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lib.rs
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/*
* "Sui: embed and extract auxillary data from binaries"
*
* Copyright (c) 2024 Divy Srivastava
* Copyright (c) 2024 the Deno authors
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
//! Sui is a library for embedding and extracting auxillary data from binary files.
//!
//! # Examples
//!
//! Embedding data in a Mach-O binary:
//! ```rust
//! use libsui::Macho;
//! use std::fs::File;
//!
//! # fn main() -> Result<(), libsui::Error> {
//! let data = b"Hello, world!";
//! let exe = std::fs::read("tests/exec_mach64")?;
//! let mut out = File::create("tests/out")?;
//!
//! Macho::from(exe)?
//! .write_section("__SECTION", data.to_vec())?
//! .build(&mut out)?;
//! # Ok(())
//! # }
//! ```
use core::mem::size_of;
use editpe::{
constants::{CODE_PAGE_ID_EN_US, RT_GROUP_ICON, RT_ICON, RT_RCDATA},
types::{IconDirectory, IconDirectoryEntry},
ResourceData, ResourceEntry, ResourceEntryName, ResourceTable,
};
use std::io::Write;
use zerocopy::{AsBytes, FromBytes, FromZeroes};
pub mod apple_codesign;
#[cfg(all(unix, not(target_vendor = "apple")))]
pub use elf::find_section;
#[cfg(target_vendor = "apple")]
pub use macho::find_section;
#[cfg(windows)]
pub use pe::find_section;
#[derive(Debug)]
pub enum Error {
InvalidObject(&'static str),
InternalError,
IoError(std::io::Error),
}
impl std::fmt::Display for Error {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self {
Error::InvalidObject(msg) => write!(f, "Invalid object: {}", msg),
Error::InternalError => write!(f, "Internal error"),
Error::IoError(err) => write!(f, "I/O error: {}", err),
}
}
}
impl From<std::io::Error> for Error {
fn from(err: std::io::Error) -> Self {
Error::IoError(err)
}
}
impl std::error::Error for Error {}
/// A portable executable (PE)
///
/// Build a new PE from existing PE and write auxillary data as
/// a resource in the .rsrc section.
pub struct PortableExecutable<'a> {
image: editpe::Image<'a>,
resource_dir: editpe::ResourceDirectory,
icons: Vec<IconDirectoryEntry>,
}
impl<'a> PortableExecutable<'a> {
/// Parse from a PE file
pub fn from(data: &'a [u8]) -> Result<Self, Error> {
Ok(Self {
image: editpe::Image::parse(data)
.map_err(|_| Error::InvalidObject("Failed to parse PE"))?,
resource_dir: editpe::ResourceDirectory::default(),
icons: Vec::new(),
})
}
/// Write a resource to the PE file
pub fn write_resource(mut self, name: &str, sectdata: Vec<u8>) -> Result<Self, Error> {
let root = self.resource_dir.root_mut();
if root.get(ResourceEntryName::ID(RT_RCDATA as u32)).is_none() {
root.insert(
ResourceEntryName::ID(RT_RCDATA as u32),
ResourceEntry::Table(ResourceTable::default()),
);
}
let rc_table = match root
.get_mut(ResourceEntryName::ID(RT_RCDATA as u32))
.unwrap()
{
ResourceEntry::Table(table) => table,
ResourceEntry::Data(_) => {
return Err(Error::InvalidObject("RCDATA is not a table"));
}
};
let name = name.to_uppercase();
rc_table.insert(
editpe::ResourceEntryName::from_string(name.clone()),
ResourceEntry::Table(ResourceTable::default()),
);
let rc_table = match rc_table
.get_mut(editpe::ResourceEntryName::from_string(name))
.unwrap()
{
ResourceEntry::Table(table) => table,
ResourceEntry::Data(_) => {
return Err(Error::InvalidObject("Resource entry is not a table"));
}
};
let mut entry = editpe::ResourceData::default();
entry.set_data(sectdata);
rc_table.insert(ResourceEntryName::ID(0), ResourceEntry::Data(entry));
Ok(self)
}
/// Set the icon of the executable.
