exploitability_linux.h

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// Copyright (c) 2013 Google Inc.

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// exploitability_linux.h: Linux specific exploitability engine.

//

// Provides a guess at the exploitability of the crash for the Linux

// platform given a minidump and process_state.

//

// Author: Matthew Riley

#ifndef GOOGLE_BREAKPAD_PROCESSOR_EXPLOITABILITY_LINUX_H_

#define GOOGLE_BREAKPAD_PROCESSOR_EXPLOITABILITY_LINUX_H_

#include "google_breakpad/common/breakpad_types.h"

#include "google_breakpad/processor/exploitability.h"

namespace google_breakpad {

class ExploitabilityLinux : public Exploitability {

 public:

  ExploitabilityLinux(Minidump *dump,

                      ProcessState *process_state);

  // Parameters are the minidump to analyze, the object representing process

  // state, and whether to enable objdump disassembly.

  // Enabling objdump will allow exploitability analysis to call out to

  // objdump for diassembly. It is used to check the identity of the

  // instruction that caused the program to crash. If there are any

  // portability concerns, this should not be enabled.

  ExploitabilityLinux(Minidump *dump,

                      ProcessState *process_state,

                      bool enable_objdump);

  virtual ExploitabilityRating CheckPlatformExploitability();

 private:

  friend class ExploitabilityLinuxTest;

  // Takes the address of the instruction pointer and returns

  // whether the instruction pointer lies in a valid instruction region.

  bool InstructionPointerInCode(uint64_t instruction_ptr);

  // Checks the exception that triggered the creation of the

  // minidump and reports whether the exception suggests no exploitability.

  bool BenignCrashTrigger(const MDRawExceptionStream *raw_exception_stream);

  // This method checks if the crash occurred during a write to read-only or

  // invalid memory. It does so by checking if the instruction at the

  // instruction pointer is a write instruction, and if the target of the

  // instruction is at a spot in memory that prohibits writes.

  bool EndedOnIllegalWrite(uint64_t instruction_ptr);

#ifndef _WIN32

  // Disassembles raw bytes via objdump and pipes the output into the provided

  // buffer, given the desired architecture, the file from which objdump will

  // read, and the buffer length. The method returns whether the disassembly

  // was a success, and the caller owns all pointers.

  static bool DisassembleBytes(const string &architecture,

                               const uint8_t *raw_bytes,

                               const unsigned int MAX_OBJDUMP_BUFFER_LEN,

                               char *objdump_output_buffer);

  // Parses the objdump output given in |objdump_output_buffer| and extracts

  // the line of the first instruction into |instruction_line|.  Returns true

  // when the instruction line is successfully extracted.

  static bool GetObjdumpInstructionLine(

      const char *objdump_output_buffer,

      string *instruction_line);

  // Tokenizes out the operation and operands from a line of instruction

  // disassembled by objdump. This method modifies the pointers to match the

  // tokens of the instruction, and returns if the tokenizing was a success.

  // The caller owns all pointers.

  static bool TokenizeObjdumpInstruction(const string &line,

                                         string *operation,

                                         string *dest,

                                         string *src);

  // Calculates the effective address of an expression in the form reg+a or

  // reg-a, where 'reg' is a register and 'a' is a constant, and writes the

  // result in the pointer. The method returns whether the calculation was

  // a success. The caller owns the pointer.

  static bool CalculateAddress(const string &address_expression,

                               const DumpContext &context,

                               uint64_t *write_address);

#endif  // _WIN32

  // Checks if the stack pointer points to a memory mapping that is not

  // labelled as the stack.

  bool StackPointerOffStack(uint64_t stack_ptr);

  // Checks if the stack or heap are marked executable according

  // to the memory mappings.

  bool ExecutableStackOrHeap();

  // Whether this exploitability engine is permitted to shell out to objdump

  // to disassemble raw bytes.

  bool enable_objdump_;

};

}  // namespace google_breakpad

#endif  // GOOGLE_BREAKPAD_PROCESSOR_EXPLOITABILITY_LINUX_H_