Add the ability to opt-out of ASan container annotations on a per-allocator basis

stl/inc/vector

@@ -493,6 +493,10 @@ private:
             return;
         }
 
+        if constexpr (!_Is_ASan_enabled_for_allocator<allocator_type>) {
+            return;
+        }
+
         const void* const _First    = _STD _Unfancy(_First_);
         const void* const _End      = _STD _Unfancy(_End_);
         const void* const _Old_last = _STD _Unfancy(_Old_last_);

stl/inc/xmemory

@@ -805,6 +805,10 @@ struct _Simple_types { // wraps types from allocators with simple addressing for
 _INLINE_VAR constexpr size_t _Asan_granularity      = 8;
 _INLINE_VAR constexpr size_t _Asan_granularity_mask = _Asan_granularity - 1;
 
+// Represents whether ASan container annotations are enabled a given allocator.
+template <class>
+constexpr bool _Is_ASan_enabled_for_allocator = true;
+
 struct _Asan_aligned_pointers {
     const void* _First;
     const void* _End;

stl/inc/xstring

@@ -632,6 +632,10 @@ private:
             return;
         }
 
+        if constexpr (!_Is_ASan_enabled_for_allocator<allocator_type>) {
+            return;
+        }
+
         // Note that `_Capacity`, `_Old_size`, and `_New_size` do not include the null terminator
         const void* const _End      = _First + _Capacity + 1;
         const void* const _Old_last = _First + _Old_size + 1;

tests/std/tests/GH_002030_asan_annotate_string/test.cpp

@@ -287,6 +287,94 @@ STATIC_ASSERT(_Container_allocation_minimum_asan_alignment<
                   basic_string<wchar_t, char_traits<wchar_t>, implicit_allocator<wchar_t>>>
               == 2);
 
+// Helper class for `ArenaAllocator`, where data is linearly allocated in a finite buffer.
+class Arena {
+public:
+    Arena(size_t allocation_size, size_t capacity):
+        data(new char[capacity* allocation_size]),
+        allocation_size(allocation_size),
+        capacity(capacity),
+        offset(0) {}
+
+    Arena(const Arena& other):
+        data(other.data),
+        allocation_size(other.allocation_size),
+        capacity(other.capacity),
+        offset(other.offset) {}
+
+    void* allocate(size_t n) {
+        assert(offset + n <= capacity && "Allocation failed: the arena is out of memory. You may call `reset` to free up space.");
+        void* result = data + (offset * allocation_size);
+        offset += n;
+        return result;
+    }
+
+    // Deallocates memory in the arena, and `memset`s it all to zero
+    void reset() noexcept {
+        offset = 0;
+        memset(data, 0, capacity*allocation_size);
+    }
+
+    char* const data;
+    const size_t allocation_size;
+    const size_t capacity;
+    size_t offset;
+};
+
+// FIXME: refactor this class into a helper class.
+// An allocator that allocates memory in a pre-allocated buffer (the arena).
+template <typename T>
+class ArenaAllocator {
+public:
+
+    using value_type = T;
+    Arena* arena;
+
+    ArenaAllocator(size_t alloc_size, size_t capacity) {
+        assert(sizeof(T) <= alloc_size && "Constructor failed: allocation size is too small for target type.");
+        arena = new Arena(alloc_size, capacity);
+    }
+
+    template <class U>
+    ArenaAllocator(const ArenaAllocator<U>& other) {
+        assert(sizeof(T) <= other.arena->allocation_size && "Constructor failed: allocation size is too small for target type.");
+        arena = other.arena;
+    }
+
+    T* allocate(size_t n) {
+        void* ptr = arena->allocate(n);
+		return reinterpret_cast<T*>(ptr);
+    }
+
+    // no-op. Memory is deallocated in the `reset` method
+    void deallocate(value_type*, size_t) noexcept {}
+
+    // Deallocates memory in the arena, and `memset`s it all to zero.
+    // the `memset` would normally trigger an ASan AV,
+    // but we'll have the ArenaAllocator opt out of ASan analysis
+    void reset() noexcept {
+        arena->reset();
+    }
+
+    template <typename U>
+    bool operator==(ArenaAllocator<U> const& other)
+    {
+        return this->arena == other.arena;
+    }
+
+    template<typename U>
+    bool operator!=(ArenaAllocator<U> const other)
+    {
+        return !(this == other);
+    }
+};
+
+// Opt out of ASan analysis for the ArenaAllocator
+// FIXME: IntelliSense claims '_Is_ASan_enabled_for_allocator is not a templateC/C++(864)',
+//  but it works somehow.
+template <typename T>
+constexpr bool _Is_ASan_enabled_for_allocator<ArenaAllocator<T>> = false;
+
 template <class Alloc>
 void test_construction() {
     using CharType = typename Alloc::value_type;
@@ -1853,6 +1941,32 @@ void run_tests() {
 #endif // ^^^ no workaround ^^^
 }
 
