[ASan][libc++] Turn on ASan annotations for short strings

This commit turns on ASan annotations in `std::basic_string` for short stings (SSO case).

Originally suggested here: https://reviews.llvm.org/D147680

String annotations added here: llvm#72677

Annotating `std::basic_string` with default allocator is implemented in llvm#72677 but annotations for short strings (SSO - Short String Optimization) are turned off there. This commit turns them on. This also removes `_LIBCPP_SHORT_STRING_ANNOTATIONS_ALLOWED`, because we do not plan to support turning on and off short string annotations.

Support in ASan API exists since llvm@dd1b7b7.
You can turn off annotations for a specific allocator based on changes from llvm@2fa1bec.

This PR is a part of a series of patches extending AddressSanitizer C++ container overflow detection capabilities by adding annotations, similar to those existing in `std::vector` and `std::deque` collections. These enhancements empower ASan to effectively detect instances where the instrumented program attempts to access memory within a collection's internal allocation that remains unused. This includes cases where access occurs before or after the stored elements in `std::deque`, or between the `std::basic_string`'s size (including the null terminator) and capacity bounds.

The introduction of these annotations was spurred by a real-world software bug discovered by Trail of Bits, involving an out-of-bounds memory access during the comparison of two strings using the `std::equals` function. This function was taking iterators (`iter1_begin`, `iter1_end`, `iter2_begin`) to perform the comparison, using a custom comparison function. When the `iter1` object exceeded the length of `iter2`, an out-of-bounds read could occur on the `iter2` object. Container sanitization, upon enabling these annotations, would effectively identify and flag this potential vulnerability.

If you have any questions, please email:

    advenam.tacet@trailofbits.com
    disconnect3d@trailofbits.com

libcxx/include/string

@@ -659,7 +659,6 @@ _LIBCPP_PUSH_MACROS
 #else
 #  define _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS
 #endif
-#define _LIBCPP_SHORT_STRING_ANNOTATIONS_ALLOWED false
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -1896,38 +1895,33 @@ private:
 #endif
   }
 
-  // ASan: short string is poisoned if and only if this function returns true.
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __asan_short_string_is_annotated() const _NOEXCEPT {
-    return _LIBCPP_SHORT_STRING_ANNOTATIONS_ALLOWED && !__libcpp_is_constant_evaluated();
-  }
-
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __annotate_new(size_type __current_size) const _NOEXCEPT {
     (void) __current_size;
 #if !defined(_LIBCPP_HAS_NO_ASAN) && defined(_LIBCPP_INSTRUMENTED_WITH_ASAN)
-    if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
+    if (!__libcpp_is_constant_evaluated())
       __annotate_contiguous_container(data() + capacity() + 1, data() + __current_size + 1);
 #endif
   }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __annotate_delete() const _NOEXCEPT {
 #if !defined(_LIBCPP_HAS_NO_ASAN) && defined(_LIBCPP_INSTRUMENTED_WITH_ASAN)
-    if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
+    if (!__libcpp_is_constant_evaluated())
       __annotate_contiguous_container(data() + size() + 1, data() + capacity() + 1);
 #endif
   }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __annotate_increase(size_type __n) const _NOEXCEPT {
     (void) __n;
 #if !defined(_LIBCPP_HAS_NO_ASAN) && defined(_LIBCPP_INSTRUMENTED_WITH_ASAN)
-    if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
+    if (!__libcpp_is_constant_evaluated())
       __annotate_contiguous_container(data() + size() + 1, data() + size() + 1 + __n);
 #endif
   }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __annotate_shrink(size_type __old_size) const _NOEXCEPT {
     (void) __old_size;
 #if !defined(_LIBCPP_HAS_NO_ASAN) && defined(_LIBCPP_INSTRUMENTED_WITH_ASAN)
-    if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
+    if (!__libcpp_is_constant_evaluated())
       __annotate_contiguous_container(data() + __old_size + 1, data() + size() + 1);
 #endif
   }

libcxx/test/libcxx/containers/strings/basic.string/asan_deque_integration.pass.cpp

