[Clang][attr] Add 'cfi_salt' attribute

clang/include/clang/AST/Type.h

@@ -4631,6 +4631,9 @@ class FunctionType : public Type {
     /// [implimits] 8 bits would be enough here.
     unsigned NumExceptionType : 10;
 
+    LLVM_PREFERRED_TYPE(bool)
+    unsigned HasExtraAttributeInfo : 1;
+
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasArmTypeAttributes : 1;
 
@@ -4639,14 +4642,26 @@ class FunctionType : public Type {
     unsigned NumFunctionEffects : 4;
 
     FunctionTypeExtraBitfields()
-        : NumExceptionType(0), HasArmTypeAttributes(false),
-          EffectsHaveConditions(false), NumFunctionEffects(0) {}
+        : NumExceptionType(0), HasExtraAttributeInfo(false),
+          HasArmTypeAttributes(false), EffectsHaveConditions(false),
+          NumFunctionEffects(0) {}
+  };
+
+  /// A holder for extra information from attributes which aren't part of an
+  /// \p AttributedType.
+  struct alignas(void *) FunctionTypeExtraAttributeInfo {
+    /// A CFI "salt" that differentiates functions with the same prototype.
+    StringRef KCFISalt;
+
+    operator bool() const { return !KCFISalt.empty(); }
+
+    void Profile(llvm::FoldingSetNodeID &ID) const { ID.AddString(KCFISalt); }
   };
 
   /// The AArch64 SME ACLE (Arm C/C++ Language Extensions) define a number
   /// of function type attributes that can be set on function types, including
   /// function pointers.
-  enum AArch64SMETypeAttributes : unsigned {
+  enum AArch64SMETypeAttributes : uint16_t {
     SME_NormalFunction = 0,
     SME_PStateSMEnabledMask = 1 << 0,
     SME_PStateSMCompatibleMask = 1 << 1,
@@ -4676,11 +4691,11 @@ class FunctionType : public Type {
   };
 
   static ArmStateValue getArmZAState(unsigned AttrBits) {
-    return (ArmStateValue)((AttrBits & SME_ZAMask) >> SME_ZAShift);
+    return static_cast<ArmStateValue>((AttrBits & SME_ZAMask) >> SME_ZAShift);
   }
 
   static ArmStateValue getArmZT0State(unsigned AttrBits) {
-    return (ArmStateValue)((AttrBits & SME_ZT0Mask) >> SME_ZT0Shift);
+    return static_cast<ArmStateValue>((AttrBits & SME_ZT0Mask) >> SME_ZT0Shift);
   }
 
   /// A holder for Arm type attributes as described in the Arm C/C++
@@ -4689,6 +4704,7 @@ class FunctionType : public Type {
   struct alignas(void *) FunctionTypeArmAttributes {
     /// Any AArch64 SME ACLE type attributes that need to be propagated
     /// on declarations and function pointers.
+    LLVM_PREFERRED_TYPE(uint16_t)
     unsigned AArch64SMEAttributes : 9;
 
     FunctionTypeArmAttributes() : AArch64SMEAttributes(SME_NormalFunction) {}
@@ -5170,6 +5186,7 @@ class FunctionProtoType final
       private llvm::TrailingObjects<
           FunctionProtoType, QualType, SourceLocation,
           FunctionType::FunctionTypeExtraBitfields,
+          FunctionType::FunctionTypeExtraAttributeInfo,
           FunctionType::FunctionTypeArmAttributes, FunctionType::ExceptionType,
           Expr *, FunctionDecl *, FunctionType::ExtParameterInfo, Qualifiers,
           FunctionEffect, EffectConditionExpr> {
@@ -5259,19 +5276,22 @@ class FunctionProtoType final
   /// the various bits of extra information about a function prototype.
   struct ExtProtoInfo {
     FunctionType::ExtInfo ExtInfo;
+    Qualifiers TypeQuals;
+    RefQualifierKind RefQualifier = RQ_None;
+    ExceptionSpecInfo ExceptionSpec;
+    const ExtParameterInfo *ExtParameterInfos = nullptr;
+    SourceLocation EllipsisLoc;
+    FunctionEffectsRef FunctionEffects;
+    FunctionTypeExtraAttributeInfo ExtraAttributeInfo;
+
     LLVM_PREFERRED_TYPE(bool)
     unsigned Variadic : 1;
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasTrailingReturn : 1;
     LLVM_PREFERRED_TYPE(bool)
     unsigned CFIUncheckedCallee : 1;
+    LLVM_PREFERRED_TYPE(uint16_t)
     unsigned AArch64SMEAttributes : 9;
-    Qualifiers TypeQuals;
-    RefQualifierKind RefQualifier = RQ_None;
-    ExceptionSpecInfo ExceptionSpec;
-    const ExtParameterInfo *ExtParameterInfos = nullptr;
-    SourceLocation EllipsisLoc;
-    FunctionEffectsRef FunctionEffects;
 
