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Clang supports indirect call Control-Flow Integrity (CFI) sanitizers
(e.g. -fsanitize=cfi-icall), which enforce an exact type match between
a function pointer and the target function. Unfortunately, Clang
doesn't provide diagnostics that would help developers avoid function
type casts that lead to runtime CFI failures. -Wcast-function-type,
while helpful, only warns about ABI incompatibility, which isn't
sufficient with CFI.
Add -Wcast-function-type-strict, which checks for a strict type
compatibility in function type casts and helps warn about casts that
can potentially lead to CFI failures.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D134831
Files:
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaCast.cpp
clang/test/Sema/warn-cast-function-type-strict.c
clang/test/SemaCXX/warn-cast-function-type-strict.cpp
Index: clang/test/SemaCXX/warn-cast-function-type-strict.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/warn-cast-function-type-strict.cpp
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -x c++ %s -fblocks -fsyntax-only -Wcast-function-type-strict -triple x86_64-- -verify
+
+int x(long);
+
+typedef int (f1)(long);
+typedef int (f2)(void*);
+typedef int (f3)(...);
+typedef void (f4)(...);
+typedef void (f5)(void);
+typedef int (f6)(long, int);
+typedef int (f7)(long,...);
+typedef int (&f8)(long, int);
+
+f1 *a;
+f2 *b;
+f3 *c;
+f4 *d;
+f5 *e;
+f6 *f;
+f7 *g;
+
+struct S
+{
+ void foo (int*);
+ void bar (int);
+};
+
+typedef void (S::*mf)(int);
+
+void foo() {
+ a = (f1 *)x;
+ b = (f2 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
+ b = reinterpret_cast<f2 *>(x); /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
+ c = (f3 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f3 *' (aka 'int (*)(...)') converts to incompatible function type}} */
+ d = (f4 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)(...)') converts to incompatible function type}} */
+ e = (f5 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f5 *' (aka 'void (*)()') converts to incompatible function type}} */
+ f = (f6 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+ g = (f7 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f7 *' (aka 'int (*)(long, ...)') converts to incompatible function type}} */
+
+ mf p1 = (mf)&S::foo; /* expected-warning {{cast from 'void (S::*)(int *)' to 'mf' (aka 'void (S::*)(int)') converts to incompatible function type}} */
+
+ f8 f2 = (f8)x; /* expected-warning {{cast from 'int (long)' to 'f8' (aka 'int (&)(long, int)') converts to incompatible function type}} */
+ (void)f2;
+
+ int (^y)(long);
+ f = (f6 *)y; /* expected-warning {{cast from 'int (^)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+}
Index: clang/test/Sema/warn-cast-function-type-strict.c
===================================================================
--- /dev/null
+++ clang/test/Sema/warn-cast-function-type-strict.c
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -x c %s -fsyntax-only -Wcast-function-type-strict -triple x86_64-- -verify
+
+int x(long);
+int y(long,...);
+
+typedef int (f1)(long);
+typedef int (f2)(void*);
+typedef int (f3)();
+typedef void (f4)();
+typedef void (f5)(void);
+typedef int (f6)(long, int);
+typedef int (f7)(long,...);
+
+f1 *a;
+f2 *b;
+f3 *c;
+f4 *d;
+f5 *e;
+f6 *f;
+f7 *g;
+
+void foo(void) {
+ a = (f1 *)x;
+ b = (f2 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
+ c = (f3 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f3 *' (aka 'int (*)()') converts to incompatible function type}} */
+ d = (f4 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)()') converts to incompatible function type}} */
+ e = (f5 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f5 *' (aka 'void (*)(void)') converts to incompatible function type}} */
+ f = (f6 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+ g = (f7 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f7 *' (aka 'int (*)(long, ...)') converts to incompatible function type}} */
+}
Index: clang/lib/Sema/SemaCast.cpp
===================================================================
--- clang/lib/Sema/SemaCast.cpp
+++ clang/lib/Sema/SemaCast.cpp
@@ -1059,11 +1059,19 @@
return Context.hasSameUnqualifiedType(SrcType, DestType);
}
-static bool checkCastFunctionType(Sema &Self, const ExprResult &SrcExpr,
- QualType DestType) {
- if (Self.Diags.isIgnored(diag::warn_cast_function_type,
- SrcExpr.get()->getExprLoc()))
- return true;
+static unsigned int checkCastFunctionType(Sema &Self, const ExprResult &SrcExpr,
+ QualType DestType) {
+ unsigned int DiagID = 0;
+ const unsigned int DiagList[] = {diag::warn_cast_function_type_strict,
+ diag::warn_cast_function_type};
+ for (auto ID : DiagList) {
+ if (!Self.Diags.isIgnored(ID, SrcExpr.get()->getExprLoc())) {
+ DiagID = ID;
+ break;
+ }
+ }
+ if (!DiagID)
+ return 0;
QualType SrcType = SrcExpr.get()->getType();
const FunctionType *SrcFTy = nullptr;
@@ -1078,10 +1086,16 @@
SrcFTy = SrcType->castAs<FunctionType>();
DstFTy = DestType.getNonReferenceType()->castAs<FunctionType>();
} else {
- return true;
+ return 0;
}
assert(SrcFTy && DstFTy);
+ if (Self.Context.hasSameType(SrcFTy, DstFTy))
+ return 0;
+ // For strict checks, ensure we have an exact match.