@@ -0,0 +1,183 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: asan
+// UNSUPPORTED: c++03
+
+#include <cassert>
+#include <array>
+#include "test_macros.h"
+#include "asan_testing.h" // includes deque and string - don't do it before
+#include "min_allocator.h"
+
+// This tests exists to check if strings work well with deque, as those
+// may be partialy annotated, we cannot simply call
+// is_double_ended_contiguous_container_asan_correct, as it assumes that
+// object memory inside is not annotated, so we check everything in a more careful way.
+
+template <typename D>
+bool verify_inside(D const& d) {
+  for (size_t i = 0; i < d.size(); ++i) {
+    if (!is_string_asan_correct(d[i]))
+      return false;
+  }
+
+  return true;
+}
+
+template <typename S, size_t N>
+S get_s(char c) {
+  S s;
+  for (size_t i = 0; i < N; ++i)
+    s.push_back(c);
+
+  return s;
+}
+
+template <class C, class S>
+void test_string() {
+  size_t const N = sizeof(S) < 256 ? (4096 / sizeof(S)) : 16;
+
+  {
+    C d1a(1), d1b(N), d1c(N + 1), d1d(32 * N);
+    assert(verify_inside(d1a));
+    assert(verify_inside(d1b));
+    assert(verify_inside(d1c));
+    assert(verify_inside(d1d));
+  }
+  {
+    C d2;
+    for (size_t i = 0; i < 16 * N; ++i) {
+      d2.push_back(get_s<S, 1>(i % 10 + 'a'));
+      assert(verify_inside(d2));
+      d2.push_back(get_s<S, 222>(i % 10 + 'b'));
+      assert(verify_inside(d2));
+
+      d2.pop_front();
+      assert(verify_inside(d2));
+    }
+  }
+  {
+    C d3;
+    for (size_t i = 0; i < 16 * N; ++i) {
+      d3.push_front(get_s<S, 1>(i % 10 + 'a'));
+      assert(verify_inside(d3));
+      d3.push_front(get_s<S, 222>(i % 10 + 'b'));
+      assert(verify_inside(d3));
+
+      d3.pop_back();
+      assert(verify_inside(d3));
+    }
+  }
+  {
+    C d4;
+    for (size_t i = 0; i < 16 * N; ++i) {
+      // When there is no SSO, all elements inside should not be poisoned,
+      // so we can verify deque poisoning.
+      d4.push_front(get_s<S, 333>(i % 10 + 'a'));
+      assert(verify_inside(d4));
+      assert(is_double_ended_contiguous_container_asan_correct(d4));
+      d4.push_back(get_s<S, 222>(i % 10 + 'b'));
+      assert(verify_inside(d4));
+      assert(is_double_ended_contiguous_container_asan_correct(d4));
+    }
+  }
+  {
+    C d5;
+    for (size_t i = 0; i < 5 * N; ++i) {
+      // In d4 we never had poisoned memory inside deque.
+      // Here we start with SSO, so part of the inside of the container,
+      // will be poisoned.
+      d5.push_front(S());
+      assert(verify_inside(d5));
+    }
+    for (size_t i = 0; i < d5.size(); ++i) {
+      // We change the size to have long string.
+      // Memory owne by deque should not be poisoned by string.
+      d5[i].resize(1000);
+      assert(verify_inside(d5));
+    }
+
+    assert(is_double_ended_contiguous_container_asan_correct(d5));
+
+    d5.erase(d5.begin() + 2);
+    assert(verify_inside(d5));
+
+    d5.erase(d5.end() - 2);
+    assert(verify_inside(d5));
+
+    assert(is_double_ended_contiguous_container_asan_correct(d5));
+  }
+  {
+    C d6a;
+    assert(is_double_ended_contiguous_container_asan_correct(d6a));
+
+    C d6b(N + 2, get_s<S, 1000>('a'));
+    d6b.push_front(get_s<S, 1001>('b'));
+    while (!d6b.empty()) {
+      d6b.pop_back();
+      assert(is_double_ended_contiguous_container_asan_correct(d6b));
+    }
+
+    C d6c(N + 2, get_s<S, 1002>('c'));
+    while (!d6c.empty()) {
+      d6c.pop_back();
+      assert(is_double_ended_contiguous_container_asan_correct(d6c));
+    }
+  }
+  {
+    C d7(9 * N + 2);
+
+    d7.insert(d7.begin() + 1, S());
+    assert(verify_inside(d7));
+
+    d7.insert(d7.end() - 3, S());
+    assert(verify_inside(d7));
+
+    d7.insert(d7.begin() + 2 * N, get_s<S, 1>('a'));
+    assert(verify_inside(d7));
+
+    d7.insert(d7.end() - 2 * N, get_s<S, 1>('b'));
+    assert(verify_inside(d7));
+
+    d7.insert(d7.begin() + 2 * N, 3 * N, get_s<S, 1>('c'));
+    assert(verify_inside(d7));
+
+    // It may not be short for big element types, but it will be checked correctly:
+    d7.insert(d7.end() - 2 * N, 3 * N, get_s<S, 2>('d'));
+    assert(verify_inside(d7));
+
+    d7.erase(d7.begin() + 2);
+    assert(verify_inside(d7));
+
+    d7.erase(d7.end() - 2);
+    assert(verify_inside(d7));
+  }
+}
+
+template <class S>
+void test_container() {
+  test_string<std::deque<S, std::allocator<S>>, S>();
+  test_string<std::deque<S, min_allocator<S>>, S>();
+  test_string<std::deque<S, safe_allocator<S>>, S>();
+}
+
+int main(int, char**) {
+  // Those tests support only types based on std::basic_string.
+  test_container<std::string>();
+  test_container<std::wstring>();
+#if TEST_STD_VER >= 11
+  test_container<std::u16string>();
+  test_container<std::u32string>();
+#endif
+#if TEST_STD_VER >= 20
+  test_container<std::u8string>();
+#endif
+
+  return 0;
+}

