pcc created this revision.
pcc added reviewers: hctim, tejohnson.
Herald added subscribers: cfe-commits, dexonsmith, steven_wu, hiraditya,
mehdi_amini.
Herald added projects: clang, LLVM.
The default behavior of Clang's indirect function call checker will replace
the address of each CFI-checked function in the output file's symbol table
with the address of a jump table entry which will pass CFI checks. We refer
to this as making the jump table `canonical`. This property allows code that
was not compiled with ``-fsanitize=cfi-icall`` to take a CFI-valid address
of a function, but it comes with a couple of caveats that are especially
relevant for users of cross-DSO CFI:
- There is a performance and code size overhead associated with each exported
function, because each such function must have an associated jump table entry,
which must be emitted even in the common case where the function is never
address-taken anywhere in the program, and must be used even for direct calls
between DSOs, in addition to the PLT overhead.
- There is no good way to take a CFI-valid address of a function written in
assembly or a language not supported by Clang. The reason is that the code
generator would need to insert a jump table in order to form a CFI-valid
address for assembly functions, but there is no way in general for the code
generator to determine the language of the function. This may be possible with
LTO in the intra-DSO case, but in the cross-DSO case the only information
available is the function declaration. One possible solution is to add a C
wrapper for each assembly function, but these wrappers can present a
significant maintenance burden for heavy users of assembly in addition to
adding runtime overhead.
For these reasons, we provide the option of making the jump table non-canonical
with the flag ``-fno-sanitize-cfi-canonical-jump-tables``. When the jump
table is made non-canonical, symbol table entries point directly to the
function body. Any instances of a function's address being taken in C will
be replaced with a jump table address.
This scheme does have its own caveats, however. It does end up breaking
function address equality more aggressively than the default behavior,
especially in cross-DSO mode which normally preserves function address
equality entirely.
Furthermore, it is occasionally necessary for code not compiled with
``-fsanitize=cfi-icall`` to take a function address that is valid
for CFI. For example, this is necessary when a function's address
is taken by assembly code and then called by CFI-checking C code. The
``__attribute__((cfi_jump_table_canonical))`` attribute may be used to make
the jump table entry of a specific function canonical so that the external
code will end up taking a address for the function that will pass CFI checks.
Fixes PR41972.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D65629
Files:
clang/docs/ControlFlowIntegrity.rst
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/include/clang/Basic/CodeGenOptions.def
clang/include/clang/Driver/Options.td
clang/include/clang/Driver/SanitizerArgs.h
clang/lib/CodeGen/CodeGenFunction.cpp
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/Driver/SanitizerArgs.cpp
clang/lib/Frontend/CompilerInvocation.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CodeGen/cfi-icall-canonical-jump-tables.c
clang/test/CodeGen/cfi-icall-cross-dso.c
clang/test/Driver/fsanitize.c
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/SemaCXX/attr-cfi-jump-table-canonical.cpp
llvm/include/llvm/Transforms/IPO/LowerTypeTests.h
llvm/lib/Transforms/IPO/CrossDSOCFI.cpp
llvm/lib/Transforms/IPO/LowerTypeTests.cpp
llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
llvm/test/Transforms/LowerTypeTests/import-icall.ll
llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-functions-canonical-jump-tables.ll
Index: llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-functions-canonical-jump-tables.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-functions-canonical-jump-tables.ll
@@ -0,0 +1,21 @@
+; RUN: opt -thinlto-bc -thinlto-split-lto-unit -o %t %s
