diff --git a/linker/linker_cfi.cpp b/linker/linker_cfi.cpp
new file mode 100644
index 0000000..f788c16
--- /dev/null
+++ b/linker/linker_cfi.cpp
@@ -0,0 +1,273 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "linker_cfi.h"
+
+#include "linker_debug.h"
+#include "linker_globals.h"
+#include "private/bionic_page.h"
+#include "private/bionic_prctl.h"
+
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <cstdint>
+
+// Update shadow without making it writable by preparing the data on the side and mremap-ing it in
+// place.
+class ShadowWrite {
+  char* shadow_start;
+  char* shadow_end;
+  char* aligned_start;
+  char* aligned_end;
+  char* tmp_start;
+
+ public:
+  ShadowWrite(uint16_t* s, uint16_t* e) {
+    shadow_start = reinterpret_cast<char*>(s);
+    shadow_end = reinterpret_cast<char*>(e);
+    aligned_start = reinterpret_cast<char*>(PAGE_START(reinterpret_cast<uintptr_t>(shadow_start)));
+    aligned_end = reinterpret_cast<char*>(PAGE_END(reinterpret_cast<uintptr_t>(shadow_end)));
+    tmp_start =
+        reinterpret_cast<char*>(mmap(nullptr, aligned_end - aligned_start, PROT_READ | PROT_WRITE,
+                                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
+    CHECK(tmp_start != MAP_FAILED);
+    memcpy(tmp_start, aligned_start, shadow_start - aligned_start);
+    memcpy(tmp_start + (shadow_end - aligned_start), shadow_end, aligned_end - shadow_end);
+  }
+
+  uint16_t* begin() {
+    return reinterpret_cast<uint16_t*>(tmp_start + (shadow_start - aligned_start));
+  }
+
+  uint16_t* end() {
+    return reinterpret_cast<uint16_t*>(tmp_start + (shadow_end - aligned_start));
+  }
+
+  ~ShadowWrite() {
+    size_t size = aligned_end - aligned_start;
+    mprotect(tmp_start, size, PROT_READ);
+    void* res = mremap(tmp_start, size, size, MREMAP_MAYMOVE | MREMAP_FIXED,
+                       reinterpret_cast<void*>(aligned_start));
+    CHECK(res != MAP_FAILED);
+  }
+};
+
+void CFIShadowWriter::FixupVmaName() {
+  prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, *shadow_start, kShadowSize, "cfi shadow");
+}
+
+void CFIShadowWriter::AddConstant(uintptr_t begin, uintptr_t end, uint16_t v) {
+  uint16_t* shadow_begin = MemToShadow(begin);
+  uint16_t* shadow_end = MemToShadow(end - 1) + 1;
+
+  ShadowWrite sw(shadow_begin, shadow_end);
+  std::fill(sw.begin(), sw.end(), v);
+}
+
+void CFIShadowWriter::AddUnchecked(uintptr_t begin, uintptr_t end) {
+  AddConstant(begin, end, kUncheckedShadow);
+}
+
+void CFIShadowWriter::AddInvalid(uintptr_t begin, uintptr_t end) {
+  AddConstant(begin, end, kInvalidShadow);
+}
+
+void CFIShadowWriter::Add(uintptr_t begin, uintptr_t end, uintptr_t cfi_check) {
+  CHECK((cfi_check & (kCfiCheckAlign - 1)) == 0);
+
+  // Don't fill anything below cfi_check. We can not represent those addresses
+  // in the shadow, and must make sure at codegen to place all valid call
+  // targets above cfi_check.
+  begin = std::max(begin, cfi_check) & ~(kShadowAlign - 1);
+  uint16_t* shadow_begin = MemToShadow(begin);
+  uint16_t* shadow_end = MemToShadow(end - 1) + 1;
+
+  ShadowWrite sw(shadow_begin, shadow_end);
+  uint16_t sv = ((begin + kShadowAlign - cfi_check) >> kCfiCheckGranularity) + kRegularShadowMin;
+
+  // With each step of the loop below, __cfi_check address computation base is increased by
+  // 2**ShadowGranularity.
+  // To compensate for that, each next shadow value must be increased by 2**ShadowGranularity /
+  // 2**CfiCheckGranularity.
+  uint16_t sv_step = 1 << (kShadowGranularity - kCfiCheckGranularity);
+  for (uint16_t& s : sw) {
+    // If there is something there already, fall back to unchecked. This may happen in rare cases
+    // with MAP_FIXED libraries. FIXME: consider using a (slow) resolution function instead.
