test-runner: add test for LoadFile and LoadFile2 protocols

This actually tests multiple things:
- LoadFile and LoadFile2 wrappers work
- (un)install_protocol_interface works
- how our API is suited to create a custom implementation of an existing
  protocol definition
- The workflow used in Linux loaders to enable the Linux EFI stub to load
  the initrd via the LOAD_FILE2 protocol.

Further what I'm doing in this test, is already deployed in the
wild: https://github.com/nix-community/lanzaboote/blob/b7f68a50e6902f28c07a9f8d41df76f4c0a9315b/rust/uefi/linux-bootloader/src/linux_loader.rs#L142

uefi-test-runner/Cargo.toml

@@ -6,6 +6,7 @@ publish = false
 edition = "2021"
 
 [dependencies]
+uefi-raw = { path = "../uefi-raw" }
 uefi = { path = "../uefi", features = ["alloc", "global_allocator", "panic_handler", "logger", "qemu"] }
 
 log.workspace = true

uefi-test-runner/src/proto/load.rs

@@ -0,0 +1,131 @@
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::ffi::c_void;
+use core::pin::Pin;
+use core::ptr;
+use core::ptr::addr_of;
+use uefi::prelude::BootServices;
+use uefi::proto::device_path::build::DevicePathBuilder;
+use uefi::proto::media::load_file::{LoadFile, LoadFile2};
+use uefi::proto::BootPolicy;
+use uefi::{Guid, Handle};
+use uefi_raw::protocol::device_path::DevicePathProtocol;
+use uefi_raw::protocol::media::{LoadFile2Protocol, LoadFileProtocol};
+use uefi_raw::Status;
+
+unsafe extern "efiapi" fn raw_load_file(
+    this: *mut LoadFile2Protocol,
+    _file_path: *const DevicePathProtocol,
+    _boot_policy: bool,
+    buffer_size: *mut usize,
+    buffer: *mut c_void,
+) -> Status {
+    log::debug!("Called static extern \"efiapi\" `raw_load_file` glue function");
+    let this = this.cast::<CustomLoadFile2Protocol>().as_ref().unwrap();
+    this.load_file(buffer_size, buffer.cast())
+}
+
+#[repr(C)]
+struct CustomLoadFile2Protocol {
+    inner: LoadFile2Protocol,
+    file_data: Vec<u8>,
+}
+
+impl CustomLoadFile2Protocol {
+    fn new(file_data: Vec<u8>) -> Pin<Box<Self>> {
+        let inner = Self {
+            inner: LoadFile2Protocol {
+                load_file: raw_load_file,
+            },
+            file_data,
+        };
+        Box::pin(inner)
+    }
+
+    fn load_file(&self, buf_len: *mut usize, buf: *mut c_void) -> Status {
+        if buf.is_null() || unsafe { *buf_len } < self.file_data.len() {
+            log::debug!("Returning buffer size");
+            unsafe { *buf_len = self.file_data.len() };
+            Status::BUFFER_TOO_SMALL
+        } else {
+            log::debug!("Writing file content to buffer");
+            unsafe {
+                ptr::copy_nonoverlapping(self.file_data.as_ptr(), buf.cast(), self.file_data.len());
+            }
+            Status::SUCCESS
+        }
+    }
+}
+
+unsafe fn install_protocol(
+    bt: &BootServices,
+    handle: Handle,
+    guid: Guid,
+    protocol: &mut CustomLoadFile2Protocol,
+) {
+    bt.install_protocol_interface(Some(handle), &guid, addr_of!(*protocol).cast())
+        .unwrap();
+}
+
+unsafe fn uninstall_protocol(
+    bt: &BootServices,
+    handle: Handle,
+    guid: Guid,
+    protocol: &mut CustomLoadFile2Protocol,
+) {
+    bt.uninstall_protocol_interface(handle, &guid, addr_of!(*protocol).cast())
+        .unwrap();
+}
+
+/// This tests the LoadFile and LoadFile2 protocols. As this protocol is not
+/// implemented in OVMF for the default handle, we implement it manually using
