random_key(EFUSE_BLK1_WDATA0_REG);
esp_efuse_burn_new_values();
// defer efuse programming step to the end
ESP_LOGI(TAG, "Read & write protecting new key...");
REG_WRITE(EFUSE_BLK0_WDATA0_REG, EFUSE_WR_DIS_BLK1 | EFUSE_RD_DIS_BLK1);
esp_efuse_burn_new_values();
new_wdata0 |= EFUSE_WR_DIS_BLK1 | EFUSE_RD_DIS_BLK1;
} else {
if(!(efuse_key_read_protected && efuse_key_write_protected)) {
@@ -122,34 +125,36 @@ static esp_err_t initialise_flash_encryption(void)
operation does nothing. Please note this is not recommended!
*/
ESP_LOGI(TAG, "Setting CRYPT_CONFIG efuse to 0xF");
REG_WRITE(EFUSE_BLK0_WDATA5_REG, EFUSE_FLASH_CRYPT_CONFIG_M);
esp_efuse_burn_new_values();
new_wdata5 |= EFUSE_FLASH_CRYPT_CONFIG_M;
uint32_t new_wdata6 = 0;
#ifndef CONFIG_SECURE_FLASH_UART_BOOTLOADER_ALLOW_ENC
ESP_LOGI(TAG, "Disable UART bootloader encryption...");
new_wdata6 |= EFUSE_DISABLE_DL_ENCRYPT;
#else
ESP_LOGW(TAG, "Not disabling UART bootloader encryption");
#endif
#ifndef CONFIG_SECURE_FLASH_UART_BOOTLOADER_ALLOW_DEC
ESP_LOGI(TAG, "Disable UART bootloader decryption...");
new_wdata6 |= EFUSE_DISABLE_DL_DECRYPT;
#else
ESP_LOGW(TAG, "Not disabling UART bootloader decryption - SECURITY COMPROMISED");
#endif
#ifndef CONFIG_SECURE_FLASH_UART_BOOTLOADER_ALLOW_CACHE
ESP_LOGI(TAG, "Disable UART bootloader MMU cache...");
new_wdata6 |= EFUSE_DISABLE_DL_CACHE;
#else
ESP_LOGW(TAG, "Not disabling UART bootloader MMU cache - SECURITY COMPROMISED");
#endif
#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
ESP_LOGI(TAG, "Disable JTAG...");
new_wdata6 |= EFUSE_RD_DISABLE_JTAG;
#else
ESP_LOGW(TAG, "Not disabling JTAG - SECURITY COMPROMISED");
#endif
#ifndef CONFIG_SECURE_BOOT_ALLOW_ROM_BASIC
ESP_LOGI(TAG, "Disable ROM BASIC interpreter fallback...");
new_wdata6 |= EFUSE_RD_CONSOLE_DEBUG_DISABLE;
@@ -157,10 +162,16 @@ static esp_err_t initialise_flash_encryption(void)
ESP_LOGW(TAG, "Not disabling ROM BASIC fallback - SECURITY COMPROMISED");
#endif
if (new_wdata6 != 0) {
REG_WRITE(EFUSE_BLK0_WDATA6_REG, new_wdata6);
esp_efuse_burn_new_values();
}
#if defined(CONFIG_SECURE_BOOT_V2_ENABLED) && !defined(CONFIG_SECURE_BOOT_V2_ALLOW_EFUSE_RD_DIS)
// This bit is set when enabling Secure Boot V2, but we can't enable it until this later point in the first boot
// otherwise the Flash Encryption key cannot be read protected
new_wdata0 |= EFUSE_WR_DIS_RD_DIS;
#endif
REG_WRITE(EFUSE_BLK0_WDATA0_REG, new_wdata0);
REG_WRITE(EFUSE_BLK0_WDATA5_REG, new_wdata5);
REG_WRITE(EFUSE_BLK0_WDATA6_REG, new_wdata6);
esp_efuse_burn_new_values();
return ESP_OK;
}

48
components/bootloader_support/src/esp32/secure_boot.c
View File

@@ -39,11 +39,6 @@
/* The following API implementations are used only when called
* from the bootloader code.