pub fn set_icon<T: AsRef<[u8]>>(mut self, icon: T) -> Result<Self, Error> {
let root = self.resource_dir.root_mut();
let icon = icon.as_ref();
// find the main icon table
if root.get(ResourceEntryName::ID(RT_ICON as u32)).is_none() {
root.insert(
ResourceEntryName::ID(RT_ICON as u32),
ResourceEntry::Table(ResourceTable::default()),
);
}
let icon_table = match root.get_mut(ResourceEntryName::ID(RT_ICON as u32)).unwrap() {
ResourceEntry::Table(table) => table,
ResourceEntry::Data(_) => {
return Err(Error::InvalidObject("icon table is not a table"));
}
};
// find the first free icon id
let first_free_icon_id = icon_table
.entries()
.into_iter()
.filter_map(|k| match k {
ResourceEntryName::ID(id) => Some(id),
_ => None,
})
.max()
.unwrap_or(&0)
+ 1;
// add the icon to the icon table
let mut icon_directory_entries = Vec::new();
let id = first_free_icon_id;
let mut inner_table = ResourceTable::default();
let data = {
let mut entry = IconDirectoryEntry::read_from_prefix(&icon[6..20]).unwrap();
entry.id = id as u16;
icon_directory_entries.push(entry);
icon[22..].to_owned()
};
let mut resource_data = ResourceData::default();
resource_data.set_codepage(CODE_PAGE_ID_EN_US as u32);
resource_data.set_data(data);
inner_table.insert(ResourceEntryName::ID(0), ResourceEntry::Data(resource_data));
icon_table.insert(ResourceEntryName::ID(id), ResourceEntry::Table(inner_table));
self.icons = icon_directory_entries;
Ok(self)
}
/// Build and write the modified PE file
pub fn build<W: std::io::Write>(mut self, writer: &mut W) -> Result<(), Error> {
// TODO: the order of the table entries matters. this works for now.
if !self.icons.is_empty() {
let root = self.resource_dir.root_mut();
// find the group icon table
if root
.get(ResourceEntryName::ID(RT_GROUP_ICON as u32))
.is_none()
{
root.insert(
ResourceEntryName::ID(RT_GROUP_ICON as u32),
ResourceEntry::Table(ResourceTable::default()),
);
}
let group_table = match root
.get_mut(ResourceEntryName::ID(RT_GROUP_ICON as u32))
.unwrap()
{
ResourceEntry::Table(table) => table,
ResourceEntry::Data(_) => {
return Err(Error::InvalidObject("group icon table is not a table"));
}
};
let data = {
let mut data = Vec::new();
let icon_directory = IconDirectory {
reserved: 0,
type_: 1,
count: self.icons.len() as u16,
};
data.extend(icon_directory.as_bytes());
for entry in self.icons {
data.extend(&entry.as_bytes()[..14]);
}
data
};
let mut resource_data = ResourceData::default();
resource_data.set_codepage(CODE_PAGE_ID_EN_US as u32);
resource_data.set_data(data);
// insert the main icon directory table
let mut inner_table = ResourceTable::default();
inner_table.insert(ResourceEntryName::ID(0), ResourceEntry::Data(resource_data));
group_table.insert_at(
ResourceEntryName::from_string("MAINICON"),
ResourceEntry::Table(inner_table),
0,
);
}
self.image
.set_resource_directory(self.resource_dir)
.map_err(|_| Error::InternalError)?;
let data = self.image.data();
writer.write_all(data)?;
Ok(())
}
}
#[cfg(windows)]
mod pe {
use std::ffi::CString;
use windows_sys::Win32::System::LibraryLoader::{
FindResourceA, LoadResource, LockResource, SizeofResource,
};
pub fn find_section(section_name: &str) -> Option<&[u8]> {
