LibELF: Map text segments read-only at first

To support upcoming W^X changes in the kernel, the dynamic loader needs
to be careful about the order in which permissions are added to shared
library text segments.

We now start by mapping text segments read-only (no-write, no-exec).
If relocations are needed, we make them writable, and then finally,
for all text segments, we finish by making them read+exec.

1 files changed, 4 insertions, 8 deletions

diff --git a/Userland/Libraries/LibELF/DynamicLoader.cpp b/Userland/Libraries/LibELF/DynamicLoader.cpp
index 5407633e9c..4e81c9d70c 100644
--- a/Userland/Libraries/LibELF/DynamicLoader.cpp
+++ b/Userland/Libraries/LibELF/DynamicLoader.cpp
@@ -209,18 +209,14 @@ void DynamicLoader::do_main_relocations(size_t total_tls_size)
 
 RefPtr<DynamicObject> DynamicLoader::load_stage_3(unsigned flags, size_t total_tls_size)
 {
-
     do_lazy_relocations(total_tls_size);
     if (flags & RTLD_LAZY) {
         setup_plt_trampoline();
     }
 
-    // Clean up our setting of .text to PROT_READ | PROT_WRITE
-    if (m_dynamic_object->has_text_relocations()) {
-        if (0 > mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_EXEC)) {
-            perror("mprotect .text: PROT_READ | PROT_EXEC"); // FIXME: dlerror?
-            return nullptr;
-        }
+    if (mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_EXEC) < 0) {
+        perror("mprotect .text: PROT_READ | PROT_EXEC"); // FIXME: dlerror?
+        return nullptr;
     }
 
     call_object_init_functions();
@@ -296,7 +292,7 @@ void DynamicLoader::load_program_headers()
     auto* text_segment_begin = (u8*)mmap_with_name(
         requested_load_address,
         total_mapping_size.value(),
-        text_region->mmap_prot(),
+        PROT_READ,
         text_mmap_flags,
         m_image_fd,
         text_region->offset(),