DynamicLoader: Some ELF data segments were allocated too small

For a data segment that starts at a non-zero offset into a 4KB page and
crosses a 4KB page boundary, we were failing to pad the VM allocation,
which would cause the memcpy() to fail.

Make sure we round the segment bases down, and segment ends up, and the
issue goes away.

Userland/Libraries/LibELF/DynamicLoader.cpp

@@ -295,19 +295,24 @@ void DynamicLoader::load_program_headers()
     // 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());
+    FlatPtr ph_text_base = text_region.value().desired_load_address().page_base().get();
+    FlatPtr ph_text_end = round_up_to_power_of_two(text_region.value().desired_load_address().offset(text_region.value().size_in_memory()).get(), PAGE_SIZE);
+    FlatPtr ph_data_base = data_region.value().desired_load_address().page_base().get();
+    FlatPtr ph_data_end = round_up_to_power_of_two(data_region.value().desired_load_address().offset(data_region.value().size_in_memory()).get(), PAGE_SIZE);
 
-    auto* reservation = mmap(requested_load_address, total_mapping_size.value(), PROT_NONE, reservation_mmap_flags, 0, 0);
+    size_t total_mapping_size = ph_data_end - ph_text_base;
+
+    size_t text_segment_size = ph_text_end - ph_text_base;
+    size_t data_segment_size = ph_data_end - ph_data_base;
+
+    auto* reservation = mmap(requested_load_address, total_mapping_size, PROT_NONE, reservation_mmap_flags, 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) {
+    if (munmap(reservation, total_mapping_size) < 0) {
         perror("munmap reservation");
         ASSERT_NOT_REACHED();
     }
@@ -315,7 +320,7 @@ void DynamicLoader::load_program_headers()
     // Now we can map the text segment at the reserved address.
     auto* text_segment_begin = (u8*)mmap_with_name(
         reservation,
-        text_region.value().required_load_size(),
+        text_segment_size,
         PROT_READ,
         MAP_FILE | MAP_SHARED | MAP_FIXED,
         m_image_fd,
@@ -328,7 +333,7 @@ void DynamicLoader::load_program_headers()
     }
 
     ASSERT(requested_load_address == nullptr || requested_load_address == text_segment_begin);
-    m_text_segment_size = text_region.value().required_load_size();
+    m_text_segment_size = text_segment_size;
     m_text_segment_load_address = VirtualAddress { (FlatPtr)text_segment_begin };
 
     if (m_elf_image.is_dynamic())
@@ -336,11 +341,14 @@ void DynamicLoader::load_program_headers()
     else
         m_dynamic_section_address = dynamic_region_desired_vaddr;
 
+    FlatPtr data_segment_offset_from_text = ph_data_base - ph_text_base;
+
     // 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_address = (u8*)text_segment_begin + data_segment_offset_from_text;
+
     auto* data_segment = (u8*)mmap_with_name(
         data_segment_address,
-        data_region.value().required_load_size(),
+        data_segment_size,
         data_region.value().mmap_prot(),
         MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED,
         0,

Userland/Libraries/LibELF/DynamicLoader.h

@@ -103,8 +103,6 @@ private:
         bool is_load() const { return type() == PT_LOAD; }
         bool is_dynamic() const { return type() == PT_DYNAMIC; }
 
-        u32 required_load_size() { return ALIGN_ROUND_UP(m_program_header.p_memsz, m_program_header.p_align); }
-
     private:
         Elf32_Phdr m_program_header; // Explicitly a copy of the PHDR in the image
     };