From 5eb5f8d8f204135d4af14adef847061ce0d2d9a1 Mon Sep 17 00:00:00 2001
From: cepetr <petr@cerninovi.cz>
Date: Tue, 1 Oct 2024 10:58:31 +0200
Subject: [PATCH] refactor(core): improve random_delays api
[no changelog]
---
core/embed/bootloader/main.c | 2 +-
core/embed/bootloader_ci/main.c | 2 +-
core/embed/kernel/main.c | 4 +-
core/embed/trezorhal/random_delays.h | 41 +++++++++++++++++---
core/embed/trezorhal/stm32f4/random_delays.c | 28 +++----------
core/embed/trezorhal/stm32f4/usb/usb.c | 4 +-
core/embed/trezorhal/unix/random_delays.c | 4 +-
core/embed/trezorhal/unix/random_delays.h | 26 -------------
8 files changed, 49 insertions(+), 62 deletions(-)
delete mode 100644 core/embed/trezorhal/unix/random_delays.h
diff --git a/core/embed/bootloader/main.c b/core/embed/bootloader/main.c
index 043e76f47b..d076a54ba2 100644
--- a/core/embed/bootloader/main.c
+++ b/core/embed/bootloader/main.c
@@ -359,7 +359,7 @@ int bootloader_main(void) {
system_init(&rsod_panic_handler);
- rdi_init();
+ random_delays_init();
#if defined TREZOR_MODEL_T
set_core_clock(CLOCK_180_MHZ);
diff --git a/core/embed/bootloader_ci/main.c b/core/embed/bootloader_ci/main.c
index 2d2339bbc6..d44584f663 100644
--- a/core/embed/bootloader_ci/main.c
+++ b/core/embed/bootloader_ci/main.c
@@ -181,7 +181,7 @@ static secbool check_vendor_header_lock(const vendor_header *const vhdr) {
int main(void) {
system_init(&rsod_panic_handler);
- rdi_init();
+ random_delays_init();
#ifdef USE_TOUCH
touch_init();
#endif
diff --git a/core/embed/kernel/main.c b/core/embed/kernel/main.c
index 376f3d2dca..d960dda178 100644
--- a/core/embed/kernel/main.c
+++ b/core/embed/kernel/main.c
@@ -77,10 +77,10 @@ void drivers_init() {
tamper_init();
#endif
- rdi_init();
+ random_delays_init();
#ifdef RDI
- rdi_start();
+ random_delays_start_rdi();
#endif
#ifdef SYSTEM_VIEW
diff --git a/core/embed/trezorhal/random_delays.h b/core/embed/trezorhal/random_delays.h
index ecdd6d44bd..46d6e0e482 100644
--- a/core/embed/trezorhal/random_delays.h
+++ b/core/embed/trezorhal/random_delays.h
@@ -22,17 +22,48 @@
#include <stdint.h>
+/*
+Random delay interrupts (RDI) is a contermeasure against side channel attacks.
+It consists of an interrupt handler that is supposed to be called every
+millisecond or so. The handler waits for a random number of cpu ticks that is a
+sample of so called floating mean distribution. That means that the number is
+the sum of two numbers generated uniformly at random in the interval [0, 255].
+The first number is generated freshly for each call of the handler, the other
+number is supposed to be refreshed when the device performs an operation that
+leaks the current state of the execution flow, such as sending or receiving an
+usb packet.
+
+See Differential Power Analysis in the Presence of Hardware Countermeasures by
+Christophe Clavier, Jean-Sebastien Coron, Nora Dabbous and Efficient Use of
+Random Delays in Embedded Software by Michael Tunstall, Olivier Benoit:
+https://link.springer.com/content/pdf/10.1007%2F3-540-44499-8_20.pdf
+https://link.springer.com/content/pdf/10.1007%2F978-3-540-72354-7_3.pdf
+*/
+
#ifdef KERNEL_MODE
-void rdi_init(void);
+// Initializes the random number generator for `wait_random()` and the RDI
+//
+// RDI is stopped by default and can be started by calling
+// `random_delays_start_rdi()`.
+void random_delays_init(void);
-void rdi_start(void);
-void rdi_stop(void);
+// Starts the RDI, introducing small random delays every millisecond via
+// systimer callback.
+void random_delays_start_rdi(void);
-#endif
+// Stops the RDI
+void random_delays_stop_rdi(void);
-void rdi_refresh_session_delay(void);
+// Refreshes the second random number in the floating mean distribution.
+// (see the module description above)
+void random_delays_refresh_rdi(void);
+// Waits for a random number (0-255) of CPU ticks.
