From 0ccfa4b0c2fd83e66b24c9fabb9562f1581be470 Mon Sep 17 00:00:00 2001 From: Mahavir Jain Date: Fri, 3 Nov 2023 15:48:00 +0530 Subject: [PATCH] fix(esp32h2): program use_hardware_k efuse bit for ECDSA key purpose In ESP32-H2, the ECDSA peripheral by default uses the TRNG (hardware) generated k value but it can be overridden to software supplied k. This can happen through by overriding the `ECDSA_SOFTWARE_SET_K` bit in the configuration register. Even though the HAL API is not exposed for this but still it could be achieved by direct register programming. And for this scenario, if sufficiently random k is not supplied by the software then it could posses a security risk. In this change, we are unconditionally programming the efuse `ESP_EFUSE_ECDSA_FORCE_USE_HARDWARE_K` bit during startup security checks itself. Additionally, same is ensured in the `esp_efuse_write_key` API as well. This always enforces the hardware k mode in the ECDSA peripheral and ensures strongest possible security. --- .../keys/with_key_purposes/esp_efuse_api_key.c | 8 +++++++- components/esp_system/startup.c | 10 ++++++++++ components/soc/esp32h2/include/soc/Kconfig.soc_caps.in | 4 ++++ components/soc/esp32h2/include/soc/soc_caps.h | 1 + 4 files changed, 22 insertions(+), 1 deletion(-) diff --git a/components/efuse/src/efuse_controller/keys/with_key_purposes/esp_efuse_api_key.c b/components/efuse/src/efuse_controller/keys/with_key_purposes/esp_efuse_api_key.c index da1afb7a6c..f41b092c45 100644 --- a/components/efuse/src/efuse_controller/keys/with_key_purposes/esp_efuse_api_key.c +++ b/components/efuse/src/efuse_controller/keys/with_key_purposes/esp_efuse_api_key.c @@ -1,5 +1,5 @@ /* - * SPDX-FileCopyrightText: 2017-2022 Espressif Systems (Shanghai) CO LTD + * SPDX-FileCopyrightText: 2017-2023 Espressif Systems (Shanghai) CO LTD * * SPDX-License-Identifier: Apache-2.0 */ @@ -312,6 +312,12 @@ esp_err_t esp_efuse_write_key(esp_efuse_block_t block, esp_efuse_purpose_t purpo purpose == ESP_EFUSE_KEY_PURPOSE_HMAC_UP) { ESP_EFUSE_CHK(esp_efuse_set_key_dis_read(block)); } +#if SOC_EFUSE_ECDSA_USE_HARDWARE_K + if (purpose == ESP_EFUSE_KEY_PURPOSE_ECDSA_KEY) { + // Permanently enable the hardware TRNG supplied k mode (most secure mode) + ESP_EFUSE_CHK(esp_efuse_write_field_bit(ESP_EFUSE_ECDSA_FORCE_USE_HARDWARE_K)); + } +#endif ESP_EFUSE_CHK(esp_efuse_set_key_purpose(block, purpose)); ESP_EFUSE_CHK(esp_efuse_set_keypurpose_dis_write(block)); return esp_efuse_batch_write_commit(); diff --git a/components/esp_system/startup.c b/components/esp_system/startup.c index 7c7207dad3..f78433f992 100644 --- a/components/esp_system/startup.c +++ b/components/esp_system/startup.c @@ -27,6 +27,7 @@ #include "esp_newlib.h" #include "esp_timer.h" #include "esp_efuse.h" +#include "esp_efuse_table.h" #include "esp_flash_encrypt.h" #include "esp_secure_boot.h" #include "esp_xt_wdt.h" @@ -364,6 +365,15 @@ static void do_core_init(void) esp_secure_boot_init_checks(); #endif +#if SOC_EFUSE_ECDSA_USE_HARDWARE_K + if (esp_efuse_find_purpose(ESP_EFUSE_KEY_PURPOSE_ECDSA_KEY, NULL)) { + // ECDSA key purpose block is present and hence permanently enable + // the hardware TRNG supplied k mode (most secure mode) + err = esp_efuse_write_field_bit(ESP_EFUSE_ECDSA_FORCE_USE_HARDWARE_K); + assert(err == ESP_OK && "Failed to enable ECDSA hardware k mode"); + } +#endif + #if CONFIG_SECURE_DISABLE_ROM_DL_MODE err = esp_efuse_disable_rom_download_mode(); assert(err == ESP_OK && "Failed to disable ROM download mode"); diff --git a/components/soc/esp32h2/include/soc/Kconfig.soc_caps.in b/components/soc/esp32h2/include/soc/Kconfig.soc_caps.in index fef4f8e043..a8c58f2a84 100644 --- a/components/soc/esp32h2/include/soc/Kconfig.soc_caps.in +++ b/components/soc/esp32h2/include/soc/Kconfig.soc_caps.in @@ -1011,6 +1011,10 @@ config SOC_EFUSE_BLOCK9_KEY_PURPOSE_QUIRK bool default y +config SOC_EFUSE_ECDSA_USE_HARDWARE_K + bool + default y + config SOC_SECURE_BOOT_V2_RSA bool default y diff --git a/components/soc/esp32h2/include/soc/soc_caps.h b/components/soc/esp32h2/include/soc/soc_caps.h index 082de55e50..5030b94456 100644 --- a/components/soc/esp32h2/include/soc/soc_caps.h +++ b/components/soc/esp32h2/include/soc/soc_caps.h @@ -418,6 +418,7 @@ #define SOC_EFUSE_SOFT_DIS_JTAG 1 #define SOC_EFUSE_DIS_ICACHE 1 #define SOC_EFUSE_BLOCK9_KEY_PURPOSE_QUIRK 1 // AES-XTS and ECDSA key purposes not supported for this block +#define SOC_EFUSE_ECDSA_USE_HARDWARE_K 1 // Force use hardware TRNG supplied K for ECDSA /*-------------------------- Secure Boot CAPS----------------------------*/ #define SOC_SECURE_BOOT_V2_RSA 1