Bootloader downgrade protection

fido2/ctap.c

@@ -1775,8 +1775,14 @@ void ctap_load_external_keys(uint8_t * keybytes){
     crypto_load_master_secret(STATE.key_space);
 }
 
+#include "version.h"
 void ctap_init()
 {
+    printf1(TAG_ERR,"Current firmware version address: %p\r\n", &firmware_version);
+    printf1(TAG_ERR,"Current firmware version: %d.%d.%d.%d (%02x.%02x.%02x.%02x)\r\n",
+            firmware_version.major, firmware_version.minor, firmware_version.patch, firmware_version.reserved,
+            firmware_version.major, firmware_version.minor, firmware_version.patch, firmware_version.reserved
+            );
     crypto_ecc256_init();
 
     authenticator_read_state(&STATE);

fido2/version.c

@@ -0,0 +1,13 @@
+#include "version.h"
+
+
+const version_t firmware_version __attribute__ ((section (".flag"))) __attribute__ ((__used__)) =  {
+  .major = SOLO_VERSION_MAJ,
+  .minor = SOLO_VERSION_MIN,
+  .patch = SOLO_VERSION_PATCH,
+  .reserved = 0
+};
+
+// from tinycbor, for a quick static_assert
+#include <compilersupport_p.h>
+cbor_static_assert(sizeof(version_t) == 4);

fido2/version.h

@@ -17,5 +17,23 @@
 #define SOLO_VERSION     __STR(SOLO_VERSION_MAJ) "." __STR(SOLO_VERSION_MIN) "." __STR(SOLO_VERSION_PATCH)
 #endif
 
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef struct {
+  union{
+    uint32_t raw;
+    struct {
+      uint8_t major;
+      uint8_t minor;
+      uint8_t patch;
+      uint8_t reserved;
+    };
+  };
+} version_t;
+
+bool is_newer(const version_t* const newer, const version_t* const older);
+const version_t firmware_version ;
+
 
 #endif

targets/stm32l432/Makefile

@@ -90,8 +90,7 @@ flash_dfu: solo.hex bootloader.hex
 	# STM32_Programmer_CLI -c port=usb1 -halt -e all --readunprotect
 	STM32_Programmer_CLI -c port=usb1 -halt -rdu  -d all.hex
 
-flashboot: solo.hex bootloader.hex
-	$(VENV) $(merge_hex) solo.hex bootloader.hex all.hex
+flashboot: bootloader.hex
 	STM32_Programmer_CLI -c port=SWD -halt -e all --readunprotect
 	STM32_Programmer_CLI -c port=SWD -halt  -d bootloader.hex -rst
 

targets/stm32l432/bootloader/bootloader.c

@@ -19,6 +19,12 @@
 #include "ctap_errors.h"
 #include "log.h"
 
+volatile version_t current_firmware_version __attribute__ ((section (".flag2"))) __attribute__ ((__used__)) =  {
+  .major = SOLO_VERSION_MAJ,
+  .minor = SOLO_VERSION_MIN,
+  .patch = SOLO_VERSION_PATCH,
+  .reserved = 0
+};
 
 extern uint8_t REBOOT_FLAG;
 
@@ -56,8 +62,6 @@ static void erase_application()
     }
 }
 
-#define LAST_ADDR       (APPLICATION_END_ADDR-2048 + 8)
-#define LAST_PAGE       (APPLICATION_END_PAGE-1)
 static void disable_bootloader()
 {
     // Clear last 4 bytes of the last application page-1, which is 108th
@@ -102,6 +106,38 @@ int is_bootloader_disabled()
     uint32_t * auth = (uint32_t *)(AUTH_WORD_ADDR+4);
     return *auth == 0;
 }
+uint8_t * last_written_app_address;
+
+#include "version.h"
+bool is_firmware_version_newer_or_equal()
+{
+
+    printf1(TAG_BOOT,"Current firmware version: %u.%u.%u.%u (%02x.%02x.%02x.%02x)\r\n",
+          current_firmware_version.major, current_firmware_version.minor, current_firmware_version.patch, current_firmware_version.reserved,
+          current_firmware_version.major, current_firmware_version.minor, current_firmware_version.patch, current_firmware_version.reserved
+          );
+  volatile version_t * new_version = ((volatile version_t *) last_written_app_address);
+  printf1(TAG_BOOT,"Uploaded firmware version: %u.%u.%u.%u (%02x.%02x.%02x.%02x)\r\n",
+          new_version->major, new_version->minor, new_version->patch, new_version->reserved,
+          new_version->major, new_version->minor, new_version->patch, new_version->reserved
+          );
+
+    const bool allowed = is_newer(new_version, &current_firmware_version) || current_firmware_version.raw == 0xFFFFFFFF;
+  if (allowed){
+    printf1(TAG_BOOT, "Update allowed, setting new firmware version as current.\r\n");
+//    current_firmware_version.raw = new_version.raw;
+    uint8_t page[PAGE_SIZE];
+    memmove(page, (uint8_t*)BOOT_VERSION_ADDR, PAGE_SIZE);
+    memmove(page, new_version, 4);
+    printf1(TAG_BOOT, "Writing\r\n");
+    flash_erase_page(BOOT_VERSION_PAGE);
+    flash_write(BOOT_VERSION_ADDR, page, PAGE_SIZE);
+    printf1(TAG_BOOT, "Finish\r\n");
+  } else {
+    printf1(TAG_BOOT, "Firmware older - update not allowed.\r\n");
+  }
+  return allowed;
+}
 