+; RUN: llvm-modextract -b -n 1 -o - %t | llvm-dis | FileCheck %s
+
+; CHECK: !"f1", i8 1
+; CHECK: !"f2", i8 1
+; CHECK: !"f3", i8 0
+
+declare !type !1 void @f1()
+
+define void @f2() !type !1 {
+ ret void
+}
+
+define void @f3() "cfi-jump-table-canonical" !type !1 {
+ ret void
+}
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 4, !"CFI Canonical Jump Tables", i32 0}
+!1 = !{i32 0, !"typeid1"}
Index: llvm/test/Transforms/LowerTypeTests/import-icall.ll
===================================================================
--- llvm/test/Transforms/LowerTypeTests/import-icall.ll
+++ llvm/test/Transforms/LowerTypeTests/import-icall.ll
@@ -3,6 +3,11 @@
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
+@llvm.used = appending global [1 x i8*] [i8* bitcast (i8* ()* @local_decl to i8*)], section "llvm.metadata"
+@llvm.compiler.used = appending global [1 x i8*] [i8* bitcast (i8* ()* @local_decl to i8*)], section "llvm.metadata"
+
+@local_decl_alias = alias i8* (), i8* ()* @local_decl
+
define i8 @local_a() {
call void @external()
call void @external_weak()
@@ -19,14 +24,16 @@
ret i8 %x
}
-define void @local_decl() {
- call void @local_decl()
- ret void
+define i8* @local_decl() {
+ call i8* @local_decl()
+ ret i8* bitcast (i8* ()* @local_decl to i8*)
}
declare void @external()
declare extern_weak void @external_weak()
+; CHECK: @local_decl_alias = alias i8* (), i8* ()* @local_decl
+
; CHECK: define hidden i8 @local_a.cfi() {
; CHECK-NEXT: call void @external()
; CHECK-NEXT: call void @external_weak()
@@ -37,8 +44,9 @@
; CHECK: define internal i8 @local_b() {
; CHECK-NEXT: call i8 @local_a()
-; CHECK: define void @local_decl()
-; CHECK-NEXT: call void @local_decl()
+; CHECK: define i8* @local_decl()
+; CHECK-NEXT: call i8* @local_decl()
+; CHECK-NEXT: ret i8* bitcast (i8* ()* @local_decl.cfi_jt to i8*)
; CHECK: declare void @external()
; CHECK: declare extern_weak void @external_weak()
Index: llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
===================================================================
--- llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
+++ llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
@@ -24,6 +24,7 @@
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/IPO/FunctionImport.h"
+#include "llvm/Transforms/IPO/LowerTypeTests.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
@@ -323,9 +324,9 @@
SmallVector<Metadata *, 4> Elts;
Elts.push_back(MDString::get(Ctx, F.getName()));
CfiFunctionLinkage Linkage;
- if (!F.isDeclarationForLinker())
+ if (lowertypetests::isJumpTableCanonical(&F))
Linkage = CFL_Definition;
- else if (F.isWeakForLinker())
+ else if (F.hasExternalWeakLinkage())
Linkage = CFL_WeakDeclaration;
else
Linkage = CFL_Declaration;
Index: llvm/lib/Transforms/IPO/LowerTypeTests.cpp
===================================================================
--- llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -230,6 +230,16 @@
Bytes[AllocByteOffset + B] |= AllocMask;
}
+bool lowertypetests::isJumpTableCanonical(Function *F) {
+ if (F->isDeclarationForLinker())
+ return false;
+ auto *CI = mdconst::extract_or_null<ConstantInt>(
+ F->getParent()->getModuleFlag("CFI Canonical Jump Tables"));
+ if (!CI || CI->getZExtValue() != 0)
+ return true;
+ return F->hasFnAttribute("cfi-jump-table-canonical");
+}
+
namespace {
struct ByteArrayInfo {
@@ -251,9 +261,12 @@
GlobalObject *GO;
size_t NTypes;
- // For functions: true if this is a definition (either in the merged module or
- // in one of the thinlto modules).
- bool IsDefinition;
+ // For functions: true if the jump table is canonical. This essentially means
+ // whether the canonical address (i.e. the symbol table entry) of the function
+ // is provided by the local jump table. This is normally the same as whether
+ // the function is defined locally, but if canonical jump tables are disabled
+ // by the user then the jump table never provides a canonical definition.
+ bool IsJumpTableCanonical;
// For functions: true if this function is either defined or used in a thinlto
// module and its jumptable entry needs to be exported to thinlto backends.
