Fix/xor dynamic register preservation

modules/encoders/x64/xor_dynamic.rb

@@ -15,12 +15,8 @@ def initialize
       )
   end
 
-  # Indicate that this module can preserve some registers
-  # ...which is currently not true. This is a temp fix
-  # until the full preserve_registers functionality is
-  # implemented.
   def can_preserve_registers?
-    true
+    false
   end
 
   def stub

modules/encoders/x86/xor_dynamic.rb

@@ -15,12 +15,8 @@ def initialize
       )
   end
 
-  # Indicate that this module can preserve some registers
-  # ...which is currently not true. This is a temp fix
-  # until the full preserve_registers functionality is
-  # implemented.
   def can_preserve_registers?
-    true
+    false
   end
 
   def stub

spec/lib/msf/core/encoded_payload/stage_encoding_spec.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'msf/core/encoded_payload'
+
+RSpec.describe 'stage encoding' do
+  include_context 'Msf::Simple::Framework#modules loading'
+
+  before do
+    expect_to_load_module_ancestors(
+      ancestor_reference_names: encoder_reference_names,
+      module_type: 'encoder',
+      modules_path: modules_path
+    )
+
+    allow(framework.encoders).to receive(:rank_modules).and_wrap_original do |original, *args|
+      original.call(*args).select do |ref_name, _metadata|
+        encoder_reference_names.include?(ref_name)
+      end
+    end
+  end
+
+  let(:encoder_reference_names) do
+    %w[
+      x64/xor_dynamic
+      x64/xor
+    ]
+  end
+
+  let(:payload) do
+    load_and_create_module(
+      ancestor_reference_names: %w[singles/linux/x64/shell_bind_tcp],
+      module_type: 'payload',
+      reference_name: 'linux/x64/shell_bind_tcp'
+    )
+  end
+
+  let(:badchars) { "\x00\x0a\x0d".b }
+
+  let(:encoded_payload) do
+    Msf::EncodedPayload.new(
+      framework,
+      payload,
+      {
+        'BadChars' => badchars,
+        'EncoderOptions' => {
+          'SaveRegisters' => 'rdi'
+        },
+        'ForceEncode' => true,
+        'ForceSaveRegisters' => true
+      }
+    )
+  end
+
+  before do
+    encoded_payload.generate("RAW\x00".b)
+  end
+
+  it 'skips x64/xor_dynamic when rdi must be preserved' do
+    expect(encoded_payload.encoder.refname).not_to eq('x64/xor_dynamic')
+  end
+
+  it 'encodes the payload' do
+    expect(encoded_payload.encoded).not_to include(badchars)
+  end
+end