rbpf/examples/load_elf.rs

// Copyright 2016 6WIND S.A. <quentin.monnet@6wind.com>
//
// Licensed under the Apache License, Version 2.0 <http://www.apache.org/licenses/LICENSE-2.0> or
// the MIT license <http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.


extern crate byteorder;
extern crate elf;
use std::path::PathBuf;

extern crate rbpf;
use rbpf::helpers;

// The following example uses an ELF file that has been compiled from this C source code:
//
// ```
// #include <linux/ip.h>
// #include <linux/in.h>
// #include <linux/tcp.h>
// #include <linux/bpf.h>
//
// #define ETH_ALEN 6
// #define ETH_P_IP 0x0008 /* htons(0x0800) */
// #define TCP_HDR_LEN 20
//
// #define BLOCKED_TCP_PORT 0x9999
//
// struct eth_hdr {
//     unsigned char   h_dest[ETH_ALEN];
//     unsigned char   h_source[ETH_ALEN];
//     unsigned short  h_proto;
// };
//
// #define SEC(NAME) __attribute__((section(NAME), used))
// SEC(".classifier")
// int handle_ingress(struct __sk_buff *skb)
// {
//     void *data = (void *)(long)skb->data;
//     void *data_end = (void *)(long)skb->data_end;
//     struct eth_hdr *eth = data;
//     struct iphdr *iph = data + sizeof(*eth);
//     struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*iph);
//
//     /* single length check */
//     if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*tcp) > data_end)
//         return 0;
//     if (eth->h_proto != ETH_P_IP)
//         return 0;
//     if (iph->protocol != IPPROTO_TCP)
//         return 0;
//     if (tcp->source == BLOCKED_TCP_PORT || tcp->dest == BLOCKED_TCP_PORT)
//         return -1;
//     return 0;
// }
// ```
//
// It was compiled with the following command:
//
// ```bash
// clang -O2 -emit-llvm -c block_a_port.c -o - | \ llc -march=bpf -filetype=obj -o block_a_port.o
// ```
//
// Once compiled, can be injected into Linux kernel, with tc for instance. Sadly, we need to bring
// some modifications to the generated bytecode in order to run it: the three instructions with
// opcode 0x61 load data from a packet area as 4-byte words, where we need to load it as 8-bytes
// double words (0x79). The kernel does the same kind of translation before running the program,
// but rbpf does not implement this.
//
// In addition, the offset at which the pointer to the packet data is stored must be changed: since
// we use 8 bytes instead of 4 for the start and end addresses of the data packet, we cannot use
// the offsets produced by clang (0x4c and 0x50), the addresses would overlap. Instead we can use,
// for example, 0x40 and 0x50.
//
// These change were applied with the following script:
//
// ```bash
// xxd block_a_port.o | sed '
//     s/6112 5000 0000 0000/7912 5000 0000 0000/ ;
//     s/6111 4c00 0000 0000/7911 4000 0000 0000/ ;
//     s/6111 2200 0000 0000/7911 2200 0000 0000/' | xxd -r > block_a_port.tmp
// mv block_a_port.tmp block_a_port.o
// ```
//
// The eBPF program was placed into the `.classifier` ELF section (see C code above), which means
// that you can retrieve the raw bytecode with `readelf -x .classifier block_a_port.o` or with
// `objdump -s -j .classifier block_a_port.o`.
//
// Once the bytecode has been edited, we can load the bytecode directly from the ELF object file.

fn main() {

    let filename = "examples/block_a_port.o";

    let path = PathBuf::from(filename);
    let file = match elf::File::open_path(&path) {
        Ok(f) => f,
        Err(e) => panic!("Error: {:?}", e),
    };

    let text_scn = match file.get_section(".classifier") {
        Some(s) => s,
        None => panic!("Failed to look up .classifier section"),
    };

    let ref prog = &text_scn.data;

    let mut packet1 = vec![
        0x01, 0x23, 0x45, 0x67, 0x89, 0xab,
        0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54,
        0x08, 0x00, // ethertype
        0x45, 0x00, 0x00, 0x3b, // start ip_hdr
        0xa6, 0xab, 0x40, 0x00,
        0x40, 0x06, 0x96, 0x0f,
        0x7f, 0x00, 0x00, 0x01,
        0x7f, 0x00, 0x00, 0x01,
        // Program matches the next two bytes: 0x9999 returns 0xffffffff, else return 0.
        0x99, 0x99, 0xc6, 0xcc, // start tcp_hdr
        0xd1, 0xe5, 0xc4, 0x9d,
        0xd4, 0x30, 0xb5, 0xd2,
        0x80, 0x18, 0x01, 0x56,
        0xfe, 0x2f, 0x00, 0x00,
        0x01, 0x01, 0x08, 0x0a, // start data
        0x00, 0x23, 0x75, 0x89,
        0x00, 0x23, 0x63, 0x2d,
        0x71, 0x64, 0x66, 0x73,
        0x64, 0x66, 0x0au8
    ];

    let mut packet2 = vec![
        0x01, 0x23, 0x45, 0x67, 0x89, 0xab,
        0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54,
        0x08, 0x00, // ethertype
        0x45, 0x00, 0x00, 0x3b, // start ip_hdr
        0xa6, 0xab, 0x40, 0x00,
        0x40, 0x06, 0x96, 0x0f,
        0x7f, 0x00, 0x00, 0x01,
        0x7f, 0x00, 0x00, 0x01,
        // Program matches the next two bytes: 0x9999 returns 0xffffffff, else return 0.
        0x98, 0x76, 0xc6, 0xcc, // start tcp_hdr
        0xd1, 0xe5, 0xc4, 0x9d,
        0xd4, 0x30, 0xb5, 0xd2,
        0x80, 0x18, 0x01, 0x56,
        0xfe, 0x2f, 0x00, 0x00,
        0x01, 0x01, 0x08, 0x0a, // start data
        0x00, 0x23, 0x75, 0x89,
        0x00, 0x23, 0x63, 0x2d,
        0x71, 0x64, 0x66, 0x73,
        0x64, 0x66, 0x0au8
    ];

    let mut vm = rbpf::EbpfVmFixedMbuff::new(&prog, 0x40, 0x50);
    vm.register_helper(helpers::BPF_TRACE_PRINTK_IDX, helpers::bpf_trace_printf);

    let res = vm.prog_exec(&mut packet1);
    println!("Packet #1, program returned: {:?} ({:#x})", res, res);
    assert_eq!(res, 0xffffffff);

    vm.jit_compile();
    unsafe {
        let res = vm.prog_exec_jit(&mut packet2);
        println!("Packet #2, program returned: {:?} ({:#x})", res, res);
        assert_eq!(res, 0);
    }
}