@@ -263,13 +276,13 @@
public:
static GlobalTypeMember *create(BumpPtrAllocator &Alloc, GlobalObject *GO,
- bool IsDefinition, bool IsExported,
+ bool IsJumpTableCanonical, bool IsExported,
ArrayRef<MDNode *> Types) {
auto *GTM = static_cast<GlobalTypeMember *>(Alloc.Allocate(
totalSizeToAlloc<MDNode *>(Types.size()), alignof(GlobalTypeMember)));
GTM->GO = GO;
GTM->NTypes = Types.size();
- GTM->IsDefinition = IsDefinition;
+ GTM->IsJumpTableCanonical = IsJumpTableCanonical;
GTM->IsExported = IsExported;
std::uninitialized_copy(Types.begin(), Types.end(),
GTM->getTrailingObjects<MDNode *>());
@@ -280,8 +293,8 @@
return GO;
}
- bool isDefinition() const {
- return IsDefinition;
+ bool isJumpTableCanonical() const {
+ return IsJumpTableCanonical;
}
bool isExported() const {
@@ -320,6 +333,49 @@
size_t NTargets;
};
+struct ScopedSaveAliaseesAndUsed {
+ Module &M;
+ SmallPtrSet<GlobalValue *, 16> Used, CompilerUsed;
+ std::vector<std::pair<GlobalIndirectSymbol *, Function *>> FunctionAliases;
+
+ ScopedSaveAliaseesAndUsed(Module &M) : M(M) {
+ // The users of this class want to replace all function references except
+ // for aliases and llvm.used/llvm.compiler.used with references to a jump
+ // table. We avoid replacing aliases in order to avoid introducing a double
+ // indirection (or an alias pointing to a declaration in ThinLTO mode), and
+ // we avoid replacing llvm.used/llvm.compiler.used because these global
+ // variables describe properties of the global, not the jump table (besides,
+ // offseted references to the jump table in llvm.used are invalid).
+ // Unfortunately, LLVM doesn't have a "RAUW except for these (possibly
+ // indirect) users", so what we do is save the list of globals referenced by
+ // llvm.used/llvm.compiler.used and aliases, erase the used lists, let RAUW
+ // replace the aliasees and then set them back to their original values at
+ // the end.
+ if (GlobalVariable *GV = collectUsedGlobalVariables(M, Used, false))
+ GV->eraseFromParent();
+ if (GlobalVariable *GV = collectUsedGlobalVariables(M, CompilerUsed, true))
+ GV->eraseFromParent();
+
+ for (auto &GIS : concat<GlobalIndirectSymbol>(M.aliases(), M.ifuncs())) {
+ // FIXME: This should look past all aliases not just interposable ones,
+ // see discussion on D65118.
+ if (auto *F =
+ dyn_cast<Function>(GIS.getIndirectSymbol()->stripPointerCasts()))
+ FunctionAliases.push_back({&GIS, F});
+ }
+ }
+
+ ~ScopedSaveAliaseesAndUsed() {
+ appendToUsed(M, std::vector<GlobalValue *>(Used.begin(), Used.end()));
+ appendToCompilerUsed(M, std::vector<GlobalValue *>(CompilerUsed.begin(),
+ CompilerUsed.end()));
+
+ for (auto P : FunctionAliases)
+ P.first->setIndirectSymbol(
+ ConstantExpr::getBitCast(P.second, P.first->getType()));
+ }
+};
+
class LowerTypeTestsModule {
Module &M;
@@ -387,7 +443,8 @@
uint8_t *exportTypeId(StringRef TypeId, const TypeIdLowering &TIL);
TypeIdLowering importTypeId(StringRef TypeId);
void importTypeTest(CallInst *CI);
- void importFunction(Function *F, bool isDefinition);
+ void importFunction(Function *F, bool isJumpTableCanonical,
+ std::vector<GlobalAlias *> &AliasesToErase);
BitSetInfo
buildBitSet(Metadata *TypeId,
@@ -421,7 +478,8 @@
ArrayRef<GlobalTypeMember *> Globals,
ArrayRef<ICallBranchFunnel *> ICallBranchFunnels);
- void replaceWeakDeclarationWithJumpTablePtr(Function *F, Constant *JT, bool IsDefinition);
+ void replaceWeakDeclarationWithJumpTablePtr(Function *F, Constant *JT,
+ bool IsJumpTableCanonical);
void moveInitializerToModuleConstructor(GlobalVariable *GV);
void findGlobalVariableUsersOf(Constant *C,
SmallSetVector<GlobalVariable *, 8> &Out);
@@ -433,7 +491,7 @@
/// the block. 'This's use list is expected to have at least one element.
