breakpad/src/processor/exploitability_linux.cc

// Copyright (c) 2013 Google Inc.
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// exploitability_linux.cc: 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

#include "processor/exploitability_linux.h"

#include "google_breakpad/common/minidump_exception_linux.h"
#include "google_breakpad/processor/call_stack.h"
#include "google_breakpad/processor/process_state.h"
#include "google_breakpad/processor/stack_frame.h"
#include "processor/logging.h"

namespace {

// This function in libc is called if the program was compiled with
// -fstack-protector and a function's stack canary changes.
const char kStackCheckFailureFunction[] = "__stack_chk_fail";

// This function in libc is called if the program was compiled with
// -D_FORTIFY_SOURCE=2, a function like strcpy() is called, and the runtime
// can determine that the call would overflow the target buffer.
const char kBoundsCheckFailureFunction[] = "__chk_fail";

}  // namespace

namespace google_breakpad {

ExploitabilityLinux::ExploitabilityLinux(Minidump *dump,
                                         ProcessState *process_state)
    : Exploitability(dump, process_state) { }

ExploitabilityRating ExploitabilityLinux::CheckPlatformExploitability() {
  // Check the crashing thread for functions suggesting a buffer overflow or
  // stack smash.
  if (process_state_->requesting_thread() != -1) {
    CallStack* crashing_thread =
        process_state_->threads()->at(process_state_->requesting_thread());
    const vector<StackFrame*>& crashing_thread_frames =
        *crashing_thread->frames();
    for (size_t i = 0; i < crashing_thread_frames.size(); ++i) {
      if (crashing_thread_frames[i]->function_name ==
          kStackCheckFailureFunction) {
        return EXPLOITABILITY_HIGH;
      }

      if (crashing_thread_frames[i]->function_name ==
          kBoundsCheckFailureFunction) {
        return EXPLOITABILITY_HIGH;
      }
    }
  }

  // Getting exception data. (It should exist for all minidumps.)
  MinidumpException *exception = dump_->GetException();
  if (exception == NULL) {
    BPLOG(INFO) << "No exception record.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }
  const MDRawExceptionStream *raw_exception_stream = exception->exception();
  if (raw_exception_stream == NULL) {
    BPLOG(INFO) << "No raw exception stream.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Checking for benign exceptions that caused the crash.
  if (this->BenignCrashTrigger(raw_exception_stream)) {
    return EXPLOITABILITY_NONE;
  }

  // Check if the instruction pointer is in a valid instruction region
  // by finding if it maps to an executable part of memory.
  uint64_t instruction_ptr = 0;
  uint64_t stack_ptr = 0;

  const MinidumpContext *context = exception->GetContext();
  if (context == NULL) {
    BPLOG(INFO) << "No exception context.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Getting the instruction pointer.
  if (!context->GetInstructionPointer(&instruction_ptr)) {
    BPLOG(INFO) << "Failed to retrieve instruction pointer.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Getting the stack pointer.
  if (!context->GetStackPointer(&stack_ptr)) {
    BPLOG(INFO) << "Failed to retrieve stack pointer.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Checking for the instruction pointer in a valid instruction region.
  if (!this->InstructionPointerInCode(instruction_ptr) ||
       this->StackPointerOffStack(stack_ptr) ||
       this->ExecutableStackOrHeap()) {
    return EXPLOITABILITY_HIGH;
  }

  // There was no strong evidence suggesting exploitability, but the minidump
  // does not appear totally benign either.
  return EXPLOITABILITY_INTERESTING;
}

bool ExploitabilityLinux::StackPointerOffStack(uint64_t stack_ptr) {
  MinidumpLinuxMapsList *linux_maps_list = dump_->GetLinuxMapsList();
  // Inconclusive if there are no mappings available.
  if (!linux_maps_list) {
    return false;
  }
  const MinidumpLinuxMaps *linux_maps =
      linux_maps_list->GetLinuxMapsForAddress(stack_ptr);
  // Checks if the stack pointer maps to a valid mapping and if the mapping
  // is not the stack. If the mapping has no name, it is inconclusive whether
  // it is off the stack.
  return !linux_maps ||
         (linux_maps->GetPathname().compare("") &&
          linux_maps->GetPathname().compare("[stack]"));
}

