### Generate XDP Program Project

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Use the aya-rs template to generate a new XDP program project. This command sets up the basic project structure for an XDP program.

```bash
cargo generate --name simple-xdp-program -d program_type=xdp \
    https://github.com/aya-rs/aya-template
```

--------------------------------

### Import Dependencies for XDP Program

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Imports necessary crates and modules for eBPF development with Aya-rs, including logging, argument parsing, and network address handling.

```rust
use anyhow::Context;
use aya::
    maps::HashMap,
    programs::{Xdp, XdpMode},
};
use aya_log::EbpfLogger;
use clap::Parser;
use log::{info, warn};
use std::net::Ipv4Addr;
use tokio::signal;
```

--------------------------------

### Full User-Space XDP Firewall Program

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

This Rust program loads an XDP program, initializes eBPF logging, attaches the program to a network interface, configures a blocklist map, and waits for a Ctrl+C signal to exit.

```rust
use anyhow::Context;
use aya::{
    maps::HashMap,
    programs::{Xdp, XdpMode},
};
use aya_log::EbpfLogger;
use clap::Parser;
use log::{info, warn};
use std::net::Ipv4Addr;
use tokio::signal;

#[derive(Debug, Parser)]
struct Opt {
    #[clap(short, long, default_value = "eth0")]
    iface: String,
}

#[tokio::main]
async fn main() -> Result<(), anyhow::Error> {
    let opt = Opt::parse();

    env_logger::init();

    let mut bpf = aya::Ebpf::load(aya::include_bytes_aligned!(concat!(
        env!("OUT_DIR"),
        "/simple-xdp-program"
    )))?;
    match EbpfLogger::init(&mut bpf) {
        Err(e) => {
            // This can happen if you remove all log statements from your eBPF program.
            warn!("failed to initialize eBPF logger: {e}");
        }
        Ok(logger) => {
            let mut logger = tokio::io::unix::AsyncFd::with_interest(
                logger,
                tokio::io::Interest::READABLE,
            )?;
            tokio::task::spawn(async move {
                loop {
                    let mut guard = logger.readable_mut().await.unwrap();
                    guard.get_inner_mut().flush();
                    guard.clear_ready();
                }
            });
        }
    }
    let program: &mut Xdp = 
        bpf.program_mut("xdp_firewall").unwrap().try_into()?;
    program.load()?;
    program.attach(&opt.iface, XdpMode::default())
        .context("failed to attach the XDP program with default mode - "
                    "try changing XdpMode::default() to "
                    "XdpMode::Skb")?;

    let mut blocklist: HashMap<_, u32, u32> = 
        HashMap::try_from(bpf.map_mut("BLOCKLIST").unwrap())?;

    let block_addr: u32 = Ipv4Addr::new(1, 1, 1, 1).into();

    blocklist.insert(block_addr, 0, 0)?;

    let ctrl_c = signal::ctrl_c();
    info!("Waiting for Ctrl-C...");
    ctrl_c.await?;
    info!("Exiting...");

    Ok(())
}

```

--------------------------------

### Main Function for XDP Firewall

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

The main entry point for the XDP firewall application. It handles argument parsing, eBPF program loading, logger initialization, XDP program attachment, IP blocklist configuration, and signal handling for graceful exit.

```rust
#[tokio::main]
async fn main() -> Result<(), anyhow::Error> {
    let opt = Opt::parse();

    env_logger::init();

    let mut bpf = aya::Ebpf::load(aya::include_bytes_aligned!(concat!(
        env!("OUT_DIR"),
        "/simple-xdp-program"
    )))?;
    match EbpfLogger::init(&mut bpf) {
        Err(e) => {
            // This can happen if you remove all log statements from your eBPF program.
            warn!("failed to initialize eBPF logger: {e}");
        }
        Ok(logger) => {
            let mut logger = tokio::io::unix::AsyncFd::with_interest(
                logger,
                tokio::io::Interest::READABLE,
            )?;
            tokio::task::spawn(async move {
                loop {
                    let mut guard = logger.readable_mut().await.unwrap();
                    guard.get_inner_mut().flush();
                    guard.clear_ready();
                }
            });
        }
    }
    let program: &mut Xdp = 
        bpf.program_mut("xdp_firewall").unwrap().try_into()?;
    program.load()?;
    program.attach(&opt.iface, XdpMode::default())
        .context("failed to attach the XDP program with default mode - "
                    "try changing XdpMode::default() to XdpMode::Skb")?;

    let mut blocklist: HashMap<_, u32, u32> = 
        HashMap::try_from(bpf.map_mut("BLOCKLIST").unwrap())?;

    let block_addr: u32 = Ipv4Addr::new(1, 1, 1, 1).into();

    blocklist.insert(block_addr, 0, 0)?;

    let ctrl_c = signal::ctrl_c();
    info!("Waiting for Ctrl-C...");
    ctrl_c.await?;
    info!("Exiting...");

    Ok(())
}
```

--------------------------------

### XDP Firewall Entry Point

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

The main XDP program function that delegates packet processing to try_xdp_firewall and handles potential errors by returning XDP_ABORTED.

```rust
#[xdp]
pub fn xdp_firewall(ctx: XdpContext) -> u32 {
    match try_xdp_firewall(ctx) {
        Ok(ret) => ret,
        Err(_) => xdp_action::XDP_ABORTED,
    }
}

```

--------------------------------

### Import necessary dependencies for Aya eBPF

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Imports required modules from aya_ebpf, aya_log_ebpf, core::mem, and network_types for eBPF program development.

```rust
#![no_std]
#![no_main]

use aya_ebpf::{
    bindings::xdp_action,
    macros::{map, xdp},
    maps::HashMap,
    programs::XdpContext,
};

use aya_log_ebpf::info;

use core::mem;
use network_types::{
    eth::{EthHdr, EtherType},
    ip::Ipv4Hdr,
};

