hwasan: Untag unwound stack frames by wrapping personality functions.

One problem with untagging memory in landing pads is that it only works
correctly if the function that catches the exception is instrumented.
If the function is uninstrumented, we have no opportunity to untag the
memory.

To address this, replace landing pad instrumentation with personality function
wrapping. Each function with an instrumented stack has its personality function
replaced with a wrapper provided by the runtime. Functions that did not have
a personality function to begin with also get wrappers if they may be unwound
past. As the unwinder calls personality functions during stack unwinding,
the original personality function is called and the function's stack frame is
untagged by the wrapper if the personality function instructs the unwinder
to keep unwinding. If unwinding stops at a landing pad, the function is
still responsible for untagging its stack frame if it resumes unwinding.

The old landing pad mechanism is preserved for compatibility with old runtimes.

Differential Revision: https://reviews.llvm.org/D66377

llvm-svn: 369721

1 files changed, 102 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
index 163ae3ec62f..874361d4755 100644
--- a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Instrumentation/HWAddressSanitizer.h"
+#include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -55,6 +56,8 @@ using namespace llvm;
 static const char *const kHwasanModuleCtorName = "hwasan.module_ctor";
 static const char *const kHwasanNoteName = "hwasan.note";
 static const char *const kHwasanInitName = "__hwasan_init";
+static const char *const kHwasanPersonalityThunkName =
+    "__hwasan_personality_thunk";
 
 static const char *const kHwasanShadowMemoryDynamicAddress =
     "__hwasan_shadow_memory_dynamic_address";
@@ -160,8 +163,12 @@ static cl::opt<bool>
 
 static cl::opt<bool>
     ClInstrumentLandingPads("hwasan-instrument-landing-pads",
-                              cl::desc("instrument landing pads"), cl::Hidden,
-                              cl::init(true));
+                            cl::desc("instrument landing pads"), cl::Hidden,
+                            cl::init(false));
+
+static cl::opt<bool> ClInstrumentPersonalityFunctions(
+    "hwasan-instrument-personality-functions",
+    cl::desc("instrument personality functions"), cl::Hidden, cl::init(false));
 
 static cl::opt<bool> ClInlineAllChecks("hwasan-inline-all-checks",
                                        cl::desc("inline all checks"),
@@ -224,6 +231,8 @@ public:
   void instrumentGlobal(GlobalVariable *GV, uint8_t Tag);
   void instrumentGlobals();
 
+  void instrumentPersonalityFunctions();
+
 private:
   LLVMContext *C;
   Module &M;
@@ -250,6 +259,7 @@ private:
   };
   ShadowMapping Mapping;
 
+  Type *VoidTy = Type::getVoidTy(M.getContext());
   Type *IntptrTy;
   Type *Int8PtrTy;
   Type *Int8Ty;
@@ -258,6 +268,7 @@ private:
 
   bool CompileKernel;
   bool Recover;
+  bool InstrumentLandingPads;
 
   Function *HwasanCtorFunction;
 
@@ -373,14 +384,27 @@ void HWAddressSanitizer::initializeModule() {
             });
 
     // Older versions of Android do not have the required runtime support for
-    // global instrumentation. On other platforms we currently require using the
-    // latest version of the runtime.
-    bool InstrumentGlobals =
+    // global or personality function instrumentation. On other platforms we
+    // currently require using the latest version of the runtime.
+    bool NewRuntime =
         !TargetTriple.isAndroid() || !TargetTriple.isAndroidVersionLT(30);
-    if (ClGlobals.getNumOccurrences())
-      InstrumentGlobals = ClGlobals;
+
+    bool InstrumentGlobals =
+        ClGlobals.getNumOccurrences() ? ClGlobals : NewRuntime;
     if (InstrumentGlobals)
       instrumentGlobals();
+
+    // If we don't have personality function support, fall back to landing pads.
+    InstrumentLandingPads = ClInstrumentLandingPads.getNumOccurrences()
+                                ? ClInstrumentLandingPads
+                                : !NewRuntime;
+
+    bool InstrumentPersonalityFunctions =
+        ClInstrumentPersonalityFunctions.getNumOccurrences()
+            ? ClInstrumentPersonalityFunctions
+            : NewRuntime;
+    if (InstrumentPersonalityFunctions)
+      instrumentPersonalityFunctions();
   }
 
   if (!TargetTriple.isAndroid()) {
@@ -1092,7 +1116,7 @@ bool HWAddressSanitizer::sanitizeFunction(Function &F) {
         if (auto *Alloca = dyn_cast_or_null<AllocaInst>(DDI->getAddress()))
           AllocaDeclareMap[Alloca].push_back(DDI);
 