     ExtProtoInfo()
         : Variadic(false), HasTrailingReturn(false), CFIUncheckedCallee(false),
@@ -5296,13 +5316,18 @@ class FunctionProtoType final
     bool requiresFunctionProtoTypeExtraBitfields() const {
       return ExceptionSpec.Type == EST_Dynamic ||
              requiresFunctionProtoTypeArmAttributes() ||
+             requiresFunctionProtoTypeExtraAttributeInfo() ||
              !FunctionEffects.empty();
     }
 
     bool requiresFunctionProtoTypeArmAttributes() const {
       return AArch64SMEAttributes != SME_NormalFunction;
     }
 
+    bool requiresFunctionProtoTypeExtraAttributeInfo() const {
+      return static_cast<bool>(ExtraAttributeInfo);
+    }
+
     void setArmSMEAttribute(AArch64SMETypeAttributes Kind, bool Enable = true) {
       if (Enable)
         AArch64SMEAttributes |= Kind;
@@ -5328,6 +5353,11 @@ class FunctionProtoType final
     return hasExtraBitfields();
   }
 
+  unsigned
+  numTrailingObjects(OverloadToken<FunctionTypeExtraAttributeInfo>) const {
+    return hasExtraAttributeInfo();
+  }
+
   unsigned numTrailingObjects(OverloadToken<ExceptionType>) const {
     return getExceptionSpecSize().NumExceptionType;
   }
@@ -5420,6 +5450,12 @@ class FunctionProtoType final
 
   }
 
+  bool hasExtraAttributeInfo() const {
+    return FunctionTypeBits.HasExtraBitfields &&
+           getTrailingObjects<FunctionTypeExtraBitfields>()
+               ->HasExtraAttributeInfo;
+  }
+
   bool hasArmTypeAttributes() const {
     return FunctionTypeBits.HasExtraBitfields &&
            getTrailingObjects<FunctionTypeExtraBitfields>()
@@ -5453,6 +5489,7 @@ class FunctionProtoType final
     EPI.TypeQuals = getMethodQuals();
     EPI.RefQualifier = getRefQualifier();
     EPI.ExtParameterInfos = getExtParameterInfosOrNull();
+    EPI.ExtraAttributeInfo = getExtraAttributeInfo();
     EPI.AArch64SMEAttributes = getAArch64SMEAttributes();
     EPI.FunctionEffects = getFunctionEffects();
     return EPI;
@@ -5640,6 +5677,13 @@ class FunctionProtoType final
     return getTrailingObjects<ExtParameterInfo>();
   }
 
+  /// Return the extra attribute information.
+  FunctionTypeExtraAttributeInfo getExtraAttributeInfo() const {
+    if (hasExtraAttributeInfo())
+      return *getTrailingObjects<FunctionTypeExtraAttributeInfo>();
+    return FunctionTypeExtraAttributeInfo();
+  }
+
   /// Return a bitmask describing the SME attributes on the function type, see
   /// AArch64SMETypeAttributes for their values.
   unsigned getAArch64SMEAttributes() const {

clang/include/clang/Basic/Attr.td

@@ -3896,6 +3896,14 @@ def CFICanonicalJumpTable : InheritableAttr {
   let SimpleHandler = 1;
 }
 
+def KCFISalt : DeclOrTypeAttr {
+  let Spellings = [Clang<"kcfi_salt">];
+  let Args = [StringArgument<"Salt">];
+  let Subjects = SubjectList<[Function, Field, Var, TypedefName], ErrorDiag>;
+  let Documentation = [KCFISaltDocs];
+  let LangOpts = [COnly];
+}
+
 // C/C++ Thread safety attributes (e.g. for deadlock, data race checking)
 // Not all of these attributes will be given a [[]] spelling. The attributes
 // which require access to function parameter names cannot use the [[]] spelling

clang/include/clang/Basic/AttrDocs.td

@@ -3643,6 +3643,64 @@ make the function's CFI jump table canonical. See :ref:`the CFI documentation
   }];
 }
 
