efi

A framework for writing UEFI applications in Rust. Acts like the Rust standard library on the UEFI platform with support for things like:

• Console I/O
• Containers such as Vec and String via a custom allocator
• Macros like println!, write!, format! etc.
• Rust I/O primitives as Read and Write traits and the related types
• UDP and TCP sockets similar to those in stdlib
• Implementation of IpAddr and its supporting types
• Domain name resolution so that you can connect sockets using a hostname

Also offers an ergonomic API for UEFI-specific functionality such as:

• Loading and starting images
• DHCP
• PXE
• Device paths

It uses the efi_ffi crate to interface with the UEFI platform.

Limitations

• Is a work in progress. API surface can change without notice.
• Currently only x64 architecture is supported.
• Tested to compile only with Rust nightly version nightly-2023-01-12. May not compile with others. You must force this version using a rust-toolchain file (as shown in the following section)

Writing a UEFI Application

To write a UEFI application using this framework follow the below steps:

1. Create a new crate for your application by running cargo new my_efi_app, where my_efi_app is the name of the application
2. Add efi = "0.3" under [dependencies] in Cargo.toml
3. Add a file named rust-toolchain containing the text nightly-2023-01-12 at the root of the crate. This will ensure that the crate is always built with nightly-2023-01-12.
4. Add the below code in my_efi_app/src/main.rs. Comments in the code explain each part:

#![no_std] // Indicates to the Rust compiler that the app does not depend on the standard library but is a 'standalone' application.
#![no_main] // Indicates that this application does not have a "main" function typically found in a Linux or Windows application (although it does have its own "main" function "efi_main" as declared below)

// Externs for efi and alloc crates (alloc crate is the one that contains definitions of String and Vec etc.)
#[macro_use] extern crate efi;
extern crate alloc;


// EFI entrypoint or main function. UEFI firmware will call this function to start the application.
// The signature and the name of this function must be exactly as below.
#[no_mangle]
pub extern "win64" fn efi_main(image_handle: efi::ffi::EFI_HANDLE, sys_table : *const efi::ffi::EFI_SYSTEM_TABLE) -> isize {
    efi::init_env(image_handle, sys_table); // Call to init_env must be the first thing in efi_main. Without it things like println!() won't work

    println!("Welcome to UEFI");

    // Your business logic here

    0
}

// A handler to respond to panics in the code. Required by the Rust compiler
#[panic_handler]
fn panic(_: &core::panic::PanicInfo) -> ! {
    loop {}
}

Building

Building the application requires the target x86_64-unknown-uefi to be installed on your machine. To install it:

1. Open a commmand shell in the root of your crate (i.e. my_efi_app folder in this case)
2. Run the command rustup target add x86_64-unknown-uefi

This must be done in the root of the crate because then the target will be installed for the Rust toolchain we specified above with the root-toolchain file.

After the target is installed, build the application with the command cargo build --target x86_64-unknown-uefi. When the build completes the resulting EFI application my_efi_app.efi will be found in target\x86_64-unknown-uefi\debug\

Running

Run the UEFI appliction in a qemu virtual machine by following the below steps:

1. Download and install qemu
2. Google for ovmf.fd and download that binary (This is the OVMF firmware under which we will run the application)
3. Start qemu by running this commandline: <path where qemu is installed>/qemu-system-x86_64 -pflash <path where you downloaded ovmf.fd>/ovmf.fd -hda fat:rw:<path to your uefi application crate>/target/x86_64-unknown-uefi/debug
4. Qemu will boot into ovmf.fd firmware and start the EFI shell
5. Wait for EFI shell command prompt. When it appears enter the application's name my_efi_app.efi and press ENTER
6. The application will run and print "Welcome to UEFI" on the qemu screen

Example Application

For a sample application see examples/sample_efi_app.rs. Build it by running cargo build --target x86_64-unknown-uefi --example sample_efi_app. The resulting binary sample_efi_app.efi will be found in target/x86_64-unknown-uefi/debug/examples.

The application performs DHCP at the start to obtain an IP address and then makes an HTTP request to a specified server. So to run it you need to follow the below steps:

1. Ensure that a DHCP server is running in your network and can give out IP addresses.
2. On the machine on which you will run the application, install a TAP adapter of your choice and note its name.
3. Connect the TAP adapter to the same LAN as the DHCP server above. If they are not on the same LAN the application will not receive an IP address.
4. Run qemu with the following commandline: <path where qemu is installed>/qemu-system-x86_64 -pflash <path where you downloaded ovmf.fd>/ovmf.fd -hda fat:rw:<path to your uefi application crate>/target/x86_64-unknown-uefi/debug/examples -net tap,ifname=<name of your TAP adapter> -net nic. With the two -net options at the end this commandline tells qemu to use the TAP adapter you installed above. Ensure that the name you specify after ifname= is that of the TAP adapter which you noted above.

The application will start, perform DHCP, get an IP address, prompt you for the name of an HTTP server and then make a GET request to that server.