289 lines
8.9 KiB
Rust
289 lines
8.9 KiB
Rust
#![no_main]
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#![no_std]
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#![feature(abi_efiapi)]
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#![feature(negative_impls)]
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#![deny(unsafe_op_in_unsafe_fn)]
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extern crate alloc;
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mod linux_loader;
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mod pe_loader;
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mod pe_section;
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mod uefi_helpers;
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use alloc::vec::Vec;
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use pe_loader::Image;
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use pe_section::{pe_section, pe_section_as_string};
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use sha2::{Digest, Sha256};
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use uefi::{
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prelude::*,
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proto::{
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console::text::Output,
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loaded_image::LoadedImage,
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media::file::{File, FileAttribute, FileMode, RegularFile},
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},
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CStr16, CString16, Result,
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};
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use crate::{
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linux_loader::InitrdLoader,
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uefi_helpers::{booted_image_file, read_all},
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};
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type Hash = sha2::digest::Output<Sha256>;
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/// Print the startup logo on boot.
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fn print_logo(output: &mut Output) -> Result<()> {
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output.clear()?;
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output.output_string(cstr16!(
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"
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_ _ _\r
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| | | | | |\r
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| | __ _ _ __ ______ _| |__ ___ ___ | |_ ___\r
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| |/ _` | '_ \\|_ / _` | '_ \\ / _ \\ / _ \\| __/ _ \\\r
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| | (_| | | | |/ / (_| | |_) | (_) | (_) | || __/\r
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|_|\\__,_|_| |_/___\\__,_|_.__/ \\___/ \\___/ \\__\\___|\r
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\r
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"
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))
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}
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/// The configuration that is embedded at build time.
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///
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/// After lanzaboote is built, lanzatool needs to embed configuration
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/// into the binary. This struct represents that information.
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struct EmbeddedConfiguration {
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/// The filename of the kernel to be booted. This filename is
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/// relative to the root of the volume that contains the
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/// lanzaboote binary.
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kernel_filename: CString16,
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/// The cryptographic hash of the kernel.
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kernel_hash: Hash,
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/// The filename of the initrd to be passed to the kernel. See
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/// `kernel_filename` for how to interpret these filenames.
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initrd_filename: CString16,
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/// The cryptographic hash of the initrd. This hash is computed
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/// over the whole PE binary, not only the embedded initrd.
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initrd_hash: Hash,
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/// The kernel command-line.
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cmdline: CString16,
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}
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/// Extract a string, stored as UTF-8, from a PE section.
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fn extract_string(file_data: &[u8], section: &str) -> Result<CString16> {
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let string = pe_section_as_string(file_data, section).ok_or(Status::INVALID_PARAMETER)?;
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Ok(CString16::try_from(string.as_str()).map_err(|_| Status::INVALID_PARAMETER)?)
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}
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/// Extract a Blake3 hash from a PE section.
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fn extract_hash(file_data: &[u8], section: &str) -> Result<Hash> {
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let array: [u8; 32] = pe_section(file_data, section)
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.ok_or(Status::INVALID_PARAMETER)?
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.try_into()
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.map_err(|_| Status::INVALID_PARAMETER)?;
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Ok(array.into())
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}
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impl EmbeddedConfiguration {
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fn new(file: &mut RegularFile) -> Result<Self> {
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file.set_position(0)?;
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let file_data = read_all(file)?;
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Ok(Self {
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kernel_filename: extract_string(&file_data, ".kernelp")?,
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kernel_hash: extract_hash(&file_data, ".kernelh")?,
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initrd_filename: extract_string(&file_data, ".initrdp")?,
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initrd_hash: extract_hash(&file_data, ".initrdh")?,
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cmdline: extract_string(&file_data, ".cmdline")?,
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})
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}
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}
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/// Boot the Linux kernel without checking the PE signature.
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///
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/// We assume that the caller has made sure that the image is safe to
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/// be loaded using other means.
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fn boot_linux_unchecked(
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handle: Handle,
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system_table: SystemTable<Boot>,
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kernel_data: Vec<u8>,
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kernel_cmdline: &CStr16,
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initrd_data: Vec<u8>,
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) -> uefi::Result<()> {
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let kernel =
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Image::load(system_table.boot_services(), &kernel_data).expect("Failed to load the kernel");
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let mut initrd_loader = InitrdLoader::new(system_table.boot_services(), handle, initrd_data)?;
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let status = unsafe { kernel.start(handle, &system_table, kernel_cmdline) };
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initrd_loader.uninstall(system_table.boot_services())?;
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status.into()
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}
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/// Boot the Linux kernel via the UEFI PE loader.
