feat(core): jump back and stay in bootloader for TT via reverse SVC call trampoline

core/.changelog.d/2284.added

@@ -0,0 +1 @@
+Jump and stay in bootloader from firmware through SVC call reverse trampoline.

core/embed/bootloader/.changelog.d/2284.added

@@ -0,0 +1 @@
+Jump and stay in bootloader from firmware through SVC call reverse trampoline.

core/embed/bootloader/main.c

@@ -242,6 +242,10 @@ static void check_bootloader_version(void) {
 #endif
 
 int main(void) {
+  // grab "stay in bootloader" flag as soon as possible
+  register uint32_t r11 __asm__("r11");
+  volatile uint32_t stay_in_bootloader_flag = r11;
+
   random_delays_init();
   // display_init_seq();
 #if defined TREZOR_MODEL_T
@@ -281,6 +285,9 @@ int main(void) {
   vendor_header vhdr;
   image_header hdr;
   secbool stay_in_bootloader = secfalse;  // flag to stay in bootloader
+  if (stay_in_bootloader_flag == STAY_IN_BOOTLOADER_FLAG) {
+    stay_in_bootloader = sectrue;
+  }
 
   // detect whether the devices contains a valid firmware
 

core/embed/extmod/modtrezorutils/modtrezorutils.c

@@ -19,6 +19,9 @@
 
 #include "py/objstr.h"
 #include "py/runtime.h"
+#ifndef TREZOR_EMULATOR
+#include "supervise.h"
+#endif
 
 #include "version.h"
 
@@ -245,6 +248,19 @@ STATIC mp_obj_t mod_trezorutils_get_firmware_chunk(const mp_obj_t index_obj,
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_trezorutils_get_firmware_chunk_obj,
                                  mod_trezorutils_get_firmware_chunk);
 
+/// def reboot_to_bootloader() -> None:
+///     """
+///     Reboots to bootloader.
+///     """
+STATIC mp_obj_t mod_trezorutils_reboot_to_bootloader() {
+#ifndef TREZOR_EMULATOR
+  svc_reboot_to_bootloader();
+#endif
+  return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(mod_trezorutils_reboot_to_bootloader_obj,
+                                 mod_trezorutils_reboot_to_bootloader);
+
 STATIC mp_obj_str_t mod_trezorutils_revision_obj = {
     {&mp_type_bytes}, 0, sizeof(SCM_REVISION) - 1, (const byte *)SCM_REVISION};
 
@@ -272,7 +288,8 @@ STATIC const mp_rom_map_elem_t mp_module_trezorutils_globals_table[] = {
      MP_ROM_PTR(&mod_trezorutils_firmware_sector_size_obj)},
     {MP_ROM_QSTR(MP_QSTR_FIRMWARE_SECTORS_COUNT),
      MP_ROM_INT(FIRMWARE_SECTORS_COUNT)},
-
+    {MP_ROM_QSTR(MP_QSTR_reboot_to_bootloader),
+     MP_ROM_PTR(&mod_trezorutils_reboot_to_bootloader_obj)},
     // various built-in constants
     {MP_ROM_QSTR(MP_QSTR_SCM_REVISION),
      MP_ROM_PTR(&mod_trezorutils_revision_obj)},

core/embed/firmware/main.c

@@ -41,6 +41,7 @@
 #include "compiler_traits.h"
 #include "display.h"
 #include "flash.h"
+#include "image.h"
 #include "mpu.h"
 #include "random_delays.h"
 #ifdef SYSTEM_VIEW
@@ -180,6 +181,13 @@ void UsageFault_Handler(void) {
   error_shutdown("Internal error", "(UF)", NULL, NULL);
 }
 
+__attribute__((noreturn)) void reboot_to_bootloader() {
+  jump_to_with_flag(BOOTLOADER_START + IMAGE_HEADER_SIZE,
+                    STAY_IN_BOOTLOADER_FLAG);
+  for (;;)
+    ;
+}
+
 void SVC_C_Handler(uint32_t *stack) {
   uint8_t svc_number = ((uint8_t *)stack[6])[-2];
   switch (svc_number) {
@@ -202,6 +210,16 @@ void SVC_C_Handler(uint32_t *stack) {
       for (;;)
         ;
       break;
+    case SVC_REBOOT_TO_BOOTLOADER:
+      mpu_config_bootloader();
+      __asm__ volatile("msr control, %0" ::"r"(0x0));
+      __asm__ volatile("isb");
+      // See stack layout in
+      // https://developer.arm.com/documentation/ka004005/latest We are changing
+      // return address in PC to land into reboot to avoid any bug with ROP and
+      // raising privileges.
+      stack[6] = (uintptr_t)reboot_to_bootloader;
+      return;
     default:
       stack[0] = 0xffffffff;
       break;

core/embed/trezorhal/common.h

@@ -49,6 +49,8 @@
   })
 #endif
 
+#define STAY_IN_BOOTLOADER_FLAG 0x0FC35A96
+
 void shutdown(void);
 
 void __attribute__((noreturn))
@@ -78,5 +80,6 @@ extern uint8_t HW_ENTROPY_DATA[HW_ENTROPY_LEN];
 void memset_reg(volatile void *start, volatile void *stop, uint32_t val);
 void jump_to(uint32_t address);
 void jump_to_unprivileged(uint32_t address);
+void jump_to_with_flag(uint32_t address, uint32_t register_flag);
 
