profiler/win32_stack_frame_unwinder.cc

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/profiler/win32_stack_frame_unwinder.h"

#include "base/containers/hash_tables.h"
#include "base/memory/singleton.h"
#include "base/stl_util.h"

namespace base {

// LeafUnwindBlacklist --------------------------------------------------------

namespace {

// Records modules that are known to have functions that violate the Microsoft
// x64 calling convention and would be dangerous to manually unwind if
// encountered as the last frame on the call stack. Functions like these have
// been observed in injected third party modules that either do not provide
// function unwind information, or do not provide the required function prologue
// and epilogue. The former case was observed in several AV products and the
// latter in a WndProc function associated with Actual Window
// Manager/aimemb64.dll. See https://crbug.com/476422.
class LeafUnwindBlacklist {
 public:
  static LeafUnwindBlacklist* GetInstance();

  // This function does not allocate memory and is safe to call between
  // SuspendThread and ResumeThread.
  bool IsBlacklisted(const void* module) const;

  // Allocates memory. Must be invoked only after ResumeThread, otherwise we
  // risk deadlocking on a heap lock held by a suspended thread.
  void AddModuleToBlacklist(const void* module);

 private:
  friend struct DefaultSingletonTraits<LeafUnwindBlacklist>;

  LeafUnwindBlacklist();
  ~LeafUnwindBlacklist();

  // The set of modules known to have functions that violate the Microsoft x64
  // calling convention.
  base::hash_set<const void*> blacklisted_modules_;

  DISALLOW_COPY_AND_ASSIGN(LeafUnwindBlacklist);
};

// static
LeafUnwindBlacklist* LeafUnwindBlacklist::GetInstance() {
  // Leaky for shutdown performance.
  return Singleton<LeafUnwindBlacklist,
                   LeakySingletonTraits<LeafUnwindBlacklist>>::get();
}

bool LeafUnwindBlacklist::IsBlacklisted(const void* module) const {
  return ContainsKey(blacklisted_modules_, module);
}

void LeafUnwindBlacklist::AddModuleToBlacklist(const void* module) {
  CHECK(module);
  blacklisted_modules_.insert(module);
}

LeafUnwindBlacklist::LeafUnwindBlacklist() {}
LeafUnwindBlacklist::~LeafUnwindBlacklist() {}

}  // namespace

// Win32StackFrameUnwinder ----------------------------------------------------

Win32StackFrameUnwinder::UnwindFunctions::~UnwindFunctions() {}
Win32StackFrameUnwinder::UnwindFunctions::UnwindFunctions() {}

Win32StackFrameUnwinder::Win32UnwindFunctions::Win32UnwindFunctions() {}

PRUNTIME_FUNCTION
Win32StackFrameUnwinder::Win32UnwindFunctions::LookupFunctionEntry(
    DWORD64 program_counter,
    PDWORD64 image_base) {
#ifdef _WIN64
  return RtlLookupFunctionEntry(program_counter, image_base, nullptr);
#else
  NOTREACHED();
  return nullptr;
#endif
}

void Win32StackFrameUnwinder::Win32UnwindFunctions::VirtualUnwind(
    DWORD64 image_base,
    DWORD64 program_counter,
    PRUNTIME_FUNCTION runtime_function,
    CONTEXT* context) {
#ifdef _WIN64
  void* handler_data;
  ULONG64 establisher_frame;
  KNONVOLATILE_CONTEXT_POINTERS nvcontext = {};
  RtlVirtualUnwind(0, image_base, program_counter, runtime_function, context,
                   &handler_data, &establisher_frame, &nvcontext);
#else
  NOTREACHED();
#endif
}

Win32StackFrameUnwinder::Win32StackFrameUnwinder()
    : Win32StackFrameUnwinder(&win32_unwind_functions_) {}