+    s = (s == kInvalidShadow) ? sv : kUncheckedShadow;
+    sv += sv_step;
+  }
+}
+
+static soinfo* find_libdl(soinfo* solist) {
+  for (soinfo* si = solist; si != nullptr; si = si->next) {
+    const char* soname = si->get_soname();
+    if (soname && strcmp(soname, "libdl.so") == 0) {
+      return si;
+    }
+  }
+  return nullptr;
+}
+
+static uintptr_t soinfo_find_symbol(soinfo* si, const char* s) {
+  SymbolName name(s);
+  const ElfW(Sym) * sym;
+  if (si->find_symbol_by_name(name, nullptr, &sym) && sym) {
+    return si->resolve_symbol_address(sym);
+  }
+  return 0;
+}
+
+uintptr_t soinfo_find_cfi_check(soinfo* si) {
+  return soinfo_find_symbol(si, "__cfi_check");
+}
+
+uintptr_t CFIShadowWriter::MapShadow() {
+  void* p =
+      mmap(nullptr, kShadowSize, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
+  CHECK(p != MAP_FAILED);
+  return reinterpret_cast<uintptr_t>(p);
+}
+
+bool CFIShadowWriter::AddLibrary(soinfo* si) {
+  CHECK(shadow_start != nullptr);
+  if (si->base == 0 || si->size == 0) {
+    return true;
+  }
+  uintptr_t cfi_check = soinfo_find_cfi_check(si);
+  if (cfi_check == 0) {
+    INFO("[ CFI add 0x%zx + 0x%zx %s ]", static_cast<uintptr_t>(si->base),
+         static_cast<uintptr_t>(si->size), si->get_soname());
+    AddUnchecked(si->base, si->base + si->size);
+    return true;
+  }
+
+  INFO("[ CFI add 0x%zx + 0x%zx %s: 0x%zx ]", static_cast<uintptr_t>(si->base),
+       static_cast<uintptr_t>(si->size), si->get_soname(), cfi_check);
+#ifdef __arm__
+  // Require Thumb encoding.
+  if ((cfi_check & 1UL) != 1UL) {
+    DL_ERR("__cfi_check in not a Thumb function in the library \"%s\"", si->get_soname());
+    return false;
+  }
+  cfi_check &= ~1UL;
+#endif
+  if ((cfi_check & (kCfiCheckAlign - 1)) != 0) {
+    DL_ERR("unaligned __cfi_check in the library \"%s\"", si->get_soname());
+    return false;
+  }
+  Add(si->base, si->base + si->size, cfi_check);
+  return true;
+}
+
+// Pass the shadow mapping address to libdl.so. In return, we get an pointer to the location
+// libdl.so uses to store the address.
+bool CFIShadowWriter::NotifyLibDl(soinfo* solist, uintptr_t p) {
+  soinfo* libdl = find_libdl(solist);
+  if (libdl == nullptr) {
+    DL_ERR("CFI could not find libdl");
+    return false;
+  }
+
+  uintptr_t cfi_init = soinfo_find_symbol(libdl, "__cfi_init");
+  CHECK(cfi_init != 0);
+  shadow_start = reinterpret_cast<uintptr_t* (*)(uintptr_t)>(cfi_init)(p);
+  CHECK(shadow_start != nullptr);
+  CHECK(*shadow_start == p);
+  return true;
+}
+
+bool CFIShadowWriter::MaybeInit(soinfo* new_si, soinfo* solist) {
+  CHECK(initial_link_done);
+  // Check if CFI shadow must be initialized at this time.
+  bool found = false;
+  if (new_si == nullptr) {
+    // This is the case when we've just completed the initial link. There may have been earlier
+    // calls to MaybeInit that were skipped. Look though the entire solist.
+    for (soinfo* si = solist; si != nullptr; si = si->next) {
+      if (soinfo_find_cfi_check(si)) {
+        found = true;
+        break;
+      }
+    }
+  } else {
+    // See if the new library uses CFI.
+    found = soinfo_find_cfi_check(new_si);
+  }
+
+  // Nothing found.
+  if (!found) {
+    return true;
+  }
+
+  // Init shadow and add all currently loaded libraries (not just the new ones).
+  if (!NotifyLibDl(solist, MapShadow()))
+    return false;
+  for (soinfo* si = solist; si != nullptr; si = si->next) {
+    if (!AddLibrary(si))
+      return false;
+  }
+  FixupVmaName();
+  return true;
+}
+
+bool CFIShadowWriter::AfterLoad(soinfo* si, soinfo* solist) {
+  if (!initial_link_done) {
+    // Too early.
+    return true;
+  }
+
+  if (shadow_start == nullptr) {
+    return MaybeInit(si, solist);
+  }
+
+  // Add the new library to the CFI shadow.
+  if (!AddLibrary(si))
+    return false;
+  FixupVmaName();
+  return true;
+}
+
+void CFIShadowWriter::BeforeUnload(soinfo* si) {
+  if (shadow_start == nullptr) return;
+  if (si->base == 0 || si->size == 0) return;
+  INFO("[ CFI remove 0x%zx + 0x%zx: %s ]", static_cast<uintptr_t>(si->base),
+       static_cast<uintptr_t>(si->size), si->get_soname());
+  AddInvalid(si->base, si->base + si->size);
+  FixupVmaName();
+}
+
+bool CFIShadowWriter::InitialLinkDone(soinfo* solist) {
+  CHECK(!initial_link_done)
+  initial_link_done = true;
+  return MaybeInit(nullptr, solist);
+}
+
+// Find __cfi_check in the caller and let it handle the problem. Since caller_pc is likely not a
+// valid CFI target, we can not use CFI shadow for lookup. This does not need to be fast, do the
+// regular symbol lookup.
+void CFIShadowWriter::CfiFail(uint64_t CallSiteTypeId, void* Ptr, void* DiagData, void* CallerPc) {
+  soinfo* si = find_containing_library(CallerPc);
+  if (!si) {
+    __builtin_trap();
+  }
+
+  uintptr_t cfi_check = soinfo_find_cfi_check(si);
+  if (!cfi_check) {
+    __builtin_trap();
+  }
+
+  reinterpret_cast<CFICheckFn>(cfi_check)(CallSiteTypeId, Ptr, DiagData);
+}