base/allocator/partition_allocator/src/partition_alloc/pointers/raw_ptr_asan_unowned_impl.h

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_SRC_PARTITION_ALLOC_POINTERS_RAW_PTR_ASAN_UNOWNED_IMPL_H_
#define BASE_ALLOCATOR_PARTITION_ALLOCATOR_SRC_PARTITION_ALLOC_POINTERS_RAW_PTR_ASAN_UNOWNED_IMPL_H_

#include <stddef.h>

#include <type_traits>

#include "partition_alloc/partition_alloc_base/compiler_specific.h"
#include "partition_alloc/partition_alloc_base/cxx20_is_constant_evaluated.h"
#include "partition_alloc/partition_alloc_buildflags.h"
#include "partition_alloc/partition_alloc_forward.h"

#if !BUILDFLAG(USE_ASAN_UNOWNED_PTR)
#error "Included under wrong build option"
#endif

namespace base::internal {

bool EndOfAliveAllocation(const volatile void* ptr, bool is_adjustable_ptr);
bool LikelySmuggledScalar(const volatile void* ptr);

template <bool IsAdjustablePtr, bool MayDangle>
struct RawPtrAsanUnownedImpl {
  // The first two are needed for correctness. The last one isn't technically a
  // must, but better to set it.
  static constexpr bool kMustZeroOnConstruct = true;
  static constexpr bool kMustZeroOnMove = true;
  static constexpr bool kMustZeroOnDestruct = true;

  // Wraps a pointer.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* WrapRawPtr(T* ptr) {
    return ptr;
  }

  // Notifies the allocator when a wrapped pointer is being removed or replaced.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr void ReleaseWrappedPtr(T* wrapped_ptr) {
    if (!partition_alloc::internal::base::is_constant_evaluated()) {
      ProbeForLowSeverityLifetimeIssue(wrapped_ptr);
    }
  }

  // Unwraps the pointer, while asserting that memory hasn't been freed. The
  // function is allowed to crash on nullptr.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* SafelyUnwrapPtrForDereference(
      T* wrapped_ptr) {
    // ASAN will catch use of dereferenced ptr without additional probing.
    return wrapped_ptr;
  }

  // Unwraps the pointer, while asserting that memory hasn't been freed. The
  // function must handle nullptr gracefully.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* SafelyUnwrapPtrForExtraction(
      T* wrapped_ptr) {
    if (!partition_alloc::internal::base::is_constant_evaluated()) {
      ProbeForLowSeverityLifetimeIssue(wrapped_ptr);
    }
    return wrapped_ptr;
  }

  // Unwraps the pointer, without making an assertion on whether memory was
  // freed or not.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* UnsafelyUnwrapPtrForComparison(
      T* wrapped_ptr) {
    return wrapped_ptr;
  }

  // Upcasts the wrapped pointer.
  template <typename To, typename From>
  PA_ALWAYS_INLINE static constexpr To* Upcast(From* wrapped_ptr) {
    static_assert(std::is_convertible_v<From*, To*>,
                  "From must be convertible to To.");
    // Note, this cast may change the address if upcasting to base that lies in
    // the middle of the derived object.
    return wrapped_ptr;
  }

  // Advance the wrapped pointer by `delta_elems`.
  template <
      typename T,
      typename Z,
      typename =
          std::enable_if_t<partition_alloc::internal::is_offset_type<Z>, void>>
  PA_ALWAYS_INLINE static constexpr T* Advance(T* wrapped_ptr, Z delta_elems) {
    return wrapped_ptr + delta_elems;
  }

  // Retreat the wrapped pointer by `delta_elems`.
  template <
      typename T,
      typename Z,
      typename =
          std::enable_if_t<partition_alloc::internal::is_offset_type<Z>, void>>
  PA_ALWAYS_INLINE static constexpr T* Retreat(T* wrapped_ptr, Z delta_elems) {
    return wrapped_ptr - delta_elems;
  }

  template <typename T>
  PA_ALWAYS_INLINE static constexpr ptrdiff_t GetDeltaElems(T* wrapped_ptr1,
                                                            T* wrapped_ptr2) {
    return wrapped_ptr1 - wrapped_ptr2;
  }

  // Returns a copy of a wrapped pointer, without making an assertion on whether
  // memory was freed or not.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* Duplicate(T* wrapped_ptr) {
    return wrapped_ptr;
  }

  template <typename T>
  static void ProbeForLowSeverityLifetimeIssue(T* wrapped_ptr) {
    if (!MayDangle && wrapped_ptr) {
      const volatile void* probe_ptr =
          reinterpret_cast<const volatile void*>(wrapped_ptr);
      if (!LikelySmuggledScalar(probe_ptr) &&
          !EndOfAliveAllocation(probe_ptr, IsAdjustablePtr)) {
        reinterpret_cast<const volatile uint8_t*>(probe_ptr)[0];
      }
    }
  }

  // `WrapRawPtrForDuplication` and `UnsafelyUnwrapPtrForDuplication` are used
  // to create a new raw_ptr<T> from another raw_ptr<T> of a different flavor.
  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* WrapRawPtrForDuplication(T* ptr) {
    return ptr;
  }

  template <typename T>
  PA_ALWAYS_INLINE static constexpr T* UnsafelyUnwrapPtrForDuplication(
      T* wrapped_ptr) {
    return wrapped_ptr;
  }

  // This is for accounting only, used by unit tests.
  PA_ALWAYS_INLINE static constexpr void IncrementSwapCountForTest() {}
  PA_ALWAYS_INLINE static constexpr void IncrementLessCountForTest() {}
};

}  // namespace base::internal

#endif  // BASE_ALLOCATOR_PARTITION_ALLOCATOR_SRC_PARTITION_ALLOC_POINTERS_RAW_PTR_ASAN_UNOWNED_IMPL_H_