[CodeGen][KCFI] Introduce llvm::getKCFITypeID to wrap hash implementation

KCFI generates hashes in two places. Instead of exposing the hash
implementation in both places, introduce a helper that wraps the
specific hash implementation in a single place.

Signed-off-by: Kees Cook <[email protected]>

Author: kees

clang/lib/CodeGen/CodeGenModule.cpp

@@ -67,10 +67,10 @@
 #include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TimeProfiler.h"
-#include "llvm/Support/xxhash.h"
 #include "llvm/TargetParser/RISCVISAInfo.h"
 #include "llvm/TargetParser/Triple.h"
 #include "llvm/TargetParser/X86TargetParser.h"
+#include "llvm/Transforms/Instrumentation/KCFI.h"
 #include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include <optional>
 #include <set>
@@ -2434,8 +2434,7 @@ llvm::ConstantInt *CodeGenModule::CreateKCFITypeId(QualType T, StringRef Salt) {
   if (getCodeGenOpts().SanitizeCfiICallGeneralizePointers)
     Out << ".generalized";
 
-  return llvm::ConstantInt::get(Int32Ty,
-                                static_cast<uint32_t>(llvm::xxHash64(OutName)));
+  return llvm::ConstantInt::get(Int32Ty, llvm::getKCFITypeID(OutName));
 }
 
 void CodeGenModule::SetLLVMFunctionAttributes(GlobalDecl GD,

llvm/include/llvm/Support/Hash.h

@@ -0,0 +1,26 @@
+//===- llvm/Support/Hash.h - Hash functions --------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides hash functions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_HASH_H
+#define LLVM_SUPPORT_HASH_H
+
+#include "llvm/ADT/StringRef.h"
+#include <cstdint>
+
+namespace llvm {
+
+/// Compute KCFI type ID from mangled type name using FNV-1a hash.
+uint32_t getKCFITypeID(StringRef MangledTypeName);
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_HASH_H

llvm/lib/Support/CMakeLists.txt

@@ -202,6 +202,7 @@ add_llvm_component_library(LLVMSupport
   FormatVariadic.cpp
   GlobPattern.cpp
   GraphWriter.cpp
+  Hash.cpp
   HexagonAttributeParser.cpp
   HexagonAttributes.cpp
   InitLLVM.cpp

llvm/lib/Support/Hash.cpp

@@ -0,0 +1,20 @@
+//===- Hash.cpp - Hash functions ---------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements hash functions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Hash.h"
+#include "llvm/Support/xxhash.h"
+
+using namespace llvm;
+
+uint32_t llvm::getKCFITypeID(StringRef MangledTypeName) {
+  return static_cast<uint32_t>(xxHash64(MangledTypeName));
+}

llvm/lib/Transforms/Instrumentation/KCFI.cpp

@@ -23,6 +23,7 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Module.h"
+#include "llvm/Support/xxhash.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 

llvm/lib/Transforms/Utils/ModuleUtils.cpp

@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/ModuleUtils.h"
-#include "llvm/Analysis/VectorUtils.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Analysis/VectorUtils.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
@@ -21,7 +21,7 @@
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/MD5.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/xxhash.h"
+#include "llvm/Transforms/Instrumentation/KCFI.h"
 
 using namespace llvm;
 
@@ -208,10 +208,10 @@ void llvm::setKCFIType(Module &M, Function &F, StringRef MangledType) {
   std::string Type = MangledType.str();
   if (M.getModuleFlag("cfi-normalize-integers"))
     Type += ".normalized";
-  F.setMetadata(LLVMContext::MD_kcfi_type,
-                MDNode::get(Ctx, MDB.createConstant(ConstantInt::get(
-                                     Type::getInt32Ty(Ctx),
-                                     static_cast<uint32_t>(xxHash64(Type))))));
+  F.setMetadata(
+      LLVMContext::MD_kcfi_type,
+      MDNode::get(Ctx, MDB.createConstant(ConstantInt::get(
+                           Type::getInt32Ty(Ctx), getKCFITypeID(Type)))));
   // If the module was compiled with -fpatchable-function-entry, ensure
   // we use the same patchable-function-prefix.
   if (auto *MD = mdconst::extract_or_null<ConstantInt>(