let Ok(section_name) = CString::new(section_name) else {
return None;
};
unsafe {
let resource_handle = FindResourceA(0, section_name.as_ptr() as _, 10 as *const _);
if resource_handle == 0 {
return None;
}
let resource_data = LoadResource(0, resource_handle);
if resource_data == 0 {
return None;
}
let resource_size = SizeofResource(0, resource_handle);
if resource_size == 0 {
return None;
}
let resource_ptr = LockResource(resource_data);
Some(std::slice::from_raw_parts(
resource_ptr as *const u8,
resource_size as usize,
))
}
}
}
#[repr(C)]
#[derive(Debug, Clone, FromBytes, FromZeroes, AsBytes)]
pub(crate) struct SegmentCommand64 {
cmd: u32,
cmdsize: u32,
segname: [u8; 16],
vmaddr: u64,
vmsize: u64,
fileoff: u64,
filesize: u64,
maxprot: u32,
initprot: u32,
nsects: u32,
flags: u32,
}
#[derive(FromBytes, FromZeroes, AsBytes)]
#[repr(C)]
pub(crate) struct Header64 {
magic: u32,
cputype: i32,
cpusubtype: u32,
filetype: u32,
ncmds: u32,
sizeofcmds: u32,
flags: u32,
reserved: u32,
}
#[repr(C)]
#[derive(Debug, Clone, FromBytes, FromZeroes, AsBytes)]
pub(crate) struct Section64 {
sectname: [u8; 16],
segname: [u8; 16],
addr: u64,
size: u64,
offset: u32,
align: u32,
reloff: u32,
nreloc: u32,
flags: u32,
reserved1: u32,
reserved2: u32,
reserved3: u32,
}
const SEG_LINKEDIT: &[u8] = b"__LINKEDIT";
const LC_SEGMENT_64: u32 = 0x19;
const LC_SYMTAB: u32 = 0x2;
const LC_DYSYMTAB: u32 = 0xb;
pub(crate) const LC_CODE_SIGNATURE: u32 = 0x1d;
const LC_FUNCTION_STARTS: u32 = 0x26;
const LC_DATA_IN_CODE: u32 = 0x29;
const LC_DYLD_INFO: u32 = 0x22;
const LC_DYLD_INFO_ONLY: u32 = 0x80000022;
const LC_DYLIB_CODE_SIGN_DRS: u32 = 0x2b;
const LC_LINKER_OPTIMIZATION_HINT: u32 = 0x2d;
const LC_DYLD_EXPORTS_TRIE: u32 = 0x80000033;
const LC_DYLD_CHAINED_FIXUPS: u32 = 0x80000034;
const CPU_TYPE_ARM_64: i32 = 0x0100000c;
fn align(size: u64, base: u64) -> u64 {
let over = size % base;
if over == 0 {
size
} else {
size + (base - over)
}
}
fn align_vmsize(size: u64, page_size: u64) -> u64 {
align(if size > 0x4000 { size } else { 0x4000 }, page_size)
}
fn shift(value: u64, amount: u64, range_min: u64, range_max: u64) -> u64 {
if value < range_min || value > (range_max + range_min) {
return value;
}
value + amount
}
pub struct Macho {
header: Header64,
commands: Vec<(u32, u32, usize)>,
linkedit_cmd: SegmentCommand64,
rest_size: u64,
data: Vec<u8>,
seg: SegmentCommand64,
sec: Section64,
sectdata: Option<Vec<u8>>,
}
pub(crate) const SEGNAME: [u8; 16] = *b"__SUI\0\0\0\0\0\0\0\0\0\0\0";
impl Macho {
pub fn from(obj: Vec<u8>) -> Result<Self, Error> {
let header = Header64::read_from_prefix(&obj)
.ok_or(Error::InvalidObject("Failed to read header"))?;
let mut commands: Vec<(u32, u32, usize)> = Vec::with_capacity(header.ncmds as usize);
let mut offset = size_of::<Header64>();
let mut linkedit_cmd = None;
for _ in 0..header.ncmds as usize {
let cmd = u32::from_le_bytes(
obj[offset..offset + 4]
.try_into()
.map_err(|_| Error::InvalidObject("Failed to read command"))?,
);
let cmdsize = u32::from_le_bytes(
obj[offset + 4..offset + 8]
.try_into()
.map_err(|_| Error::InvalidObject("Failed to read command size"))?,
);
if cmd == LC_SEGMENT_64 {
let segcmd = SegmentCommand64::read_from_prefix(&obj[offset..])
