src/verifier/method_verifier.h

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_SRC_VERIFIER_METHOD_VERIFIER_H_
#define ART_SRC_VERIFIER_METHOD_VERIFIER_H_

#include <deque>
#include <limits>
#include <set>
#include <vector>

#include "casts.h"
#include "compiler.h"
#include "dex_file.h"
#include "dex_instruction.h"
#include "macros.h"
#include "object.h"
#include "reg_type.h"
#include "reg_type_cache.h"
#include "register_line.h"
#include "safe_map.h"
#include "stl_util.h"
#include "UniquePtr.h"

namespace art {

struct ReferenceMap2Visitor;

#if defined(ART_USE_LLVM_COMPILER)
namespace compiler_llvm {
  class InferredRegCategoryMap;
}  // namespace compiler_llvm
#endif

namespace verifier {

class MethodVerifier;
class InsnFlags;
class PcToReferenceMap;

/*
 * Set this to enable dead code scanning. This is not required, but it's very useful when testing
 * changes to the verifier (to make sure we're not skipping over stuff). The only reason not to do
 * it is that it slightly increases the time required to perform verification.
 */
#define DEAD_CODE_SCAN kIsDebugBuild

/*
 * "Direct" and "virtual" methods are stored independently. The type of call used to invoke the
 * method determines which list we search, and whether we travel up into superclasses.
 *
 * (<clinit>, <init>, and methods declared "private" or "static" are stored in the "direct" list.
 * All others are stored in the "virtual" list.)
 */
enum MethodType {
  METHOD_UNKNOWN  = 0,
  METHOD_DIRECT,      // <init>, private
  METHOD_STATIC,      // static
  METHOD_VIRTUAL,     // virtual, super
  METHOD_INTERFACE    // interface
};

/*
 * An enumeration of problems that can turn up during verification.
 * Both VERIFY_ERROR_BAD_CLASS_SOFT and VERIFY_ERROR_BAD_CLASS_HARD denote failures that cause
 * the entire class to be rejected. However, VERIFY_ERROR_BAD_CLASS_SOFT denotes a soft failure
 * that can potentially be corrected, and the verifier will try again at runtime.
 * VERIFY_ERROR_BAD_CLASS_HARD denotes a hard failure that can't be corrected, and will cause
 * the class to remain uncompiled. Other errors denote verification errors that cause bytecode
 * to be rewritten to fail at runtime.
 */
enum VerifyError {
  VERIFY_ERROR_NONE = 0,       // No error; must be zero.
  VERIFY_ERROR_BAD_CLASS_HARD, // VerifyError; hard error that skips compilation.
  VERIFY_ERROR_BAD_CLASS_SOFT, // VerifyError; soft error that verifies again at runtime.

  VERIFY_ERROR_NO_CLASS,       // NoClassDefFoundError.
  VERIFY_ERROR_NO_FIELD,       // NoSuchFieldError.
  VERIFY_ERROR_NO_METHOD,      // NoSuchMethodError.
  VERIFY_ERROR_ACCESS_CLASS,   // IllegalAccessError.
  VERIFY_ERROR_ACCESS_FIELD,   // IllegalAccessError.
  VERIFY_ERROR_ACCESS_METHOD,  // IllegalAccessError.
  VERIFY_ERROR_CLASS_CHANGE,   // IncompatibleClassChangeError.
  VERIFY_ERROR_INSTANTIATION,  // InstantiationError.
};
std::ostream& operator<<(std::ostream& os, const VerifyError& rhs);

/*
 * Identifies the type of reference in the instruction that generated the verify error
 * (e.g. VERIFY_ERROR_ACCESS_CLASS could come from a method, field, or class reference).
 *
 * This must fit in two bits.
 */
enum VerifyErrorRefType {
  VERIFY_ERROR_REF_CLASS  = 0,
  VERIFY_ERROR_REF_FIELD  = 1,
  VERIFY_ERROR_REF_METHOD = 2,
};
const int kVerifyErrorRefTypeShift = 6;

