1 files changed, 235 insertions, 0 deletions
diff --git a/tools/fuzzing/libfuzzer/FuzzerInterceptors.cpp b/tools/fuzzing/libfuzzer/FuzzerInterceptors.cpp
new file mode 100644
index 0000000000..a1a64780de
--- /dev/null
+++ b/tools/fuzzing/libfuzzer/FuzzerInterceptors.cpp
@@ -0,0 +1,235 @@
+//===-- FuzzerInterceptors.cpp --------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// Intercept certain libc functions to aid fuzzing.
+// Linked only when other RTs that define their own interceptors are not linked.
+//===----------------------------------------------------------------------===//
+
+#include "FuzzerPlatform.h"
+
+#if LIBFUZZER_LINUX
+
+#define GET_CALLER_PC() __builtin_return_address(0)
+
+#define PTR_TO_REAL(x) real_##x
+#define REAL(x) __interception::PTR_TO_REAL(x)
+#define FUNC_TYPE(x) x##_type
+#define DEFINE_REAL(ret_type, func, ...)                                       \
+  typedef ret_type (*FUNC_TYPE(func))(__VA_ARGS__);                            \
+  namespace __interception {                                                   \
+  FUNC_TYPE(func) PTR_TO_REAL(func);                                           \
+  }
+
+#include <cassert>
+#include <cstdint>
+#include <dlfcn.h> // for dlsym()
+#include <sanitizer/common_interface_defs.h>
+
+static void *getFuncAddr(const char *name, uintptr_t wrapper_addr) {
+  void *addr = dlsym(RTLD_NEXT, name);
+  if (!addr) {
+    // If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
+    // later in the library search order than the DSO that we are trying to
+    // intercept, which means that we cannot intercept this function. We still
+    // want the address of the real definition, though, so look it up using
+    // RTLD_DEFAULT.
+    addr = dlsym(RTLD_DEFAULT, name);
+
+    // In case `name' is not loaded, dlsym ends up finding the actual wrapper.
+    // We don't want to intercept the wrapper and have it point to itself.
+    if (reinterpret_cast<uintptr_t>(addr) == wrapper_addr)
+      addr = nullptr;
+  }
+  return addr;
+}
+
+static int FuzzerInited = 0;
+static bool FuzzerInitIsRunning;
+
+static void fuzzerInit();
+
+static void ensureFuzzerInited() {
+  assert(!FuzzerInitIsRunning);
+  if (!FuzzerInited) {
+    fuzzerInit();
+  }
+}
+
+static int internal_strcmp_strncmp(const char *s1, const char *s2, bool strncmp,
+                                   size_t n) {
+  size_t i = 0;
+  while (true) {
+    if (strncmp) {
+      if (i == n)
+        break;
+      i++;
+    }
+    unsigned c1 = *s1;
+    unsigned c2 = *s2;
+    if (c1 != c2)
+      return (c1 < c2) ? -1 : 1;
+    if (c1 == 0)
+      break;
+    s1++;
+    s2++;
+  }
+  return 0;
+}
+
+static int internal_strncmp(const char *s1, const char *s2, size_t n) {
+  return internal_strcmp_strncmp(s1, s2, true, n);
+}
+
+static int internal_strcmp(const char *s1, const char *s2) {
+  return internal_strcmp_strncmp(s1, s2, false, 0);
+}
+
+static int internal_memcmp(const void *s1, const void *s2, size_t n) {
+  const uint8_t *t1 = static_cast<const uint8_t *>(s1);
+  const uint8_t *t2 = static_cast<const uint8_t *>(s2);
+  for (size_t i = 0; i < n; ++i, ++t1, ++t2)
+    if (*t1 != *t2)
+      return *t1 < *t2 ? -1 : 1;
+  return 0;
+}
+
+static size_t internal_strlen(const char *s) {
+  size_t i = 0;
+  while (s[i])
+    i++;
+  return i;
+}
+
+static char *internal_strstr(const char *haystack, const char *needle) {
+  // This is O(N^2), but we are not using it in hot places.
