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LibELF: Make a dummy VM reservation before mapping dynamic objects

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Using the text segment for the VM reservation ran into trouble when
there was a discrepancy between the p_filesz and p_memsz.

Simplify this mechanism and avoid trouble by making the reservation
as a MAP_PRIVATE | MAP_NORESERVE throwaway mapping instead.

Fixes #5225.
This commit is contained in:
Andreas Kling 2021-02-03 23:42:18 +01:00
parent c9cd5ff6bb
commit 3a3270eb68
Notes: sideshowbarker 2024-07-18 22:36:07 +09:00
1 changed files with 22 additions and 15 deletions
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37
Userland/Libraries/LibELF/DynamicLoader.cpp
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@ -286,25 +286,38 @@ void DynamicLoader::load_program_headers()
ASSERT(!text_region.value().is_writable());
// First, we map the text *and* data segments, in order to allocate enough VM
// to hold both contiguously in the address space.
// First, we make a dummy reservation mapping, in order to allocate enough VM
// to hold both text+data contiguously in the address space.
Checked<size_t> total_mapping_size;
total_mapping_size = text_region.value().required_load_size();
total_mapping_size += data_region.value().required_load_size();
ASSERT(!total_mapping_size.has_overflow());
auto* reservation = mmap(requested_load_address, total_mapping_size.value(), PROT_NONE, MAP_ANON | MAP_PRIVATE | MAP_NORESERVE, 0, 0);
if (reservation == MAP_FAILED) {
perror("mmap reservation");
ASSERT_NOT_REACHED();
}
// Then we unmap the reservation.
if (munmap(reservation, total_mapping_size.value()) < 0) {
perror("munmap reservation");
ASSERT_NOT_REACHED();
}
// Now we can map the text segment at the reserved address.
auto* text_segment_begin = (u8*)mmap_with_name(
requested_load_address,
total_mapping_size.value(),
reservation,
text_region.value().required_load_size(),
PROT_READ,
text_mmap_flags,
m_image_fd,
text_region.value().offset(),
String::formatted("{}: .text", m_filename).characters());
if (MAP_FAILED == text_segment_begin) {
perror("mmap text / initial segment");
if (text_segment_begin == MAP_FAILED) {
perror("mmap text");
ASSERT_NOT_REACHED();
}
@ -312,19 +325,13 @@ void DynamicLoader::load_program_headers()
m_text_segment_size = text_region.value().required_load_size();
m_text_segment_load_address = VirtualAddress { (FlatPtr)text_segment_begin };
// Then, we unmap the data segment part of the above combined VM allocation.
auto* data_segment_address = (u8*)text_segment_begin + text_region.value().required_load_size();
if (munmap(data_segment_address, data_region.value().required_load_size()) < 0) {
perror("munmap");
ASSERT_NOT_REACHED();
}
if (m_elf_image.is_dynamic())
m_dynamic_section_address = dynamic_region_desired_vaddr.offset(m_text_segment_load_address.get());
else
m_dynamic_section_address = dynamic_region_desired_vaddr;
// Finally, we remap the data segment, this time privately.
// Finally, we make an anonymous mapping for the data segment. Contents are then copied from the file.
auto* data_segment_address = (u8*)text_segment_begin + text_region.value().required_load_size();
auto* data_segment = (u8*)mmap_with_name(
data_segment_address,
data_region.value().required_load_size(),
@ -335,7 +342,7 @@ void DynamicLoader::load_program_headers()
String::formatted("{}: .data", m_filename).characters());
if (MAP_FAILED == data_segment) {
perror("mmap data segment");
perror("mmap data");
ASSERT_NOT_REACHED();
}