+ else if (DiagID == diag::warn_cast_function_type_strict)
+ return DiagID;
+
auto IsVoidVoid = [](const FunctionType *T) {
if (!T->getReturnType()->isVoidType())
return false;
@@ -1092,16 +1106,16 @@
// Skip if either function type is void(*)(void)
if (IsVoidVoid(SrcFTy) || IsVoidVoid(DstFTy))
- return true;
+ return 0;
// Check return type.
if (!argTypeIsABIEquivalent(SrcFTy->getReturnType(), DstFTy->getReturnType(),
Self.Context))
- return false;
+ return DiagID;
// Check if either has unspecified number of parameters
if (SrcFTy->isFunctionNoProtoType() || DstFTy->isFunctionNoProtoType())
- return true;
+ return 0;
// Check parameter types.
@@ -1114,19 +1128,19 @@
unsigned DstNumParams = DstFPTy->getNumParams();
if (NumParams > DstNumParams) {
if (!DstFPTy->isVariadic())
- return false;
+ return DiagID;
NumParams = DstNumParams;
} else if (NumParams < DstNumParams) {
if (!SrcFPTy->isVariadic())
- return false;
+ return DiagID;
}
for (unsigned i = 0; i < NumParams; ++i)
if (!argTypeIsABIEquivalent(SrcFPTy->getParamType(i),
DstFPTy->getParamType(i), Self.Context))
- return false;
+ return DiagID;
- return true;
+ return 0;
}
/// CheckReinterpretCast - Check that a reinterpret_cast\<DestType\>(SrcExpr) is
@@ -1167,8 +1181,8 @@
checkObjCConversion(Sema::CCK_OtherCast);
DiagnoseReinterpretUpDownCast(Self, SrcExpr.get(), DestType, OpRange);
- if (!checkCastFunctionType(Self, SrcExpr, DestType))
- Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
+ if (auto DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+ Self.Diag(OpRange.getBegin(), DiagID)
<< SrcExpr.get()->getType() << DestType << OpRange;
} else {
SrcExpr = ExprError();
@@ -2797,8 +2811,8 @@
if (Kind == CK_BitCast)
checkCastAlign();
- if (!checkCastFunctionType(Self, SrcExpr, DestType))
- Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
+ if (auto DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+ Self.Diag(OpRange.getBegin(), DiagID)
<< SrcExpr.get()->getType() << DestType << OpRange;
} else {
@@ -3125,9 +3139,8 @@
}
}
- if (!checkCastFunctionType(Self, SrcExpr, DestType))
- Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
- << SrcType << DestType << OpRange;
+ if (auto DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+ Self.Diag(OpRange.getBegin(), DiagID) << SrcType << DestType << OpRange;
if (isa<PointerType>(SrcType) && isa<PointerType>(DestType)) {
QualType SrcTy = cast<PointerType>(SrcType)->getPointeeType();
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8682,6 +8682,8 @@
def warn_cast_function_type : Warning<
"cast %diff{from $ to $ |}0,1converts to incompatible function type">,
InGroup<CastFunctionType>, DefaultIgnore;
+def warn_cast_function_type_strict : Warning<warn_cast_function_type.Text>,
+ InGroup<CastFunctionTypeStrict>, DefaultIgnore;
def err_cast_pointer_to_non_pointer_int : Error<
"pointer cannot be cast to type %0">;
def err_cast_to_bfloat16 : Error<"cannot type-cast to __bf16">;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -539,6 +539,7 @@
def FunctionDefInObjCContainer : DiagGroup<"function-def-in-objc-container">;
def BadFunctionCast : DiagGroup<"bad-function-cast">;
def CastFunctionType : DiagGroup<"cast-function-type">;
+def CastFunctionTypeStrict : DiagGroup<"cast-function-type-strict">;
def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
def ObjCPropertyAssignOnObjectType : DiagGroup<"objc-property-assign-on-object-type">;
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