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[DFSan] Print an error before calling null extern_weak functions, incase dfsan instrumentation optimized out a null check.

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Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D124051
This commit is contained in:
Andrew Browne 2022-04-19 15:45:28 -07:00
parent 700442dee3
commit 204c12eef9
3 changed files with 46 additions and 1 deletions
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11
compiler-rt/lib/dfsan/dfsan.cpp
View file

@ -128,6 +128,17 @@ void __dfsan_unimplemented(char *fname) {
fname);
}
extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __dfsan_wrapper_extern_weak_null(
const void *addr, char *fname) {
if (!addr)
Report(
"ERROR: DataFlowSanitizer: dfsan generated wrapper calling null "
"extern_weak function %s\nIf this only happens with dfsan, the "
"dfsan instrumentation pass may be accidentally optimizing out a "
"null check\n",
fname);
}
// Use '-mllvm -dfsan-debug-nonzero-labels' and break on this function
// to try to figure out where labels are being introduced in a nominally
// label-free program.

31
llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
View file

@ -439,6 +439,7 @@ class DataFlowSanitizer {
FunctionType *DFSanUnionLoadFnTy;
FunctionType *DFSanLoadLabelAndOriginFnTy;
FunctionType *DFSanUnimplementedFnTy;
FunctionType *DFSanWrapperExternWeakNullFnTy;
FunctionType *DFSanSetLabelFnTy;
FunctionType *DFSanNonzeroLabelFnTy;
FunctionType *DFSanVarargWrapperFnTy;
@ -454,6 +455,7 @@ class DataFlowSanitizer {
FunctionCallee DFSanUnionLoadFn;
FunctionCallee DFSanLoadLabelAndOriginFn;
FunctionCallee DFSanUnimplementedFn;
FunctionCallee DFSanWrapperExternWeakNullFn;
FunctionCallee DFSanSetLabelFn;
FunctionCallee DFSanNonzeroLabelFn;
FunctionCallee DFSanVarargWrapperFn;
@ -490,6 +492,7 @@ class DataFlowSanitizer {
TransformedFunction getCustomFunctionType(FunctionType *T);
WrapperKind getWrapperKind(Function *F);
void addGlobalNameSuffix(GlobalValue *GV);
void buildExternWeakCheckIfNeeded(IRBuilder<> &IRB, Function *F);
Function *buildWrapperFunction(Function *F, StringRef NewFName,
GlobalValue::LinkageTypes NewFLink,
FunctionType *NewFT);
@ -1041,6 +1044,10 @@ bool DataFlowSanitizer::initializeModule(Module &M) {
/*isVarArg=*/false);
DFSanUnimplementedFnTy = FunctionType::get(
Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
Type *DFSanWrapperExternWeakNullArgs[2] = {Int8Ptr, Int8Ptr};
DFSanWrapperExternWeakNullFnTy =
FunctionType::get(Type::getVoidTy(*Ctx), DFSanWrapperExternWeakNullArgs,
/*isVarArg=*/false);
Type *DFSanSetLabelArgs[4] = {PrimitiveShadowTy, OriginTy,
Type::getInt8PtrTy(*Ctx), IntptrTy};
DFSanSetLabelFnTy = FunctionType::get(Type::getVoidTy(*Ctx),
@ -1132,6 +1139,23 @@ void DataFlowSanitizer::addGlobalNameSuffix(GlobalValue *GV) {
}
}
void DataFlowSanitizer::buildExternWeakCheckIfNeeded(IRBuilder<> &IRB,
Function *F) {
// If the function we are wrapping was ExternWeak, it may be null.
// The original code before calling this wrapper may have checked for null,