// We don't need to store the register data for many instructions, because we either only need
// it at branch points (for verification) or GC points and branches (for verification +
// type-precise register analysis).
enum RegisterTrackingMode {
  kTrackRegsBranches,
  kTrackRegsGcPoints,
  kTrackRegsAll,
};

class PcToRegisterLineTable {
 public:
  PcToRegisterLineTable() {}
  ~PcToRegisterLineTable() {
    STLDeleteValues(&pc_to_register_line_);
  }

  // Initialize the RegisterTable. Every instruction address can have a different set of information
  // about what's in which register, but for verification purposes we only need to store it at
  // branch target addresses (because we merge into that).
  void Init(RegisterTrackingMode mode, InsnFlags* flags, uint32_t insns_size,
            uint16_t registers_size, MethodVerifier* verifier);

  RegisterLine* GetLine(size_t idx) {
    Table::iterator result = pc_to_register_line_.find(idx);  // TODO: C++0x auto
    if (result == pc_to_register_line_.end()) {
      return NULL;
    } else {
      return result->second;
    }
  }

 private:
  typedef SafeMap<int32_t, RegisterLine*> Table;
  // Map from a dex pc to the register status associated with it
  Table pc_to_register_line_;
};

// The verifier
class MethodVerifier {
 public:
  /* Verify a class. Returns "true" on success. */
  static bool VerifyClass(const Class* klass, std::string& error);

  /*
   * Structurally verify a class. Returns "true" on success. Used at compile time
   * when the pointer for the method or declaring class can't be resolved.
   */
  static bool VerifyClass(const DexFile* dex_file, DexCache* dex_cache,
      const ClassLoader* class_loader, uint32_t class_def_idx, std::string& error);

  uint8_t EncodePcToReferenceMapData() const;

  uint32_t DexFileVersion() const {
    return dex_file_->GetVersion();
  }

  RegTypeCache* GetRegTypeCache() {
    return &reg_types_;
  }

  // Verification failed
  std::ostream& Fail(VerifyError error);

  // Log for verification information
  std::ostream& LogVerifyInfo() {
    return info_messages_ << "VFY: " << PrettyMethod(method_)
                          << '[' << reinterpret_cast<void*>(work_insn_idx_) << "] : ";
  }

  // Dump the state of the verifier, namely each instruction, what flags are set on it, register
  // information
  void Dump(std::ostream& os);

  static const std::vector<uint8_t>* GetGcMap(Compiler::MethodReference ref);
  static void InitGcMaps();
  static void DeleteGcMaps();

#if defined(ART_USE_LLVM_COMPILER)
  static const compiler_llvm::InferredRegCategoryMap* GetInferredRegCategoryMap(Compiler::MethodReference ref);
  static void InitInferredRegCategoryMaps();
  static void DeleteInferredRegCategoryMaps();
#endif

  static bool IsClassRejected(Compiler::ClassReference ref);

 private:

  explicit MethodVerifier(Method* method);
  explicit MethodVerifier(const DexFile* dex_file, DexCache* dex_cache,
      const ClassLoader* class_loader, uint32_t class_def_idx, const DexFile::CodeItem* code_item);

  /*
   * Perform verification on a single method.
   *
   * We do this in three passes:
   *  (1) Walk through all code units, determining instruction locations,
   *      widths, and other characteristics.
   *  (2) Walk through all code units, performing static checks on
   *      operands.
   *  (3) Iterate through the method, checking type safety and looking
   *      for code flow problems.
   *
   * Some checks may be bypassed depending on the verification mode. We can't
   * turn this stuff off completely if we want to do "exact" GC.
   *
   * Confirmed here:
   * - code array must not be empty
   * Confirmed by ComputeWidthsAndCountOps():
   * - opcode of first instruction begins at index 0
   * - only documented instructions may appear
   * - each instruction follows the last
   * - last byte of last instruction is at (code_length-1)
   */
  static bool VerifyMethod(Method* method);
  static void VerifyMethodAndDump(Method* method);

