[ASan][libc++] std::basic_string annotations (#72677)

This commit introduces basic annotations for `std::basic_string`,
mirroring the approach used in `std::vector` and `std::deque`.
Initially, only long strings with the default allocator will be
annotated. Short strings (_SSO - short string optimization_) and strings
with non-default allocators will be annotated in the near future, with
separate commits dedicated to enabling them. The process will be similar
to the workflow employed for enabling annotations in `std::deque`.

**Please note**: these annotations function effectively only when libc++
and libc++abi dylibs are instrumented (with ASan). This aligns with the
prevailing behavior of Memory Sanitizer.

To avoid breaking everything, this commit also appends
`_LIBCPP_INSTRUMENTED_WITH_ASAN` to `__config_site` whenever libc++ is
compiled with ASan. If this macro is not defined, string annotations are
not enabled. However, linking a binary that does **not** annotate
strings with a dynamic library that annotates strings, is not permitted.

Originally proposed here: https://reviews.llvm.org/D132769

Related patches on Phabricator:
- Turning on annotations for short strings:
https://reviews.llvm.org/D147680
- Turning on annotations for all allocators:
https://reviews.llvm.org/D146214

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.

This Pull Request introduces basic annotations for `std::basic_string`.
Long strings exhibit structural similarities to `std::vector` and will
be annotated accordingly. Short strings are already implemented, but
will be turned on separately in a forthcoming commit. Look at [a
comment](https://github.com/llvm/llvm-project/pull/72677#issuecomment-1850554465)
below to read about SSO issues at current moment.

Due to the functionality introduced in
[D132522](https://github.com/llvm/llvm-project/commit/dd1b7b797a116eed588fd752fbe61d34deeb24e4),
the `__sanitizer_annotate_contiguous_container` function now offers
compatibility with all allocators. However, enabling this support will
be done in a subsequent commit. For the time being, only strings with
the default allocator will be annotated.

If you have any questions, please email:
- advenam.tacet@trailofbits.com
- disconnect3d@trailofbits.com

1 files changed, 3 insertions, 0 deletions

diff --git a/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer.pass.cpp b/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer.pass.cpp
index 68f5838ccf2f..af334eb080c3 100644
--- a/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer.pass.cpp
@@ -16,12 +16,14 @@
 
 #include "test_macros.h"
 #include "min_allocator.h"
+#include "asan_testing.h"
 
 template <class S>
 TEST_CONSTEXPR_CXX20 void test(S s, const typename S::value_type* str, S expected) {
   s.append(str);
   LIBCPP_ASSERT(s.__invariants());
   assert(s == expected);
+  LIBCPP_ASSERT(is_string_asan_correct(s));
 }
 
 template <class S>
@@ -43,6 +45,7 @@ TEST_CONSTEXPR_CXX20 bool test() {
   test_string<std::string>();
 #if TEST_STD_VER >= 11
   test_string<std::basic_string<char, std::char_traits<char>, min_allocator<char>>>();
+  test_string<std::basic_string<char, std::char_traits<char>, safe_allocator<char>>>();
 #endif
 
   { // test appending to self