/// Unlike replaceAllUsesWith this function skips blockaddr and direct call
/// uses.
- void replaceCfiUses(Function *Old, Value *New, bool IsDefinition);
+ void replaceCfiUses(Function *Old, Value *New, bool IsJumpTableCanonical);
/// replaceDirectCalls - Go through the uses list for this definition and
/// replace each use, which is a direct function call.
@@ -982,14 +1040,16 @@
}
// ThinLTO backend: the function F has a jump table entry; update this module
-// accordingly. isDefinition describes the type of the jump table entry.
-void LowerTypeTestsModule::importFunction(Function *F, bool isDefinition) {
+// accordingly. isJumpTableCanonical describes the type of the jump table entry.
+void LowerTypeTestsModule::importFunction(
+ Function *F, bool isJumpTableCanonical,
+ std::vector<GlobalAlias *> &AliasesToErase) {
assert(F->getType()->getAddressSpace() == 0);
GlobalValue::VisibilityTypes Visibility = F->getVisibility();
std::string Name = F->getName();
- if (F->isDeclarationForLinker() && isDefinition) {
+ if (F->isDeclarationForLinker() && isJumpTableCanonical) {
// Non-dso_local functions may be overriden at run time,
// don't short curcuit them
if (F->isDSOLocal()) {
@@ -1004,12 +1064,13 @@
}
Function *FDecl;
- if (F->isDeclarationForLinker() && !isDefinition) {
- // Declaration of an external function.
+ if (!isJumpTableCanonical) {
+ // Either a declaration of an external function or a reference to a locally
+ // defined jump table.
FDecl = Function::Create(F->getFunctionType(), GlobalValue::ExternalLinkage,
F->getAddressSpace(), Name + ".cfi_jt", &M);
FDecl->setVisibility(GlobalValue::HiddenVisibility);
- } else if (isDefinition) {
+ } else {
F->setName(Name + ".cfi");
F->setLinkage(GlobalValue::ExternalLinkage);
FDecl = Function::Create(F->getFunctionType(), GlobalValue::ExternalLinkage,
@@ -1018,8 +1079,8 @@
Visibility = GlobalValue::HiddenVisibility;
// Delete aliases pointing to this function, they'll be re-created in the
- // merged output
- SmallVector<GlobalAlias*, 4> ToErase;
+ // merged output. Don't do it yet though because ScopedSaveAliaseesAndUsed
+ // will want to reset the aliasees first.
for (auto &U : F->uses()) {
if (auto *A = dyn_cast<GlobalAlias>(U.getUser())) {
Function *AliasDecl = Function::Create(
@@ -1027,24 +1088,15 @@
F->getAddressSpace(), "", &M);
AliasDecl->takeName(A);
A->replaceAllUsesWith(AliasDecl);
- ToErase.push_back(A);
+ AliasesToErase.push_back(A);
}
}
- for (auto *A : ToErase)
- A->eraseFromParent();
- } else {
- // Function definition without type metadata, where some other translation
- // unit contained a declaration with type metadata. This normally happens
- // during mixed CFI + non-CFI compilation. We do nothing with the function
- // so that it is treated the same way as a function defined outside of the
- // LTO unit.
- return;
}
- if (F->isWeakForLinker())
- replaceWeakDeclarationWithJumpTablePtr(F, FDecl, isDefinition);
+ if (F->hasExternalWeakLinkage())
+ replaceWeakDeclarationWithJumpTablePtr(F, FDecl, isJumpTableCanonical);
else
- replaceCfiUses(F, FDecl, isDefinition);
+ replaceCfiUses(F, FDecl, isJumpTableCanonical);
// Set visibility late because it's used in replaceCfiUses() to determine
// whether uses need to to be replaced.
