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Add explicit read only data and executable data segment

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This commit is contained in:
Brendan Hansknecht 2021-09-01 16:55:36 -07:00
parent 029daab497
commit b61ca970a6
1 changed files with 66 additions and 45 deletions
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109
linker/src/lib.rs
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@ -588,8 +588,7 @@ pub fn preprocess(matches: &ArgMatches) -> io::Result<i32> {
let platform_gen_start = SystemTime::now();
// Copy header and shift everything to enable more program sections.
// We eventually want at least 3 new sections: executable code, read only data, read write data.
let added_header_count = 1;
let added_header_count = 2;
md.added_byte_count = ph_ent_size as u64 * added_header_count;
md.added_byte_count = md.added_byte_count
+ (MIN_SECTION_ALIGNMENT as u64 - md.added_byte_count % MIN_SECTION_ALIGNMENT as u64);
@ -983,9 +982,7 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
let mut offset = sh_offset as usize;
offset = align_by_constraint(offset, MIN_SECTION_ALIGNMENT);
// TODO: Switch to using multiple segments.
let new_segment_offset = offset;
let new_data_section_offset = offset;
let new_rodata_section_offset = offset;
// Align physical and virtual address of new segment.
let mut virt_offset = align_to_offset_by_constraint(
@ -993,10 +990,13 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
offset,
md.load_align_constraint as usize,
);
let new_segment_vaddr = virt_offset as u64;
let new_rodata_section_vaddr = virt_offset;
if verbose {
println!();
println!("New Virtual Segment Address: {:+x?}", new_segment_vaddr);
println!(
"New Virtual Rodata Section Address: {:+x?}",
new_rodata_section_vaddr
);
}
// First decide on sections locations and then recode every exact symbol locations.
@ -1015,6 +1015,7 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
.filter(|sec| sec.name().unwrap_or_default().starts_with(".rodata"))
.collect();
// bss section is like rodata section, but it has zero file size and non-zero virtual size.
let bss_sections: Vec<Section> = app_obj
.sections()
.filter(|sec| sec.name().unwrap_or_default().starts_with(".bss"))
@ -1029,6 +1030,8 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
return Ok(-1);
}
// Calculate addresses and load symbols.
// Note, it is important the bss sections come after the rodata sections.
for sec in rodata_sections
.iter()
.chain(bss_sections.iter())
@ -1062,25 +1065,33 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
Some((_, size)) => size,
None => 0,
};
if section_size != sec.size() {
if sec.name().unwrap_or_default().starts_with(".bss") {
// bss sections only modify the virtual size.
virt_offset += sec.size() as usize;
} else if section_size != sec.size() {
println!(
"We do not yet deal with sections that have different on disk and in memory sizes"
"We do not deal with non bss sections that have different on disk and in memory sizes"
);
return Ok(-1);
}
} else {
offset += section_size as usize;
virt_offset += sec.size() as usize;
}
}
if verbose {
println!("Data Relocation Offsets: {:+x?}", symbol_vaddr_map);
println!("Found App Function Symbols: {:+x?}", app_func_vaddr_map);
}
let new_text_section_offset = text_sections
let (new_text_section_offset, new_text_section_vaddr) = text_sections
.iter()
.map(|sec| section_offset_map.get(&sec.index()).unwrap().0)
.map(|sec| section_offset_map.get(&sec.index()).unwrap())
.min()
.unwrap();
let (new_text_section_offset, new_text_section_vaddr) =
(*new_text_section_offset, *new_text_section_vaddr);
// Move data and deal with relocations.
for sec in rodata_sections
.iter()
.chain(bss_sections.iter())
@ -1207,11 +1218,14 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
offset += sh_size;
// Flush app only data to speed up write to disk.
exec_mmap.flush_async_range(new_segment_offset, offset - new_segment_offset)?;
exec_mmap.flush_async_range(
new_rodata_section_offset,
offset - new_rodata_section_offset,
)?;
// TODO: look into merging symbol tables, debug info, and eh frames to enable better debugger experience.
// Add 2 new sections.
// Add 2 new sections and segments.