  /*
   * Perform structural verification on a single method. Used at compile time
   * when the pointer for the method or declaring class can't be resolved.
   *
   * We do this in two passes:
   *  (1) Walk through all code units, determining instruction locations,
   *      widths, and other characteristics.
   *  (2) Walk through all code units, performing static checks on
   *      operands.
   *
   * Code flow verification is skipped since a resolved method and class are
   * necessary to perform all the checks.
   */
  static bool VerifyMethod(uint32_t method_idx, const DexFile* dex_file, DexCache* dex_cache,
      const ClassLoader* class_loader, uint32_t class_def_idx, const DexFile::CodeItem* code_item);

  /* Run both structural and code flow verification on the method. */
  bool VerifyAll();

  /* Perform structural verification on a single method. */
  bool VerifyStructure();

  /*
   * Compute the width of the instruction at each address in the instruction stream, and store it in
   * insn_flags_. Addresses that are in the middle of an instruction, or that are part of switch
   * table data, are not touched (so the caller should probably initialize "insn_flags" to zero).
   *
   * The "new_instance_count_" and "monitor_enter_count_" fields in vdata are also set.
   *
   * Performs some static checks, notably:
   * - opcode of first instruction begins at index 0
   * - only documented instructions may appear
   * - each instruction follows the last
   * - last byte of last instruction is at (code_length-1)
   *
   * Logs an error and returns "false" on failure.
   */
  bool ComputeWidthsAndCountOps();

  /*
   * Set the "in try" flags for all instructions protected by "try" statements. Also sets the
   * "branch target" flags for exception handlers.
   *
   * Call this after widths have been set in "insn_flags".
   *
   * Returns "false" if something in the exception table looks fishy, but we're expecting the
   * exception table to be somewhat sane.
   */
  bool ScanTryCatchBlocks();

  /*
   * Perform static verification on all instructions in a method.
   *
   * Walks through instructions in a method calling VerifyInstruction on each.
   */
  bool VerifyInstructions();

  /*
   * Perform static verification on an instruction.
   *
   * As a side effect, this sets the "branch target" flags in InsnFlags.
   *
   * "(CF)" items are handled during code-flow analysis.
   *
   * v3 4.10.1
   * - target of each jump and branch instruction must be valid
   * - targets of switch statements must be valid
   * - operands referencing constant pool entries must be valid
   * - (CF) operands of getfield, putfield, getstatic, putstatic must be valid
   * - (CF) operands of method invocation instructions must be valid
   * - (CF) only invoke-direct can call a method starting with '<'
   * - (CF) <clinit> must never be called explicitly
   * - operands of instanceof, checkcast, new (and variants) must be valid
   * - new-array[-type] limited to 255 dimensions
   * - can't use "new" on an array class
   * - (?) limit dimensions in multi-array creation
   * - local variable load/store register values must be in valid range
   *
   * v3 4.11.1.2
   * - branches must be within the bounds of the code array
   * - targets of all control-flow instructions are the start of an instruction
   * - register accesses fall within range of allocated registers
   * - (N/A) access to constant pool must be of appropriate type
   * - code does not end in the middle of an instruction
   * - execution cannot fall off the end of the code
   * - (earlier) for each exception handler, the "try" area must begin and
   *   end at the start of an instruction (end can be at the end of the code)
   * - (earlier) for each exception handler, the handler must start at a valid
   *   instruction
   */
  bool VerifyInstruction(const Instruction* inst, uint32_t code_offset);

  /* Ensure that the register index is valid for this code item. */
  bool CheckRegisterIndex(uint32_t idx);

  /* Ensure that the wide register index is valid for this code item. */
  bool CheckWideRegisterIndex(uint32_t idx);

  // Perform static checks on a field get or set instruction. All we do here is ensure that the
  // field index is in the valid range.
  bool CheckFieldIndex(uint32_t idx);

  // Perform static checks on a method invocation instruction. All we do here is ensure that the
  // method index is in the valid range.
  bool CheckMethodIndex(uint32_t idx);

  // Perform static checks on a "new-instance" instruction. Specifically, make sure the class
  // reference isn't for an array class.
  bool CheckNewInstance(uint32_t idx);

