[ASan][libcxx] A way to turn off annotations for containers with a specific allocator

This revision is part of our efforts to support container annotations with (almost) every allocator.
That patch is necessary to enable support for most annotations (D136765). Without a way to turn off annotations, it's hard to use ASan with area allocators (no calls to destructors).

This is an answer to a request about it. This patch provides a solution to the aforementioned issue by introducing a new template structure `__asan_annotate_container_with_allocator`, which allows the disabling of container annotations for a specific allocator.

This patch also introduces `_LIBCPP_HAS_ASAN_CONTAINER_ANNOTATIONS_FOR_ALL_ALLOCATORS` FTM.

To turn off annotations, it is sufficient to create a template specialization with a false value using a [Unary Type Trait](https://en.cppreference.com/w/cpp/types/integral_constant).

The proposed structure is being used in the code enabling annotations for all allocators in `std::vector`, `std::basic_string`, and `std::deque`. (D136765 D146214 D146815)

Possibility to do it was added to ASan API in rGdd1b7b797a116eed588fd752fbe61d34deeb24e4 commit.

For context on not calling a destructor, look at https://eel.is/c++draft/basic.life#5 and notes there, you may also read a discussion in D136765.

Reviewed By: ldionne, philnik, #libc, hans

Spies: EricWF, mikhail.ramalho, #sanitizers, libcxx-commits, hans, vitalybuka

Differential Revision: https://reviews.llvm.org/D145628

diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
index ce944b5..a7ab788 100644 (file)
--- a/libcxx/docs/UsingLibcxx.rst
+++ b/libcxx/docs/UsingLibcxx.rst
@@ -523,3 +523,32 @@ Standard. Libc++ retroactively updates the Unicode Standard in older C++
 versions. This allows the library to have better estimates for newly introduced
 Unicode code points, without requiring the user to use the latest C++ version
 in their code base.
+=======
+Turning off ASan annotation in containers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``__asan_annotate_container_with_allocator`` is a customization point to allow users to disable
+`Address Sanitizer annotations for containers <https://github.com/google/sanitizers/wiki/AddressSanitizerContainerOverflow>`_ for specific allocators. This may be necessary for allocators that access allocated memory.
+This customization point exists only when ``_LIBCPP_HAS_ASAN_CONTAINER_ANNOTATIONS_FOR_ALL_ALLOCATORS`` Feature Test Macro is defined.
+
+For allocators not running destructors, it is also possible to `bulk-unpoison memory <https://github.com/google/sanitizers/wiki/AddressSanitizerManualPoisoning>`_ instead of disabling annotations altogether.
+
+The struct may be specialized for user-defined allocators. It is a `Cpp17UnaryTypeTrait <http://eel.is/c++draft/type.traits#meta.rqmts>`_ with a base characteristic of ``true_type`` if the container is allowed to use annotations and ``false_type`` otherwise.
+
+The annotations for a ``user_allocator`` can be disabled like this:
+
+.. code-block:: cpp
+
+  #ifdef _LIBCPP_HAS_ASAN_CONTAINER_ANNOTATIONS_FOR_ALL_ALLOCATORS
+  template <class T>
+  struct std::__asan_annotate_container_with_allocator<user_allocator<T>> : std::false_type {};
+  #endif
+
+Why may I want to turn it off?
+------------------------------
+
+There are a few reasons why you may want to turn off annotations for an allocator.
+Unpoisoning may not be an option, if (for example) you are not maintaining the allocator.
+
+* You are using allocator, which does not call destructor during deallocation.
+* You are aware that memory allocated with an allocator may be accessed, even when unused by container.

diff --git a/libcxx/include/__memory/allocator_traits.h b/libcxx/include/__memory/allocator_traits.h
index 57f88a3..4ed4416 100644 (file)
--- a/libcxx/include/__memory/allocator_traits.h
+++ b/libcxx/include/__memory/allocator_traits.h
@@ -401,6 +401,25 @@ struct __is_cpp17_copy_insertable<_Alloc, __enable_if_t<
     : __is_cpp17_move_insertable<_Alloc>
 { };
 
+// ASan choices
+#ifndef _LIBCPP_HAS_NO_ASAN
+#   define _LIBCPP_HAS_ASAN_CONTAINER_ANNOTATIONS_FOR_ALL_ALLOCATORS 1
+#endif
+
+#ifdef _LIBCPP_HAS_ASAN_CONTAINER_ANNOTATIONS_FOR_ALL_ALLOCATORS
+template <class _Alloc>
+struct __asan_annotate_container_with_allocator
+#   if defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 1600
+      : true_type {};
+#   else
+      // TODO LLVM18: Remove the special-casing
+      : false_type {};
+#   endif
+
+template <class _Tp>
+struct __asan_annotate_container_with_allocator<allocator<_Tp> > : true_type {};
+#endif
+
 #undef _LIBCPP_ALLOCATOR_TRAITS_HAS_XXX
 
 _LIBCPP_END_NAMESPACE_STD