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https://github.com/RGBCube/serenity
synced 2025-07-25 17:17:44 +00:00
LibELF: Don't copy read-only data sections
The dynamic loader was mistakenly assuming that there are only two types of program load headers: text (RX) and data (RW). Now that we're linking with `-z separate-code`, we will also get some read-onlydata (R) segments. These can be memory-mapped directly without making a private per-process copy. To solve this, the code now instead separates the headers into map/copy instead of text/data. Writable segments get copied, while non-writable segments get memory-mapped. :^)
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parent
10f5a046c4
commit
9206efaabe
1 changed files with 28 additions and 30 deletions
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@ -246,8 +246,8 @@ void DynamicLoader::do_lazy_relocations()
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void DynamicLoader::load_program_headers()
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{
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Vector<ProgramHeaderRegion> load_regions;
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Vector<ProgramHeaderRegion> text_regions;
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Vector<ProgramHeaderRegion> data_regions;
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Vector<ProgramHeaderRegion> map_regions;
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Vector<ProgramHeaderRegion> copy_regions;
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Optional<ProgramHeaderRegion> tls_region;
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Optional<ProgramHeaderRegion> relro_region;
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@ -263,10 +263,10 @@ void DynamicLoader::load_program_headers()
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if (region.size_in_memory() == 0)
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return;
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load_regions.append(region);
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if (region.is_executable()) {
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text_regions.append(region);
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if (region.is_writable()) {
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copy_regions.append(region);
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} else {
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data_regions.append(region);
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map_regions.append(region);
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}
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} else if (region.is_dynamic()) {
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dynamic_region_desired_vaddr = region.desired_load_address();
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@ -276,15 +276,15 @@ void DynamicLoader::load_program_headers()
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}
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});
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VERIFY(!text_regions.is_empty() || !data_regions.is_empty());
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VERIFY(!map_regions.is_empty() || !copy_regions.is_empty());
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auto compare_load_address = [](ProgramHeaderRegion& a, ProgramHeaderRegion& b) {
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return a.desired_load_address().as_ptr() < b.desired_load_address().as_ptr();
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};
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quick_sort(load_regions, compare_load_address);
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quick_sort(text_regions, compare_load_address);
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quick_sort(data_regions, compare_load_address);
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quick_sort(map_regions, compare_load_address);
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quick_sort(copy_regions, compare_load_address);
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// Process regions in order: .text, .data, .tls
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void* requested_load_address = m_elf_image.is_dynamic() ? nullptr : load_regions.first().desired_load_address().as_ptr();
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@ -295,9 +295,6 @@ void DynamicLoader::load_program_headers()
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else
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reservation_mmap_flags |= MAP_FIXED;
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for (auto& text_region : text_regions)
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VERIFY(!text_region.is_writable());
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// First, we make a dummy reservation mapping, in order to allocate enough VM
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// to hold all regions contiguously in the address space.
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@ -320,27 +317,28 @@ void DynamicLoader::load_program_headers()
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VERIFY_NOT_REACHED();
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}
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for (auto& text_region : text_regions) {
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FlatPtr ph_text_desired_base = text_region.desired_load_address().get();
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FlatPtr ph_text_base = text_region.desired_load_address().page_base().get();
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FlatPtr ph_text_end = ph_text_base + round_up_to_power_of_two(text_region.size_in_memory() + text_region.desired_load_address().get() - ph_text_base, PAGE_SIZE);
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for (auto& region : map_regions) {
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FlatPtr ph_desired_base = region.desired_load_address().get();
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FlatPtr ph_base = region.desired_load_address().page_base().get();
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FlatPtr ph_end = ph_base + round_up_to_power_of_two(region.size_in_memory() + region.desired_load_address().get() - ph_base, PAGE_SIZE);
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// Now we can map the text segment at the reserved address.
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auto* text_segment_begin = (u8*)mmap_with_name(
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(u8*)reservation + ph_text_base - ph_load_base,
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ph_text_desired_base - ph_text_base + text_region.size_in_image(),
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auto* segment_base = (u8*)mmap_with_name(
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(u8*)reservation + ph_base - ph_load_base,
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ph_desired_base - ph_base + region.size_in_image(),
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PROT_READ,
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MAP_FILE | MAP_SHARED | MAP_FIXED,
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m_image_fd,
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VirtualAddress { text_region.offset() }.page_base().get(),
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VirtualAddress { region.offset() }.page_base().get(),
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String::formatted("{}: .text", m_filename).characters());
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if (text_segment_begin == MAP_FAILED) {
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perror("mmap text");
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if (segment_base == MAP_FAILED) {
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perror("mmap non-writable");
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VERIFY_NOT_REACHED();
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}
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m_text_segments.append({ VirtualAddress { (FlatPtr)text_segment_begin }, ph_text_end - ph_text_base });
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if (region.is_executable())
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m_text_segments.append({ VirtualAddress { segment_base }, ph_end - ph_base });
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}
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VERIFY(requested_load_address == nullptr || requested_load_address == reservation);
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@ -355,9 +353,9 @@ void DynamicLoader::load_program_headers()
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else
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m_dynamic_section_address = dynamic_region_desired_vaddr;
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for (auto& data_region : data_regions) {
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FlatPtr ph_data_base = data_region.desired_load_address().page_base().get();
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FlatPtr ph_data_end = ph_data_base + round_up_to_power_of_two(data_region.size_in_memory() + data_region.desired_load_address().get() - ph_data_base, PAGE_SIZE);
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for (auto& region : copy_regions) {
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FlatPtr ph_data_base = region.desired_load_address().page_base().get();
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FlatPtr ph_data_end = ph_data_base + round_up_to_power_of_two(region.size_in_memory() + region.desired_load_address().get() - ph_data_base, PAGE_SIZE);
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auto* data_segment_address = (u8*)reservation + ph_data_base - ph_load_base;
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size_t data_segment_size = ph_data_end - ph_data_base;
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@ -373,19 +371,19 @@ void DynamicLoader::load_program_headers()
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String::formatted("{}: .data", m_filename).characters());
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if (MAP_FAILED == data_segment) {
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perror("mmap data");
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perror("mmap writable");
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VERIFY_NOT_REACHED();
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}
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VirtualAddress data_segment_start;
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if (m_elf_image.is_dynamic())
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data_segment_start = VirtualAddress { (u8*)reservation + data_region.desired_load_address().get() };
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data_segment_start = VirtualAddress { (u8*)reservation + region.desired_load_address().get() };
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else
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data_segment_start = data_region.desired_load_address();
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data_segment_start = region.desired_load_address();
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VERIFY(data_segment_start.as_ptr() + data_region.size_in_memory() <= data_segment + data_segment_size);
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VERIFY(data_segment_start.as_ptr() + region.size_in_memory() <= data_segment + data_segment_size);
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memcpy(data_segment_start.as_ptr(), (u8*)m_file_data + data_region.offset(), data_region.size_in_image());
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memcpy(data_segment_start.as_ptr(), (u8*)m_file_data + region.offset(), region.size_in_image());
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}
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// FIXME: Initialize the values in the TLS section. Currently, it is zeroed.
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