Cinch

A system for interposing on USB transfers and several security modules. See the paper here. Our current prototype works with Linux KVM hypervisor (it supports any guest OS as we describe in the paper).

Compiling Cinch

Cinch is written in Rust and compiles under the nightly compiler. To choose the nightly compiler simply run:

$ rustup install nightly
$ rustup default nightly

To compile Cinch with debug symbols simply run: $ cargo build. The resulting binary will be found in target/debug/cinch. To compile Cinch with all optimizations run: $ cargo build --release. The resulting binary will be found in target/release/cinch.

Replicating the setup described in the paper

Our setup requires a machine with an IOMMU running Linux with QEMU/KVM installed.

Unbinding the USB host controller

The first step is to unbind the host controller from the Linux machine so that we can redirect it to the red machine VM.

Use the iommu_setup script found in scripts to unbind the machine's USB host controller. Modify the values at the beginning of the script with those belonging to your particular host controller.

Then run: $ scripts/iommu_setup start.

Creating and configuring the Red machine VM

Create a new QEMU VM image and install Linux on it (we use Debian but any distribution works). Ensure tht the VM has a network connection to the Linux hypervisor (we did this by setting up a network bridge).

Install usbredir on the Red machine

Now that the VM has network support, install usbredir version 0.7.1 on the Red machine VM.

In Debian, you can run: # apt-get install usbredir. In Arch, you can run # pacman -S usbredir.

Other distributions may have similar packages. Otherwise install it from source.

Blacklist.conf

Depending on the Red machine OS that you install, its USB stack might be up to date and prevent many of the CVE exploits that we test in the paper. To ensure that this is not the case (and let Cinch do the heavy lifting) blacklist all the relevant drivers.

In the red machine add the following to /etc/modprobe.d/blacklist.conf

blacklist snd-usb-audio
blacklist ati_remote2
blacklist powermate
blacklist gtco
blacklist iowarrior
blacklist visor
blacklist mct_u232
blacklist cypress_m8
blacklist wacom
blacklist digi_acceleport
blacklist ims_pcu
blacklist cdc_acm

This will prevent any of these drivers from loading on the Red VM.

Launch the Red VM with the USB host controller

Launch the red machine and bind the host controller to it using the IOMMU. See the launch-red script found in scripts for the command line that we used to launch our red machine VM.

Creating and configuring the Blue machine VM

For the blue machine VM you may use any OS supported by QEMU (e.g., Windows, *BSD, Linux). The blue machine does not require any special configuration.

Launch the Blue VM

To launch the blue machine use the launch-blue script found in scripts. It allows us to connect to the QEMU monitor using telnet which we leverage to hot-plug USB devices.

Connecting devices from the Red to the Blue VM

First start Cinch with the default configuration (see next section for how to specify other configurations):

$ target/release/cinch -c [CONFIG_FILE]

Exporting devices through Cinch

To export devices, first connect the device to the (physical) machine. The device should then appear on the Red VM. Use the device_setup found in scripts to export this device (this is done from the Linux/KVM hypervisor).

$ scripts/device_setup ls # shows ids of available devices
$ scripts/device_setup export [ID] # unbinds device ID [ID] from Red VM and readies it for exporting to blue VM
$ scripts/device_setup start # hotplugs the device to the Blue VM through Cinch

Exporting devices without Cinch

If you want to run this setup without Cinch, simply replace the CINCH_IP and CINCH_PORT to the IP of the Red VM and the port to 8000 (which is hardcoded in the script's export function).

Configuring Cinch, Logging, and Signatures

Cinch Configuration Format

Our current prototype has 8 options that can be specified.

red_addr: the IP:Port of the red machine. Cinch will connect to this address once the device has been hotplugged.

cinch_addr: The IP:Port of the Linux/KVM hypervisor instance running Cinch.

log: boolean flag stating whether to log all traffic or not.

log_prefix: path (and optional prefix name) for log files. For instance, if /home/cinch-user/logs/trace is specified, all traffic will be stored in a file called: trace-TIMESTAMP.log. The timestamp has the format "day-month-year-hour-minute-second".

checks_active: boolean flag stating whether to perform compliance checks. If false, Cinch simply acts as a transparent proxy.

patch_active: boolean flag stating whether to perform signature checks.

patches: absolute path to the directory holding signatures (we call them patches in the source code). Each signature should be in a different file (see below for format). Cinch will automatically load all signatures in the given directory.

third_party_folder: absolute path to the directory holding third party constraints. Each constraint should be in a different JSON file.

Below is a sample config file (JSON).

"red_addr": "192.168.1.100:8000",
"cinch_addr": "192.168.1.7:5555",
"log": true,
"log_prefix": "/home/cinch-user/log/experiment1",
"checks_active": true,
"patch_active": true,
"patches": "/home/cinch-user/cinch/signatures",
"third_party_folder": "/home/cinch-user/cinch/third-party-checks"

The IP addresess correspond to a local network between the Red VM and Cinch.

Signature format

Our current prototype can handle signatures for 3 types of packets: Bulk transfers, initial connection, and control packets. Interrupt and Iso signatures are not yet implemented, but supporting them is relatively straightforward. See src/modules/patcher.rs.

Signatures consist of metadata and data that are used to match on packets.

p_type: packet type. Available options are: control, connect, bulk.

vendor_id: if p_type = connect, this filters all devices from a particular vendor.

product_id: if p_type = connect, this filters all devices with a particular product id.

request: corresponds to bRequest in the USB setup packet. This is used when p_type = control in combination with requesttype to specify on which requests to perform the signature check.

requesttype: corresponds to bmRequestType in the USB setup packet (see above).

patch_id: a unique identifier for this signature/patch. Each signature in the signature folder must have a different identifier unless they belong to the same group (see below).

min_matches: integer specifiying how many signatures (out of a set of signatures) must match before the packet is filtered. For instance, if I have 10 signatures with the same patch_id, these signatures form a group. Setting min_matches to 3 means that if any 3 signatures of the same group match on a packet the packet will be dropped.

data: hex-encoded payload string to match.

Below are two sample signature files (JSON).

{
  "meta": {
    "p_type": "bulk",
    "vendor_id": 0,
    "product_id": 0,
    "request": 0,
    "requesttype": 0,
    "patch_id": 1,
    "min_matches": 1
  },

  "data": "496e76616c6964205061727469746f6e207461626c65"
}

The above signature matches any packet sent from the red machine that has the above data anywhere.

{
  "meta": {
    "p_type": "connect",
    "vendor_id": 1133,
    "product_id": 49257,
    "request": 0,
    "requesttype": 0,
    "patch_id": 1,
    "min_matches": 1
  },

  "data": ""
}

The above signature prevents a Logitech Corded Mouse M500 from connecting to the blue machine. 1133 is Logitech's vendor id (0x046d). 49257 is the mouse's product id (0xc069). Both specified in decimal.