[clang][RISCV] Introduce command line options for Zicfilp-backed forward-edge CFI

This patch enables the following command line flags for RISC-V targets:

+ `-fcf-protection=branch` turns on forward-edge control-flow integrity conditioning on RISC-V targets with Zicfilp extension
+ `-mcf-branch-label-scheme=unlabeled|func-sig` selects the label scheme used in the forward-edge CFI conditioning

Author: mylai-mtk

clang/include/clang/Basic/CFProtectionOptions.def

@@ -0,0 +1,15 @@
+//===-- CFProtectionOptions.def - cf-protection options ---------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+
+#ifdef CF_BRANCH_LABEL_SCHEME
+CF_BRANCH_LABEL_SCHEME(Unlabeled, unlabeled)
+CF_BRANCH_LABEL_SCHEME(FuncSig, func-sig)
+
+#undef CF_BRANCH_LABEL_SCHEME
+#endif // #ifdef CF_BRANCH_LABEL_SCHEME

clang/include/clang/Basic/CFProtectionOptions.h

@@ -0,0 +1,38 @@
+//===--- CFProtectionOptions.h ----------------------------------*- 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 defines constants for -fcf-protection and other related flags.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H
+#define LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H
+
+#include "llvm/Support/ErrorHandling.h"
+
+namespace clang {
+
+enum class CFBranchLabelSchemeKind {
+  Default,
+#define CF_BRANCH_LABEL_SCHEME(Kind, FlagVal) Kind,
+#include "clang/Basic/CFProtectionOptions.def"
+};
+
+static inline const char *
+getCFBranchLabelSchemeFlagVal(const CFBranchLabelSchemeKind Scheme) {
+#define CF_BRANCH_LABEL_SCHEME(Kind, FlagVal)                                  \
+  if (Scheme == CFBranchLabelSchemeKind::Kind)                                 \
+    return #FlagVal;
+#include "clang/Basic/CFProtectionOptions.def"
+
+  llvm::report_fatal_error("invalid scheme");
+}
+
+} // namespace clang
+
+#endif // #ifndef LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H

clang/include/clang/Basic/CodeGenOptions.def

@@ -110,6 +110,8 @@ CODEGENOPT(CFProtectionReturn , 1, 0) ///< if -fcf-protection is
                                       ///< set to full or return.
 CODEGENOPT(CFProtectionBranch , 1, 0) ///< if -fcf-protection is
                                       ///< set to full or branch.
+ENUM_CODEGENOPT(CFBranchLabelScheme, CFBranchLabelSchemeKind, 2,
+    CFBranchLabelSchemeKind::Default) ///< if -mcf-branch-label-scheme is set.
 CODEGENOPT(FunctionReturnThunks, 1, 0) ///< -mfunction-return={keep|thunk-extern}
 CODEGENOPT(IndirectBranchCSPrefix, 1, 0) ///< if -mindirect-branch-cs-prefix
                                          ///< is set.

clang/include/clang/Basic/CodeGenOptions.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_BASIC_CODEGENOPTIONS_H
 #define LLVM_CLANG_BASIC_CODEGENOPTIONS_H
 
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/PointerAuthOptions.h"
 #include "clang/Basic/Sanitizers.h"
 #include "clang/Basic/XRayInstr.h"

clang/include/clang/Basic/LangOptions.def

@@ -364,6 +364,8 @@ BENIGN_LANGOPT(CompatibilityQualifiedIdBlockParamTypeChecking, 1, 0,
 LANGOPT(ObjCDisableDirectMethodsForTesting, 1, 0,
         "Disable recognition of objc_direct methods")
 LANGOPT(CFProtectionBranch , 1, 0, "Control-Flow Branch Protection enabled")
+ENUM_LANGOPT(CFBranchLabelScheme, CFBranchLabelSchemeKind, 2, CFBranchLabelSchemeKind::Default,
+             "Control-Flow Branch Protection Label Scheme")
 LANGOPT(FakeAddressSpaceMap , 1, 0, "OpenCL fake address space map")
 ENUM_LANGOPT(AddressSpaceMapMangling , AddrSpaceMapMangling, 2, ASMM_Target, "OpenCL address space map mangling mode")
 LANGOPT(IncludeDefaultHeader, 1, 0, "Include default header file for OpenCL")

clang/include/clang/Basic/LangOptions.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_CLANG_BASIC_LANGOPTIONS_H
 #define LLVM_CLANG_BASIC_LANGOPTIONS_H
 
