heap/base/stack.cc

// Copyright 2020 the V8 project 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 "src/heap/base/stack.h"

#include <limits>

#include "src/base/platform/platform.h"
#include "src/base/sanitizer/asan.h"
#include "src/base/sanitizer/msan.h"
#include "src/base/sanitizer/tsan.h"

namespace heap {
namespace base {

using IterateStackCallback = void (*)(const Stack*, StackVisitor*, intptr_t*);
extern "C" void PushAllRegistersAndIterateStack(const Stack*, StackVisitor*,
                                                IterateStackCallback);

Stack::Stack(const void* stack_start) : stack_start_(stack_start) {}

void Stack::SetStackStart(const void* stack_start) {
  stack_start_ = stack_start;
}

bool Stack::IsOnStack(void* slot) const {
  DCHECK_NOT_NULL(stack_start_);
#ifdef V8_USE_ADDRESS_SANITIZER
  // If the slot is part of a fake frame, then it is definitely on the stack.
  if (__asan_addr_is_in_fake_stack(__asan_get_current_fake_stack(),
                                   reinterpret_cast<void*>(slot), nullptr,
                                   nullptr)) {
    return true;
  }
  // Fall through as there is still a regular stack present even when running
  // with ASAN fake stacks.
#endif  // V8_USE_ADDRESS_SANITIZER
#if defined(__has_feature)
#if __has_feature(safe_stack)
  if (__builtin___get_unsafe_stack_top() >= slot &&
      slot >= __builtin___get_unsafe_stack_ptr()) {
    return true;
  }
#endif  // __has_feature(safe_stack)
#endif  // defined(__has_feature)
  return v8::base::Stack::GetCurrentStackPosition() <= slot &&
         slot <= stack_start_;
}

namespace {

#ifdef V8_USE_ADDRESS_SANITIZER

// No ASAN support as accessing fake frames otherwise results in
// "stack-use-after-scope" warnings.
DISABLE_ASAN
// No TSAN support as the stack may not be exclusively owned by the current
// thread, e.g., for interrupt handling. Atomic reads are not enough as the
// other thread may use a lock to synchronize the access.
DISABLE_TSAN
void IterateAsanFakeFrameIfNecessary(StackVisitor* visitor,
                                     void* asan_fake_stack,
                                     const void* stack_start,
                                     const void* stack_end, void* address) {
  // When using ASAN fake stack a pointer to the fake frame is kept on the
  // native frame. In case |addr| points to a fake frame of the current stack
  // iterate the fake frame. Frame layout see
  // https://github.com/google/sanitizers/wiki/AddressSanitizerUseAfterReturn
  if (asan_fake_stack) {
    void* fake_frame_begin;
    void* fake_frame_end;
    void* real_stack_frame = __asan_addr_is_in_fake_stack(
        asan_fake_stack, address, &fake_frame_begin, &fake_frame_end);
    if (real_stack_frame) {
      // |address| points to a fake frame. Check that the fake frame is part
      // of this stack.
      if (stack_start >= real_stack_frame && real_stack_frame >= stack_end) {
        // Iterate the fake frame.
        for (void** current = reinterpret_cast<void**>(fake_frame_begin);
             current < fake_frame_end; ++current) {
          void* addr = *current;
          if (addr == nullptr) continue;
          visitor->VisitPointer(addr);
        }
      }
    }
  }
}

#endif  // V8_USE_ADDRESS_SANITIZER

void IterateUnsafeStackIfNecessary(StackVisitor* visitor) {
#if defined(__has_feature)
#if __has_feature(safe_stack)
  // Source:
  // https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/safestack/safestack.cpp
  constexpr size_t kSafeStackAlignmentBytes = 16;
  void* stack_end = __builtin___get_unsafe_stack_ptr();
  void* stack_start = __builtin___get_unsafe_stack_top();
  CHECK_GT(stack_start, stack_end);
  CHECK_EQ(0u, reinterpret_cast<uintptr_t>(stack_end) &
                   (kSafeStackAlignmentBytes - 1));
  CHECK_EQ(0u, reinterpret_cast<uintptr_t>(stack_start) &
                   (kSafeStackAlignmentBytes - 1));
  void** current = reinterpret_cast<void**>(stack_end);
  for (; current < stack_start; ++current) {
    void* address = *current;
    if (address == nullptr) continue;
    visitor->VisitPointer(address);
  }
#endif  // __has_feature(safe_stack)
#endif  // defined(__has_feature)
}

// Called by the trampoline that pushes registers on the stack. This method
// should never be inlined to ensure that a possible redzone cannot contain
// any data that needs to be scanned.
V8_NOINLINE
// No ASAN support as method accesses redzones while walking the stack.
DISABLE_ASAN
// No TSAN support as the stack may not be exclusively owned by the current
// thread, e.g., for interrupt handling. Atomic reads are not enough as the
// other thread may use a lock to synchronize the access.
DISABLE_TSAN
void IteratePointersImpl(const Stack* stack, StackVisitor* visitor,
                         intptr_t* stack_end) {
#ifdef V8_USE_ADDRESS_SANITIZER
  void* asan_fake_stack = __asan_get_current_fake_stack();
#endif  // V8_USE_ADDRESS_SANITIZER
  // All supported platforms should have their stack aligned to at least
  // sizeof(void*).
  constexpr size_t kMinStackAlignment = sizeof(void*);
  void** current = reinterpret_cast<void**>(stack_end);
  CHECK_EQ(0u, reinterpret_cast<uintptr_t>(current) & (kMinStackAlignment - 1));
  for (; current < stack->stack_start(); ++current) {
    // MSAN: Instead of unpoisoning the whole stack, the slot's value is copied
    // into a local which is unpoisoned.
    void* address = *current;
    MSAN_MEMORY_IS_INITIALIZED(&address, sizeof(address));
    if (address == nullptr) continue;
    visitor->VisitPointer(address);
#ifdef V8_USE_ADDRESS_SANITIZER
    IterateAsanFakeFrameIfNecessary(visitor, asan_fake_stack,
                                    stack->stack_start(), stack_end, address);
#endif  // V8_USE_ADDRESS_SANITIZER
  }
}

}  // namespace

void Stack::IteratePointers(StackVisitor* visitor) const {
  DCHECK_NOT_NULL(stack_start_);
  PushAllRegistersAndIterateStack(this, visitor, &IteratePointersImpl);
  // No need to deal with callee-saved registers as they will be kept alive by
  // the regular conservative stack iteration.
  // TODO(chromium:1056170): Add support for SIMD and/or filtering.
  IterateUnsafeStackIfNecessary(visitor);
}

void Stack::IteratePointersUnsafe(StackVisitor* visitor,
                                  uintptr_t stack_end) const {
  IteratePointersImpl(this, visitor, reinterpret_cast<intptr_t*>(stack_end));
}

const void* Stack::GetCurrentStackPointerForLocalVariables() {
#if defined(__has_feature)
#if __has_feature(safe_stack)
  return __builtin___get_unsafe_stack_ptr();
#else   // __has_feature(safe_stack)
  return v8::base::Stack::GetCurrentStackPosition();
#endif  // __has_feature(safe_stack)
#else   // defined(__has_feature)
  return v8::base::Stack::GetCurrentStackPosition();
#endif  // defined(__has_feature)
}

}  // namespace base
}  // namespace heap