@@ -1232,7 +1284,7 @@
// Replace all uses of F with (F ? JT : 0).
void LowerTypeTestsModule::replaceWeakDeclarationWithJumpTablePtr(
- Function *F, Constant *JT, bool IsDefinition) {
+ Function *F, Constant *JT, bool IsJumpTableCanonical) {
// The target expression can not appear in a constant initializer on most
// (all?) targets. Switch to a runtime initializer.
SmallSetVector<GlobalVariable *, 8> GlobalVarUsers;
@@ -1246,7 +1298,7 @@
Function::Create(cast<FunctionType>(F->getValueType()),
GlobalValue::ExternalWeakLinkage,
F->getAddressSpace(), "", &M);
- replaceCfiUses(F, PlaceholderFn, IsDefinition);
+ replaceCfiUses(F, PlaceholderFn, IsJumpTableCanonical);
Constant *Target = ConstantExpr::getSelect(
ConstantExpr::getICmp(CmpInst::ICMP_NE, F,
@@ -1283,8 +1335,9 @@
unsigned ArmCount = 0, ThumbCount = 0;
for (const auto GTM : Functions) {
- if (!GTM->isDefinition()) {
+ if (!GTM->isJumpTableCanonical()) {
// PLT stubs are always ARM.
+ // FIXME: This is the wrong heuristic for non-canonical jump tables.
++ArmCount;
continue;
}
@@ -1445,47 +1498,53 @@
lowerTypeTestCalls(TypeIds, JumpTable, GlobalLayout);
- // Build aliases pointing to offsets into the jump table, and replace
- // references to the original functions with references to the aliases.
- for (unsigned I = 0; I != Functions.size(); ++I) {
- Function *F = cast<Function>(Functions[I]->getGlobal());
- bool IsDefinition = Functions[I]->isDefinition();
-
- Constant *CombinedGlobalElemPtr = ConstantExpr::getBitCast(
- ConstantExpr::getInBoundsGetElementPtr(
- JumpTableType, JumpTable,
- ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
- ConstantInt::get(IntPtrTy, I)}),
- F->getType());
- if (Functions[I]->isExported()) {
- if (IsDefinition) {
- ExportSummary->cfiFunctionDefs().insert(F->getName());
+ {
+ ScopedSaveAliaseesAndUsed S(M);
+
+ // Build aliases pointing to offsets into the jump table, and replace
+ // references to the original functions with references to the aliases.
+ for (unsigned I = 0; I != Functions.size(); ++I) {
+ Function *F = cast<Function>(Functions[I]->getGlobal());
+ bool IsJumpTableCanonical = Functions[I]->isJumpTableCanonical();
+
+ Constant *CombinedGlobalElemPtr = ConstantExpr::getBitCast(
+ ConstantExpr::getInBoundsGetElementPtr(
+ JumpTableType, JumpTable,
+ ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
+ ConstantInt::get(IntPtrTy, I)}),
+ F->getType());
+ if (Functions[I]->isExported()) {
+ if (IsJumpTableCanonical) {
+ ExportSummary->cfiFunctionDefs().insert(F->getName());
+ } else {
+ GlobalAlias *JtAlias = GlobalAlias::create(
+ F->getValueType(), 0, GlobalValue::ExternalLinkage,
+ F->getName() + ".cfi_jt", CombinedGlobalElemPtr, &M);
+ JtAlias->setVisibility(GlobalValue::HiddenVisibility);
+ ExportSummary->cfiFunctionDecls().insert(F->getName());
+ }
+ }
+ if (!IsJumpTableCanonical) {
+ if (F->hasExternalWeakLinkage())
+ replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr,
+ IsJumpTableCanonical);
+ else
+ replaceCfiUses(F, CombinedGlobalElemPtr, IsJumpTableCanonical);
} else {
- GlobalAlias *JtAlias = GlobalAlias::create(
- F->getValueType(), 0, GlobalValue::ExternalLinkage,
- F->getName() + ".cfi_jt", CombinedGlobalElemPtr, &M);