+// Tests that ASan analysis can be disabled for a vector with an arena allocator.
+void run_asan_disablement_test() {
+
+    // The arena allocator stores integers in 32-bit alignment.
+    // It can hold up to 100 such allocations.
+    // The 32-bit alignment is a bit excessive for `char`s, but it ensures the allocator
+    // can be rebound to allocate larger types as well (up to 32-bit types).
+    const int size = 100;
+    const int alloc_size = 32;
+    ArenaAllocator<char> allocator(alloc_size, size);
+
+    std::basic_string<char, std::char_traits<char>, ArenaAllocator<char>> myString(allocator);
+    myString.reserve(50);
+    myString.push_back('A');
+
+    // When calling reset, the arena would memset all 100 entries of it's buffer to zero.
+    // If the allocator was naively annotated by ASan, this would trigger an AV, because
+    // the arena is accessing memory not tracked by the vector's ASan annotations.
+
+    // However, the allocator is annotated to opt out of ASan analysis through,
+    // `_Is_ASan_enabled_for_allocator`, so this should not trigger an AV.
+    allocator.reset();
+
+    // TODO: is it possible to add a 'negative' test case here? One where ASan expectedly fails?
+}
+
 template <class CharType, template <class, class, class> class Alloc>
 void run_custom_allocator_matrix() {
     run_tests<Alloc<CharType, true_type, true_type>>();
@@ -1867,6 +1981,7 @@ void run_allocator_matrix() {
     run_custom_allocator_matrix<CharType, aligned_allocator>();
     run_custom_allocator_matrix<CharType, explicit_allocator>();
     run_custom_allocator_matrix<CharType, implicit_allocator>();
+    run_asan_disablement_test();
 }
 
 void test_DevCom_10116361() {

tests/std/tests/GH_002030_asan_annotate_vector/test.cpp

@@ -274,6 +274,93 @@ struct implicit_allocator : custom_test_allocator<T, Pocma, Stateless> {
 STATIC_ASSERT(_Container_allocation_minimum_asan_alignment<vector<char, implicit_allocator<char>>> == 1);
 STATIC_ASSERT(_Container_allocation_minimum_asan_alignment<vector<wchar_t, implicit_allocator<wchar_t>>> == 2);
 
