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nac3ld: replace unsafe code

This commit is contained in:
occheung 2022-06-06 14:37:48 +08:00
parent 7cb9be0f81
commit 50ed04b787
2 changed files with 141 additions and 116 deletions
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227
nac3ld/src/dwarf.rs
View File

@ -2,6 +2,8 @@
use std::mem;
use byteorder::{ByteOrder, LittleEndian};
pub const DW_EH_PE_omit: u8 = 0xFF;
pub const DW_EH_PE_absptr: u8 = 0x00;
@ -22,44 +24,29 @@ pub const DW_EH_PE_aligned: u8 = 0x50;
pub const DW_EH_PE_indirect: u8 = 0x80;
pub struct DwarfReader {
pub ptr: *const u8,
pub struct DwarfReader<'a> {
pub slice: &'a [u8],
pub virt_addr: u32,
}
#[repr(C, packed)]
struct Unaligned<T>(T);
impl DwarfReader {
pub fn new(ptr: *const u8, virt_addr: u32) -> DwarfReader {
DwarfReader { ptr, virt_addr }
impl<'a> DwarfReader<'a> {
pub fn new(slice: &[u8], virt_addr: u32) -> DwarfReader {
DwarfReader { slice, virt_addr }
}
// DWARF streams are packed, so e.g., a u32 would not necessarily be aligned
// on a 4-byte boundary. This may cause problems on platforms with strict
// alignment requirements. By wrapping data in a "packed" struct, we are
// telling the backend to generate "misalignment-safe" code.
pub unsafe fn read<T: Copy>(&mut self) -> T {
let Unaligned(result) = *(self.ptr as *const Unaligned<T>);
let addr_increment = mem::size_of::<T>();
self.ptr = self.ptr.add(addr_increment);
self.virt_addr += addr_increment as u32;
result
}
pub unsafe fn offset(&mut self, offset: i32) {
self.ptr = self.ptr.offset(offset as isize);
pub fn offset(&mut self, offset: i32) {
self.slice = &self.slice[offset as usize..];
self.virt_addr = self.virt_addr.wrapping_add(offset as u32);
}
// ULEB128 and SLEB128 encodings are defined in Section 7.6 - "Variable
// Length Data".
pub unsafe fn read_uleb128(&mut self) -> u64 {
pub fn read_uleb128(&mut self) -> u64 {
let mut shift: usize = 0;
let mut result: u64 = 0;
let mut byte: u8;
loop {
byte = self.read::<u8>();
byte = self.read_u8();
result |= ((byte & 0x7F) as u64) << shift;
shift += 7;
if byte & 0x80 == 0 {
@ -69,12 +56,12 @@ impl DwarfReader {
result
}
pub unsafe fn read_sleb128(&mut self) -> i64 {
pub fn read_sleb128(&mut self) -> i64 {
let mut shift: u32 = 0;
let mut result: u64 = 0;
let mut byte: u8;
loop {
byte = self.read::<u8>();
byte = self.read_u8();
result |= ((byte & 0x7F) as u64) << shift;
shift += 7;
if byte & 0x80 == 0 {
@ -87,49 +74,90 @@ impl DwarfReader {
}
result as i64
}
}
pub struct DwarfWriter {
pub ptr: *mut u8,
}
impl DwarfWriter {
pub fn new(ptr: *mut u8) -> DwarfWriter {
DwarfWriter { ptr }
}
pub unsafe fn write<T: Copy>(&mut self, data: T) {
*(self.ptr as *mut Unaligned<T>) = Unaligned(data);
self.ptr = self.ptr.add(mem::size_of::<T>());
pub fn read_u8(&mut self) -> u8 {
let val = self.slice[0];
self.slice = &self.slice[1..];
val
}
}
unsafe fn read_encoded_pointer(reader: &mut DwarfReader, encoding: u8) -> Result<usize, ()> {
macro_rules! impl_read_fn {
( $($type: ty, $byteorder_fn: ident);* ) => {
impl<'a> DwarfReader<'a> {
$(
pub fn $byteorder_fn(&mut self) -> $type {
let val = LittleEndian::$byteorder_fn(self.slice);
self.slice = &self.slice[mem::size_of::<$type>()..];
val
}
)*
}
}
}
impl_read_fn!(
u16, read_u16;
u32, read_u32;
u64, read_u64;
i16, read_i16;
i32, read_i32;
i64, read_i64
);
pub struct DwarfWriter<'a> {
pub slice: &'a mut [u8],
