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fix(esp32h2): program use_hardware_k efuse bit for ECDSA key purpose

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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.
This commit is contained in:
Mahavir Jain 2023-11-03 15:48:00 +05:30
parent 35013d90a3
commit d3b4acf7a0
4 changed files with 22 additions and 1 deletions
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8
components/efuse/src/efuse_controller/keys/with_key_purposes/esp_efuse_api_key.c
View File

@ -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
*/
@ -315,6 +315,12 @@ 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();

10
components/esp_system/startup.c
View File

@ -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"
@ -348,6 +349,15 @@ 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");

4
components/soc/esp32h2/include/soc/Kconfig.soc_caps.in
View File

@ -1079,6 +1079,10 @@ 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

1
components/soc/esp32h2/include/soc/soc_caps.h
View File

@ -441,6 +441,7 @@
#define SOC_EFUSE_SOFT_DIS_JTAG 1
#define SOC_EFUSE_DIS_ICACHE 1
#define SOC_EFUSE_BLOCK9_KEY_PURPOSE_QUIRK 1 // XTS-AES 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