Lorenzo Fontana fntlnz

The eBPF verifier

Important: This article was written by Github Copilot, while it's not entirely accurate, it's quite good to see what it ended up with.

The bpf verifier is a tool that can be used to check the correctness of eBPF programs. It is implemented in C and is used by the kernel. When the kernel is built with CONFIG_BPF_JIT, it does further optimization on the BPF programs.

To write a valid eBPF program you need to follow a few rules:

Flux as a Library Example

Flux is a lightweight scripting language for querying databases (like InfluxDB) and working with data. It's part of InfluxDB 1.7 and 2.0, but can be run independently of those.

This gist contains a main.go file that shows how flux can be used as a library in your programs.

Components

The main components you need are:

Seccomp BPF filter example

Use bpf programs as filters for seccomp, the one in the example will block all the write syscalls after it's loaded.

Usage

Compile it with just

gcc main.c

InfluxDB and Chronograf in Kubernetes

Create the namespace

kubectl create ns monitoring

Deploy influxdb

kubectl apply -f influxdb.yml

docker service create --mode global --mount type=volume,volume-opt=o=addr=10.3.20.25,volume-opt=device=:/share/poc1/pluto,volume-opt=type=nfs,source=pluto,target=/pluto --name nfstest alpine top

Create Root CA (Done once)

Create Root Key

Attention: this is the key used to sign the certificate requests, anyone holding this can sign certificates on your behalf. So keep it in a safe place!

openssl genrsa -des3 -out rootCA.key 4096

	#include <linux/bpf.h>
	#include <linux/in.h>
	#include <linux/if_ether.h>
	#include <linux/ip.h>

	#define SEC(NAME) __attribute__((section(NAME), used))

	SEC("dropper_main")
	int dropper(struct xdp_md *ctx) {
	int ipsize = 0;

	[[constraint]]
	name = "k8s.io/api"
	version = "kubernetes-1.11.0"

	[[constraint]]
	name = "k8s.io/apimachinery"
	version = "kubernetes-1.11.0"

	[[constraint]]
	name = "k8s.io/client-go"

	1. Calculate the offset

	offset(fn) = virtual_address(fn) - virtual_address(.text) + offset(.text)


	2. Virtual address:
	readelf -S /home/fntlnz/go/bin/influx \| grep -i text
	[ 1] .text PROGBITS 0000000000401000 00001000

	So, virtual address= 0x0000000000401000