[libc] Unify and extend no_sanitize attributes for strlen. (#161316)

Fast strlen implementations (naive wide-reads, SIMD-based, and
x86_64/aarch64-optimized versions) all may perform
technically-out-of-bound reads, which leads to reports under ASan,
HWASan (on ARM machines), and also TSan (which also has the capability
to detect heap out-of-bound reads). So, we need to explicitly disable
instrumentation in all three cases.

Tragically, Clang didn't support `[[gnu::no_sanitize]]` syntax until
recently, and since we're supporting both GCC and Clang, we have to
revert to `__attribute__` syntax.

Author: vonosmas

libc/src/__support/macros/attributes.h

@@ -81,4 +81,14 @@ LIBC_THREAD_MODE_EXTERNAL.
 #define LIBC_HAS_VECTOR_TYPE 0
 #endif
 
+#if __has_attribute(no_sanitize)
+// Disable regular and hardware-supported ASan for functions that may
+// intentionally make out-of-bounds access. Disable TSan as well, as it detects
+// out-of-bounds accesses to heap memory.
+#define LIBC_NO_SANITIZE_OOB_ACCESS                                            \
+  __attribute__((no_sanitize("address", "hwaddress", "thread")))
+#else
+#define LIBC_NO_SANITIZE_OOB_ACCESS
+#endif
+
 #endif // LLVM_LIBC_SRC___SUPPORT_MACROS_ATTRIBUTES_H

libc/src/string/CMakeLists.txt

@@ -22,6 +22,7 @@ add_header_library(
     libc.src.__support.CPP.type_traits
     libc.src.__support.CPP.simd
     libc.src.__support.common
+    libc.src.__support.macros.attributes
     libc.src.string.memory_utils.inline_memcpy
   ${string_config_options}
 )

libc/src/string/memory_utils/aarch64/inline_strlen.h

@@ -17,7 +17,7 @@
 namespace LIBC_NAMESPACE_DECL {
 
 namespace neon {
-[[gnu::no_sanitize_address]] [[maybe_unused]] LIBC_INLINE static size_t
+[[maybe_unused]] LIBC_NO_SANITIZE_OOB_ACCESS LIBC_INLINE static size_t
 string_length(const char *src) {
   using Vector __attribute__((may_alias)) = uint8x8_t;
 

libc/src/string/memory_utils/generic/inline_strlen.h

@@ -24,8 +24,7 @@ LIBC_INLINE constexpr cpp::simd_mask<char> shift_mask(cpp::simd_mask<char> m,
   return cpp::bit_cast<cpp::simd_mask<char>>(r);
 }
 
-[[clang::no_sanitize("address")]] LIBC_INLINE size_t
-string_length(const char *src) {
+LIBC_NO_SANITIZE_OOB_ACCESS LIBC_INLINE size_t string_length(const char *src) {
   constexpr cpp::simd<char> null_byte = cpp::splat('\0');
 
   size_t alignment = alignof(cpp::simd<char>);

libc/src/string/memory_utils/x86_64/inline_strlen.h

@@ -18,12 +18,12 @@ namespace LIBC_NAMESPACE_DECL {
 namespace string_length_internal {
 // Return a bit-mask with the nth bit set if the nth-byte in block_ptr is zero.
 template <typename Vector, typename Mask>
-[[gnu::no_sanitize_address]] LIBC_INLINE static Mask
+LIBC_NO_SANITIZE_OOB_ACCESS LIBC_INLINE static Mask
 compare_and_mask(const Vector *block_ptr);
 
 template <typename Vector, typename Mask,
           decltype(compare_and_mask<Vector, Mask>)>
-[[gnu::no_sanitize_address]] LIBC_INLINE static size_t
+LIBC_NO_SANITIZE_OOB_ACCESS LIBC_INLINE static size_t
 string_length_vector(const char *src) {
   uintptr_t misalign_bytes = reinterpret_cast<uintptr_t>(src) % sizeof(Vector);
 

libc/src/string/string_utils.h

@@ -19,6 +19,7 @@
 #include "hdr/types/size_t.h"
 #include "src/__support/CPP/bitset.h"
 #include "src/__support/CPP/type_traits.h" // cpp::is_same_v
+#include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h"
 #include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
 #include "src/string/memory_utils/inline_memcpy.h"
@@ -119,7 +120,7 @@ template <typename T> LIBC_INLINE size_t string_length(const T *src) {
 }
 
 template <typename Word>
-[[gnu::no_sanitize_address]] LIBC_INLINE void *
+LIBC_NO_SANITIZE_OOB_ACCESS LIBC_INLINE void *
 find_first_character_wide_read(const unsigned char *src, unsigned char ch,
                                size_t n) {
   const unsigned char *char_ptr = src;

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -5336,6 +5336,7 @@ libc_support_library(
         ":__support_common",
         ":__support_cpp_bitset",
         ":__support_cpp_type_traits",
+        ":__support_macros_attributes",
         ":__support_macros_optimization",
         ":hdr_limits_macros",
         ":llvm_libc_types_size_t",