let new_section_count = 2;
offset += new_section_count * sh_ent_size as usize;
let section_headers = load_structs_inplace_mut::<elf::SectionHeader64<LittleEndian>>(
@ -1220,21 +1234,23 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
sh_num as usize + new_section_count,
);
let new_data_section_vaddr = new_segment_vaddr;
let new_data_section_size = new_text_section_offset - new_data_section_offset;
let new_text_section_vaddr = new_data_section_vaddr + new_data_section_size as u64;
let new_rodata_section_size = new_text_section_offset as u64 - new_rodata_section_offset as u64;
let new_rodata_section_virtual_size =
new_text_section_vaddr as u64 - new_rodata_section_vaddr as u64;
let new_text_section_vaddr = new_rodata_section_vaddr as u64 + new_rodata_section_size as u64;
let new_text_section_size = new_sh_offset as u64 - new_text_section_offset as u64;
let new_data_section = &mut section_headers[section_headers.len() - 2];
new_data_section.sh_name = endian::U32::new(LittleEndian, 0);
new_data_section.sh_type = endian::U32::new(LittleEndian, elf::SHT_PROGBITS);
new_data_section.sh_flags = endian::U64::new(LittleEndian, (elf::SHF_ALLOC) as u64);
new_data_section.sh_addr = endian::U64::new(LittleEndian, new_data_section_vaddr);
new_data_section.sh_offset = endian::U64::new(LittleEndian, new_data_section_offset as u64);
new_data_section.sh_size = endian::U64::new(LittleEndian, new_data_section_size as u64);
new_data_section.sh_link = endian::U32::new(LittleEndian, 0);
new_data_section.sh_info = endian::U32::new(LittleEndian, 0);
new_data_section.sh_addralign = endian::U64::new(LittleEndian, 16);
new_data_section.sh_entsize = endian::U64::new(LittleEndian, 0);
let new_rodata_section = &mut section_headers[section_headers.len() - 2];
new_rodata_section.sh_name = endian::U32::new(LittleEndian, 0);
new_rodata_section.sh_type = endian::U32::new(LittleEndian, elf::SHT_PROGBITS);
new_rodata_section.sh_flags = endian::U64::new(LittleEndian, (elf::SHF_ALLOC) as u64);
new_rodata_section.sh_addr = endian::U64::new(LittleEndian, new_rodata_section_vaddr as u64);
new_rodata_section.sh_offset = endian::U64::new(LittleEndian, new_rodata_section_offset as u64);
new_rodata_section.sh_size = endian::U64::new(LittleEndian, new_rodata_section_size);
new_rodata_section.sh_link = endian::U32::new(LittleEndian, 0);
new_rodata_section.sh_info = endian::U32::new(LittleEndian, 0);
new_rodata_section.sh_addralign = endian::U64::new(LittleEndian, 16);
new_rodata_section.sh_entsize = endian::U64::new(LittleEndian, 0);
let new_text_section_index = section_headers.len() - 1;
let new_text_section = &mut section_headers[new_text_section_index];
@ -1244,10 +1260,7 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
endian::U64::new(LittleEndian, (elf::SHF_ALLOC | elf::SHF_EXECINSTR) as u64);
new_text_section.sh_addr = endian::U64::new(LittleEndian, new_text_section_vaddr);
new_text_section.sh_offset = endian::U64::new(LittleEndian, new_text_section_offset as u64);
new_text_section.sh_size = endian::U64::new(
LittleEndian,
new_sh_offset as u64 - new_text_section_offset as u64,
);
new_text_section.sh_size = endian::U64::new(LittleEndian, new_text_section_size);
new_text_section.sh_link = endian::U32::new(LittleEndian, 0);
new_text_section.sh_info = endian::U32::new(LittleEndian, 0);
new_text_section.sh_addralign = endian::U64::new(LittleEndian, 16);
@ -1258,23 +1271,31 @@ pub fn surgery(matches: &ArgMatches) -> io::Result<i32> {
file_header.e_shoff = endian::U64::new(LittleEndian, new_sh_offset as u64);
file_header.e_shnum = endian::U16::new(LittleEndian, sh_num + new_section_count as u16);
// Add new segment.
// Add 2 new segments that match the new sections.
let program_headers = load_structs_inplace_mut::<elf::ProgramHeader64<LittleEndian>>(
&mut exec_mmap,
ph_offset as usize,
ph_num as usize,
);
let new_segment = program_headers.last_mut().unwrap();
new_segment.p_type = endian::U32::new(LittleEndian, elf::PT_LOAD);
// This is terrible but currently needed. Just bash everything to get how and make it read-write-execute.
new_segment.p_flags = endian::U32::new(LittleEndian, elf::PF_R | elf::PF_X | elf::PF_W);
new_segment.p_offset = endian::U64::new(LittleEndian, new_segment_offset as u64);
new_segment.p_vaddr = endian::U64::new(LittleEndian, new_segment_vaddr);
new_segment.p_paddr = endian::U64::new(LittleEndian, new_segment_vaddr);
let new_segment_size = (new_sh_offset - new_segment_offset) as u64;
new_segment.p_filesz = endian::U64::new(LittleEndian, new_segment_size);
new_segment.p_memsz = endian::U64::new(LittleEndian, new_segment_size);
new_segment.p_align = endian::U64::new(LittleEndian, md.load_align_constraint);
let new_rodata_segment = &mut program_headers[program_headers.len() - 2];
new_rodata_segment.p_type = endian::U32::new(LittleEndian, elf::PT_LOAD);
new_rodata_segment.p_flags = endian::U32::new(LittleEndian, elf::PF_R);
new_rodata_segment.p_offset = endian::U64::new(LittleEndian, new_rodata_section_offset as u64);
new_rodata_segment.p_vaddr = endian::U64::new(LittleEndian, new_rodata_section_vaddr as u64);
new_rodata_segment.p_paddr = endian::U64::new(LittleEndian, new_rodata_section_vaddr as u64);
new_rodata_segment.p_filesz = endian::U64::new(LittleEndian, new_rodata_section_size);
new_rodata_segment.p_memsz = endian::U64::new(LittleEndian, new_rodata_section_virtual_size);
new_rodata_segment.p_align = endian::U64::new(LittleEndian, md.load_align_constraint);
let new_text_segment = &mut program_headers[program_headers.len() - 1];
new_text_segment.p_type = endian::U32::new(LittleEndian, elf::PT_LOAD);
new_text_segment.p_flags = endian::U32::new(LittleEndian, elf::PF_R | elf::PF_X);
new_text_segment.p_offset = endian::U64::new(LittleEndian, new_text_section_offset as u64);
new_text_segment.p_vaddr = endian::U64::new(LittleEndian, new_text_section_vaddr);
new_text_segment.p_paddr = endian::U64::new(LittleEndian, new_text_section_vaddr);
new_text_segment.p_filesz = endian::U64::new(LittleEndian, new_text_section_size);
new_text_segment.p_memsz = endian::U64::new(LittleEndian, new_text_section_size);
new_text_segment.p_align = endian::U64::new(LittleEndian, md.load_align_constraint);
// Update calls from platform and dynamic symbols.
let dynsym_offset = md.dynamic_symbol_table_section_offset + md.added_byte_count;