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 <elf.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;

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

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

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

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

LinuxArchitectureType ExploitabilityLinux::ArchitectureType() {
  // GetContextCPU() should have already been successfully called before
  // calling this method. Thus there should be a raw exception stream for
  // the minidump.
  MinidumpException *exception = dump_->GetException();
  const DumpContext *dump_context =
      exception ?
      exception->GetContext() : NULL;
  if (dump_context == NULL) {
    BPLOG(INFO) << "No raw dump context.";
    return UNSUPPORTED_ARCHITECTURE;
  }

  // Check the architecture type.
  switch (dump_context->GetContextCPU()) {
    case MD_CONTEXT_ARM:
    case MD_CONTEXT_X86:
      return LINUX_32_BIT;
    case MD_CONTEXT_ARM64:
    case MD_CONTEXT_AMD64:
      return LINUX_64_BIT;
    default:
      // This should not happen. The four architectures above should be
      // the only Linux architectures.
      BPLOG(INFO) << "Unsupported architecture.";
      return UNSUPPORTED_ARCHITECTURE;
  }
}

bool ExploitabilityLinux::InstructionPointerInCode(uint64_t instruction_ptr) {
  // Get memory mapping. Most minidumps will not contain a memory
  // mapping, so processing will commonly resort to checking modules.
  MinidumpMemoryInfoList *mem_info_list = dump_->GetMemoryInfoList();
  const MinidumpMemoryInfo *mem_info =
      mem_info_list ?
      mem_info_list->GetMemoryInfoForAddress(instruction_ptr) : NULL;

  // Check if the memory mapping at the instruction pointer is executable.
  // If there is no memory mapping, processing will use modules as reference.
  if (mem_info != NULL) {
    return mem_info->IsExecutable();
  }

  // If the memory mapping retrieval fails, check the modules
  // to see if the instruction pointer is inside a module.
  MinidumpModuleList *minidump_module_list = dump_->GetModuleList();
  const MinidumpModule *minidump_module =
      minidump_module_list ?
      minidump_module_list->GetModuleForAddress(instruction_ptr) : NULL;

  // If the instruction pointer isn't in a module, return false.
  if (minidump_module == NULL) {
    return false;
  }

  // Get ELF header data from the instruction pointer's module.
  const uint64_t base_address = minidump_module->base_address();
  MinidumpMemoryList *memory_list = dump_->GetMemoryList();
  MinidumpMemoryRegion *memory_region =
      memory_list ?
      memory_list->GetMemoryRegionForAddress(base_address) : NULL;

  // The minidump does not have the correct memory region.
  // This returns true because even though there is no memory data available,
  // the evidence so far suggests that the instruction pointer is not at a
  // bad location.
  if (memory_region == NULL) {
    return true;
  }

  // Examine ELF headers. Depending on the architecture, the size of the
  // ELF headers can differ.
  LinuxArchitectureType architecture =  this->ArchitectureType();
  if (architecture == LINUX_32_BIT) {
    // Check if the ELF header is within the memory region and if the
    // instruction pointer lies within the ELF header.
    if (memory_region->GetSize() < sizeof(Elf32_Ehdr) ||
        instruction_ptr < base_address + sizeof(Elf32_Ehdr)) {
      return false;
    }
    // Load 32-bit ELF header.
    Elf32_Ehdr header;
    this->LoadElfHeader(memory_region, base_address, &header);
    // Check if the program header table is within the memory region, and
    // validate that the program header entry size is correct.
    if (header.e_phentsize != sizeof(Elf32_Phdr) ||
        memory_region->GetSize() <
        header.e_phoff +
        ((uint64_t) header.e_phentsize * (uint64_t) header.e_phnum)) {
      return false;
    }
    // Load 32-bit Program Header Table.
    scoped_array<Elf32_Phdr> program_headers(new Elf32_Phdr[header.e_phnum]);
    this->LoadElfHeaderTable(memory_region,
                             base_address + header.e_phoff,
                             header.e_phnum,
                             program_headers.get());
    // Find correct program header that corresponds to the instruction pointer.
    for (int i = 0; i < header.e_phnum; i++) {
      const Elf32_Phdr& program_header = program_headers[i];
      // Check if instruction pointer lies within this program header's region.
      if (instruction_ptr >= program_header.p_vaddr &&
          instruction_ptr < program_header.p_vaddr + program_header.p_memsz) {
        // Return whether this program header region is executable.
        return program_header.p_flags & PF_X;
      }
    }
  } else if (architecture == LINUX_64_BIT) {
    // Check if the ELF header is within the memory region and if the
    // instruction pointer lies within the ELF header.
    if (memory_region->GetSize() < sizeof(Elf64_Ehdr) ||
        instruction_ptr < base_address + sizeof(Elf64_Ehdr)) {
      return false;
    }
    // Load 64-bit ELF header.
    Elf64_Ehdr header;
    this->LoadElfHeader(memory_region, base_address, &header);
    // Check if the program header table is within the memory region, and
    // validate that the program header entry size is correct.
    if (header.e_phentsize != sizeof(Elf64_Phdr) ||
        memory_region->GetSize() <
        header.e_phoff +
        ((uint64_t) header.e_phentsize * (uint64_t) header.e_phnum)) {
      return false;
    }
    // Load 64-bit Program Header Table.
    scoped_array<Elf64_Phdr> program_headers(new Elf64_Phdr[header.e_phnum]);
    this->LoadElfHeaderTable(memory_region,
                             base_address + header.e_phoff,
                             header.e_phnum,
                             program_headers.get());
    // Find correct program header that corresponds to the instruction pointer.
    for (int i = 0; i < header.e_phnum; i++) {
      const Elf64_Phdr& program_header = program_headers[i];
      // Check if instruction pointer lies within this program header's region.
      if (instruction_ptr >= program_header.p_vaddr &&
          instruction_ptr < program_header.p_vaddr + program_header.p_memsz) {
        // Return whether this program header region is executable.
        return program_header.p_flags & PF_X;
      }
    }
  }

  // The instruction pointer was not in an area identified by the ELF headers.
  return 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