 /**
  * Execute bootloader commands
@@ -125,10 +161,7 @@ int bootloader_bridge(int klen, uint8_t * keyh)
         return CTAP1_ERR_INVALID_LENGTH;
     }
 #ifndef SOLO_HACKER
-    uint8_t * pubkey = (uint8_t*)"\xd2\xa4\x2f\x8f\xb2\x31\x1c\xc1\xf7\x0c\x7e\x64\x32\xfb\xbb\xb4\xa3\xdd\x32\x20"
-                                 "\x0f\x1b\x88\x9c\xda\x62\xc2\x83\x25\x93\xdd\xb8\x75\x9d\xf9\x86\xee\x03\x6c\xce"
-                                 "\x34\x47\x71\x36\xb3\xb2\xad\x6d\x12\xb7\xbe\x49\x3e\x20\xa4\x61\xac\xc7\x71\xc7"
-                                 "\x1f\xa8\x14\xf2";
+    extern uint8_t *pubkey_boot;
 
     const struct uECC_Curve_t * curve = NULL;
 #endif
@@ -165,12 +198,11 @@ int bootloader_bridge(int klen, uint8_t * keyh)
             }
             // Do the actual write
             flash_write((uint32_t)ptr,req->payload, len);
-
-
+            last_written_app_address = (uint8_t *)ptr + len - 8 + 4;
             break;
         case BootDone:
             // Writing to flash finished. Request code validation.
-            printf1(TAG_BOOT, "BootDone: ");
+            printf1(TAG_BOOT, "BootDone: \r\n");
 #ifndef SOLO_HACKER
             if (len != 64)
             {
@@ -185,17 +217,23 @@ int bootloader_bridge(int klen, uint8_t * keyh)
             crypto_sha256_final(hash);
             curve = uECC_secp256r1();
             // Verify incoming signature made over the SHA256 hash
-            if (! uECC_verify(pubkey,
-                        hash,
-                        32,
-                        req->payload,
-                        curve))
+            if (
+                    !uECC_verify(pubkey_boot, hash, 32, req->payload, curve)
+            )
             {
+              printf1(TAG_BOOT, "Signature invalid\r\n");
                 return CTAP2_ERR_OPERATION_DENIED;
             }
+            if (!is_firmware_version_newer_or_equal()){
+              printf1(TAG_BOOT, "Firmware older - update not allowed.\r\n");
+              printf1(TAG_BOOT, "Rebooting...\r\n");
+              REBOOT_FLAG = 1;
+              return CTAP2_ERR_OPERATION_DENIED;
+            }
 #endif
             // Set the application validated, and mark for reboot.
             authorize_application();
+
             REBOOT_FLAG = 1;
             break;
         case BootCheck:
@@ -218,6 +256,7 @@ int bootloader_bridge(int klen, uint8_t * keyh)
             break;
         case BootReboot:
             printf1(TAG_BOOT, "BootReboot.\r\n");
+            printf1(TAG_BOOT, "Application authorized: %d.\r\n", is_authorized_to_boot());
             REBOOT_FLAG = 1;
             break;
         case BootDisable:

targets/stm32l432/bootloader/main.c

@@ -138,6 +138,14 @@ int main()
 
     printf1(TAG_GEN,"recv'ing hid msg \n");
 
