ARM validator: fix sandbox escape with SP update at the end of the last bundle

src/trusted/validator_arm/model.h

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_ARM_V2_MODEL_H
 #define NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_ARM_V2_MODEL_H
 
 /*
@@ skipping 268 matching lines @@
 // The number of bits in a word of a THUMB instruction.
 static const int kThumbWordSize = 16;
 
 // Special ARM instructions for sandboxing.
 static const uint32_t kLiteralPoolHead = NACL_INSTR_ARM_LITERAL_POOL_HEAD;
 static const uint32_t kBreakpoint = NACL_INSTR_ARM_BREAKPOINT;
 static const uint32_t kHaltFill = NACL_INSTR_ARM_HALT_FILL;
 static const uint32_t kAbortNow = NACL_INSTR_ARM_ABORT_NOW;
 static const uint32_t kFailValidation = NACL_INSTR_ARM_FAIL_VALIDATION;
 
+// Not-so-special instructions.
+static const uint32_t kNop = NACL_INSTR_ARM_NOP;
+
 // Models an instruction, either a 32-bit ARM instruction of unspecified type,
 // or one word (16-bit) and two word (32-bit) THUMB instructions.
 //
 // This class is designed for efficiency:
 //  - Its public methods for bitfield extraction are short and inline.
 //  - It has no vtable, so on 32-bit platforms it's exactly the size of the
 //    instruction it models.
 //  - API's exist for accessing both ARM (32-bit) instructions and
 //    THUMB instructions (which are 1 or two (16-bit) words).
 class Instruction {
@@ skipping 218 matching lines @@
   }
 
  private:
   uint32_t bits_;
   Instruction& operator=(const Instruction& insn);  // Disallow assignment.
 };
 
 }  // namespace nacl_arm_dec
 
 #endif  // NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_ARM_V2_MODEL_H