pub offset: usize,
}
impl<'a> DwarfWriter<'a> {
pub fn new(slice: &mut [u8]) -> DwarfWriter {
DwarfWriter { slice, offset: 0 }
}
pub fn write_u8(&mut self, data: u8) {
self.slice[self.offset] = data;
self.offset += 1;
}
pub fn write_u32(&mut self, data: u32) {
LittleEndian::write_u32(&mut self.slice[self.offset..], data);
self.offset += 4;
}
}
fn read_encoded_pointer(reader: &mut DwarfReader, encoding: u8) -> Result<usize, ()> {
if encoding == DW_EH_PE_omit {
return Err(());
}
// DW_EH_PE_aligned implies it's an absolute pointer value
// However, we are linking library for 32-bits architecture
// The size of variable should be 4 bytes instead
if encoding == DW_EH_PE_aligned {
reader.ptr = round_up(reader.ptr as usize, mem::size_of::<usize>())? as *const u8;
return Ok(reader.read::<usize>());
let shifted_virt_addr = round_up(reader.virt_addr as usize, mem::size_of::<u32>())?;
let addr_inc = shifted_virt_addr - reader.virt_addr as usize;
reader.slice = &reader.slice[addr_inc..];
reader.virt_addr = shifted_virt_addr as u32;
return Ok(reader.read_u32() as usize);
}
match encoding & 0x0F {
DW_EH_PE_absptr => Ok(reader.read::<usize>()),
DW_EH_PE_absptr => Ok(reader.read_u32() as usize),
DW_EH_PE_uleb128 => Ok(reader.read_uleb128() as usize),
DW_EH_PE_udata2 => Ok(reader.read::<u16>() as usize),
DW_EH_PE_udata4 => Ok(reader.read::<u32>() as usize),
DW_EH_PE_udata8 => Ok(reader.read::<u64>() as usize),
DW_EH_PE_udata2 => Ok(reader.read_u16() as usize),
DW_EH_PE_udata4 => Ok(reader.read_u32() as usize),
DW_EH_PE_udata8 => Ok(reader.read_u64() as usize),
DW_EH_PE_sleb128 => Ok(reader.read_sleb128() as usize),
DW_EH_PE_sdata2 => Ok(reader.read::<i16>() as usize),
DW_EH_PE_sdata4 => Ok(reader.read::<i32>() as usize),
DW_EH_PE_sdata8 => Ok(reader.read::<i64>() as usize),
DW_EH_PE_sdata2 => Ok(reader.read_i16() as usize),
DW_EH_PE_sdata4 => Ok(reader.read_i32() as usize),
DW_EH_PE_sdata8 => Ok(reader.read_i64() as usize),
_ => Err(()),
}
}
unsafe fn read_encoded_pointer_with_pc(
fn read_encoded_pointer_with_pc(
reader: &mut DwarfReader,
encoding: u8,
) -> Result<usize, ()> {
@ -177,25 +205,25 @@ fn round_up(unrounded: usize, align: usize) -> Result<usize, ()> {
// frame information (CFI) record, so there should be only 1 common information entry (CIE).
// So the class parses the only CIE on init, cache the encoding info, then parse the FDE on
// iterations based on the cached encoding format.
pub struct EH_Frame {
pub struct EH_Frame<'a> {
// It refers to the augmentation data that corresponds to 'R' in the augmentation string
pub fde_pointer_encoding: u8,
pub fde_reader: DwarfReader,
pub fde_reader: DwarfReader<'a>,
pub fde_sz: usize,
}
impl EH_Frame {
pub unsafe fn new(eh_frame_slice: &[u8], eh_frame_addr: u32) -> Result<EH_Frame, ()> {
let mut cie_reader = DwarfReader::new(eh_frame_slice.as_ptr(), eh_frame_addr);
impl<'a> EH_Frame<'a> {
pub fn new(eh_frame_slice: &[u8], eh_frame_addr: u32) -> Result<EH_Frame, ()> {
let mut cie_reader = DwarfReader::new(eh_frame_slice, eh_frame_addr);
let eh_frame_size = eh_frame_slice.len();
let length = cie_reader.read::<u32>();
let length = cie_reader.read_u32();
let fde_reader = match length {
// eh_frame with 0 lengths means the CIE is terminated
// while length == u32::MAX means that the length is only representable with 64 bits,
// which does not make sense in a system with 32-bit address.