+    extern volatile version_t current_firmware_version;
+    printf1(TAG_BOOT,"Current firmware version address: %p\r\n", &current_firmware_version);
+    printf1(TAG_BOOT,"Current firmware version: %d.%d.%d.%d (%02x.%02x.%02x.%02x)\r\n",
+            current_firmware_version.major, current_firmware_version.minor, current_firmware_version.patch, current_firmware_version.reserved,
+            current_firmware_version.major, current_firmware_version.minor, current_firmware_version.patch, current_firmware_version.reserved
+    );
+    dump_hex1(TAG_BOOT, (uint8_t*)(&current_firmware_version) - 16, 32);
+
 
     while(1)
     {

targets/stm32l432/bootloader/pubkey_bootloader.c

@@ -0,0 +1,6 @@
+#include "stdint.h"
+
+uint8_t * pubkey_boot = (uint8_t*)"\xd2\xa4\x2f\x8f\xb2\x31\x1c\xc1\xf7\x0c\x7e\x64\x32\xfb\xbb\xb4\xa3\xdd\x32\x20"
+                        "\x0f\x1b\x88\x9c\xda\x62\xc2\x83\x25\x93\xdd\xb8\x75\x9d\xf9\x86\xee\x03\x6c\xce"
+                        "\x34\x47\x71\x36\xb3\xb2\xad\x6d\x12\xb7\xbe\x49\x3e\x20\xa4\x61\xac\xc7\x71\xc7"
+                        "\x1f\xa8\x14\xf2";

targets/stm32l432/bootloader/version_check.c

@@ -0,0 +1,8 @@
+#include "version.h"
+
+//  FIXME test version check function
+bool is_newer(const version_t* const newer, const version_t* const older){
+  return (newer->major > older->major) ||
+         (newer->major == older->major &&  newer->minor > older->minor) ||
+         (newer->major == older->major &&  newer->minor == older->minor &&  newer->patch >= older->patch);
+}

targets/stm32l432/build/application.mk

@@ -10,6 +10,7 @@ SRC += $(DRIVER_LIBS) $(USB_LIB)
 SRC += ../../fido2/apdu.c ../../fido2/util.c ../../fido2/u2f.c ../../fido2/test_power.c
 SRC += ../../fido2/stubs.c ../../fido2/log.c  ../../fido2/ctaphid.c  ../../fido2/ctap.c
 SRC += ../../fido2/ctap_parse.c ../../fido2/main.c
+SRC += ../../fido2/version.c
 SRC += ../../fido2/data_migration.c
 SRC += ../../fido2/extensions/extensions.c ../../fido2/extensions/solo.c
 SRC += ../../fido2/extensions/wallet.c
@@ -70,6 +71,7 @@ all: $(TARGET).elf
 
 %.elf: $(OBJ)
 	$(CC) $^ $(HW) $(LDFLAGS) -o $@
+	@echo "Built version: $(VERSION_FLAGS)"
 
 %.hex: %.elf
 	$(SZ) $^

targets/stm32l432/build/bootloader.mk

@@ -2,6 +2,7 @@ include build/common.mk
 
 # ST related
 SRC = bootloader/main.c bootloader/bootloader.c
+SRC += bootloader/pubkey_bootloader.c bootloader/version_check.c
 SRC += src/init.c src/redirect.c src/flash.c src/rng.c src/led.c src/device.c
 SRC += src/fifo.c src/crypto.c src/attestation.c src/sense.c
 SRC += src/startup_stm32l432xx.s src/system_stm32l4xx.c
@@ -65,6 +66,7 @@ all: $(TARGET).elf
 
 %.elf: $(OBJ)
 	$(CC) $^ $(HW) $(LDFLAGS) -o $@
+	arm-none-eabi-size $@
 
 %.hex: %.elf
 	$(CP) -O ihex $^ $(TARGET).hex

targets/stm32l432/linker/bootloader_stm32l4xx.ld

@@ -12,9 +12,17 @@ _estack = 0x2000c000;
 
 _MIN_STACK_SIZE = 0x400;
 
+/*
+flash_cfg is for storing bootloader data, like last used firmware version.
+bootloader_configuration should be equal to (APPLICATION_END_PAGE) page address, from targets/stm32l432/src/memory_layout.h:30; and equal to flash_cfg origin
+*/
+
+bootloader_configuration = 0x08000000 + 216*1024+8;
+
 MEMORY
 {
     flash (rx)      : ORIGIN = 0x08000000, LENGTH = 20K
+    flash_cfg (rx)  : ORIGIN = 0x08000000 + 216*1024+8, LENGTH = 2K-8
     ram (xrw)       : ORIGIN = 0x20000000, LENGTH = 48K
     sram2 (rw)      : ORIGIN = 0x10000000, LENGTH = 16K
 }
@@ -39,6 +47,11 @@ SECTIONS
         _etext = .;
     } >flash
 
+    .flag2 bootloader_configuration :
+    {
+      KEEP(*(.flag2)) ;
+    } > flash_cfg
+
     _sidata = LOADADDR(.data);
 