libcxx/test/libcxx/containers/strings/basic.string/asan_short.pass.cpp

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: asan
+// UNSUPPORTED: c++03
+
+// <string>
+
+// Basic test if ASan annotations work for short strings.
+
+#include <string>
+#include <cassert>
+#include <cstdlib>
+
+#include "asan_testing.h"
+#include "min_allocator.h"
+#include "test_iterators.h"
+#include "test_macros.h"
+
+extern "C" void __sanitizer_set_death_callback(void (*callback)(void));
+
+void do_exit() { exit(0); }
+
+int main(int, char**) {
+  {
+    typedef cpp17_input_iterator<char*> MyInputIter;
+    // Should not trigger ASan.
+    std::basic_string<char, std::char_traits<char>, safe_allocator<char>> v;
+    char i[] = {'a', 'b', 'c', 'd'};
+
+    v.insert(v.begin(), MyInputIter(i), MyInputIter(i + 4));
+    assert(v[0] == 'a');
+    assert(is_string_asan_correct(v));
+  }
+
+  __sanitizer_set_death_callback(do_exit);
+  {
+    using T     = char;
+    using C     = std::basic_string<T, std::char_traits<T>, safe_allocator<T>>;
+    const T t[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g'};
+    C c(std::begin(t), std::end(t));
+    assert(is_string_asan_correct(c));
+    assert(__sanitizer_verify_contiguous_container(c.data(), c.data() + c.size() + 1, c.data() + c.capacity() + 1) !=
+           0);
+    volatile T foo = c[c.size() + 1]; // should trigger ASAN. Use volatile to prevent being optimized away.
+    assert(false);                    // if we got here, ASAN didn't trigger
+    ((void)foo);
+  }
+
+  return 0;
+}