Win32StackFrameUnwinder::~Win32StackFrameUnwinder() {
  if (pending_blacklisted_module_) {
    LeafUnwindBlacklist::GetInstance()->AddModuleToBlacklist(
        pending_blacklisted_module_);
  }
}

bool Win32StackFrameUnwinder::TryUnwind(CONTEXT* context) {
#ifdef _WIN64
  CHECK(!at_top_frame_ || unwind_info_present_for_all_frames_);
  CHECK(!pending_blacklisted_module_);

  ULONG64 image_base;
  // Try to look up unwind metadata for the current function.
  PRUNTIME_FUNCTION runtime_function =
      unwind_functions_->LookupFunctionEntry(context->Rip, &image_base);

  if (runtime_function) {
    unwind_functions_->VirtualUnwind(image_base, context->Rip, runtime_function,
                                     context);
    at_top_frame_ = false;
  } else {
    // RtlLookupFunctionEntry didn't find unwind information. This could mean
    // the code at the instruction pointer is in:
    //
    // 1. a true leaf function (i.e. a function that neither calls a function,
    //    nor allocates any stack space itself) in which case the return
    //    address is at RSP, or
    //
    // 2. a function that doesn't adhere to the Microsoft x64 calling
    //    convention, either by not providing the required unwind information,
    //    or by not having the prologue or epilogue required for unwinding;
    //    this case has been observed in crash data in injected third party
    //    DLLs.
    //
    // In valid code, case 1 can only occur (by definition) as the last frame
    // on the stack. This happens in about 5% of observed stacks and can
    // easily be unwound by popping RSP and using it as the next frame's
    // instruction pointer.
    //
    // Case 2 can occur anywhere on the stack, and attempting to unwind the
    // stack will result in treating whatever value happens to be on the stack
    // at RSP as the next frame's instruction pointer. This is certainly wrong
    // and very likely to lead to crashing by deferencing invalid pointers in
    // the next RtlVirtualUnwind call.
    //
    // If we see case 2 at a location not the last frame, and all the previous
    // frame had valid unwind information, then this is definitely bad code.
    // We blacklist the module as untrustable for unwinding if we encounter a
    // function in it that doesn't have unwind information.

    if (at_top_frame_) {
      at_top_frame_ = false;

      // We are at the end of the stack. It's very likely that we're in case 1
      // since the vast majority of code adheres to the Microsoft x64 calling
      // convention. But there's a small chance we might be unlucky and be in
      // case 2. If this module is known to have bad code according to the
      // leaf unwind blacklist, stop here, otherwise manually unwind.
      if (LeafUnwindBlacklist::GetInstance()->IsBlacklisted(
              reinterpret_cast<const void*>(image_base))) {
        return false;
      }

      context->Rip = context->Rsp;
      context->Rsp += 8;
      unwind_info_present_for_all_frames_ = false;
    } else {
      // We're not at the end of the stack. This frame is untrustworthy and we
      // can't safely unwind from here.
      if (unwind_info_present_for_all_frames_) {
        // Unwind information was present for all previous frames, so we can
        // be confident this is case 2. Record the module to be blacklisted.
        pending_blacklisted_module_ = reinterpret_cast<const void*>(image_base);
      } else {
        // We started off on a function without unwind information. It's very
        // likely that all frames up to this point have been good, and this
        // frame is case 2. But it's possible that the initial frame was case
        // 2 but hadn't been blacklisted yet, and we've started to go off into
        // the weeds. Since we can't be sure, just bail out without
        // blacklisting the module; chances are we'll later encounter the same
        // function on a stack with full unwind information.
      }
      return false;
    }
  }

  return true;
#else
  NOTREACHED();
  return false;
#endif
}

Win32StackFrameUnwinder::Win32StackFrameUnwinder(
    UnwindFunctions* unwind_functions)
    : at_top_frame_(true),
      unwind_info_present_for_all_frames_(true),
      pending_blacklisted_module_(nullptr),
      unwind_functions_(unwind_functions) {}

}  // namespace base