     .data :

targets/stm32l432/linker/bootloader_stm32l4xx_extra.ld

@@ -12,9 +12,17 @@ _estack = 0x2000c000;
 
 _MIN_STACK_SIZE = 0x400;
 
+/*
+flash_cfg is for storing bootloader data, like last used firmware version.
+bootloader_configuration should be equal to (APPLICATION_END_PAGE) page address, from targets/stm32l432/src/memory_layout.h:30; and equal to flash_cfg origin
+*/
+
+bootloader_configuration = 0x08000000 + 216*1024+8;
+
 MEMORY
 {
     flash (rx)      : ORIGIN = 0x08000000, LENGTH = 32K
+    flash_cfg (rx)  : ORIGIN = 0x08000000 + 216*1024+8, LENGTH = 2K-8
     ram (xrw)       : ORIGIN = 0x20000000, LENGTH = 48K
     sram2 (rw)      : ORIGIN = 0x10000000, LENGTH = 16K
 }
@@ -39,6 +47,11 @@ SECTIONS
         _etext = .;
     } >flash
 
+    .flag2 bootloader_configuration :
+    {
+      KEEP(*(.flag2)) ;
+    } > flash_cfg
+
     _sidata = LOADADDR(.data);
 
     .data :

targets/stm32l432/linker/stm32l4xx.ld

@@ -13,14 +13,21 @@ _estack = 0x2000c000;
 _MIN_STACK_SIZE = 0x400;
 
 /*
-    Memory layout of device:
-        20 KB            198KB-8            38 KB
-    | bootloader |    application     |  secrets/data |
+len  |   20 KB/10p|      196KB-8-8/98p   |        2kB/1p         |      38 KB/19p  |
+pos  |   0->20 KB |     20->216KB-8-8    |   216kB -> 218 kB     |   218->256 KB   |
+posp |    0-10    |      10-113          |        113-114        |       113-128   |
+desc | bootloader |       application    | bootloader data       |  secrets/data   |
+
+    Last 8 bytes in application space are occupied by bootloader flags - app
+    authorization and bootloader activation flag.
  */
 
+/* Current firmware version number is concatenated to the firmware code - see .flag marker */
+/* flash length is (APPLICATION_END_PAGE-20*1024), where 20K is bootloader */
+
 MEMORY
 {
-    flash (rx)      : ORIGIN = 0x08005000, LENGTH = 198K - 8
+    flash (rx)      : ORIGIN = 0x08000000 + 20K, LENGTH = 216K - 20K - 8
     ram (xrw)       : ORIGIN = 0x20000000, LENGTH = 48K
     sram2 (rw)      : ORIGIN = 0x10000000, LENGTH = 16K
 }
@@ -56,6 +63,12 @@ SECTIONS
         _edata = .;
     } >ram AT> flash
 
+    .flag :
+    {
+        . = ALIGN(8);
+      KEEP(*(.flag)) ;
+    } > flash
+
     .bss :
     {
         . = ALIGN(4);

targets/stm32l432/linker/stm32l4xx_extra.ld

@@ -12,9 +12,22 @@ _estack = 0x2000c000;
 
 _MIN_STACK_SIZE = 0x400;
 
+/*
+len  |   32 KB/16p|      184KB-8-8/92p   |        2kB/1p         |      38 KB/19p  |
+pos  |   0->32 KB |     32->216KB-8-8    |   216kB -> 218 kB     |   218->256 KB   |
+posp |    0-16    |      16-113          |        113-114        |       113-128   |
+desc | bootloader |       application    | bootloader data       |  secrets/data   |
+
+    Last 8 bytes in application space are occupied by bootloader flags - app
+    authorization and bootloader activation flag.
+ */
+
+/* Current firmware version number is concatenated to the firmware code - see .flag marker */
+/* flash length is (APPLICATION_END_PAGE-20*1024), where 20K is bootloader */
+
 MEMORY
 {
-    flash (rx)      : ORIGIN = 0x08008000, LENGTH = 186K - 8
+    flash (rx)      : ORIGIN = 0x08000000 + 20K + 12K, LENGTH = 216K - 20K - 12K - 8
     ram (xrw)       : ORIGIN = 0x20000000, LENGTH = 48K
     sram2 (rw)      : ORIGIN = 0x10000000, LENGTH = 16K
 }
@@ -50,6 +63,12 @@ SECTIONS
         _edata = .;
     } >ram AT> flash
 
+    .flag :
+    {
+        . = ALIGN(8);
+      KEEP(*(.flag)) ;
+    } > flash
+
     .bss :
     {
         . = ALIGN(4);