+//
+// This function is independent of the RDI and can be used in any context.
void wait_random(void);
+#endif // KERNEL_MODE
+
#endif // TREZORHAL_RANDOM_DELAYS_H
diff --git a/core/embed/trezorhal/stm32f4/random_delays.c b/core/embed/trezorhal/stm32f4/random_delays.c
index 9dbbe0a9d5..3861c1f8d8 100644
--- a/core/embed/trezorhal/stm32f4/random_delays.c
+++ b/core/embed/trezorhal/stm32f4/random_delays.c
@@ -17,24 +17,6 @@
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
-/*
-Random delay interrupts (RDI) is a contermeasure against side channel attacks.
-It consists of an interrupt handler that is supposed to be called every
-millisecond or so. The handler waits for a random number of cpu ticks that is a
-sample of so called floating mean distribution. That means that the number is
-the sum of two numbers generated uniformly at random in the interval [0, 255].
-The first number is generated freshly for each call of the handler, the other
-number is supposed to be refreshed when the device performs an operation that
-leaks the current state of the execution flow, such as sending or receiving an
-usb packet.
-
-See Differential Power Analysis in the Presence of Hardware Countermeasures by
-Christophe Clavier, Jean-Sebastien Coron, Nora Dabbous and Efficient Use of
-Random Delays in Embedded Software by Michael Tunstall, Olivier Benoit:
-https://link.springer.com/content/pdf/10.1007%2F3-540-44499-8_20.pdf
-https://link.springer.com/content/pdf/10.1007%2F978-3-540-72354-7_3.pdf
-*/
-
#include "random_delays.h"
#include <stdatomic.h>
@@ -157,15 +139,15 @@ static void wait(uint32_t delay) {
// forward declaration
static void rdi_handler(void *context);
-void rdi_init() {
+void random_delays_init() {
drbg_init();
systimer_t *timer = systimer_create(rdi_handler, NULL);
- ensure(sectrue * (timer != NULL), "rdi_init failed");
+ ensure(sectrue * (timer != NULL), "random_delays_init failed");
systimer_set_periodic(timer, 1);
}
-void rdi_start(void) {
+void random_delays_start_rdi(void) {
ensure(drbg_initialized, NULL);
if (rdi_disabled == sectrue) { // if rdi disabled
@@ -174,14 +156,14 @@ void rdi_start(void) {
}
}
-void rdi_stop(void) {
+void random_delays_stop_rdi(void) {
if (rdi_disabled == secfalse) { // if rdi enabled
rdi_disabled = sectrue;
session_delay = 0;
}
}
-void rdi_refresh_session_delay(void) {
+void random_delays_refresh_rdi(void) {
if (rdi_disabled == secfalse) // if rdi enabled
refresh_session_delay = true;
}
diff --git a/core/embed/trezorhal/stm32f4/usb/usb.c b/core/embed/trezorhal/stm32f4/usb/usb.c
index b4e7a974fd..4875f34cc0 100644
--- a/core/embed/trezorhal/stm32f4/usb/usb.c
+++ b/core/embed/trezorhal/stm32f4/usb/usb.c
@@ -644,7 +644,7 @@ static uint8_t usb_class_data_in(USBD_HandleTypeDef *dev, uint8_t ep_num) {
usb_driver_t *drv = &g_usb_driver;
#ifdef RDI
- rdi_refresh_session_delay();
+ random_delays_refresh_rdi();
#endif
for (int i = 0; i < USBD_MAX_NUM_INTERFACES; i++) {
@@ -664,7 +664,7 @@ static uint8_t usb_class_data_out(USBD_HandleTypeDef *dev, uint8_t ep_num) {
usb_driver_t *drv = &g_usb_driver;
#ifdef RDI
- rdi_refresh_session_delay();
+ random_delays_refresh_rdi();
#endif
for (int i = 0; i < USBD_MAX_NUM_INTERFACES; i++) {
diff --git a/core/embed/trezorhal/unix/random_delays.c b/core/embed/trezorhal/unix/random_delays.c
index b9bcbe5ca4..075cb5ea3c 100644
--- a/core/embed/trezorhal/unix/random_delays.c
+++ b/core/embed/trezorhal/unix/random_delays.c
@@ -19,6 +19,6 @@
#include "random_delays.h"
-void wait_random(void) {}
+void random_delays_init(void) {}
-void rdi_init(void) {}
+void wait_random(void) {}
diff --git a/core/embed/trezorhal/unix/random_delays.h b/core/embed/trezorhal/unix/random_delays.h
deleted file mode 100644
index 01191b24cf..0000000000
--- a/core/embed/trezorhal/unix/random_delays.h
+++ /dev/null
@@ -1,26 +0,0 @@
-/*
- * This file is part of the Trezor project, https://trezor.io/
- *
- * Copyright (c) SatoshiLabs
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program. If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef __TREZORHAL_RANDOM_DELAYS_H__
-#define __TREZORHAL_RANDOM_DELAYS_H__
-
-void rdi_init(void);
-void wait_random(void);
-
-#endif