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LibELF: Use MAP_PRIVATE for file-backed mmaps in ELFDynamicLoader

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Clean up some unused code, clean up FIXMEs, and remove premature
--dynamic-loader/-pie from LinkDemo (so it runs again on master)
This commit is contained in:
Andrew Kaster 2020-02-28 22:47:39 -07:00 committed by Andreas Kling
parent c616eb6aaf
commit c678b35043
Notes: sideshowbarker 2024-07-19 08:58:16 +09:00 
Author: https://github.com/ADKaster
Commit: https://github.com/SerenityOS/serenity/commit/c678b35043d
Pull-request: https://github.com/SerenityOS/serenity/pull/1325
2 changed files with 7 additions and 15 deletions
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1
Demos/DynamicLink/LinkDemo/Makefile
View File

@ -4,6 +4,5 @@ OBJS = \
PROGRAM = LinkDemo
SUBPROJECT_CXXFLAGS = -fPIC
LDFLAGS = -pie -Wl,--dynamic-linker=/lib/ld-elf.so
include ../../../Makefile.common

21
Libraries/LibELF/ELFDynamicLoader.cpp
View File

@ -58,8 +58,7 @@ ELFDynamicLoader::ELFDynamicLoader(const char* filename, int fd, size_t size)
{
String file_mmap_name = String::format("ELF_DYN: %s", m_filename.characters());
// FIXME: When MAP_PRIVATE is implemented for file-backed regions, change to MAP_PRIVATE
m_file_mapping = mmap_with_name(nullptr, size, PROT_READ, MAP_SHARED, m_image_fd, 0, file_mmap_name.characters());
m_file_mapping = mmap_with_name(nullptr, size, PROT_READ, MAP_PRIVATE, m_image_fd, 0, file_mmap_name.characters());
if (MAP_FAILED == m_file_mapping) {
m_valid = false;
}
@ -97,6 +96,10 @@ bool ELFDynamicLoader::load_from_image(unsigned flags)
load_program_headers(elf_image);
// Don't need this private mapping anymore
munmap(m_file_mapping, m_file_size);
m_file_mapping = MAP_FAILED;
m_dynamic_object = AK::make<ELFDynamicObject>(m_text_segment_load_address, m_dynamic_section_address);
return load_stage_2(flags);
@ -112,6 +115,7 @@ bool ELFDynamicLoader::load_stage_2(unsigned flags)
#endif
if (m_dynamic_object->has_text_relocations()) {
dbg() << "Someone linked non -fPIC code into " << m_filename << " :(";
ASSERT(m_text_segment_load_address.get() != 0);
if (0 > mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_WRITE)) {
perror("mprotect .text: PROT_READ | PROT_WRITE"); // FIXME: dlerror?
@ -140,8 +144,6 @@ bool ELFDynamicLoader::load_stage_2(unsigned flags)
void ELFDynamicLoader::load_program_headers(const ELFImage& elf_image)
{
size_t total_required_allocation_size = 0; // NOTE: If we don't have any TEXTREL, we can keep RO data RO, which would be nice
Vector<ProgramHeaderRegion> program_headers;
ProgramHeaderRegion* text_region_ptr = nullptr;
@ -152,8 +154,6 @@ void ELFDynamicLoader::load_program_headers(const ELFImage& elf_image)
elf_image.for_each_program_header([&](const ELFImage::ProgramHeader& program_header) {
ProgramHeaderRegion new_region;
new_region.set_program_header(program_header.raw_header());
if (new_region.is_load())
total_required_allocation_size += new_region.required_load_size();
program_headers.append(move(new_region));
auto& region = program_headers.last();
if (region.is_tls_template())
@ -173,19 +173,12 @@ void ELFDynamicLoader::load_program_headers(const ELFImage& elf_image)
// Process regions in order: .text, .data, .tls
auto* region = text_region_ptr;
// FIXME: When MAP_PRIVATE is implemented for file-backed regions, change to MAP_PRIVATE without the mprotect and memcpy
//void* text_segment_begin = mmap_with_name(nullptr, region->required_load_size(), region->mmap_prot(), MAP_PRIVATE, m_image_fd, region->offset(), String::format(".text: %s", m_filename.characters()).characters());
void* text_segment_begin = mmap_with_name(nullptr, region->required_load_size(), PROT_READ | PROT_WRITE , MAP_ANONYMOUS | MAP_PRIVATE, 0, 0, String::format(".text: %s", m_filename.characters()).characters());
void* text_segment_begin = mmap_with_name(nullptr, region->required_load_size(), region->mmap_prot(), MAP_PRIVATE, m_image_fd, region->offset(), String::format(".text: %s", m_filename.characters()).characters());
if (MAP_FAILED == text_segment_begin) {
ASSERT_NOT_REACHED();
}
m_text_segment_size = region->required_load_size();
m_text_segment_load_address = VirtualAddress { (u32)text_segment_begin };
memcpy(m_text_segment_load_address.as_ptr(), (u8*)m_file_mapping + region->offset(), region->size_in_image());
if (0 > mprotect(text_segment_begin, m_text_segment_size, region->mmap_prot())) {
perror("mprotect .text PROT_READ | PROT_EXEC");
ASSERT_NOT_REACHED();
}
m_dynamic_section_address = dynamic_region_desired_vaddr.offset(m_text_segment_load_address.get());