bool ExploitabilityLinux::ExecutableStackOrHeap() {
  MinidumpLinuxMapsList *linux_maps_list = dump_->GetLinuxMapsList();
  if (linux_maps_list) {
    for (size_t i = 0; i < linux_maps_list->get_maps_count(); i++) {
      const MinidumpLinuxMaps *linux_maps =
          linux_maps_list->GetLinuxMapsAtIndex(i);
      // Check for executable stack or heap for each mapping.
      if (linux_maps &&
          (!linux_maps->GetPathname().compare("[stack]") ||
           !linux_maps->GetPathname().compare("[heap]")) &&
          linux_maps->IsExecutable()) {
        return true;
      }
    }
  }
  return false;
}

bool ExploitabilityLinux::InstructionPointerInCode(uint64_t instruction_ptr) {
  // Get Linux memory mapping from /proc/self/maps. Checking whether the
  // region the instruction pointer is in has executable permission can tell
  // whether it is in a valid code region. If there is no mapping for the
  // instruction pointer, it is indicative that the instruction pointer is
  // not within a module, which implies that it is outside a valid area.
  MinidumpLinuxMapsList *linux_maps_list = dump_->GetLinuxMapsList();
  const MinidumpLinuxMaps *linux_maps =
      linux_maps_list ?
      linux_maps_list->GetLinuxMapsForAddress(instruction_ptr) : NULL;
  return linux_maps ? linux_maps->IsExecutable() : false;
}

bool ExploitabilityLinux::BenignCrashTrigger(const MDRawExceptionStream
                                                  *raw_exception_stream) {
  // Check the cause of crash.
  // If the exception of the crash is a benign exception,
  // it is probably not exploitable.
  switch (raw_exception_stream->exception_record.exception_code) {
    case MD_EXCEPTION_CODE_LIN_SIGHUP:
    case MD_EXCEPTION_CODE_LIN_SIGINT:
    case MD_EXCEPTION_CODE_LIN_SIGQUIT:
    case MD_EXCEPTION_CODE_LIN_SIGTRAP:
    case MD_EXCEPTION_CODE_LIN_SIGABRT:
    case MD_EXCEPTION_CODE_LIN_SIGFPE:
    case MD_EXCEPTION_CODE_LIN_SIGKILL:
    case MD_EXCEPTION_CODE_LIN_SIGUSR1:
    case MD_EXCEPTION_CODE_LIN_SIGUSR2:
    case MD_EXCEPTION_CODE_LIN_SIGPIPE:
    case MD_EXCEPTION_CODE_LIN_SIGALRM:
    case MD_EXCEPTION_CODE_LIN_SIGTERM:
    case MD_EXCEPTION_CODE_LIN_SIGCHLD:
    case MD_EXCEPTION_CODE_LIN_SIGCONT:
    case MD_EXCEPTION_CODE_LIN_SIGSTOP:
    case MD_EXCEPTION_CODE_LIN_SIGTSTP:
    case MD_EXCEPTION_CODE_LIN_SIGTTIN:
    case MD_EXCEPTION_CODE_LIN_SIGTTOU:
    case MD_EXCEPTION_CODE_LIN_SIGURG:
    case MD_EXCEPTION_CODE_LIN_SIGXCPU:
    case MD_EXCEPTION_CODE_LIN_SIGXFSZ:
    case MD_EXCEPTION_CODE_LIN_SIGVTALRM:
    case MD_EXCEPTION_CODE_LIN_SIGPROF:
    case MD_EXCEPTION_CODE_LIN_SIGWINCH:
    case MD_EXCEPTION_CODE_LIN_SIGIO:
    case MD_EXCEPTION_CODE_LIN_SIGPWR:
    case MD_EXCEPTION_CODE_LIN_SIGSYS:
    case MD_EXCEPTION_CODE_LIN_DUMP_REQUESTED:
      return true;
      break;
    default:
      return false;
      break;
  }
}

}  // namespace google_breakpad