Bpflock : eBPF Driven Security For Locking And Auditing Linux Machines

bpflock uses eBPF to strength Linux security. By restricting access to a various range of Linux features, bpflock is able to reduce the attack surface and block some well known attack techniques.

Only programs like container managers, systemd and other containers/programs that run in the host pid and network namespaces are allowed access to full Linux features, containers and applications that run on their own namespace will be restricted. If bpflock bpf programs run under the restricted profile then all programs/containers including privileged ones will have their access denied.

bpflock protects Linux machines by taking advantage of multiple security features including Linux Security Modules + BPF.

Architecture and Security design notes:

• bpflock is not a mandatory access control labeling solution, and it does not intent to replace AppArmor, SELinux, and other MAC solutions. bpflock uses a simple declarative security profile.
• bpflock offers multiple small bpf programs that can be reused in multiple contexts from Cloud Native deployments to Linux IoT devices.
• bpflock is able to restrict root from accessing certain Linux features, however it does not protect against evil root.

Functionality Overview

Security features

bpflock offer multiple security protections that can be classified as:

• Memory Protections
  • Kernel Image Lock-down
  • Kernel Modules Protection
  • BPF Protection
• Process Protections
  • Fileless Memory Execution
  • Namespaces protection
• Hardware Addition Attacks
  • USB Additions Protection
• System and Application tracing
  • Trace Application Execution
  • Trace Privileged System Operations
• Filesystem Protections
  • Read-only root filesystem protection
  • sysfs protection
• Network protections
  • bpflock may include in future a simple network protection that can be used in single machine workload or Linux-IoT, but will not include a Cloud Native protection. Cilium and other kubernetes CNI related solutions are by far better.

Semantics

bpflock keeps the security semantics simple. It support three global profiles to broadly cover the security sepctrum, and restrict access to specific Linux features.

• profile: this is the global profile that can be applied per bpf program, it takes one of the followings:
  • allow|none|privileged : they are the same, they define the least secure profile. In this profile access is logged and allowed for all processes. Useful to log security events.
  • baseline : restrictive profile where access is denied for all processes, except privileged applications and containers that run in the host namespaces, or per cgroup allowed profiles in the bpflock_cgroupmap bpf map.
  • restricted : heavily restricted profile where access is denied for all processes.
• Allowed or blocked operations/commands:Under the allow|privileged or baseline profiles, a list of allowed or blocked commands can be specified and will be applied.
  • --protection-allow : comma-separated list of allowed operations. Valid under baseline profile, this is useful for applications that are too specific and perform privileged operations. It will reduce the use of the allow | privileged profile, so instead of using the privileged profile, we can specify the baseline one and add a set of allowed commands to offer a case-by-case definition for such applications.
  • --protection-block : comma-separated list of blocked operations. Valid under allow|privileged and baseline profiles, it allows to restrict access to some features without using the full restricted profile that might break some specific applications. Using baseline or privileged profiles opens the gate to access most Linux features, but with the --protection-block option some of this access can be blocked.

For bpf security examples check bpflock configuration examples

Deployment

Prerequisites

bpflock needs the following:

• Linux kernel version >= 5.13 with the following configuration:

CONFIG_BPF_SYSCALL=y
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_BTF=y
CONFIG_KPROBES=y
CONFIG_LSM=”…,bpf”
CONFIG_BPF_LSM=y

• Obviously a BTF enabled kernel.

Enable BPF LSM support

If your kernel was compiled with CONFIG_BPF_LSM=y check the /boot/config-* to confirm, but when running bpflock it fails with:

must have a kernel with ‘CONFIG_BPF_LSM=y’ ‘CONFIG_LSM=\”…,bpf\”‘”

Then to enable BPF LSM as an example on Ubuntu:

• Open the /etc/default/grub file as privileged of course.
• Append the following to the GRUB_CMDLINE_LINUX variable and save

“lsm=lockdown,capability,yama,apparmor,bpf”

or

GRUB_CMDLINE_LINUX=”lsm=lockdown,capability,yama,apparmor,bpf”

Update grub config with

sudo update-grub2

• Reboot into your kernel.

Docker deployment

To run using the default allow or privileged profile (the least secure profile):

docker run –name bpflock -it –rm –cgroupns=host \
–pid=host –privileged \
-v /sys/kernel/:/sys/kernel/ \
-v /sys/fs/bpf:/sys/fs/bpf linuxlock/bpflock

Configuration and Environment file

Passing configuration as bind mounts can be achieved using the following command.

Assuming bpflock.yaml and bpf.d profiles configs are in current directory inside bpflock directory, then we can just use:

ls bpflock/
bpf.d bpflock.d bpflock.yaml

docker run –name bpflock -it –rm –cgroupns=host –pid=host –privileged \
-v $(pwd)/bpflock/:/etc/bpflock \
-v /sys/kernel/:/sys/kernel/ \
-v /sys/fs/bpf:/sys/fs/bpf linuxlock/bpflock

Passing environment variables can also be done with files using --env-file. All parameters can be passed as environment variables using the BPFLOCK_$VARIABLE_NAME=VALUE format.

Example run with environment variables in a file:

docker run –name bpflock -it –rm –cgroupns=host –pid=host –privileged \
–env-file bpflock.env.list \
-v /sys/kernel/:/sys/kernel/ \
-v /sys/fs/bpf:/sys/fs/bpf linuxlock/bpflock

Build

bpflock uses docker BuildKit to build and Golang to make some checks and run tests. bpflock is built inside Ubuntu container that downloads the standard golang package.

Run the following to build the bpflock docker container:

git submodule update –init –recursive
make

Bpf programs are built using libbpf. The docker image used is Ubuntu.

If you want to only build the bpf programs directly without using docker, then on Ubuntu:

sudo apt install -y pkg-config bison binutils-dev build-essential \
flex libc6-dev clang-12 libllvm12 llvm-12-dev libclang-12-dev \
zlib1g-dev libelf-dev libfl-dev gcc-multilib zlib1g-dev \
libcap-dev libiberty-dev libbfd-dev