From eadb0dbb1d07e7f54ec72abe08f3c95ce5765843 Mon Sep 17 00:00:00 2001
From: George Hotz <geohot@gmail.com>
Date: Tue, 10 Dec 2019 08:14:30 -0800
Subject: [PATCH] security upgrades (#397)

* security upgrades

* Gated DFU entry from debug console as well
---
 board/bootstub.c    | 10 ++++++++++
 board/main.c        | 13 ++++++++-----
 board/spi_flasher.h |  5 +++++
 crypto/sign.py      |  6 ++++++
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/board/bootstub.c b/board/bootstub.c
index ac75c9c072ec5f..1521b5324030d0 100644
--- a/board/bootstub.c
+++ b/board/bootstub.c
@@ -1,5 +1,8 @@
 #define BOOTSTUB
 
+#define VERS_TAG 0x53524556
+#define MIN_VERSION 2
+
 #include "config.h"
 #include "obj/gitversion.h"
 
@@ -90,6 +93,13 @@ int main(void) {
   uint8_t digest[SHA_DIGEST_SIZE];
   SHA_hash(&_app_start[1], len-4, digest);
 
+  // verify version, last bytes in the signed area
+  uint32_t vers[2] = {0};
+  memcpy(&vers, ((void*)&_app_start[0]) + len - sizeof(vers), sizeof(vers));
+  if (vers[0] != VERS_TAG || vers[1] < MIN_VERSION) {
+    goto fail;
+  }
+
   // verify RSA signature
   if (RSA_verify(&release_rsa_key, ((void*)&_app_start[0]) + len, RSANUMBYTES, digest, SHA_DIGEST_SIZE)) {
     goto good;
diff --git a/board/main.c b/board/main.c
index 2b6c78a94a82a7..dd4edb33d1e6c7 100644
--- a/board/main.c
+++ b/board/main.c
@@ -72,11 +72,14 @@ void debug_ring_callback(uart_ring *ring) {
   while (getc(ring, &rcv)) {
     (void)putc(ring, rcv);  // misra-c2012-17.7: cast to void is ok: debug function
 
-    // jump to DFU flash
-    if (rcv == 'z') {
-      enter_bootloader_mode = ENTER_BOOTLOADER_MAGIC;
-      NVIC_SystemReset();
-    }
+    // only allow bootloader entry on debug builds
+    #ifdef ALLOW_DEBUG
+      // jump to DFU flash
+      if (rcv == 'z') {
+        enter_bootloader_mode = ENTER_BOOTLOADER_MAGIC;
+        NVIC_SystemReset();
+      }
+    #endif
 
     // normal reset
     if (rcv == 'x') {
diff --git a/board/spi_flasher.h b/board/spi_flasher.h
index 3fe15961c8cf9f..fbdbab8a61e0cf 100644
--- a/board/spi_flasher.h
+++ b/board/spi_flasher.h
@@ -65,7 +65,12 @@ int usb_cb_control_msg(USB_Setup_TypeDef *setup, uint8_t *resp, bool hardwired)
       // so it's blocked over wifi
       switch (setup->b.wValue.w) {
         case 0:
+          #ifdef ALLOW_DEBUG
           if (hardwired) {
+          #else
+          // no more bootstub on UNO
+          if (hardwired && hw_type != HW_TYPE_UNO) {
+          #endif
             puts("-> entering bootloader\n");
             enter_bootloader_mode = ENTER_BOOTLOADER_MAGIC;
             NVIC_SystemReset();
diff --git a/crypto/sign.py b/crypto/sign.py
index 0f1ce030815b6d..8cbe6f4195f1c6 100755
--- a/crypto/sign.py
+++ b/crypto/sign.py
@@ -6,6 +6,9 @@
 from Crypto.PublicKey import RSA
 import binascii
 
+# increment this to make new hardware not run old versions
+VERSION = 2
+
 rsa = RSA.importKey(open(sys.argv[3]).read())
 
 with open(sys.argv[1], "rb") as f:
@@ -15,6 +18,9 @@
 
 with open(sys.argv[2], "wb") as f:
   if os.getenv("SETLEN") is not None:
+    # add the version at the end
+    dat += b"VERS" + struct.pack("I", VERSION)
+    # add the length at the beginning
     x = struct.pack("I", len(dat)) + dat[4:]
     # mock signature of dat[4:]
     dd = hashlib.sha1(dat[4:]).digest()