// Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
extern crate sys_util;
use std::error::{self, Error as KernelLoaderError};
use std::ffi::CStr;
use std::fmt::{self, Display};
use std::io::{Read, Seek, SeekFrom};
use std::mem;
use sys_util::{GuestAddress, GuestMemory};
#[allow(dead_code)]
#[allow(non_camel_case_types)]
#[allow(non_snake_case)]
#[allow(non_upper_case_globals)]
#[cfg_attr(feature = "cargo-clippy", allow(clippy))]
mod elf;
#[derive(Debug, PartialEq)]
pub enum Error {
BigEndianElfOnLittle,
CommandLineCopy,
CommandLineOverflow,
InvalidElfMagicNumber,
InvalidProgramHeaderSize,
InvalidProgramHeaderOffset,
InvalidProgramHeaderAddress,
ReadElfHeader,
ReadKernelImage,
ReadProgramHeader,
SeekKernelStart,
SeekElfStart,
SeekProgramHeader,
}
pub type Result<T> = std::result::Result<T, Error>;
impl error::Error for Error {
fn description(&self) -> &str {
match self {
Error::BigEndianElfOnLittle => {
"Trying to load big-endian binary on little-endian machine"
}
Error::CommandLineCopy => "Failed writing command line to guest memory",
Error::CommandLineOverflow => "Command line overflowed guest memory",
Error::InvalidElfMagicNumber => "Invalid Elf magic number",
Error::InvalidProgramHeaderSize => "Invalid program header size",
Error::InvalidProgramHeaderOffset => "Invalid program header offset",
Error::InvalidProgramHeaderAddress => "Invalid Program Header Address",
Error::ReadElfHeader => "Unable to read elf header",
Error::ReadKernelImage => "Unable to read kernel image",
Error::ReadProgramHeader => "Unable to read program header",
Error::SeekKernelStart => "Unable to seek to kernel start",
Error::SeekElfStart => "Unable to seek to elf start",
Error::SeekProgramHeader => "Unable to seek to program header",
}
}
}
impl Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "Kernel Loader Error: {}", Error::description(self))
}
}
/// Loads a kernel from a vmlinux elf image to a slice
///
/// # Arguments
///
/// * `guest_mem` - The guest memory region the kernel is written to.
/// * `kernel_start` - The offset into `guest_mem` at which to load the kernel.
/// * `kernel_image` - Input vmlinux image.
pub fn load_kernel<F>(
guest_mem: &GuestMemory,
kernel_start: GuestAddress,
kernel_image: &mut F,
) -> Result<()>
where
F: Read + Seek,
{
let mut ehdr: elf::Elf64_Ehdr = Default::default();
kernel_image
.seek(SeekFrom::Start(0))
.map_err(|_| Error::SeekElfStart)?;
unsafe {
// read_struct is safe when reading a POD struct. It can be used and dropped without issue.
sys_util::read_struct(kernel_image, &mut ehdr).map_err(|_| Error::ReadElfHeader)?;
}
// Sanity checks
if ehdr.e_ident[elf::EI_MAG0 as usize] != elf::ELFMAG0 as u8
|| ehdr.e_ident[elf::EI_MAG1 as usize] != elf::ELFMAG1
|| ehdr.e_ident[elf::EI_MAG2 as usize] != elf::ELFMAG2
|| ehdr.e_ident[elf::EI_MAG3 as usize] != elf::ELFMAG3
{
return Err(Error::InvalidElfMagicNumber);
}
if ehdr.e_ident[elf::EI_DATA as usize] != elf::ELFDATA2LSB as u8 {
return Err(Error::BigEndianElfOnLittle);
}
if ehdr.e_phentsize as usize != mem::size_of::<elf::Elf64_Phdr>() {
return Err(Error::InvalidProgramHeaderSize);
}
if (ehdr.e_phoff as usize) < mem::size_of::<elf::Elf64_Ehdr>() {
// If the program header is backwards, bail.
return Err(Error::InvalidProgramHeaderOffset);
}
kernel_image
.seek(SeekFrom::Start(ehdr.e_phoff))
.map_err(|_| Error::SeekProgramHeader)?;
let phdrs: Vec<elf::Elf64_Phdr> = unsafe {
// Reading the structs is safe for a slice of POD structs.
sys_util::read_struct_slice(kernel_image, ehdr.e_phnum as usize)
.map_err(|_| Error::ReadProgramHeader)?
};
// Read in each section pointed to by the program headers.
for phdr in &phdrs {
if phdr.p_type != elf::PT_LOAD || phdr.p_filesz == 0 {
continue;
}
kernel_image
.seek(SeekFrom::Start(phdr.p_offset))
.map_err(|_| Error::SeekKernelStart)?;
let mem_offset = kernel_start
.checked_add(phdr.p_paddr)
.ok_or(Error::InvalidProgramHeaderAddress)?;
guest_mem
.read_to_memory(mem_offset, kernel_image, phdr.p_filesz as usize)
.map_err(|_| Error::ReadKernelImage)?;
}
Ok(())
}
/// Writes the command line string to the given memory slice.