+// Helper class for `ArenaAllocator`, where data is linearly allocated in a finite buffer.
+class Arena {
+public:
+    Arena(size_t allocation_size, size_t capacity):
+        data(new char[capacity* allocation_size]),
+        allocation_size(allocation_size),
+        capacity(capacity),
+        offset(0) {}
+
+    Arena(const Arena& other):
+        data(other.data),
+        allocation_size(other.allocation_size),
+        capacity(other.capacity),
+        offset(other.offset) {}
+
+    void* allocate(size_t n) {
+        assert(offset + n <= capacity && "Allocation failed: the arena is out of memory. You may call `reset` to free up space.");
+        void* result = data + (offset * allocation_size);
+        offset += n;
+        return result;
+    }
+
+    // Deallocates memory in the arena, and `memset`s it all to zero
+    void reset() noexcept {
+        offset = 0;
+        memset(data, 0, capacity*allocation_size);
+    }
+
+    char* const data;
+    const size_t allocation_size;
+    const size_t capacity;
+    size_t offset;
+};
+
+// An allocator that allocates memory in a pre-allocated buffer (the arena).
+template <typename T>
+class ArenaAllocator {
+public:
+
+    using value_type = T;
+    Arena* arena;
+
+    ArenaAllocator(size_t alloc_size, size_t capacity) {
+        assert(sizeof(T) <= alloc_size && "Constructor failed: allocation size is too small for target type.");
+        arena = new Arena(alloc_size, capacity);
+    }
+
+    template <class U>
+    ArenaAllocator(const ArenaAllocator<U>& other) {
+        assert(sizeof(T) <= other.arena->allocation_size && "Constructor failed: allocation size is too small for target type.");
+        arena = other.arena;
+    }
+
+    T* allocate(size_t n) {
+        void* ptr = arena->allocate(n);
+		return reinterpret_cast<T*>(ptr);
+    }
+
+    // no-op. Memory is deallocated in the `reset` method
+    void deallocate(value_type*, size_t) noexcept {}
+
+    // Deallocates memory in the arena, and `memset`s it all to zero.
+    // the `memset` would normally trigger an ASan AV,
+    // but we'll have the ArenaAllocator opt out of ASan analysis
+    void reset() noexcept {
+        arena->reset();
+    }
+
+    template <typename U>
+    bool operator==(ArenaAllocator<U> const& other)
+    {
+        return this->arena == other.arena;
+    }
+
+    template<typename U>
+    bool operator!=(ArenaAllocator<U> const other)
+    {
+        return !(this == other);
+    }
+};
+
+// Opt out of ASan analysis for the ArenaAllocator
+// FIXME: IntelliSense claims '_Is_ASan_enabled_for_allocator is not a templateC/C++(864)',
+//  but it works somehow.
+template <typename T>
+constexpr bool _Is_ASan_enabled_for_allocator<ArenaAllocator<T>> = false;
+
 template <class Alloc>
 void test_push_pop() {
     using T = typename Alloc::value_type;
@@ -1002,12 +1089,40 @@ void run_custom_allocator_matrix() {
     run_tests<AllocT<T, false_type, false_type>>();
 }
 
+// Tests that ASan analysis can be disabled for a vector with an arena allocator.
+void run_asan_disablement_test() {
+
+    // The arena allocator stores integers in 32-bit alignment.
+    // It can hold up to 100 such allocations.
+    // The 32-bit alignment is a bit excessive for `int`s, but it ensures the allocator
+    // can be rebound to allocate larger types as well (up to 32-bit types).
+    const int size = 100;
+    const int alloc_size = 32;
+    ArenaAllocator<int> allocator(alloc_size, size);
+
+    // We'll give the vector capacity 1, and allocate a single integer (99).
+    std::vector<int, ArenaAllocator<int>> vec(allocator);
+    vec.reserve(1);
+    vec.push_back(99);
+
+    // When calling reset, the arena would memset all 100 entries of it's buffer to zero.
+    // If the allocator was naively annotated by ASan, this would trigger an AV, because
+    // the arena is accessing memory not tracked by the vector's ASan annotations.
+
+    // However, the allocator is annotated to opt out of ASan analysis through,
+    // `_Is_ASan_enabled_for_allocator`, so this should not trigger an AV.
+    allocator.reset();
+
+    // TODO: is it possible to add a 'negative' test case here? One where ASan expectedly fails?
+}
+
 template <class T>
 void run_allocator_matrix() {
     run_tests<allocator<T>>();
     run_custom_allocator_matrix<T, aligned_allocator>();
     run_custom_allocator_matrix<T, explicit_allocator>();
     run_custom_allocator_matrix<T, implicit_allocator>();
+    run_asan_disablement_test();
 }
 
 int main() {