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///
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/// This should only succeed when UEFI Secure Boot is off (or
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/// broken...), because the Lanzaboote tool does not sign the kernel.
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///
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/// In essence, we can use this routine to detect whether Secure Boot
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/// is actually enabled.
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fn boot_linux_uefi(
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handle: Handle,
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system_table: SystemTable<Boot>,
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kernel_data: Vec<u8>,
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kernel_cmdline: &CStr16,
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initrd_data: Vec<u8>,
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) -> uefi::Result<()> {
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let kernel_handle = system_table.boot_services().load_image(
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handle,
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uefi::table::boot::LoadImageSource::FromBuffer {
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buffer: &kernel_data,
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file_path: None,
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},
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)?;
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let mut kernel_image = system_table
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.boot_services()
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.open_protocol_exclusive::<LoadedImage>(kernel_handle)?;
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unsafe {
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kernel_image.set_load_options(
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kernel_cmdline.as_ptr() as *const u8,
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// This unwrap is "safe" in the sense that any
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// command-line that doesn't fit 4G is surely broken.
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u32::try_from(kernel_cmdline.num_bytes()).unwrap(),
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);
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}
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let mut initrd_loader = InitrdLoader::new(system_table.boot_services(), handle, initrd_data)?;
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let status = system_table
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.boot_services()
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.start_image(kernel_handle)
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.status();
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initrd_loader.uninstall(system_table.boot_services())?;
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status.into()
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}
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#[entry]
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fn main(handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
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uefi_services::init(&mut system_table).unwrap();
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print_logo(system_table.stdout()).unwrap();
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let config: EmbeddedConfiguration =
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EmbeddedConfiguration::new(&mut booted_image_file(system_table.boot_services()).unwrap())
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.expect("Failed to extract configuration from binary. Did you run lanzatool?");
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let kernel_data;
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let initrd_data;
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{
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let mut file_system = system_table
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.boot_services()
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.get_image_file_system(handle)
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.expect("Failed to get file system handle");
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let mut root = file_system
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.open_volume()
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.expect("Failed to find ESP root directory");
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let mut kernel_file = root
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.open(
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&config.kernel_filename,
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FileMode::Read,
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FileAttribute::empty(),
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)
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.expect("Failed to open kernel file for reading")
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.into_regular_file()
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.expect("Kernel is not a regular file");
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kernel_data = read_all(&mut kernel_file).expect("Failed to read kernel file into memory");
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let mut initrd_file = root
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.open(
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&config.initrd_filename,
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FileMode::Read,
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FileAttribute::empty(),
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)
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.expect("Failed to open initrd for reading")
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.into_regular_file()
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.expect("Initrd is not a regular file");
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initrd_data = read_all(&mut initrd_file).expect("Failed to read kernel file into memory");
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}
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let is_kernel_hash_correct = Sha256::digest(&kernel_data) == config.kernel_hash;
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let is_initrd_hash_correct = Sha256::digest(&initrd_data) == config.initrd_hash;
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if !is_kernel_hash_correct {
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system_table
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.stdout()
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.output_string(cstr16!("Hash mismatch for kernel!\r\n"))
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.unwrap();
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}
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if !is_initrd_hash_correct {
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system_table
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.stdout()
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.output_string(cstr16!("Hash mismatch for initrd!\r\n"))
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.unwrap();
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}
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if is_kernel_hash_correct && is_initrd_hash_correct {
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boot_linux_unchecked(
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handle,
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system_table,
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kernel_data,
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&config.cmdline,
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initrd_data,
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)
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.status()
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} else {
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// There is no good way to detect whether Secure Boot is
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// enabled. This is unfortunate, because we want to give the
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// user a way to recover from hash mismatches when Secure Boot
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// is off.
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//
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// So in case we get a hash mismatch, we will try to load the
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// Linux image using LoadImage. What happens then depends on
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// whether Secure Boot is enabled:
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//
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// **With Secure Boot**, the firmware will reject loading the
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// image with status::SECURITY_VIOLATION.
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//
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// **Without Secure Boot**, the firmware will just load the
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// Linux kernel.
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//
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// This is the behavior we want. A slight turd is that we
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// increase the attack surface here by exposing the unverfied
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// Linux image to the UEFI firmware. But in case the PE loader
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// of the firmware is broken, we have little hope of security
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// anyway.
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system_table
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.stdout()
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.output_string(cstr16!("WARNING: Trying to continue as non-Secure Boot. This will fail when Secure Boot is enabled.\r\n"))
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.unwrap();
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boot_linux_uefi(
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handle,
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system_table,
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kernel_data,
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&config.cmdline,
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initrd_data,
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)
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.status()
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}
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}
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