- JtAlias->setVisibility(GlobalValue::HiddenVisibility);
- ExportSummary->cfiFunctionDecls().insert(F->getName());
+ assert(F->getType()->getAddressSpace() == 0);
+
+ GlobalAlias *FAlias =
+ GlobalAlias::create(F->getValueType(), 0, F->getLinkage(), "",
+ CombinedGlobalElemPtr, &M);
+ FAlias->setVisibility(F->getVisibility());
+ FAlias->takeName(F);
+ if (FAlias->hasName())
+ F->setName(FAlias->getName() + ".cfi");
+ replaceCfiUses(F, FAlias, IsJumpTableCanonical);
+ if (!F->hasLocalLinkage())
+ F->setVisibility(GlobalVariable::HiddenVisibility);
}
}
- if (!IsDefinition) {
- if (F->isWeakForLinker())
- replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr, IsDefinition);
- else
- replaceCfiUses(F, CombinedGlobalElemPtr, IsDefinition);
- } else {
- assert(F->getType()->getAddressSpace() == 0);
-
- GlobalAlias *FAlias = GlobalAlias::create(
- F->getValueType(), 0, F->getLinkage(), "", CombinedGlobalElemPtr, &M);
- FAlias->setVisibility(F->getVisibility());
- FAlias->takeName(F);
- if (FAlias->hasName())
- F->setName(FAlias->getName() + ".cfi");
- replaceCfiUses(F, FAlias, IsDefinition);
- if (!F->hasLocalLinkage())
- F->setVisibility(GlobalVariable::HiddenVisibility);
- }
}
createJumpTable(JumpTableFn, Functions);
@@ -1650,7 +1709,8 @@
return false;
}
-void LowerTypeTestsModule::replaceCfiUses(Function *Old, Value *New, bool IsDefinition) {
+void LowerTypeTestsModule::replaceCfiUses(Function *Old, Value *New,
+ bool IsJumpTableCanonical) {
SmallSetVector<Constant *, 4> Constants;
auto UI = Old->use_begin(), E = Old->use_end();
for (; UI != E;) {
@@ -1662,7 +1722,7 @@
continue;
// Skip direct calls to externally defined or non-dso_local functions
- if (isDirectCall(U) && (Old->isDSOLocal() || !IsDefinition))
+ if (isDirectCall(U) && (Old->isDSOLocal() || !IsJumpTableCanonical))
continue;
// Must handle Constants specially, we cannot call replaceUsesOfWith on a
@@ -1741,10 +1801,16 @@
Decls.push_back(&F);
}
- for (auto F : Defs)
- importFunction(F, /*isDefinition*/ true);
- for (auto F : Decls)
- importFunction(F, /*isDefinition*/ false);
+ std::vector<GlobalAlias *> AliasesToErase;
+ {
+ ScopedSaveAliaseesAndUsed S(M);
+ for (auto F : Defs)
+ importFunction(F, /*isJumpTableCanonical*/ true, AliasesToErase);
+ for (auto F : Decls)
+ importFunction(F, /*isJumpTableCanonical*/ false, AliasesToErase);
+ }
+ for (GlobalAlias *GA : AliasesToErase)
+ GA->eraseFromParent();
return true;
}
@@ -1878,24 +1944,26 @@
Types.clear();
GO.getMetadata(LLVMContext::MD_type, Types);
- bool IsDefinition = !GO.isDeclarationForLinker();
+ bool IsJumpTableCanonical = false;
bool IsExported = false;
if (Function *F = dyn_cast<Function>(&GO)) {
+ IsJumpTableCanonical = isJumpTableCanonical(F);
if (ExportedFunctions.count(F->getName())) {
- IsDefinition |= ExportedFunctions[F->getName()].Linkage == CFL_Definition;
+ IsJumpTableCanonical |=
+ ExportedFunctions[F->getName()].Linkage == CFL_Definition;
IsExported = true;
// TODO: The logic here checks only that the function is address taken,
// not that the address takers are live. This can be updated to check
// their liveness and emit fewer jumptable entries once monolithic LTO
// builds also emit summaries.