  /* Ensure that the string index is in the valid range. */
  bool CheckStringIndex(uint32_t idx);

  // Perform static checks on an instruction that takes a class constant. Ensure that the class
  // index is in the valid range.
  bool CheckTypeIndex(uint32_t idx);

  // Perform static checks on a "new-array" instruction. Specifically, make sure they aren't
  // creating an array of arrays that causes the number of dimensions to exceed 255.
  bool CheckNewArray(uint32_t idx);

  // Verify an array data table. "cur_offset" is the offset of the fill-array-data instruction.
  bool CheckArrayData(uint32_t cur_offset);

  // Verify that the target of a branch instruction is valid. We don't expect code to jump directly
  // into an exception handler, but it's valid to do so as long as the target isn't a
  // "move-exception" instruction. We verify that in a later stage.
  // The dex format forbids certain instructions from branching to themselves.
  // Updates "insnFlags", setting the "branch target" flag.
  bool CheckBranchTarget(uint32_t cur_offset);

  // Verify a switch table. "cur_offset" is the offset of the switch instruction.
  // Updates "insnFlags", setting the "branch target" flag.
  bool CheckSwitchTargets(uint32_t cur_offset);

  // Check the register indices used in a "vararg" instruction, such as invoke-virtual or
  // filled-new-array.
  // - vA holds word count (0-5), args[] have values.
  // There are some tests we don't do here, e.g. we don't try to verify that invoking a method that
  // takes a double is done with consecutive registers. This requires parsing the target method
  // signature, which we will be doing later on during the code flow analysis.
  bool CheckVarArgRegs(uint32_t vA, uint32_t arg[]);

  // Check the register indices used in a "vararg/range" instruction, such as invoke-virtual/range
  // or filled-new-array/range.
  // - vA holds word count, vC holds index of first reg.
  bool CheckVarArgRangeRegs(uint32_t vA, uint32_t vC);

  // Extract the relative offset from a branch instruction.
  // Returns "false" on failure (e.g. this isn't a branch instruction).
  bool GetBranchOffset(uint32_t cur_offset, int32_t* pOffset, bool* pConditional,
                       bool* selfOkay);

  /* Perform detailed code-flow analysis on a single method. */
  bool VerifyCodeFlow();

  // Set the register types for the first instruction in the method based on the method signature.
  // This has the side-effect of validating the signature.
  bool SetTypesFromSignature();

  /*
   * Perform code flow on a method.
   *
   * The basic strategy is as outlined in v3 4.11.1.2: set the "changed" bit on the first
   * instruction, process it (setting additional "changed" bits), and repeat until there are no
   * more.
   *
   * v3 4.11.1.1
   * - (N/A) operand stack is always the same size
   * - operand stack [registers] contain the correct types of values
   * - local variables [registers] contain the correct types of values
   * - methods are invoked with the appropriate arguments
   * - fields are assigned using values of appropriate types
   * - opcodes have the correct type values in operand registers
   * - there is never an uninitialized class instance in a local variable in code protected by an
   *   exception handler (operand stack is okay, because the operand stack is discarded when an
   *   exception is thrown) [can't know what's a local var w/o the debug info -- should fall out of
   *   register typing]
   *
   * v3 4.11.1.2
   * - execution cannot fall off the end of the code
   *
   * (We also do many of the items described in the "static checks" sections, because it's easier to
   * do them here.)
   *
   * We need an array of RegType values, one per register, for every instruction. If the method uses
   * monitor-enter, we need extra data for every register, and a stack for every "interesting"
   * instruction. In theory this could become quite large -- up to several megabytes for a monster
   * function.
   *
   * NOTE:
   * The spec forbids backward branches when there's an uninitialized reference in a register. The
   * idea is to prevent something like this:
   *   loop:
   *     move r1, r0
   *     new-instance r0, MyClass
   *     ...
   *     if-eq rN, loop  // once
   *   initialize r0
   *
   * This leaves us with two different instances, both allocated by the same instruction, but only
   * one is initialized. The scheme outlined in v3 4.11.1.4 wouldn't catch this, so they work around
   * it by preventing backward branches. We achieve identical results without restricting code
   * reordering by specifying that you can't execute the new-instance instruction if a register
   * contains an uninitialized instance created by that same instruction.
   */
  bool CodeFlowVerifyMethod();