.ok_or(Error::InvalidObject("Failed to read segment command"))?;
if segcmd.segname[..SEG_LINKEDIT.len()] == *SEG_LINKEDIT {
linkedit_cmd = Some(segcmd);
}
}
commands.push((cmd, cmdsize, offset));
offset += cmdsize as usize;
}
let Some(linkedit_cmd) = linkedit_cmd else {
return Err(Error::InvalidObject("Linkedit segment not found"));
};
let rest_size =
linkedit_cmd.fileoff - size_of::<Header64>() as u64 - header.sizeofcmds as u64;
Ok(Self {
header,
commands,
linkedit_cmd,
data: obj,
rest_size,
seg: SegmentCommand64::new_zeroed(),
sec: Section64::new_zeroed(),
sectdata: None,
})
}
pub fn write_section(mut self, name: &str, sectdata: Vec<u8>) -> Result<Self, Error> {
let page_size = if self.header.cputype == CPU_TYPE_ARM_64 {
0x10000
} else {
0x1000
};
self.seg = SegmentCommand64 {
cmd: LC_SEGMENT_64,
cmdsize: size_of::<SegmentCommand64>() as u32 + size_of::<Section64>() as u32,
segname: SEGNAME,
vmaddr: self.linkedit_cmd.vmaddr,
vmsize: align_vmsize(sectdata.len() as u64, page_size),
filesize: align_vmsize(sectdata.len() as u64, page_size),
fileoff: self.linkedit_cmd.fileoff,
maxprot: 0x01,
initprot: 0x01,
nsects: 1,
flags: 0,
};
let mut sectname = [0; 16];
sectname[..name.len()].copy_from_slice(name.as_bytes());
self.sec = Section64 {
addr: self.seg.vmaddr,
size: sectdata.len() as u64,
offset: self.linkedit_cmd.fileoff as u32,
align: if sectdata.len() < 16 { 0 } else { 4 },
segname: SEGNAME,
sectname,
..self.sec
};
self.linkedit_cmd.vmaddr += self.seg.vmsize;
let linkedit_fileoff = self.linkedit_cmd.fileoff;
self.linkedit_cmd.fileoff += self.seg.filesize;
macro_rules! shift_cmd {
($cmd:expr) => {
$cmd = shift(
$cmd as _,
self.seg.filesize,
linkedit_fileoff,
self.linkedit_cmd.filesize,
) as _;
};
}
for (cmd, _, offset) in self.commands.iter_mut() {
match *cmd {
LC_SYMTAB => {
#[derive(FromBytes, FromZeroes, AsBytes)]
#[repr(C)]
pub struct SymtabCommand {
pub cmd: u32,
pub cmdsize: u32,
pub symoff: u32,
pub nsyms: u32,
pub stroff: u32,
pub strsize: u32,
}
let cmd = SymtabCommand::mut_from_prefix(&mut self.data[*offset..])
.ok_or(Error::InvalidObject("Failed to read symtab command"))?;
shift_cmd!(cmd.symoff);
shift_cmd!(cmd.stroff);
}
LC_DYSYMTAB => {
#[derive(FromBytes, FromZeroes, AsBytes)]
#[repr(C)]
pub struct DysymtabCommand {
pub cmd: u32,
pub cmdsize: u32,
pub ilocalsym: u32,
pub nlocalsym: u32,
pub iextdefsym: u32,
pub nextdefsym: u32,
pub iundefsym: u32,
pub nundefsym: u32,
pub tocoff: u32,
pub ntoc: u32,
pub modtaboff: u32,
pub nmodtab: u32,
pub extrefsymoff: u32,
pub nextrefsyms: u32,
pub indirectsymoff: u32,
pub nindirectsyms: u32,
pub extreloff: u32,
pub nextrel: u32,
pub locreloff: u32,
pub nlocrel: u32,
}
let cmd = DysymtabCommand::mut_from_prefix(&mut self.data[*offset..])