*/
/* Burn values written to the efuse write registers */
static inline void burn_efuses(void)
{
esp_efuse_burn_new_values();
}
#ifdef CONFIG_SECURE_BOOT_V1_ENABLED
static const char *TAG = "secure_boot_v1";
@@ -140,7 +135,7 @@ esp_err_t esp_secure_boot_generate_digest(void)
&& REG_READ(EFUSE_BLK2_RDATA7_REG) == 0) {
ESP_LOGI(TAG, "Generating new secure boot key...");
esp_efuse_write_random_key(EFUSE_BLK2_WDATA0_REG);
burn_efuses();
esp_efuse_burn_new_values();
} else {
ESP_LOGW(TAG, "Using pre-loaded secure boot key in EFUSE block 2");
}
@@ -163,6 +158,9 @@ esp_err_t esp_secure_boot_generate_digest(void)
esp_err_t esp_secure_boot_permanently_enable(void)
{
uint32_t new_wdata0 = 0;
uint32_t new_wdata6 = 0;
if (esp_secure_boot_enabled()) {
ESP_LOGI(TAG, "bootloader secure boot is already enabled, continuing..");
return ESP_OK;
@@ -174,8 +172,7 @@ esp_err_t esp_secure_boot_permanently_enable(void)
if (efuse_key_read_protected == false
&& efuse_key_write_protected == false) {
ESP_LOGI(TAG, "Read & write protecting new key...");
REG_WRITE(EFUSE_BLK0_WDATA0_REG, EFUSE_WR_DIS_BLK2 | EFUSE_RD_DIS_BLK2);
burn_efuses();
new_wdata0 = EFUSE_WR_DIS_BLK2 | EFUSE_RD_DIS_BLK2;
efuse_key_read_protected = true;
efuse_key_write_protected = true;
}
@@ -192,7 +189,7 @@ esp_err_t esp_secure_boot_permanently_enable(void)
ESP_LOGI(TAG, "blowing secure boot efuse...");
ESP_LOGD(TAG, "before updating, EFUSE_BLK0_RDATA6 %x", REG_READ(EFUSE_BLK0_RDATA6_REG));
uint32_t new_wdata6 = EFUSE_RD_ABS_DONE_0;
new_wdata6 |= EFUSE_RD_ABS_DONE_0;
#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
ESP_LOGI(TAG, "Disable JTAG...");
@@ -208,8 +205,9 @@ esp_err_t esp_secure_boot_permanently_enable(void)
ESP_LOGW(TAG, "Not disabling ROM BASIC fallback - SECURITY COMPROMISED");
#endif
REG_WRITE(EFUSE_BLK0_WDATA0_REG, new_wdata0);
REG_WRITE(EFUSE_BLK0_WDATA6_REG, new_wdata6);
burn_efuses();
esp_efuse_burn_new_values();
uint32_t after = REG_READ(EFUSE_BLK0_RDATA6_REG);
ESP_LOGD(TAG, "after updating, EFUSE_BLK0_RDATA6 %x", after);
if (after & EFUSE_RD_ABS_DONE_0) {
@@ -293,6 +291,9 @@ done:
esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *image_data)
{
uint32_t new_wdata0 = 0;
uint32_t new_wdata6 = 0;
ESP_LOGI(TAG, "enabling secure boot v2...");
esp_err_t ret;
if (esp_secure_boot_enabled()) {
@@ -306,7 +307,7 @@ esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *imag
return ESP_ERR_NOT_SUPPORTED;
}
/* Verify the bootloader */
/* Verify the bootloader */
esp_image_metadata_t bootloader_data = { 0 };
ret = esp_image_verify_bootloader_data(&bootloader_data);
if (ret != ESP_OK) {
@@ -343,7 +344,7 @@ esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *imag
}
ESP_LOGI(TAG, "Write protecting public key digest...");
REG_WRITE(EFUSE_BLK0_WDATA0_REG, EFUSE_WR_DIS_BLK2);
new_wdata0 |= EFUSE_WR_DIS_BLK2;
efuse_key_write_protected = true;
efuse_key_read_protected = false;
} else {
@@ -375,7 +376,7 @@ esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *imag
ESP_LOGI(TAG, "blowing secure boot efuse...");
ESP_LOGD(TAG, "before updating, EFUSE_BLK0_RDATA6 %x", REG_READ(EFUSE_BLK0_RDATA6_REG));
uint32_t new_wdata6 = EFUSE_RD_ABS_DONE_1;
new_wdata6 |= EFUSE_RD_ABS_DONE_1;
#ifndef CONFIG_SECURE_BOOT_ALLOW_JTAG
ESP_LOGI(TAG, "Disable JTAG...");
@@ -391,10 +392,27 @@ esp_err_t esp_secure_boot_v2_permanently_enable(const esp_image_metadata_t *imag
ESP_LOGW(TAG, "Not disabling ROM BASIC fallback - SECURITY COMPROMISED");
#endif
#ifndef CONFIG_SECURE_BOOT_V2_ALLOW_EFUSE_RD_DIS
bool rd_dis_now = true;
#ifdef CONFIG_SECURE_FLASH_ENC_ENABLED
/* If flash encryption is not enabled yet then don't read-disable efuses yet, do it later in the boot
when Flash Encryption is being enabled */
rd_dis_now = esp_flash_encryption_enabled();
#endif
if (rd_dis_now) {
ESP_LOGI(TAG, "Prevent read disabling of additional efuses...");
new_wdata0 |= EFUSE_WR_DIS_RD_DIS;
}
#else
ESP_LOGW(TAG, "Allowing read disabling of additional efuses - SECURITY COMPROMISED");
#endif
REG_WRITE(EFUSE_BLK0_WDATA0_REG, new_wdata0);
REG_WRITE(EFUSE_BLK0_WDATA6_REG, new_wdata6);
burn_efuses();
esp_efuse_burn_new_values();
uint32_t after = REG_READ(EFUSE_BLK0_RDATA6_REG);
ESP_LOGD(TAG, "after updating, EFUSE_BLK0_RDATA6 %x", after);
ESP_LOGD(TAG, "after updating, EFUSE_BLK0_RDATA0 0x%08x EFUSE_BLK0_RDATA6 0x%08x",
REG_READ(EFUSE_BLK0_RDATA0_REG), after);
if (after & EFUSE_RD_ABS_DONE_1) {
ESP_LOGI(TAG, "secure boot v2 is now enabled.");
return ESP_OK;