crashpad/snapshot/linux/process_reader.cc

// Copyright 2017 The Crashpad Authors. All rights reserved.
//
// 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.

#include "snapshot/linux/process_reader.h"

#include <dirent.h>
#include <errno.h>
#include <sched.h>
#include <stdio.h>
#include <string.h>
#include <sys/resource.h>

#include <algorithm>

#include "base/logging.h"
#include "base/strings/string_number_conversions.h"
#include "build/build_config.h"
#include "util/posix/scoped_dir.h"

namespace crashpad {

namespace {

bool ShouldMergeStackMappings(const MemoryMap::Mapping& stack_mapping,
                              const MemoryMap::Mapping& adj_mapping) {
  DCHECK(stack_mapping.readable);
  return adj_mapping.readable && stack_mapping.device == adj_mapping.device &&
         stack_mapping.inode == adj_mapping.inode;
}

}  // namespace

ProcessReader::Thread::Thread()
    : thread_context(),
      float_context(),
      thread_specific_data_address(0),
      stack_region_address(0),
      stack_region_size(0),
      tid(-1),
      static_priority(-1),
      nice_value(-1) {}

ProcessReader::Thread::~Thread() {}

bool ProcessReader::Thread::InitializePtrace() {
  ThreadInfo thread_info;
  if (!thread_info.Initialize(tid)) {
    return false;
  }

  thread_info.GetGeneralPurposeRegisters(&thread_context);

  if (!thread_info.GetFloatingPointRegisters(&float_context)) {
    return false;
  }

  if (!thread_info.GetThreadArea(&thread_specific_data_address)) {
    return false;
  }

  // TODO(jperaza): Starting with Linux 3.14, scheduling policy, static
  // priority, and nice value can be collected all in one call with
  // sched_getattr().
  int res = sched_getscheduler(tid);
  if (res < 0) {
    PLOG(ERROR) << "sched_getscheduler";
    return false;
  }
  sched_policy = res;

  sched_param param;
  if (sched_getparam(tid, &param) != 0) {
    PLOG(ERROR) << "sched_getparam";
    return false;
  }
  static_priority = param.sched_priority;

  errno = 0;
  res = getpriority(PRIO_PROCESS, tid);
  if (res == -1 && errno) {
    PLOG(ERROR) << "getpriority";
    return false;
  }
  nice_value = res;

  return true;
}

void ProcessReader::Thread::InitializeStack(ProcessReader* reader) {
  LinuxVMAddress stack_pointer;
#if defined(ARCH_CPU_X86_FAMILY)
  stack_pointer =
      reader->Is64Bit() ? thread_context.t64.rsp : thread_context.t32.esp;
#elif defined(ARCH_CPU_ARM_FAMILY)
  stack_pointer =
      reader->Is64Bit() ? thread_context.t64.sp : thread_context.t32.sp;
#else
#error Port.
#endif

  const MemoryMap* memory_map = reader->GetMemoryMap();

  // If we can't find the mapping, it's probably a bad stack pointer
  const MemoryMap::Mapping* mapping = memory_map->FindMapping(stack_pointer);
  if (!mapping) {
    LOG(WARNING) << "no stack mapping";
    return;
  }
  LinuxVMAddress stack_region_start = stack_pointer;

  // We've hit what looks like a guard page; skip to the end and check for a
  // mapped stack region.
  if (!mapping->readable) {
    stack_region_start = mapping->range.End();
    mapping = memory_map->FindMapping(stack_region_start);
    if (!mapping) {
      LOG(WARNING) << "no stack mapping";
      return;
    }
  } else {
#if defined(ARCH_CPU_X86_FAMILY)
    // Adjust start address to include the red zone
    if (reader->Is64Bit()) {
      const LinuxVMSize kRedZoneSize = 128;
      LinuxVMAddress red_zone_base =
          stack_region_start - std::min(kRedZoneSize, stack_region_start);

