Add Windows Control Flow Guard checks (/guard:cf).

Summary:
A new function pass (Transforms/CFGuard/CFGuard.cpp) inserts CFGuard checks on
indirect function calls, using either the check mechanism (X86, ARM, AArch64) or
or the dispatch mechanism (X86-64). The check mechanism requires a new calling
convention for the supported targets. The dispatch mechanism adds the target as
an operand bundle, which is processed by SelectionDAG. Another pass
(CodeGen/CFGuardLongjmp.cpp) identifies and emits valid longjmp targets, as
required by /guard:cf. This feature is enabled using the `cfguard` CC1 option.

Reviewers: thakis, rnk, theraven, pcc

Subscribers: ychen, hans, metalcanine, dmajor, tomrittervg, alex, mehdi_amini, mgorny, javed.absar, kristof.beyls, hiraditya, steven_wu, dexonsmith, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D65761

Author: ajpaverd

clang/docs/ClangCommandLineReference.rst

@@ -124,7 +124,11 @@ Output path for the plist report
 
 .. option:: -cfguard
 
-Emit tables required for Windows Control Flow Guard.
+Emit tables and checks for Windows Control Flow Guard.
+
+.. option:: -cfguard-no-checks
+
+Emit tables required for Windows Control Flow Guard without checks.
 
 .. option:: -client\_name<arg>
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -37,6 +37,7 @@ CODEGENOPT(AssumeSaneOperatorNew , 1, 1) ///< implicit __attribute__((malloc)) o
 CODEGENOPT(Autolink          , 1, 1) ///< -fno-autolink
 CODEGENOPT(ObjCAutoRefCountExceptions , 1, 0) ///< Whether ARC should be EH-safe.
 CODEGENOPT(Backchain         , 1, 0) ///< -mbackchain
+CODEGENOPT(ControlFlowGuardNoChecks  , 1, 0) ///< -cfguard-no-checks
 CODEGENOPT(ControlFlowGuard  , 1, 0) ///< -cfguard
 CODEGENOPT(CoverageExtraChecksum, 1, 0) ///< Whether we need a second checksum for functions in GCNO files.
 CODEGENOPT(CoverageNoFunctionNamesInData, 1, 0) ///< Do not include function names in GCDA files.

clang/include/clang/Driver/CC1Options.td

@@ -400,6 +400,10 @@ def msign_return_address_key_EQ : Joined<["-"], "msign-return-address-key=">,
     Values<"a_key,b_key">;
 def mbranch_target_enforce : Flag<["-"], "mbranch-target-enforce">;
 def fno_dllexport_inlines : Flag<["-"], "fno-dllexport-inlines">;
+def cfguard_no_checks : Flag<["-"], "cfguard-no-checks">,
+    HelpText<"Emit Windows Control Flow Guard tables only (no checks)">;
+def cfguard : Flag<["-"], "cfguard">,
+    HelpText<"Emit Windows Control Flow Guard tables and checks">;
 
 //===----------------------------------------------------------------------===//
 // Dependency Output Options

clang/include/clang/Driver/Options.td

@@ -503,8 +503,6 @@ def bind__at__load : Flag<["-"], "bind_at_load">;
 def bundle__loader : Separate<["-"], "bundle_loader">;
 def bundle : Flag<["-"], "bundle">;
 def b : JoinedOrSeparate<["-"], "b">, Flags<[Unsupported]>;
-def cfguard : Flag<["-"], "cfguard">, Flags<[CC1Option]>,
-  HelpText<"Emit tables required for Windows Control Flow Guard.">;
 def cl_opt_disable : Flag<["-"], "cl-opt-disable">, Group<opencl_Group>, Flags<[CC1Option]>,
   HelpText<"OpenCL only. This option disables all optimizations. By default optimizations are enabled.">;
 def cl_strict_aliasing : Flag<["-"], "cl-strict-aliasing">, Group<opencl_Group>, Flags<[CC1Option]>,

clang/lib/CodeGen/CodeGenModule.cpp

@@ -482,8 +482,11 @@ void CodeGenModule::Release() {
     getModule().addModuleFlag(llvm::Module::Warning, "CodeViewGHash", 1);
   }
   if (CodeGenOpts.ControlFlowGuard) {
-    // We want function ID tables for Control Flow Guard.
-    getModule().addModuleFlag(llvm::Module::Warning, "cfguardtable", 1);
+    // Function ID tables and checks for Control Flow Guard (cfguard=2).
+    getModule().addModuleFlag(llvm::Module::Warning, "cfguard", 2);
+  } else if (CodeGenOpts.ControlFlowGuardNoChecks) {
+    // Function ID tables for Control Flow Guard (cfguard=1).
+    getModule().addModuleFlag(llvm::Module::Warning, "cfguard", 1);
   }
   if (CodeGenOpts.OptimizationLevel > 0 && CodeGenOpts.StrictVTablePointers) {
     // We don't support LTO with 2 with different StrictVTablePointers