+def KCFISaltDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Use ``__attribute__((kcfi_salt("<salt>")))`` on a function declaration, function
+definition, or typedef to help distinguish CFI hashes between functions with
+the same type signature.
+
+Example use:
+
+.. code-block:: c
+
+  // .h file:
+  #define __kcfi_salt __attribute__((kcfi_salt("vogon")))
+
+  // Convenient typedefs to avoid nested declarator syntax.
+  typedef int (*fptr_t)(void); // Non-salted function call.
+  typedef int (*fptr_salted_t)(void) __kcfi_salt;
+
+  struct widget_generator {
+    fptr_t init;
+    fptr_salted_t exec;
+    fptr_t teardown;
+  };
+
+  // 1st .c file:
+  static int internal_init(void) { /* ... */ }
+  static int internal_salted_exec(void) __kcfi_salt { /* ... */ }
+  static int internal_teardown(void) { /* ... */ }
+
+  static struct widget_generator _generator = {
+    .init = internal_init,
+    .exec = internal_salted_exec,
+    .teardown = internal_teardown,
+  }
+
+  struct widget_generator *widget_gen = _generator;
+
+  // 2nd .c file:
+  int generate_a_widget(void) {
+    int ret;
+
+    // Called with non-salted CFI.
+    ret = widget_gen.init();
+    if (ret)
+      return ret;
+
+    // Called with salted CFI.
+    ret = widget_gen.exec();
+    if (ret)
+      return ret;
+
+    // Called with non-salted CFI.
+    return widget_gen.teardown();
+  }
+
+  }];
+}
+
 def DocCatTypeSafety : DocumentationCategory<"Type Safety Checking"> {
   let Content = [{
 Clang supports additional attributes to enable checking type safety properties

clang/lib/AST/ASTContext.cpp

@@ -5123,10 +5123,12 @@ QualType ASTContext::getFunctionTypeInternal(
       EPI.ExceptionSpec.Type, EPI.ExceptionSpec.Exceptions.size());
   size_t Size = FunctionProtoType::totalSizeToAlloc<
       QualType, SourceLocation, FunctionType::FunctionTypeExtraBitfields,
+      FunctionType::FunctionTypeExtraAttributeInfo,
       FunctionType::FunctionTypeArmAttributes, FunctionType::ExceptionType,
       Expr *, FunctionDecl *, FunctionProtoType::ExtParameterInfo, Qualifiers,
       FunctionEffect, EffectConditionExpr>(
       NumArgs, EPI.Variadic, EPI.requiresFunctionProtoTypeExtraBitfields(),
+      EPI.requiresFunctionProtoTypeExtraAttributeInfo(),
       EPI.requiresFunctionProtoTypeArmAttributes(), ESH.NumExceptionType,
       ESH.NumExprPtr, ESH.NumFunctionDeclPtr,
       EPI.ExtParameterInfos ? NumArgs : 0,

clang/lib/AST/Type.cpp

@@ -3677,6 +3677,16 @@ FunctionProtoType::FunctionProtoType(QualType result, ArrayRef<QualType> params,
     FunctionTypeBits.HasExtraBitfields = false;
   }
 
+  // Propagate any extra attribute information.
+  if (epi.requiresFunctionProtoTypeExtraAttributeInfo()) {
+    auto &ExtraAttrInfo = *getTrailingObjects<FunctionTypeExtraAttributeInfo>();
+    ExtraAttrInfo.KCFISalt = epi.ExtraAttributeInfo.KCFISalt;
+
+    // Also set the bit in FunctionTypeExtraBitfields.
+    auto &ExtraBits = *getTrailingObjects<FunctionTypeExtraBitfields>();
+    ExtraBits.HasExtraAttributeInfo = true;
+  }
+
   if (epi.requiresFunctionProtoTypeArmAttributes()) {
     auto &ArmTypeAttrs = *getTrailingObjects<FunctionTypeArmAttributes>();
     ArmTypeAttrs = FunctionTypeArmAttributes();
@@ -3894,7 +3904,8 @@ void FunctionProtoType::Profile(llvm::FoldingSetNodeID &ID, QualType Result,
   // This is followed by the ext info:
   //      int
   // Finally we have a trailing return type flag (bool)
-  // combined with AArch64 SME Attributes, to save space:
+  // combined with AArch64 SME Attributes and extra attribute info, to save
+  // space:
   //      int
   // combined with any FunctionEffects
   //
@@ -3929,6 +3940,7 @@ void FunctionProtoType::Profile(llvm::FoldingSetNodeID &ID, QualType Result,
   }
 
   epi.ExtInfo.Profile(ID);
+  epi.ExtraAttributeInfo.Profile(ID);
 
   unsigned EffectCount = epi.FunctionEffects.size();
   bool HasConds = !epi.FunctionEffects.Conditions.empty();

clang/lib/AST/TypePrinter.cpp

@@ -2106,6 +2106,10 @@ void TypePrinter::printAttributedAfter(const AttributedType *T,
   case attr::ExtVectorType:
     OS << "ext_vector_type";
     break;
+  case attr::KCFISalt:
+    OS << "kcfi_salt(\"" << cast<KCFISaltAttr>(T->getAttr())->getSalt()
+       << "\")";
+    break;
   }
   OS << "))";
 }