///
/// # Arguments
///
/// * `guest_mem` - A u8 slice that will be partially overwritten by the command line.
/// * `guest_addr` - The address in `guest_mem` at which to load the command line.
/// * `cmdline` - The kernel command line.
pub fn load_cmdline(
guest_mem: &GuestMemory,
guest_addr: GuestAddress,
cmdline: &CStr,
) -> Result<()> {
let len = cmdline.to_bytes().len();
if len == 0 {
return Ok(());
}
let end = guest_addr
.checked_add(len as u64 + 1)
.ok_or(Error::CommandLineOverflow)?; // Extra for null termination.
if end > guest_mem.end_addr() {
return Err(Error::CommandLineOverflow)?;
}
guest_mem
.write_at_addr(cmdline.to_bytes_with_nul(), guest_addr)
.map_err(|_| Error::CommandLineCopy)?;
Ok(())
}
#[cfg(test)]
mod test {
use super::*;
use std::io::Cursor;
use sys_util::{GuestAddress, GuestMemory};
const MEM_SIZE: u64 = 0x8000;
fn create_guest_mem() -> GuestMemory {
GuestMemory::new(&vec![(GuestAddress(0x0), MEM_SIZE)]).unwrap()
}
#[test]
fn cmdline_overflow() {
let gm = create_guest_mem();
let cmdline_address = GuestAddress(MEM_SIZE - 5);
assert_eq!(
Err(Error::CommandLineOverflow),
load_cmdline(
&gm,
cmdline_address,
CStr::from_bytes_with_nul(b"12345\0").unwrap()
)
);
}
#[test]
fn cmdline_write_end() {
let gm = create_guest_mem();
let mut cmdline_address = GuestAddress(45);
assert_eq!(
Ok(()),
load_cmdline(
&gm,
cmdline_address,
CStr::from_bytes_with_nul(b"1234\0").unwrap()
)
);
let val: u8 = gm.read_obj_from_addr(cmdline_address).unwrap();
assert_eq!(val, '1' as u8);
cmdline_address = cmdline_address.unchecked_add(1);
let val: u8 = gm.read_obj_from_addr(cmdline_address).unwrap();
assert_eq!(val, '2' as u8);
cmdline_address = cmdline_address.unchecked_add(1);
let val: u8 = gm.read_obj_from_addr(cmdline_address).unwrap();
assert_eq!(val, '3' as u8);
cmdline_address = cmdline_address.unchecked_add(1);
let val: u8 = gm.read_obj_from_addr(cmdline_address).unwrap();
assert_eq!(val, '4' as u8);
cmdline_address = cmdline_address.unchecked_add(1);
let val: u8 = gm.read_obj_from_addr(cmdline_address).unwrap();
assert_eq!(val, '\0' as u8);
}
// Elf64 image that prints hello world on x86_64.
fn make_elf_bin() -> Vec<u8> {
let mut v = Vec::new();
v.extend_from_slice(include_bytes!("test_elf.bin"));
v
}
#[test]
fn load_elf() {
let gm = create_guest_mem();
let kernel_addr = GuestAddress(0x0);
let image = make_elf_bin();
assert_eq!(
Ok(()),
load_kernel(&gm, kernel_addr, &mut Cursor::new(&image))
);
}
#[test]
fn bad_magic() {
let gm = create_guest_mem();
let kernel_addr = GuestAddress(0x0);
let mut bad_image = make_elf_bin();
bad_image[0x1] = 0x33;
assert_eq!(
Err(Error::InvalidElfMagicNumber),
load_kernel(&gm, kernel_addr, &mut Cursor::new(&bad_image))
);
}
#[test]
fn bad_endian() {
// Only little endian is supported
let gm = create_guest_mem();
let kernel_addr = GuestAddress(0x0);
let mut bad_image = make_elf_bin();
bad_image[0x5] = 2;
assert_eq!(
Err(Error::BigEndianElfOnLittle),
load_kernel(&gm, kernel_addr, &mut Cursor::new(&bad_image))
);
}
#[test]
fn bad_phoff() {
// program header has to be past the end of the elf header
let gm = create_guest_mem();
let kernel_addr = GuestAddress(0x0);
let mut bad_image = make_elf_bin();
bad_image[0x20] = 0x10;
assert_eq!(
Err(Error::InvalidProgramHeaderOffset),
load_kernel(&gm, kernel_addr, &mut Cursor::new(&bad_image))
);
}
}