      // Only include the red zone if it is part of a valid mapping
      if (red_zone_base >= mapping->range.Base()) {
        stack_region_start = red_zone_base;
      } else {
        const MemoryMap::Mapping* rz_mapping =
            memory_map->FindMapping(red_zone_base);
        if (rz_mapping && ShouldMergeStackMappings(*mapping, *rz_mapping)) {
          stack_region_start = red_zone_base;
        } else {
          stack_region_start = mapping->range.Base();
        }
      }
    }
#endif
  }
  stack_region_address = stack_region_start;

  // If there are more mappings at the end of this one, they may be a
  // continuation of the stack.
  LinuxVMAddress stack_end = mapping->range.End();
  const MemoryMap::Mapping* next_mapping;
  while ((next_mapping = memory_map->FindMapping(stack_end)) &&
         ShouldMergeStackMappings(*mapping, *next_mapping)) {
    stack_end = next_mapping->range.End();
  }

  // The main thread should have an entry in the maps file just for its stack,
  // so we'll assume the base of the stack is at the end of the region. Other
  // threads' stacks may not have their own entries in the maps file if they
  // were user-allocated within a larger mapping, but pthreads places the TLS
  // at the high-address end of the stack so we can try using that to shrink
  // the stack region.
  stack_region_size = stack_end - stack_region_address;
  if (tid != reader->ProcessID() &&
      thread_specific_data_address > stack_region_address &&
      thread_specific_data_address < stack_end) {
    stack_region_size = thread_specific_data_address - stack_region_address;
  }
}

ProcessReader::ProcessReader()
    : process_info_(),
      memory_map_(),
      threads_(),
      process_memory_(),
      is_64_bit_(false),
      initialized_threads_(false),
      initialized_() {}

ProcessReader::~ProcessReader() {}

bool ProcessReader::Initialize(pid_t pid) {
  INITIALIZATION_STATE_SET_INITIALIZING(initialized_);
  if (!process_info_.Initialize(pid)) {
    return false;
  }

  if (!memory_map_.Initialize(pid)) {
    return false;
  }

  process_memory_.reset(new ProcessMemory());
  if (!process_memory_->Initialize(pid)) {
    return false;
  }

  if (!process_info_.Is64Bit(&is_64_bit_)) {
    return false;
  }

  INITIALIZATION_STATE_SET_VALID(initialized_);
  return true;
}

const std::vector<ProcessReader::Thread>& ProcessReader::Threads() {
  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
  if (!initialized_threads_) {
    InitializeThreads();
  }
  return threads_;
}

void ProcessReader::InitializeThreads() {
  DCHECK(threads_.empty());

  pid_t pid = ProcessID();
  if (pid == getpid()) {
    // TODO(jperaza): ptrace can't be used on threads in the same thread group.
    // Using clone to create a new thread in it's own thread group doesn't work
    // because glibc doesn't support threads it didn't create via pthreads.
    // Fork a new process to snapshot us and copy the data back?
    LOG(ERROR) << "not implemented";
    return;
  }

  char path[32];
  snprintf(path, arraysize(path), "/proc/%d/task", pid);
  DIR* dir = opendir(path);
  if (!dir) {
    PLOG(ERROR) << "opendir";
    return;
  }
  ScopedDIR scoped_dir(dir);

  Thread main_thread;
  main_thread.tid = pid;
  if (main_thread.InitializePtrace()) {
    main_thread.InitializeStack(this);
    threads_.push_back(main_thread);
  } else {
    LOG(WARNING) << "Couldn't initialize main thread.";
  }

  bool main_thread_found = false;
  dirent* dir_entry;
  while ((dir_entry = readdir(scoped_dir.get()))) {
    if (strncmp(dir_entry->d_name, ".", arraysize(dir_entry->d_name)) == 0 ||
        strncmp(dir_entry->d_name, "..", arraysize(dir_entry->d_name)) == 0) {
      continue;
    }
    pid_t tid;
    if (!base::StringToInt(dir_entry->d_name, &tid)) {
      LOG(ERROR) << "format error";
      continue;
    }

    if (tid == pid) {
      DCHECK(!main_thread_found);
      main_thread_found = true;
      continue;
    }

    Thread thread;
    thread.tid = tid;
    if (thread.InitializePtrace()) {
      thread.InitializeStack(this);
      threads_.push_back(thread);
    }
  }
  DCHECK(main_thread_found);
}

}  // namespace crashpad