+/// `install_protocol_interface`. Then, we load a file from our custom installed
+/// protocol leveraging our protocol abstraction.
+///
+/// The way we are implementing the LoadFile(2) protocol is roughly what certain
+/// Linux loaders do so that Linux can find its initrd [0, 1].
+///
+/// [0] https://github.com/u-boot/u-boot/commit/ec80b4735a593961fe701cc3a5d717d4739b0fd0#diff-1f940face4d1cf74f9d2324952759404d01ee0a81612b68afdcba6b49803bdbbR171
+/// [1] https://github.com/torvalds/linux/blob/ee9a43b7cfe2d8a3520335fea7d8ce71b8cabd9d/drivers/firmware/efi/libstub/efi-stub-helper.c#L550
+pub fn test(bt: &BootServices) {
+    let image = bt.image_handle();
+
+    let load_data_msg = "Example file content.";
+    let load_data = load_data_msg.to_string().into_bytes();
+    let mut proto_load_file = CustomLoadFile2Protocol::new(load_data);
+    // Get the ptr to the inner value, not the wrapping smart pointer type.
+    let proto_load_file_ptr = proto_load_file.as_mut().get_mut();
+
+    // Install our custom protocol implementation as LoadFile and LoadFile2
+    // protocol.
+    unsafe {
+        install_protocol(bt, image, LoadFileProtocol::GUID, proto_load_file_ptr);
+        install_protocol(bt, image, LoadFile2Protocol::GUID, proto_load_file_ptr);
+    }
+
+    let mut dvp_vec = Vec::new();
+    let dvp = DevicePathBuilder::with_vec(&mut dvp_vec);
+    let dvp = dvp.finalize().unwrap();
+
+    let mut opened_load_file_protocol = bt.open_protocol_exclusive::<LoadFile>(image).unwrap();
+    let loadfile_file = opened_load_file_protocol
+        .load_file(dvp, BootPolicy::BootSelection)
+        .unwrap();
+    let loadfile_file_string = String::from_utf8(loadfile_file.to_vec()).unwrap();
+
+    let mut opened_load_file2_protocol = bt.open_protocol_exclusive::<LoadFile2>(image).unwrap();
+    let loadfile2_file = opened_load_file2_protocol.load_file(dvp).unwrap();
+    let loadfile2_file_string = String::from_utf8(loadfile2_file.to_vec()).unwrap();
+
+    assert_eq!(load_data_msg, &loadfile_file_string);
+    assert_eq!(load_data_msg, &loadfile2_file_string);
+
+    // Cleanup: Uninstall protocols again.
+    drop(opened_load_file_protocol);
+    drop(opened_load_file2_protocol);
+    unsafe {
+        uninstall_protocol(bt, image, LoadFileProtocol::GUID, proto_load_file_ptr);
+        uninstall_protocol(bt, image, LoadFile2Protocol::GUID, proto_load_file_ptr);
+    }
+}

uefi-test-runner/src/proto/mod.rs

@@ -17,6 +17,7 @@ pub fn test(st: &mut SystemTable<Boot>) {
     debug::test(bt);
     device_path::test(bt);
     driver::test(bt);
+    load::test(bt);
     loaded_image::test(bt);
     media::test(bt);
     network::test(bt);
@@ -78,6 +79,7 @@ mod console;
 mod debug;
 mod device_path;
 mod driver;
+mod load;
 mod loaded_image;
 mod media;
 mod misc;

uefi/CHANGELOG.md

@@ -21,7 +21,9 @@ details of the new `system`/`boot`/`runtime` modules, and upcoming deprecations.
   This comes with some changes. Read below. We recommend to directly use the
   implementations instead of the traits.
 - Added `LoadFile` and `LoadFile2` which abstracts over the `LOAD_FILE` and
-  `LOAD_FILE2` protocols.
+  `LOAD_FILE2` protocols. The UEFI test runner includes an integration test
+  that shows how Linux loaders can use this to implement the initrd loading
+  mechanism used in Linux.
 
 ## Changed
 - **Breaking:** `uefi::helpers::init` no longer takes an argument.