// but replacing with a known-to-not-be-null wrapper can break this check.
// When replacing uses of the extern weak function with the wrapper we try
// to avoid replacing uses in conditionals, but this is not perfect.
// In the case where we fail, and accidentially optimize out a null check
// for a extern weak function, add a check here to help identify the issue.
if (GlobalValue::isExternalWeakLinkage(F->getLinkage())) {
std::vector<Value *> Args;
Args.push_back(IRB.CreatePointerCast(F, IRB.getInt8PtrTy()));
Args.push_back(IRB.CreateGlobalStringPtr(F->getName()));
IRB.CreateCall(DFSanWrapperExternWeakNullFn, Args);
}
}
Function *
DataFlowSanitizer::buildWrapperFunction(Function *F, StringRef NewFName,
GlobalValue::LinkageTypes NewFLink,
@ -1184,6 +1208,8 @@ void DataFlowSanitizer::initializeRuntimeFunctions(Module &M) {
}
DFSanUnimplementedFn =
Mod->getOrInsertFunction("__dfsan_unimplemented", DFSanUnimplementedFnTy);
DFSanWrapperExternWeakNullFn = Mod->getOrInsertFunction(
"__dfsan_wrapper_extern_weak_null", DFSanWrapperExternWeakNullFnTy);
{
AttributeList AL;
AL = AL.addParamAttribute(M.getContext(), 0, Attribute::ZExt);
@ -1227,6 +1253,8 @@ void DataFlowSanitizer::initializeRuntimeFunctions(Module &M) {
DFSanLoadLabelAndOriginFn.getCallee()->stripPointerCasts());
DFSanRuntimeFunctions.insert(
DFSanUnimplementedFn.getCallee()->stripPointerCasts());
DFSanRuntimeFunctions.insert(
DFSanWrapperExternWeakNullFn.getCallee()->stripPointerCasts());
DFSanRuntimeFunctions.insert(
DFSanSetLabelFn.getCallee()->stripPointerCasts());
DFSanRuntimeFunctions.insert(
@ -2860,16 +2888,19 @@ bool DFSanVisitor::visitWrappedCallBase(Function &F, CallBase &CB) {
CB.setCalledFunction(&F);
IRB.CreateCall(DFSF.DFS.DFSanUnimplementedFn,
IRB.CreateGlobalStringPtr(F.getName()));
DFSF.DFS.buildExternWeakCheckIfNeeded(IRB, &F);
DFSF.setShadow(&CB, DFSF.DFS.getZeroShadow(&CB));
DFSF.setOrigin(&CB, DFSF.DFS.ZeroOrigin);
return true;
case DataFlowSanitizer::WK_Discard:
CB.setCalledFunction(&F);
DFSF.DFS.buildExternWeakCheckIfNeeded(IRB, &F);
DFSF.setShadow(&CB, DFSF.DFS.getZeroShadow(&CB));
DFSF.setOrigin(&CB, DFSF.DFS.ZeroOrigin);
return true;
case DataFlowSanitizer::WK_Functional:
CB.setCalledFunction(&F);
DFSF.DFS.buildExternWeakCheckIfNeeded(IRB, &F);
visitInstOperands(CB);
return true;
case DataFlowSanitizer::WK_Custom:

5
llvm/test/Instrumentation/DataFlowSanitizer/extern_weak.ll
View file

@ -11,12 +11,15 @@ declare extern_weak i8 @ExternWeak(i8)
define noundef i8 @call_if_exists() local_unnamed_addr {
; CHECK-LABEL: @call_if_exists.dfsan
; Ensure comparison is preserved
; CHECK: br i1 icmp ne ([[FUNCPTRTY:.*]] @ExternWeak, [[FUNCPTRTY]] null), label %use_func, label %avoid_func
br i1 icmp ne (i8 (i8)* @ExternWeak, i8 (i8)* null), label %use_func, label %avoid_func
use_func:
; CHECK: use_func:
; CHECK: call i8 @ExternWeak(i8 {{.*}})
; Ensure extern weak function is validated before being called.
; CHECK: call void @__dfsan_wrapper_extern_weak_null({{[^,]*}}@ExternWeak{{[^,]*}}, {{.*}})
; CHECK-NEXT: call i8 @ExternWeak(i8 {{.*}})
%1 = call i8 @ExternWeak(i8 4)
br label %end