0 | 0xFFFFFFFF => unimplemented!(),
_ => {
let mut fde_reader = DwarfReader::new(cie_reader.ptr, cie_reader.virt_addr);
let mut fde_reader = DwarfReader::new(cie_reader.slice, cie_reader.virt_addr);
fde_reader.offset(length as i32);
fde_reader
}
@ -203,21 +231,21 @@ impl EH_Frame {
let fde_sz = eh_frame_size - mem::size_of::<u32>() - length as usize;
// Routine check on the .eh_frame well-formness, in terms of CIE ID & Version args.
assert_eq!(cie_reader.read::<u32>(), 0);
assert_eq!(cie_reader.read::<u8>(), 1);
assert_eq!(cie_reader.read_u32(), 0);
assert_eq!(cie_reader.read_u8(), 1);
// Parse augmentation string
// The first character must be 'z', there is no way to proceed otherwise
assert_eq!(cie_reader.read::<u8>(), b'z');
assert_eq!(cie_reader.read_u8(), b'z');
// Establish a pointer that skips ahead of the string
// Skip code/data alignment factors & return address register along the way as well
// We only tackle the case where 'z' and 'R' are part of the augmentation string, otherwise
// we cannot get the addresses to make .eh_frame_hdr
let mut aug_data_reader = DwarfReader::new(cie_reader.ptr, cie_reader.virt_addr);
let mut aug_data_reader = DwarfReader::new(cie_reader.slice, cie_reader.virt_addr);
let mut aug_str_len = 0;
loop {
if aug_data_reader.read::<u8>() == b'\0' {
if aug_data_reader.read_u8() == b'\0' {
break;
}
aug_str_len += 1;
@ -231,18 +259,18 @@ impl EH_Frame {
aug_data_reader.read_uleb128(); // Augmentation data length
let mut fde_pointer_encoding = DW_EH_PE_omit;
for _ in 0..aug_str_len {
match cie_reader.read::<u8>() {
match cie_reader.read_u8() {
b'L' => {
aug_data_reader.read::<u8>();
aug_data_reader.read_u8();
}
b'P' => {
let encoding = aug_data_reader.read::<u8>();
let encoding = aug_data_reader.read_u8();
read_encoded_pointer(&mut aug_data_reader, encoding)?;
}
b'R' => {
fde_pointer_encoding = aug_data_reader.read::<u8>();
fde_pointer_encoding = aug_data_reader.read_u8();
}
// Other characters are not supported
@ -254,30 +282,30 @@ impl EH_Frame {
Ok(EH_Frame { fde_pointer_encoding, fde_reader, fde_sz })
}
pub unsafe fn iterate_fde(&self, callback: &mut dyn FnMut(u32, u32)) -> Result<(), ()> {
pub fn iterate_fde(&self, callback: &mut dyn FnMut(u32, u32)) -> Result<(), ()> {
// Parse each FDE to obtain the starting address that the FDE applies to
// Send the FDE offset and the mentioned address to a callback that write up the
// .eh_frame_hdr section
let mut remaining_len = self.fde_sz;
let mut reader = DwarfReader::new(self.fde_reader.ptr, self.fde_reader.virt_addr);
let mut reader = DwarfReader::new(self.fde_reader.slice, self.fde_reader.virt_addr);
loop {
if remaining_len == 0 {
break;
}
let fde_virt_addr = reader.virt_addr;
let length = match reader.read::<u32>() {
let length = match reader.read_u32() {
0 | 0xFFFFFFFF => unimplemented!(),
other => other,
};
// Remove the length of the header and the content from the counter
remaining_len -= length as usize + mem::size_of::<u32>();
let mut next_fde_reader = DwarfReader::new(reader.ptr, reader.virt_addr);
let mut next_fde_reader = DwarfReader::new(reader.slice, reader.virt_addr);
next_fde_reader.offset(length as i32);
// Skip CIE pointer offset
reader.read::<u32>();
reader.read_u32();
// Parse PC Begin using the encoding scheme mentioned in the CIE
let pc_begin = read_encoded_pointer_with_pc(&mut reader, self.fde_pointer_encoding)?;
@ -291,74 +319,73 @@ impl EH_Frame {
}
}
pub struct EH_Frame_Hdr {
fde_writer: DwarfWriter,
fde_count_ptr: *mut u8,
pub struct EH_Frame_Hdr<'a> {
fde_writer: DwarfWriter<'a>,
eh_frame_hdr_addr: u32,
fdes: Vec<(u32, u32)>,
}
impl EH_Frame_Hdr {
impl<'a> EH_Frame_Hdr<'a> {
// Create a EH_Frame_Hdr object, and write out the fixed fields of .eh_frame_hdr to memory
// eh_frame_ptr_enc will be 0x1B (PC-relative, 4 bytes)
// table_enc will be 0x3B (Relative to the start of .eh_frame_hdr, 4 bytes)
// Load address is not known at this point.
