x86 emulator

lib/one_gadget/emulators/amd64.rb

@@ -4,6 +4,12 @@ module OneGadget
   module Emulators
     # Emulator of amd64 instruction set.
     class Amd64 < X86
+      class << self
+        def stack_pointer
+          'rsp'
+        end
+      end
+
       REGISTERS = %w(rax rbx rcx rdx rdi rsi rbp rsp rip) + 7.upto(15).map { |i| "r#{i}" }
 
       # Instantiate a {Amd64} object.

lib/one_gadget/emulators/i386.rb

@@ -4,7 +4,6 @@ module OneGadget
   module Emulators
     # Emulator of amd64 instruction set.
     class I386 < X86
-      REGISTERS = %w(eax ebx ecx edx edi esi ebp esp eip).freeze
       class << self
         def bits
           32
@@ -15,6 +14,7 @@ module OneGadget
         end
       end
 
+      REGISTERS = %w(eax ebx ecx edx edi esi ebp esp eip).freeze
       # Instantiate a {I386} object.
       def initialize
         super(REGISTERS)

lib/one_gadget/emulators/x86.rb

@@ -50,9 +50,22 @@ module OneGadget
 
       private
 
+      def register?(reg)
+        @registers.include?(reg)
+      end
+
       def inst_mov(tar, src)
         src = OneGadget::Emulators::Lambda.parse(src, predefined: @registers)
-        @registers[tar] = src
+        if register?(tar)
+          @registers[tar] = src
+        else
+          # Just ignore strange case...
+          return unless tar.include?(self.class.stack_pointer)
+          tar = OneGadget::Emulators::Lambda.parse(tar, predefined: @registers)
+          return if tar.deref_count != 1 # should not happened
+          tar.ref!
+          @stack[tar.evaluate(eval_dict)] = src
+        end
       end
 
       def inst_lea(tar, src)
@@ -64,9 +77,7 @@ module OneGadget
       def inst_push(val)
         val = OneGadget::Emulators::Lambda.parse(val, predefined: @registers)
         @registers[self.class.stack_pointer] -= bytes
-        dict = {}
-        dict[self.class.stack_pointer] = 0
-        cur_top = @registers[self.class.stack_pointer].evaluate(dict)
+        cur_top = @registers[self.class.stack_pointer].evaluate(eval_dict)
         raise ArgumentError, "Corrupted stack pointer: #{cur_top}" unless cur_top.is_a?(Integer)
         @stack[cur_top] = val
       end
@@ -84,6 +95,12 @@ module OneGadget
       def bytes
         self.class.bits / 8
       end
+
+      def eval_dict
+        dict = {}
+        dict[self.class.stack_pointer] = 0
+        dict
+      end
     end
   end
 end

spec/emulators/i386_spec.rb

@@ -24,6 +24,7 @@ describe OneGadget::Emulators::I386 do
       expect(@processor.stack[0].to_s).to eq 'esi-0x55f61'
       expect(@processor.stack[4].to_s).to eq 'esp+0x34'
       expect(@processor.stack[8].to_s).to eq '[[esi-0xb8]]'
+      # The defualt value of stack is a lambda
       expect(@processor.stack[3].to_s).to eq '[esp+0x3]'
     end
 
@@ -57,5 +58,21 @@ describe OneGadget::Emulators::I386 do
       expect(@processor.stack[-0x3c].to_s).to eq '1337'
       expect(@processor.stack[-0x4].to_s).to eq '1'
     end
+
+    it 'libc-2.19' do
+      gadget = <<-'EOS'
+  64c60: mov DWORD PTR [esp+0x8],eax
+  64c64: lea eax,[ebx-0x4956f]
+  64c6a: mov DWORD PTR [esp+0x4],eax
+  64c6e: lea eax,[ebx-0x49574]
+  64c74: mov DWORD PTR [esp],eax
+  64c77: call b5170 <execl@@GLIBC_2.0>
+      EOS
+      gadget.lines.each { |s| @processor.process(s) }
+      expect(@processor.registers['esp'].to_s).to eq 'esp'
+      expect(@processor.stack[0].to_s).to eq 'ebx-0x49574'
+      expect(@processor.stack[4].to_s).to eq 'ebx-0x4956f'
+      expect(@processor.stack[8].to_s).to eq 'eax'
+    end
   end
 end