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -2905,10 +2905,16 @@ void CodeGenFunction::EmitSanitizerStatReport(llvm::SanitizerStatKind SSK) {
 
 void CodeGenFunction::EmitKCFIOperandBundle(
     const CGCallee &Callee, SmallVectorImpl<llvm::OperandBundleDef> &Bundles) {
-  const FunctionProtoType *FP =
-      Callee.getAbstractInfo().getCalleeFunctionProtoType();
-  if (FP)
-    Bundles.emplace_back("kcfi", CGM.CreateKCFITypeId(FP->desugar()));
+  const CGCalleeInfo &CI = Callee.getAbstractInfo();
+  const FunctionProtoType *FP = CI.getCalleeFunctionProtoType();
+  if (!FP)
+    return;
+
+  StringRef Salt;
+  if (const auto &Info = FP->getExtraAttributeInfo())
+    Salt = Info.KCFISalt;
+
+  Bundles.emplace_back("kcfi", CGM.CreateKCFITypeId(FP->desugar(), Salt));
 }
 
 llvm::Value *

clang/lib/CodeGen/CodeGenModule.cpp

@@ -2338,7 +2338,7 @@ llvm::ConstantInt *CodeGenModule::CreateCrossDsoCfiTypeId(llvm::Metadata *MD) {
   return llvm::ConstantInt::get(Int64Ty, llvm::MD5Hash(MDS->getString()));
 }
 
-llvm::ConstantInt *CodeGenModule::CreateKCFITypeId(QualType T) {
+llvm::ConstantInt *CodeGenModule::CreateKCFITypeId(QualType T, StringRef Salt) {
   if (auto *FnType = T->getAs<FunctionProtoType>())
     T = getContext().getFunctionType(
         FnType->getReturnType(), FnType->getParamTypes(),
@@ -2349,6 +2349,9 @@ llvm::ConstantInt *CodeGenModule::CreateKCFITypeId(QualType T) {
   getCXXABI().getMangleContext().mangleCanonicalTypeName(
       T, Out, getCodeGenOpts().SanitizeCfiICallNormalizeIntegers);
 
+  if (!Salt.empty())
+    Out << "." << Salt;
+
   if (getCodeGenOpts().SanitizeCfiICallNormalizeIntegers)
     Out << ".normalized";
 
@@ -3015,9 +3018,15 @@ void CodeGenModule::createFunctionTypeMetadataForIcall(const FunctionDecl *FD,
 void CodeGenModule::setKCFIType(const FunctionDecl *FD, llvm::Function *F) {
   llvm::LLVMContext &Ctx = F->getContext();
   llvm::MDBuilder MDB(Ctx);
+  llvm::StringRef Salt;
+
+  if (const auto *FP = FD->getType()->getAs<FunctionProtoType>())
+    if (const auto &Info = FP->getExtraAttributeInfo())
+      Salt = Info.KCFISalt;
+
   F->setMetadata(llvm::LLVMContext::MD_kcfi_type,
-                 llvm::MDNode::get(
-                     Ctx, MDB.createConstant(CreateKCFITypeId(FD->getType()))));
+                 llvm::MDNode::get(Ctx, MDB.createConstant(CreateKCFITypeId(
+                                            FD->getType(), Salt))));
 }
 
 static bool allowKCFIIdentifier(StringRef Name) {

clang/lib/CodeGen/CodeGenModule.h

@@ -1621,7 +1621,7 @@ class CodeGenModule : public CodeGenTypeCache {
   llvm::ConstantInt *CreateCrossDsoCfiTypeId(llvm::Metadata *MD);
 
   /// Generate a KCFI type identifier for T.
-  llvm::ConstantInt *CreateKCFITypeId(QualType T);
+  llvm::ConstantInt *CreateKCFITypeId(QualType T, StringRef Salt);
 
   /// Create a metadata identifier for the given type. This may either be an
   /// MDString (for external identifiers) or a distinct unnamed MDNode (for