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/CommentOptions.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangStandard.h"
@@ -73,6 +74,7 @@ class LangOptionsBase {
 public:
   using Visibility = clang::Visibility;
   using RoundingMode = llvm::RoundingMode;
+  using CFBranchLabelSchemeKind = clang::CFBranchLabelSchemeKind;
 
   enum GCMode { NonGC, GCOnly, HybridGC };
   enum StackProtectorMode { SSPOff, SSPOn, SSPStrong, SSPReq };

clang/include/clang/Basic/TargetInfo.h

@@ -16,6 +16,7 @@
 
 #include "clang/Basic/AddressSpaces.h"
 #include "clang/Basic/BitmaskEnum.h"
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/CodeGenOptions.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
@@ -1727,6 +1728,13 @@ class TargetInfo : public TransferrableTargetInfo,
   virtual bool
   checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const;
 
+  /// Get the target default CFBranchLabelScheme scheme
+  virtual CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const;
+
+  virtual bool
+  checkCFBranchLabelSchemeSupported(const CFBranchLabelSchemeKind Scheme,
+                                    DiagnosticsEngine &Diags) const;
+
   /// Check if the target supports CFProtection return.
   virtual bool
   checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const;

clang/include/clang/Driver/Options.td

@@ -2841,6 +2841,10 @@ def fcf_protection : Flag<["-"], "fcf-protection">, Group<f_Group>,
   Visibility<[ClangOption, CLOption, CC1Option]>,
   Alias<fcf_protection_EQ>, AliasArgs<["full"]>,
   HelpText<"Enable cf-protection in 'full' mode">;
+def mcf_branch_label_scheme_EQ : Joined<["-"], "mcf-branch-label-scheme=">,
+  Visibility<[ClangOption, CC1Option]>, Group<m_Group>,
+  HelpText<"Select label scheme for branch control-flow architecture protection">,
+  Values<"unlabeled,func-sig">;
 def mfunction_return_EQ : Joined<["-"], "mfunction-return=">,
   Group<m_Group>, Visibility<[ClangOption, CLOption, CC1Option]>,
   HelpText<"Replace returns with jumps to ``__x86_return_thunk`` (x86 only, error otherwise)">,

clang/lib/Basic/TargetInfo.cpp

@@ -198,6 +198,21 @@ TargetInfo::checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const {
   return false;
 }
 
+CFBranchLabelSchemeKind TargetInfo::getDefaultCFBranchLabelScheme() const {
+  // if this hook is called, the target should override it to return a
+  // non-default scheme
+  llvm::report_fatal_error("not implemented");
+}
+
+bool TargetInfo::checkCFBranchLabelSchemeSupported(
+    const CFBranchLabelSchemeKind Scheme, DiagnosticsEngine &Diags) const {
+  Diags.Report(diag::err_opt_not_valid_on_target)
+      << (Twine("mcf-branch-label-scheme=") +
+          getCFBranchLabelSchemeFlagVal(Scheme))
+             .str();
+  return false;
+}
+
 bool
 TargetInfo::checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const {
   Diags.Report(diag::err_opt_not_valid_on_target) << "cf-protection=return";

clang/lib/Basic/Targets/RISCV.h

@@ -134,6 +134,28 @@ class RISCVTargetInfo : public TargetInfo {
 
   bool validateGlobalRegisterVariable(StringRef RegName, unsigned RegSize,
                                       bool &HasSizeMismatch) const override;
+
+  bool checkCFProtectionBranchSupported(DiagnosticsEngine &) const override {
+    // Always generate Zicfilp lpad insns
+    // Non-zicfilp CPUs would read them as NOP
+    return true;
+  }
+
+  CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const override {
+    return CFBranchLabelSchemeKind::FuncSig;
+  }
+
+  bool
+  checkCFBranchLabelSchemeSupported(const CFBranchLabelSchemeKind Scheme,
+                                    DiagnosticsEngine &Diags) const override {
+    switch (Scheme) {
+    case CFBranchLabelSchemeKind::Default:
+    case CFBranchLabelSchemeKind::Unlabeled:
+    case CFBranchLabelSchemeKind::FuncSig:
+      return true;
+    }
+    return TargetInfo::checkCFBranchLabelSchemeSupported(Scheme, Diags);
+  }
 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public: