windows: Use RW/RX permissions for injection

- Use a dedicated memory page for the injected code.
- Use RW permissions when writing the injected code and data.
- Switch the code page to RX permissions after writing.

This makes Frida injection compatible with more software. In particular,
Mozilla Firefox rejects thread startup if the start address is RWX.

src/windows/frida-helper-backend-glue.c

@@ -305,10 +305,11 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
   gpointer code;
   guint code_size;
   GumX86Writer cw;
-  const gsize data_alignment = 4;
   const gchar * loadlibrary_failed = "loadlibrary_failed";
   const gchar * skip_unload = "skip_unload";
   const gchar * return_result = "return_result";
+  SIZE_T page_size, alloc_size;
+  DWORD old_protect;
 
   gum_init ();
 
@@ -347,7 +348,7 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
       GUM_ARG_REGISTER, GUM_X86_XSI,
       GUM_ARG_REGISTER, GUM_X86_XDX);
 
-  /* xax (xbx->entrypoint_data, &stay_resident, NULL) */
+  /* xax (xbx->entrypoint_data, &xbx->stay_resident, NULL) */
   gum_x86_writer_put_lea_reg_reg_offset (&cw, GUM_X86_XCX,
       GUM_X86_XBX, G_STRUCT_OFFSET (FridaRemoteWorkerContext, entrypoint_data));
   gum_x86_writer_put_lea_reg_reg_offset (&cw, GUM_X86_XDX,
@@ -358,7 +359,7 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
       GUM_ARG_REGISTER, GUM_X86_XDX,
       GUM_ARG_ADDRESS, GUM_ADDRESS (0));
 
-  /* if (!stay_resident) { */
+  /* if (!xbx->stay_resident) { */
   gum_x86_writer_put_mov_reg_reg_offset_ptr (&cw, GUM_X86_EAX,
       GUM_X86_XBX, G_STRUCT_OFFSET (FridaRemoteWorkerContext, stay_resident));
   gum_x86_writer_put_test_reg_reg (&cw, GUM_X86_EAX, GUM_X86_EAX);
@@ -403,19 +404,24 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
   StringCbCopyA (rwc->entrypoint_name, sizeof (rwc->entrypoint_name), details->entrypoint_name);
   StringCbCopyA (rwc->entrypoint_data, sizeof (rwc->entrypoint_data), details->entrypoint_data);
 
-  rwc->entrypoint = VirtualAllocEx (details->process_handle, NULL,
-      code_size + data_alignment + sizeof (FridaRemoteWorkerContext), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
+  page_size = gum_query_page_size ();
+  g_assert (code_size <= page_size);
+
+  alloc_size = page_size + sizeof (FridaRemoteWorkerContext);
+  rwc->entrypoint = VirtualAllocEx (details->process_handle, NULL, alloc_size, MEM_COMMIT, PAGE_READWRITE);
   if (rwc->entrypoint == NULL)
-    goto virtual_alloc_failed;
+    goto virtual_alloc_ex_failed;
 
   if (!WriteProcessMemory (details->process_handle, rwc->entrypoint, code, code_size, NULL))
     goto write_process_memory_failed;
 
-  rwc->argument = GSIZE_TO_POINTER (
-      (GPOINTER_TO_SIZE (rwc->entrypoint) + code_size + data_alignment - 1) & ~(data_alignment - 1));
+  rwc->argument = GSIZE_TO_POINTER (GPOINTER_TO_SIZE (rwc->entrypoint) + page_size);
   if (!WriteProcessMemory (details->process_handle, rwc->argument, rwc, sizeof (FridaRemoteWorkerContext), NULL))
     goto write_process_memory_failed;
 
+  if (!VirtualProtectEx (details->process_handle, rwc->entrypoint, page_size, PAGE_EXECUTE_READ, &old_protect))
+    goto virtual_protect_ex_failed;
+
   gum_free_pages (code);
   return TRUE;
 
@@ -428,12 +434,12 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
         "Unexpected error while resolving kernel32 functions");
     goto error_common;
   }
-virtual_alloc_failed:
+virtual_alloc_ex_failed:
   {
     g_set_error (error,
         FRIDA_ERROR,
         FRIDA_ERROR_NOT_SUPPORTED,
-        "Unexpected error allocating memory in target process (VirtualAlloc returned 0x%08lx)",
+        "Unexpected error allocating memory in target process (VirtualAllocEx returned 0x%08lx)",
         GetLastError ());
     goto error_common;
   }
@@ -446,6 +452,15 @@ frida_remote_worker_context_init (FridaRemoteWorkerContext * rwc, FridaInjection
         GetLastError ());
     goto error_common;
   }
+virtual_protect_ex_failed:
+  {
+    g_set_error (error,
+        FRIDA_ERROR,
+        FRIDA_ERROR_NOT_SUPPORTED,
+        "Unexpected error changing memory permission in target process (VirtualProtectEx returned 0x%08lx)",
+        GetLastError ());
+    goto error_common;
+  }
 error_common:
   {
     frida_remote_worker_context_destroy (rwc, details);