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5975,26 +5975,19 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
   }
 
   if (Arg *A = Args.getLastArg(options::OPT__SLASH_guard)) {
-    SmallVector<StringRef, 1> SplitArgs;
-    StringRef(A->getValue()).split(SplitArgs, ",");
-    bool Instrument = false;
-    bool NoChecks = false;
-    for (StringRef Arg : SplitArgs) {
-      if (Arg.equals_lower("cf"))
-        Instrument = true;
-      else if (Arg.equals_lower("cf-"))
-        Instrument = false;
-      else if (Arg.equals_lower("nochecks"))
-        NoChecks = true;
-      else if (Arg.equals_lower("nochecks-"))
-        NoChecks = false;
-      else
-        D.Diag(diag::err_drv_invalid_value) << A->getSpelling() << Arg;
-    }
-    // Currently there's no support emitting CFG instrumentation; the flag only
-    // emits the table of address-taken functions.
-    if (Instrument || NoChecks)
+    StringRef GuardArgs = A->getValue();
+    // The only valid options are "cf", "cf,nochecks", and "cf-".
+    if (GuardArgs.equals_lower("cf")) {
+      // Emit CFG instrumentation and the table of address-taken functions.
       CmdArgs.push_back("-cfguard");
+    } else if (GuardArgs.equals_lower("cf,nochecks")) {
+      // Emit only the table of address-taken functions.
+      CmdArgs.push_back("-cfguard-no-checks");
+    } else if (GuardArgs.equals_lower("cf-")) {
+      // Do nothing, but we might want to emit a security warning in future.
+    } else {
+      D.Diag(diag::err_drv_invalid_value) << A->getSpelling() << GuardArgs;
+    }
   }
 }
 

clang/lib/Driver/ToolChains/MSVC.cpp

@@ -422,6 +422,17 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   Args.AddAllArgValues(CmdArgs, options::OPT__SLASH_link);
 
+  // Control Flow Guard checks
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_guard)) {
+    StringRef GuardArgs = A->getValue();
+    if (GuardArgs.equals_lower("cf") || GuardArgs.equals_lower("cf,nochecks")) {
+      // MSVC doesn't yet support the "nochecks" modifier.
+      CmdArgs.push_back("-guard:cf");
+    } else if (GuardArgs.equals_lower("cf-")) {
+      CmdArgs.push_back("-guard:cf-");
+    }
+  }
+
   if (Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
                    options::OPT_fno_openmp, false)) {
     CmdArgs.push_back("-nodefaultlib:vcomp.lib");
@@ -679,6 +690,17 @@ std::unique_ptr<Command> visualstudio::Compiler::GetCommand(
                           : "/Zc:threadSafeInit-");
   }
 
+  // Control Flow Guard checks
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_guard)) {
+    StringRef GuardArgs = A->getValue();
+    if (GuardArgs.equals_lower("cf") || GuardArgs.equals_lower("cf,nochecks")) {
+      // MSVC doesn't yet support the "nochecks" modifier.
+      CmdArgs.push_back("/guard:cf");
+    } else if (GuardArgs.equals_lower("cf-")) {
+      CmdArgs.push_back("/guard:cf-");
+    }
+  }
+
   // Pass through all unknown arguments so that the fallback command can see
   // them too.
   Args.AddAllArgs(CmdArgs, options::OPT_UNKNOWN);

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1003,6 +1003,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.MainFileName = Args.getLastArgValue(OPT_main_file_name);
   Opts.VerifyModule = !Args.hasArg(OPT_disable_llvm_verifier);
 
+  Opts.ControlFlowGuardNoChecks = Args.hasArg(OPT_cfguard_no_checks);
   Opts.ControlFlowGuard = Args.hasArg(OPT_cfguard);
 
   Opts.DisableGCov = Args.hasArg(OPT_test_coverage);

clang/test/CodeGen/cfguardtable.c

@@ -1,6 +1,8 @@
-// RUN: %clang_cc1 -cfguard -emit-llvm %s -o - | FileCheck %s
-
-void f() {}
-
-// Check that the cfguardtable metadata flag gets set on the module.
-// CHECK: !"cfguardtable", i32 1}
+// RUN: %clang_cc1 -cfguard-no-checks -emit-llvm %s -o - | FileCheck %s -check-prefix=CFGUARDNOCHECKS
+// RUN: %clang_cc1 -cfguard -emit-llvm %s -o - | FileCheck %s -check-prefix=CFGUARD
+
+void f() {}
+
+// Check that the cfguard metadata flag gets correctly set on the module.
+// CFGUARDNOCHECKS: !"cfguard", i32 1}
+// CFGUARD: !"cfguard", i32 2}

clang/test/Driver/cl-fallback.c

@@ -2,7 +2,7 @@
 // command-line option, e.g. on Mac where %s is commonly under /Users.
 
 // RUN: %clang_cl --target=i686-pc-win32 /fallback /Dfoo=bar /Ubaz /Ifoo /O0 /Ox /GR /GR- /GS /GS- /Gy /Gy- \
-// RUN:   /Gw /Gw- /LD /LDd /EHs /EHs- /Zl /MD /MDd /MTd /MT /FImyheader.h /Zi \
+// RUN:   /Gw /Gw- /LD /LDd /EHs /EHs- /Zl /MD /MDd /MTd /MT /guard:cf /guard:cf- /FImyheader.h /Zi \
 // RUN:   -garbage -moregarbage \
 // RUN:   -### -- %s 2>&1 \
 // RUN:   | FileCheck %s
@@ -33,6 +33,7 @@
 // CHECK: "/EHs-"
 // CHECK: "/Zl"
 // CHECK: "/MT"
+// CHECK: "/guard:cf-"
 // CHECK: "-garbage"
 // CHECK: "-moregarbage"
 // CHECK: "/Tc" "{{.*cl-fallback.c}}"