  /*
   * Perform verification for a single instruction.
   *
   * This requires fully decoding the instruction to determine the effect it has on registers.
   *
   * Finds zero or more following instructions and sets the "changed" flag if execution at that
   * point needs to be (re-)evaluated. Register changes are merged into "reg_types_" at the target
   * addresses. Does not set or clear any other flags in "insn_flags_".
   */
  bool CodeFlowVerifyInstruction(uint32_t* start_guess);

  // Perform verification of a new array instruction
  void VerifyNewArray(const DecodedInstruction& dec_insn, bool is_filled,
                      bool is_range);

  // Perform verification of an aget instruction. The destination register's type will be set to
  // be that of component type of the array unless the array type is unknown, in which case a
  // bottom type inferred from the type of instruction is used. is_primitive is false for an
  // aget-object.
  void VerifyAGet(const DecodedInstruction& insn, const RegType& insn_type,
                  bool is_primitive);

  // Perform verification of an aput instruction.
  void VerifyAPut(const DecodedInstruction& insn, const RegType& insn_type,
                  bool is_primitive);

  // Lookup instance field and fail for resolution violations
  Field* GetInstanceField(const RegType& obj_type, int field_idx);

  // Lookup static field and fail for resolution violations
  Field* GetStaticField(int field_idx);

  // Perform verification of an iget or sget instruction.
  void VerifyISGet(const DecodedInstruction& insn, const RegType& insn_type,
                   bool is_primitive, bool is_static);

  // Perform verification of an iput or sput instruction.
  void VerifyISPut(const DecodedInstruction& insn, const RegType& insn_type,
                   bool is_primitive, bool is_static);

  // Resolves a class based on an index and performs access checks to ensure the referrer can
  // access the resolved class.
  const RegType& ResolveClassAndCheckAccess(uint32_t class_idx);

  /*
   * For the "move-exception" instruction at "work_insn_idx_", which must be at an exception handler
   * address, determine the Join of all exceptions that can land here. Fails if no matching
   * exception handler can be found or if the Join of exception types fails.
   */
  const RegType& GetCaughtExceptionType();

  /*
   * Resolves a method based on an index and performs access checks to ensure
   * the referrer can access the resolved method.
   * Does not throw exceptions.
   */
  Method* ResolveMethodAndCheckAccess(uint32_t method_idx, MethodType method_type);

  /*
   * Verify the arguments to a method. We're executing in "method", making
   * a call to the method reference in vB.
   *
   * If this is a "direct" invoke, we allow calls to <init>. For calls to
   * <init>, the first argument may be an uninitialized reference. Otherwise,
   * calls to anything starting with '<' will be rejected, as will any
   * uninitialized reference arguments.
   *
   * For non-static method calls, this will verify that the method call is
   * appropriate for the "this" argument.
   *
   * The method reference is in vBBBB. The "is_range" parameter determines
   * whether we use 0-4 "args" values or a range of registers defined by
   * vAA and vCCCC.
   *
   * Widening conversions on integers and references are allowed, but
   * narrowing conversions are not.
   *
   * Returns the resolved method on success, NULL on failure (with *failure
   * set appropriately).
   */
  Method* VerifyInvocationArgs(const DecodedInstruction& dec_insn,
                               MethodType method_type, bool is_range, bool is_super);

  /*
   * Return the register type for the method. We can't just use the already-computed
   * DalvikJniReturnType, because if it's a reference type we need to do the class lookup.
   * Returned references are assumed to be initialized. Returns kRegTypeUnknown for "void".
   */
  const RegType& GetMethodReturnType();

  /*
   * Verify that the target instruction is not "move-exception". It's important that the only way
   * to execute a move-exception is as the first instruction of an exception handler.
   * Returns "true" if all is well, "false" if the target instruction is move-exception.
   */
  bool CheckNotMoveException(const uint16_t* insns, int insn_idx);

  /*
   * Replace an instruction with "throw-verification-error". This allows us to
   * defer error reporting until the code path is first used.
   */
  void ReplaceFailingInstruction();

  /*
  * Control can transfer to "next_insn". Merge the registers from merge_line into the table at
  * next_insn, and set the changed flag on the target address if any of the registers were changed.
  * Returns "false" if an error is encountered.
  */
  bool UpdateRegisters(uint32_t next_insn, const RegisterLine* merge_line);

#if defined(ART_USE_LLVM_COMPILER)
  /*
   * Generate the inferred register category for LLVM-based code generator.
   * Returns a pointer to a two-dimension Class array, or NULL on failure.
   */
  const compiler_llvm::InferredRegCategoryMap* GenerateInferredRegCategoryMap();
#endif

  /*
   * Generate the GC map for a method that has just been verified (i.e. we're doing this as part of
   * verification). For type-precise determination we have all the data we need, so we just need to
   * encode it in some clever fashion.
   * Returns a pointer to a newly-allocated RegisterMap, or NULL on failure.
   */
  const std::vector<uint8_t>* GenerateGcMap();

  // Verify that the GC map associated with method_ is well formed
  void VerifyGcMap(const std::vector<uint8_t>& data);

  // Compute sizes for GC map data
  void ComputeGcMapSizes(size_t* gc_points, size_t* ref_bitmap_bits, size_t* log2_max_gc_pc);

  InsnFlags* CurrentInsnFlags();

  // All the GC maps that the verifier has created
  typedef SafeMap<const Compiler::MethodReference, const std::vector<uint8_t>*> GcMapTable;
  static Mutex* gc_maps_lock_;
  static GcMapTable* gc_maps_;
  static void SetGcMap(Compiler::MethodReference ref, const std::vector<uint8_t>& gc_map);

#if defined(ART_USE_LLVM_COMPILER)
  // All the inferred register category maps that the verifier has created
  typedef SafeMap<const Compiler::MethodReference,
                  const compiler_llvm::InferredRegCategoryMap*> InferredRegCategoryMapTable;
  static Mutex* inferred_reg_category_maps_lock_;
  static InferredRegCategoryMapTable* inferred_reg_category_maps_;
  static void SetInferredRegCategoryMap(Compiler::MethodReference ref,
                                        const compiler_llvm::InferredRegCategoryMap& m);
#endif

  static void AddRejectedClass(Compiler::ClassReference ref);

  RegTypeCache reg_types_;

  PcToRegisterLineTable reg_table_;

  // Storage for the register status we're currently working on.
  UniquePtr<RegisterLine> work_line_;

  // The address of the instruction we're currently working on, note that this is in 2 byte
  // quantities
  uint32_t work_insn_idx_;

  // Storage for the register status we're saving for later.
  UniquePtr<RegisterLine> saved_line_;

  Method* method_;  // The method we're working on.
  const DexFile* dex_file_;  // The dex file containing the method.
  DexCache* dex_cache_;  // The dex_cache for the declaring class of the method.
  const ClassLoader* class_loader_;  // The class loader for the declaring class of the method.
  uint32_t class_def_idx_;  // The class def index of the declaring class of the method.
  const DexFile::CodeItem* code_item_;  // The code item containing the code for the method.
  UniquePtr<InsnFlags[]> insn_flags_;  // Instruction widths and flags, one entry per code unit.

  // The type of any error that occurs
  VerifyError failure_;

  // Failure message log
  std::ostringstream fail_messages_;
  // Info message log
  std::ostringstream info_messages_;

  // The number of occurrences of specific opcodes.
  size_t new_instance_count_;
  size_t monitor_enter_count_;

  friend struct art::ReferenceMap2Visitor; // for VerifyMethodAndDump
};

}  // namespace verifier
}  // namespace art

#endif  // ART_SRC_VERIFIER_METHOD_VERIFIER_H_