.ok_or(Error::InvalidObject("Failed to read dysymtab command"))?;
shift_cmd!(cmd.tocoff);
shift_cmd!(cmd.modtaboff);
shift_cmd!(cmd.extrefsymoff);
shift_cmd!(cmd.indirectsymoff);
shift_cmd!(cmd.extreloff);
shift_cmd!(cmd.locreloff);
}
LC_CODE_SIGNATURE
| LC_FUNCTION_STARTS
| LC_DATA_IN_CODE
| LC_DYLIB_CODE_SIGN_DRS
| LC_LINKER_OPTIMIZATION_HINT
| LC_DYLD_EXPORTS_TRIE
| LC_DYLD_CHAINED_FIXUPS => {
#[derive(FromBytes, FromZeroes, AsBytes)]
#[repr(C)]
struct LinkeditDataCommand {
cmd: u32,
cmdsize: u32,
dataoff: u32,
datasize: u32,
}
let cmd = LinkeditDataCommand::mut_from_prefix(&mut self.data[*offset..])
.ok_or(Error::InvalidObject("Failed to read linkedit data command"))?;
shift_cmd!(cmd.dataoff);
}
LC_DYLD_INFO | LC_DYLD_INFO_ONLY => {
#[derive(FromBytes, FromZeroes, AsBytes)]
#[repr(C)]
pub struct DyldInfoCommand {
pub cmd: u32,
pub cmdsize: u32,
pub rebase_off: u32,
pub rebase_size: u32,
pub bind_off: u32,
pub bind_size: u32,
pub weak_bind_off: u32,
pub weak_bind_size: u32,
pub lazy_bind_off: u32,
pub lazy_bind_size: u32,
pub export_off: u32,
pub export_size: u32,
}
let dyld_info = DyldInfoCommand::mut_from_prefix(&mut self.data[*offset..])
.ok_or(Error::InvalidObject("Failed to read dyld info command"))?;
shift_cmd!(dyld_info.rebase_off);
shift_cmd!(dyld_info.bind_off);
shift_cmd!(dyld_info.weak_bind_off);
shift_cmd!(dyld_info.lazy_bind_off);
shift_cmd!(dyld_info.export_off);
}
_ => {}
}
}
self.header.ncmds += 1;
self.header.sizeofcmds += self.seg.cmdsize;
self.sectdata = Some(sectdata);
Ok(self)
}
/// Build and write the modified Mach-O file
pub fn build<W: Write>(mut self, writer: &mut W) -> Result<(), Error> {
writer.write_all(self.header.as_bytes())?;
for (cmd, cmdsize, offset) in self.commands.iter_mut() {
if *cmd == LC_SEGMENT_64 {
let segcmd = SegmentCommand64::read_from_prefix(&self.data[*offset..])
.ok_or(Error::InvalidObject("Failed to read segment command"))?;
if segcmd.segname[..SEG_LINKEDIT.len()] == *SEG_LINKEDIT {
writer.write_all(self.seg.as_bytes())?;
writer.write_all(self.sec.as_bytes())?;
writer.write_all(self.linkedit_cmd.as_bytes())?;
continue;
}
}
writer.write_all(&self.data[*offset..*offset + *cmdsize as usize])?;
}
let mut off = self.header.sizeofcmds as usize + size_of::<Header64>();
let len = self.rest_size as usize - self.seg.cmdsize as usize;
writer.write_all(&self.data[off..off + len])?;
off += len;
if let Some(sectdata) = self.sectdata {
writer.write_all(§data)?;
if self.seg.filesize > sectdata.len() as u64 {
let padding = vec![0; (self.seg.filesize - sectdata.len() as u64) as usize];
writer.write_all(&padding)?;
}
}
writer.write_all(&self.data[off..off + self.linkedit_cmd.filesize as usize])?;
Ok(())
}
pub fn build_and_sign<W: Write>(self, mut writer: W) -> Result<(), Error> {
if self.header.cputype == CPU_TYPE_ARM_64 {
let mut data = Vec::new();
self.build(&mut data)?;
let codesign = apple_codesign::MachoSigner::new(data)?;
codesign.sign(writer)
} else {
self.build(&mut writer)
}
}
}
#[cfg(target_vendor = "apple")]
mod macho {
use super::SEGNAME;
use std::ffi::CString;
use std::os::raw::c_char;
extern "C" {
pub fn getsectdata(
segname: *const c_char,
sectname: *const c_char,
size: *mut usize,
) -> *mut c_char;
pub fn _dyld_get_image_vmaddr_slide(image_index: usize) -> usize;
}
pub fn find_section(section_name: &str) -> Option<&[u8]> {
let mut section_size: usize = 0;
let section_name = CString::new(section_name).ok()?;
unsafe {
let mut ptr = getsectdata(
SEGNAME.as_ptr() as *const c_char,
section_name.as_ptr() as *const c_char,
&mut section_size as *mut usize,
);
if ptr.is_null() {
return None;
}
// Add the "virtual memory address slide" amount to ensure a valid pointer
// in cases where the virtual memory address have been adjusted by the OS.
ptr = ptr.wrapping_add(_dyld_get_image_vmaddr_slide(0));
Some(std::slice::from_raw_parts(ptr as *const u8, section_size))
}
}
}
pub struct Elf<'a> {
data: &'a [u8],
}
// Unsecure, makeshift hash function
fn hash(name: &str) -> u32 {
let mut hash: u32 = 0;
for c in name.bytes() {
hash = hash.wrapping_add(c as u32);
}
hash
}
impl<'a> Elf<'a> {
pub fn new(data: &'a [u8]) -> Self {
Self { data }
}
pub fn append<W: Write>(
&self,
name: &str,
sectdata: &[u8],
writer: &mut W,
) -> Result<(), Error> {
let mut elf = self.data.to_vec();
elf.extend_from_slice(sectdata);
// hash the name to 4 bytes int
const MAGIC: u32 = 0x501e;
elf.extend_from_slice(&MAGIC.to_le_bytes());
elf.extend_from_slice(&hash(name).to_le_bytes());
elf.extend_from_slice(&(sectdata.len() as u32 + 12).to_le_bytes());
writer.write_all(&elf)?;
Ok(())
}
}
#[cfg(all(unix, not(target_vendor = "apple")))]
mod elf {
use std::io::Read;
use std::io::Seek;
use std::io::SeekFrom;
pub fn find_section(name: &str) -> Option<&[u8]> {
let Ok(exe) = std::env::current_exe() else {
return None;
};
let Ok(mut file) = std::fs::File::open(exe) else {
return None;
};
file.seek(SeekFrom::End(-12)).unwrap();
let mut buf = [0; 12];
file.read_exact(&mut buf).unwrap();
let magic = u32::from_le_bytes([buf[0], buf[1], buf[2], buf[3]]);
if magic != 0x501e {
return None;
}
let hash = u32::from_le_bytes([buf[4], buf[5], buf[6], buf[7]]);
let name_hash = super::hash(name);
if hash != name_hash {
return None;
}
let offset = u32::from_le_bytes([buf[8], buf[9], buf[10], buf[11]]) as u64;
file.seek(SeekFrom::End(-(offset as i64))).unwrap();
// Read section data
let mut buf = Vec::new();
file.read_to_end(&mut buf).unwrap();
let data = buf[..buf.len() - 12].to_vec();
Some(Box::leak(data.into_boxed_slice()))
}
}
/// Utilities for detecting binary formats
pub mod utils {
/// Check if the given data is an ELF64 binary
pub fn is_elf(data: &[u8]) -> bool {
let magic = u32::from_be_bytes([data[0], data[1], data[2], data[3]]);
magic == 0x7f454c46
}
/// Check if the given data is a 64-bit Mach-O binary
pub fn is_macho(data: &[u8]) -> bool {
let magic = u32::from_le_bytes([data[0], data[1], data[2], data[3]]);
magic == 0xfeedfacf
}
/// Check if the given data is a PE32+ binary
pub fn is_pe(data: &[u8]) -> bool {
let magic = u16::from_le_bytes([data[0], data[1]]);
magic == 0x5a4d
}
}