pub unsafe fn new(
pub fn new(
eh_frame_hdr_slice: &mut [u8],
eh_frame_hdr_addr: u32,
eh_frame_addr: u32,
) -> EH_Frame_Hdr {
let mut writer = DwarfWriter::new(eh_frame_hdr_slice.as_mut_ptr());
writer.write::<u8>(1);
writer.write::<u8>(0x1B);
writer.write::<u8>(0x03);
writer.write::<u8>(0x3B);
let mut writer = DwarfWriter::new(eh_frame_hdr_slice);
writer.write_u8(1);
writer.write_u8(0x1B);
writer.write_u8(0x03);
writer.write_u8(0x3B);
let eh_frame_offset =
(eh_frame_addr).wrapping_sub(eh_frame_hdr_addr + ((mem::size_of::<u8>() as u32) * 4));
writer.write(eh_frame_offset);
let fde_count_ptr = writer.ptr;
writer.write::<u32>(0);
writer.write_u32(eh_frame_offset);
writer.write_u32(0);
EH_Frame_Hdr { fde_writer: writer, fde_count_ptr, eh_frame_hdr_addr, fdes: Vec::new() }
EH_Frame_Hdr { fde_writer: writer, eh_frame_hdr_addr, fdes: Vec::new() }
}
pub unsafe fn add_fde(&mut self, init_loc: u32, addr: u32) {
fn fde_count_offset() -> usize {
8
}
pub fn add_fde(&mut self, init_loc: u32, addr: u32) {
self.fdes.push((
init_loc.wrapping_sub(self.eh_frame_hdr_addr),
addr.wrapping_sub(self.eh_frame_hdr_addr),
));
}
pub unsafe fn finalize_fde(mut self) {
pub fn finalize_fde(mut self) {
self.fdes
.sort_by(|(left_init_loc, _), (right_init_loc, _)| left_init_loc.cmp(right_init_loc));
for (init_loc, addr) in &self.fdes {
self.fde_writer.write(init_loc);
self.fde_writer.write(addr);
self.fde_writer.write_u32(*init_loc);
self.fde_writer.write_u32(*addr);
}
let mut fde_count_writer = DwarfWriter::new(self.fde_count_ptr);
fde_count_writer.write::<u32>(self.fdes.len() as u32);
LittleEndian::write_u32(&mut self.fde_writer.slice[Self::fde_count_offset()..], self.fdes.len() as u32);
}
pub unsafe fn size_from_eh_frame(eh_frame: &[u8]) -> usize {
// The virtual address of the EH frame does no matter in this case
pub fn size_from_eh_frame(eh_frame: &[u8]) -> usize {
// The virtual address of the EH frame does not matter in this case
// Calculation of size does not involve modifying any headers
let mut reader = DwarfReader::new(eh_frame.as_ptr(), 0);
let end_addr = eh_frame.as_ptr() as usize + eh_frame.len();
let mut reader = DwarfReader::new(eh_frame, 0);
let mut fde_count = 0;
while (reader.ptr as usize) < end_addr {
while !reader.slice.is_empty() {
// The original length field should be able to hold the entire value.
// The device memory space is limited to 32-bits addresses anyway.
let entry_length = reader.read::<u32>();
let next_ptr = reader.ptr.offset(entry_length as isize);
let entry_length = reader.read_u32();
if entry_length == 0 || entry_length == 0xFFFFFFFF {
unimplemented!()
}
if reader.read::<u32>() != 0 {
if reader.read_u32() != 0 {
fde_count += 1;
}
reader.ptr = next_ptr;
reader.offset(entry_length as i32 - mem::size_of::<u32>() as i32)
}
12 + fde_count * 8
}

4
nac3ld/src/lib.rs
View File

@ -549,7 +549,6 @@ impl<'a> Linker<'a> {
let eh_frame_slice = eh_frame_rec.data.as_slice();
// Prepare a new buffer to dodge borrow check
let mut eh_frame_hdr_vec: Vec<u8> = vec![0; eh_frame_hdr_rec.shdr.sh_size as usize];
unsafe {
let eh_frame = EH_Frame::new(eh_frame_slice, eh_frame_rec.shdr.sh_offset)
.map_err(|()| "cannot read EH frame")?;
let mut eh_frame_hdr = EH_Frame_Hdr::new(
@ -564,7 +563,6 @@ impl<'a> Linker<'a> {
// Sort FDE entries in .eh_frame_hdr
eh_frame_hdr.finalize_fde();
}
// Replace the data buffer in the record
get_mut_section_by_name!(self, ".eh_frame_hdr")
@ -727,7 +725,7 @@ impl<'a> Linker<'a> {
// Allocate memory for .eh_frame_hdr
// Calculate the size by parsing .eh_frame at coarse as possible
let eh_frame_hdr_size = unsafe { EH_Frame_Hdr::size_from_eh_frame(eh_frame) };
let eh_frame_hdr_size = EH_Frame_Hdr::size_from_eh_frame(eh_frame);
// Describe the .eh_frame_hdr with a dummy shdr.
let eh_frame_hdr_shdr = Elf32_Shdr {