```

--------------------------------

### Define Command-Line Arguments for Network Interface

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Defines a struct for command-line argument parsing using clap, allowing users to specify the network interface name.

```rust
#[derive(Debug, Parser)]
struct Opt {
    #[clap(short, long, default_value = "eth0")]
    iface: String,
}
```

--------------------------------

### Full Aya eBPF XDP Firewall Code

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

The complete source code for the eBPF XDP firewall, including all necessary imports, panic handler, blocklist definition, and packet processing logic.

```rust
#![no_std]
#![no_main]
#![allow(nonstandard_style, dead_code)]

use aya_ebpf::{
    bindings::xdp_action,
    macros::{map, xdp},
    maps::HashMap,
    programs::XdpContext,
};
use aya_log_ebpf::info;

use core::mem;
use network_types::{
    eth::{EthHdr, EtherType},
    ip::Ipv4Hdr,
};

#[cfg(not(test))]
#[panic_handler]

```

--------------------------------

### Define eBPF Blocklist HashMap

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Defines a static HashMap named BLOCKLIST to store blocked IP addresses (u32) with a maximum capacity of 1024 entries.

```rust
#[map]
static BLOCKLIST: HashMap<u32, u32> = HashMap::with_max_entries(1024, 0);

```

--------------------------------

### XDP Firewall eBPF Program

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

This eBPF program implements an XDP firewall. It checks incoming IPv4 packets against a blocklist and drops packets from blocked IPs. Requires the `xdp_action` enum and `EthHdr`, `Ipv4Hdr` types.

```rust
fn panic(_info: &core::panic::PanicInfo) -> ! {
    loop {}
}

#[map]
static IP_BLOCKLIST: HashMap<u32, u32> = HashMap::with_max_entries(1024, 0);

#[xdp]
pub fn xdp_firewall(ctx: XdpContext) -> u32 {
    match try_xdp_firewall(ctx) {
        Ok(ret) => ret,
        Err(_) => xdp_action::XDP_ABORTED,
    }
}

#[inline(always)]
unsafe fn ptr_at<T>(
    ctx: &XdpContext,
    offset: usize,
) -> Result<*const T, ()> {
    let start = ctx.data();
    let end = ctx.data_end();
    let len = mem::size_of::<T>();

    if start + offset + len > end {
        return Err(());
    }

    let ptr = (start + offset) as *const T;
    Ok(&*ptr)
}

fn block_ip(address: u32) -> bool {
    unsafe { IP_BLOCKLIST.get(&address).is_some() }
}

fn try_xdp_firewall(ctx: XdpContext) -> Result<u32, ()> {
    let ethhdr: *const EthHdr = unsafe { ptr_at(&ctx, 0)? };
    match unsafe { (*ethhdr).ether_type() } {
        Ok(EtherType::Ipv4) => {}
        _ => return Ok(xdp_action::XDP_PASS),
    }

    let ipv4hdr: *const Ipv4Hdr = unsafe { ptr_at(&ctx, EthHdr::LEN)? };
    let source = u32::from_be_bytes(unsafe { (*ipv4hdr).src_addr });

    let action = if block_ip(source) {
        xdp_action::XDP_DROP
    } else {
        xdp_action::XDP_PASS
    };
    info!(&ctx, "SRC: {:i}, ACTION: {}", source, action);

    Ok(action)
}
```

--------------------------------

### eBPF Panic Handler

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Provides a minimal panic handler required for eBPF programs, as they cannot use the default behavior.

```rust
#[cfg(not(test))]
#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> !
{
    loop {}
}

```

--------------------------------

### XDP Firewall Packet Processing Logic

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

Processes incoming packets, checks if the source IP is in the blocklist, and returns XDP_DROP or XDP_PASS accordingly. Logs the source IP and action taken.

```rust
fn block_ip(address: u32) -> bool {
    unsafe { BLOCKLIST.get(&address).is_some() }
}

fn try_xdp_firewall(ctx: XdpContext) -> Result<u32, ()> {
    let ethhdr: *const EthHdr = unsafe { ptr_at(&ctx, 0)? };
    match unsafe { (*ethhdr).ether_type() } {
        Ok(EtherType::Ipv4) => {} // Process IPv4 packets
        _ => return Ok(xdp_action::XDP_PASS), // Pass non-IPv4 packets
    }

    let ipv4hdr: *const Ipv4Hdr = unsafe { ptr_at(&ctx, EthHdr::LEN)? };
    let source = u32::from_be_bytes(unsafe { (*ipv4hdr).src_addr });

    let action = if block_ip(source) {
        xdp_action::XDP_DROP
    } else {
        xdp_action::XDP_PASS
    };
    info!(&ctx, "SRC: {:i}, ACTION: {}", source, action);

    Ok(action)
}

```

--------------------------------

### Safe Pointer Access for eBPF Context

Source: https://github.com/aya-rs/book/blob/main/src/book/programs/xdp.md

A helper function to safely access data within an XdpContext at a given offset, performing bounds checking to prevent out-of-bounds reads.

```rust
#[inline(always)]
unsafe fn ptr_at<T>(
    ctx: &XdpContext,
    offset: usize,
) -> Result<*const T, ()> {
    let start = ctx.data();
    let end = ctx.data_end();
    let len = mem::size_of::<T>();

    if start + offset + len > end {
        return Err(());
    }

    let ptr = (start + offset) as *const T;
    Ok(&*ptr)
}

```