+  size_t len1 = internal_strlen(haystack);
+  size_t len2 = internal_strlen(needle);
+  if (len1 < len2)
+    return nullptr;
+  for (size_t pos = 0; pos <= len1 - len2; pos++) {
+    if (internal_memcmp(haystack + pos, needle, len2) == 0)
+      return const_cast<char *>(haystack) + pos;
+  }
+  return nullptr;
+}
+
+extern "C" {
+
+DEFINE_REAL(int, bcmp, const void *, const void *, size_t)
+DEFINE_REAL(int, memcmp, const void *, const void *, size_t)
+DEFINE_REAL(int, strncmp, const char *, const char *, size_t)
+DEFINE_REAL(int, strcmp, const char *, const char *)
+DEFINE_REAL(int, strncasecmp, const char *, const char *, size_t)
+DEFINE_REAL(int, strcasecmp, const char *, const char *)
+DEFINE_REAL(char *, strstr, const char *, const char *)
+DEFINE_REAL(char *, strcasestr, const char *, const char *)
+DEFINE_REAL(void *, memmem, const void *, size_t, const void *, size_t)
+
+ATTRIBUTE_INTERFACE int bcmp(const char *s1, const char *s2, size_t n) {
+  if (!FuzzerInited)
+    return internal_memcmp(s1, s2, n);
+  int result = REAL(bcmp)(s1, s2, n);
+  __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int memcmp(const void *s1, const void *s2, size_t n) {
+  if (!FuzzerInited)
+    return internal_memcmp(s1, s2, n);
+  int result = REAL(memcmp)(s1, s2, n);
+  __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strncmp(const char *s1, const char *s2, size_t n) {
+  if (!FuzzerInited)
+    return internal_strncmp(s1, s2, n);
+  int result = REAL(strncmp)(s1, s2, n);
+  __sanitizer_weak_hook_strncmp(GET_CALLER_PC(), s1, s2, n, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strcmp(const char *s1, const char *s2) {
+  if (!FuzzerInited)
+    return internal_strcmp(s1, s2);
+  int result = REAL(strcmp)(s1, s2);
+  __sanitizer_weak_hook_strcmp(GET_CALLER_PC(), s1, s2, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strncasecmp(const char *s1, const char *s2, size_t n) {
+  ensureFuzzerInited();
+  int result = REAL(strncasecmp)(s1, s2, n);
+  __sanitizer_weak_hook_strncasecmp(GET_CALLER_PC(), s1, s2, n, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strcasecmp(const char *s1, const char *s2) {
+  ensureFuzzerInited();
+  int result = REAL(strcasecmp)(s1, s2);
+  __sanitizer_weak_hook_strcasecmp(GET_CALLER_PC(), s1, s2, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE char *strstr(const char *s1, const char *s2) {
+  if (!FuzzerInited)
+    return internal_strstr(s1, s2);
+  char *result = REAL(strstr)(s1, s2);
+  __sanitizer_weak_hook_strstr(GET_CALLER_PC(), s1, s2, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE char *strcasestr(const char *s1, const char *s2) {
+  ensureFuzzerInited();
+  char *result = REAL(strcasestr)(s1, s2);
+  __sanitizer_weak_hook_strcasestr(GET_CALLER_PC(), s1, s2, result);
+  return result;
+}
+
+ATTRIBUTE_INTERFACE
+void *memmem(const void *s1, size_t len1, const void *s2, size_t len2) {
+  ensureFuzzerInited();
+  void *result = REAL(memmem)(s1, len1, s2, len2);
+  __sanitizer_weak_hook_memmem(GET_CALLER_PC(), s1, len1, s2, len2, result);
+  return result;
+}
+
+__attribute__((section(".preinit_array"),
+               used)) static void (*__local_fuzzer_preinit)(void) = fuzzerInit;
+
+} // extern "C"
+
+static void fuzzerInit() {
+  assert(!FuzzerInitIsRunning);
+  if (FuzzerInited)
+    return;
+  FuzzerInitIsRunning = true;
+
+  REAL(bcmp) = reinterpret_cast<memcmp_type>(
+      getFuncAddr("bcmp", reinterpret_cast<uintptr_t>(&bcmp)));
+  REAL(memcmp) = reinterpret_cast<memcmp_type>(
+      getFuncAddr("memcmp", reinterpret_cast<uintptr_t>(&memcmp)));
+  REAL(strncmp) = reinterpret_cast<strncmp_type>(
+      getFuncAddr("strncmp", reinterpret_cast<uintptr_t>(&strncmp)));
+  REAL(strcmp) = reinterpret_cast<strcmp_type>(
+      getFuncAddr("strcmp", reinterpret_cast<uintptr_t>(&strcmp)));
+  REAL(strncasecmp) = reinterpret_cast<strncasecmp_type>(
+      getFuncAddr("strncasecmp", reinterpret_cast<uintptr_t>(&strncasecmp)));
+  REAL(strcasecmp) = reinterpret_cast<strcasecmp_type>(
+      getFuncAddr("strcasecmp", reinterpret_cast<uintptr_t>(&strcasecmp)));
+  REAL(strstr) = reinterpret_cast<strstr_type>(
+      getFuncAddr("strstr", reinterpret_cast<uintptr_t>(&strstr)));
+  REAL(strcasestr) = reinterpret_cast<strcasestr_type>(
+      getFuncAddr("strcasestr", reinterpret_cast<uintptr_t>(&strcasestr)));
+  REAL(memmem) = reinterpret_cast<memmem_type>(
+      getFuncAddr("memmem", reinterpret_cast<uintptr_t>(&memmem)));
+
+  FuzzerInitIsRunning = false;
+  FuzzerInited = 1;
+}
+
+#endif