-      if (ClInstrumentLandingPads && isa<LandingPadInst>(Inst))
+      if (InstrumentLandingPads && isa<LandingPadInst>(Inst))
         LandingPadVec.push_back(&Inst);
 
       Value *MaybeMask = nullptr;
@@ -1111,6 +1135,13 @@ bool HWAddressSanitizer::sanitizeFunction(Function &F) {
   if (!LandingPadVec.empty())
     instrumentLandingPads(LandingPadVec);
 
+  if (AllocasToInstrument.empty() && F.hasPersonalityFn() &&
+      F.getPersonalityFn()->getName() == kHwasanPersonalityThunkName) {
+    // __hwasan_personality_thunk is a no-op for functions without an
+    // instrumented stack, so we can drop it.
+    F.setPersonalityFn(nullptr);
+  }
+
   if (AllocasToInstrument.empty() && ToInstrument.empty())
     return false;
 
@@ -1386,6 +1417,69 @@ void HWAddressSanitizer::instrumentGlobals() {
   }
 }
 
+void HWAddressSanitizer::instrumentPersonalityFunctions() {
+  // We need to untag stack frames as we unwind past them. That is the job of
+  // the personality function wrapper, which either wraps an existing
+  // personality function or acts as a personality function on its own. Each
+  // function that has a personality function or that can be unwound past has
+  // its personality function changed to a thunk that calls the personality
+  // function wrapper in the runtime.
+  MapVector<Constant *, std::vector<Function *>> PersonalityFns;
+  for (Function &F : M) {
+    if (F.isDeclaration() || !F.hasFnAttribute(Attribute::SanitizeHWAddress))
+      continue;
+
+    if (F.hasPersonalityFn()) {
+      PersonalityFns[F.getPersonalityFn()->stripPointerCasts()].push_back(&F);
+    } else if (!F.hasFnAttribute(Attribute::NoUnwind)) {
+      PersonalityFns[nullptr].push_back(&F);
+    }
+  }
+
+  if (PersonalityFns.empty())
+    return;
+
+  FunctionCallee HwasanPersonalityWrapper = M.getOrInsertFunction(
+      "__hwasan_personality_wrapper", Int32Ty, Int32Ty, Int32Ty, Int64Ty,
+      Int8PtrTy, Int8PtrTy, Int8PtrTy, Int8PtrTy, Int8PtrTy);
+  FunctionCallee UnwindGetGR = M.getOrInsertFunction("_Unwind_GetGR", VoidTy);
+  FunctionCallee UnwindGetCFA = M.getOrInsertFunction("_Unwind_GetCFA", VoidTy);
+
+  for (auto &P : PersonalityFns) {
+    std::string ThunkName = kHwasanPersonalityThunkName;
+    if (P.first)
+      ThunkName += ("." + P.first->getName()).str();
+    FunctionType *ThunkFnTy = FunctionType::get(
+        Int32Ty, {Int32Ty, Int32Ty, Int64Ty, Int8PtrTy, Int8PtrTy}, false);
+    bool IsLocal = P.first && (!isa<GlobalValue>(P.first) ||
+                               cast<GlobalValue>(P.first)->hasLocalLinkage());
+    auto *ThunkFn = Function::Create(ThunkFnTy,
+                                     IsLocal ? GlobalValue::InternalLinkage
+                                             : GlobalValue::LinkOnceODRLinkage,
+                                     ThunkName, &M);
+    if (!IsLocal) {
+      ThunkFn->setVisibility(GlobalValue::HiddenVisibility);
+      ThunkFn->setComdat(M.getOrInsertComdat(ThunkName));
+    }
+
+    auto *BB = BasicBlock::Create(*C, "entry", ThunkFn);
+    IRBuilder<> IRB(BB);
+    CallInst *WrapperCall = IRB.CreateCall(
+        HwasanPersonalityWrapper,
+        {ThunkFn->getArg(0), ThunkFn->getArg(1), ThunkFn->getArg(2),
+         ThunkFn->getArg(3), ThunkFn->getArg(4),
+         P.first ? IRB.CreateBitCast(P.first, Int8PtrTy)
+                 : Constant::getNullValue(Int8PtrTy),
+         IRB.CreateBitCast(UnwindGetGR.getCallee(), Int8PtrTy),
+         IRB.CreateBitCast(UnwindGetCFA.getCallee(), Int8PtrTy)});
+    WrapperCall->setTailCall();
+    IRB.CreateRet(WrapperCall);
+
+    for (Function *F : P.second)
+      F->setPersonalityFn(ThunkFn);
+  }
+}
+
 void HWAddressSanitizer::ShadowMapping::init(Triple &TargetTriple) {
   Scale = kDefaultShadowScale;
   if (ClMappingOffset.getNumOccurrences() > 0) {