 #endif

core/embed/trezorhal/supervise.h

@@ -4,9 +4,11 @@
 #define SVC_DISABLE_IRQ 1
 #define SVC_SET_PRIORITY 2
 #define SVC_SHUTDOWN 4
+#define SVC_REBOOT_TO_BOOTLOADER 5
 
 // from util.s
 extern void shutdown_privileged(void);
+extern void reboot_to_bootloader(void);
 
 static inline uint32_t is_mode_unprivileged(void) {
   uint32_t r0;
@@ -50,3 +52,10 @@ static inline void svc_shutdown(void) {
     shutdown_privileged();
   }
 }
+static inline void svc_reboot_to_bootloader(void) {
+  if (is_mode_unprivileged()) {
+    __asm__ __volatile__("svc %0" ::"i"(SVC_REBOOT_TO_BOOTLOADER) : "memory");
+  } else {
+    reboot_to_bootloader();
+  }
+}

core/embed/trezorhal/util.s

@@ -16,10 +16,22 @@ memset_reg:
   bne .L_loop_begin
   bx lr
 
+  // Jump to address given in first argument R0 that points to next's stage's VTOR
+  // Clear memory and all registers before jump
   .global jump_to
   .type jump_to, STT_FUNC
 jump_to:
+  ldr r1, =0
+  bl jump_to_with_flag
+
+  // Jump to address given in first argument R0 that points to next's stage's VTOR
+  // Clear memory and all registers before jump. Second argument R1 is copied to R11
+  // and kept after jump.
+  .global jump_to_with_flag
+  .type jump_to_with_flag, STT_FUNC
+jump_to_with_flag:
   mov r4, r0            // save input argument r0 (the address of the next stage's vector table) (r4 is callee save)
+  mov r11, r1           // save second argument in "flag" register because we'll be cleaning RAM
   // this subroutine re-points the exception handlers before the C code
   // that comprises them has been given a good environment to run.
   // therefore, this code needs to disable interrupts before the VTOR
@@ -39,7 +51,7 @@ jump_to:
   ldr r2, =0            // r2 - the word-sized value to be written
   bl memset_reg
   mov lr, r4
-  // clear out the general purpose registers before the next stage's code can run (even the NMI exception handler)
+  // clear out the general purpose registers before the next stage's except the register with flag R11
   ldr r0, =0
   mov r1, r0
   mov r2, r0
@@ -51,7 +63,6 @@ jump_to:
   mov r8, r0
   mov r9, r0
   mov r10, r0
-  mov r11, r0
   mov r12, r0
   // give the next stage a fresh main stack pointer
   ldr r0, [lr]          // set r0 to the main stack pointer in the next stage's vector table

core/mocks/generated/trezorutils.pyi

@@ -72,6 +72,13 @@ def get_firmware_chunk(index: int, offset: int, buffer: bytearray) -> None:
     """
     Reads a chunk of the firmware into `buffer`.
     """
+
+
+# extmod/modtrezorutils/modtrezorutils.c
+def reboot_to_bootloader() -> None:
+    """
+    Reboots to bootloader.
+    """
 SCM_REVISION: bytes
 VERSION_MAJOR: int
 VERSION_MINOR: int

core/src/all_modules.py

@@ -371,6 +371,8 @@ apps.management.get_next_u2f_counter
 import apps.management.get_next_u2f_counter
 apps.management.get_nonce
 import apps.management.get_nonce
+apps.management.reboot_to_bootloader
+import apps.management.reboot_to_bootloader
 apps.management.recovery_device
 import apps.management.recovery_device
 apps.management.recovery_device.homescreen

core/src/apps/management/reboot_to_bootloader.py

@@ -0,0 +1,17 @@
+from typing import TYPE_CHECKING
+
+from trezor import utils, wire
+from trezor.messages import RebootToBootloader, Success
+
+if TYPE_CHECKING:
+    from typing import NoReturn
+
+    pass
+
+
+async def reboot_to_bootloader(ctx: wire.Context, msg: RebootToBootloader) -> NoReturn:
+    await ctx.write(Success())
+    # writing synchronously twice makes USB flush properly before reboot
+    await ctx.write(Success())
+    utils.reboot_to_bootloader()
+    raise RuntimeError

core/src/apps/workflow_handlers.py

@@ -49,6 +49,8 @@ def find_message_handler_module(msg_type: int) -> str:
         return "apps.management.change_wipe_code"
     elif msg_type == MessageType.GetNonce:
         return "apps.management.get_nonce"
+    elif msg_type == MessageType.RebootToBootloader:
+        return "apps.management.reboot_to_bootloader"
 
     if utils.MODEL in ("T",) and msg_type == MessageType.SdProtect:
         return "apps.management.sd_protect"

core/src/trezor/utils.py

@@ -16,6 +16,7 @@ from trezorutils import (  # noqa: F401
     get_firmware_chunk,
     halt,
     memcpy,
+    reboot_to_bootloader,
 )
 from typing import TYPE_CHECKING
 

python/.changelog.d/2284.added

@@ -0,0 +1 @@
+Jump and stay in bootloader from firmware through SVC call reverse trampoline.

python/src/trezorlib/cli/device.py

@@ -278,8 +278,4 @@ def reboot_to_bootloader(obj: "TrezorConnection") -> str:
     # avoid using @with_client because it closes the session afterwards,
     # which triggers double prompt on device
     with obj.client_context() as client:
-        if client.features.model != "1":
-            click.echo(
-                f"Warning: Rebooting into bootloader not supported on Trezor {client.features.model}"
-            )
         return device.reboot_to_bootloader(client)