} else if (!F->hasAddressTaken()) {
- if (!CrossDsoCfi || !IsDefinition || F->hasLocalLinkage())
+ if (!CrossDsoCfi || !IsJumpTableCanonical || F->hasLocalLinkage())
continue;
}
}
- auto *GTM =
- GlobalTypeMember::create(Alloc, &GO, IsDefinition, IsExported, Types);
+ auto *GTM = GlobalTypeMember::create(Alloc, &GO, IsJumpTableCanonical,
+ IsExported, Types);
GlobalTypeMembers[&GO] = GTM;
for (MDNode *Type : Types) {
verifyTypeMDNode(&GO, Type);
Index: llvm/lib/Transforms/IPO/CrossDSOCFI.cpp
===================================================================
--- llvm/lib/Transforms/IPO/CrossDSOCFI.cpp
+++ llvm/lib/Transforms/IPO/CrossDSOCFI.cpp
@@ -84,13 +84,9 @@
for (GlobalObject &GO : M.global_objects()) {
Types.clear();
GO.getMetadata(LLVMContext::MD_type, Types);
- for (MDNode *Type : Types) {
- // Sanity check. GO must not be a function declaration.
- assert(!isa<Function>(&GO) || !cast<Function>(&GO)->isDeclaration());
-
+ for (MDNode *Type : Types)
if (ConstantInt *TypeId = extractNumericTypeId(Type))
TypeIds.insert(TypeId->getZExtValue());
- }
}
NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions");
Index: llvm/include/llvm/Transforms/IPO/LowerTypeTests.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/LowerTypeTests.h
+++ llvm/include/llvm/Transforms/IPO/LowerTypeTests.h
@@ -193,6 +193,8 @@
uint64_t &AllocByteOffset, uint8_t &AllocMask);
};
+bool isJumpTableCanonical(Function *F);
+
} // end namespace lowertypetests
class LowerTypeTestsPass : public PassInfoMixin<LowerTypeTestsPass> {
Index: clang/test/SemaCXX/attr-cfi-jump-table-canonical.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/attr-cfi-jump-table-canonical.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsyntax-only -verify %s
+
+__attribute__((cfi_jump_table_canonical)) void f() {}
+
+struct S {
+ __attribute__((cfi_jump_table_canonical)) void f() {}
+};
+
+__attribute__((cfi_jump_table_canonical)) int i; // expected-error {{'cfi_jump_table_canonical' attribute only applies to functions}}
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -21,6 +21,7 @@
// CHECK-NEXT: Availability ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_implementation, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
// CHECK-NEXT: CFAuditedTransfer (SubjectMatchRule_function)
// CHECK-NEXT: CFConsumed (SubjectMatchRule_variable_is_parameter)
+// CHECK-NEXT: CFIJumpTableCanonical (SubjectMatchRule_function)
// CHECK-NEXT: CFUnknownTransfer (SubjectMatchRule_function)
// CHECK-NEXT: CPUDispatch (SubjectMatchRule_function)
// CHECK-NEXT: CPUSpecific (SubjectMatchRule_function)
Index: clang/test/Driver/fsanitize.c
===================================================================
--- clang/test/Driver/fsanitize.c
+++ clang/test/Driver/fsanitize.c
@@ -621,6 +621,12 @@
// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fsanitize-cfi-icall-generalize-pointers -fsanitize-cfi-cross-dso -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-GENERALIZE-AND-CROSS-DSO
// CHECK-CFI-GENERALIZE-AND-CROSS-DSO: error: invalid argument '-fsanitize-cfi-cross-dso' not allowed with '-fsanitize-cfi-icall-generalize-pointers'
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fsanitize-cfi-canonical-jump-tables -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-CANONICAL-JUMP-TABLES
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fno-sanitize-cfi-canonical-jump-tables -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-CFI-CANONICAL-JUMP-TABLES
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-CANONICAL-JUMP-TABLES
+// CHECK-CFI-CANONICAL-JUMP-TABLES: -fsanitize-cfi-canonical-jump-tables
+// CHECK-NO-CFI-CANONICAL-JUMP-TABLES-NOT: -fsanitize-cfi-canonical-jump-tables
+
// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi -fsanitize-stats -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-STATS
// CHECK-CFI-STATS: -fsanitize-stats
Index: clang/test/CodeGen/cfi-icall-cross-dso.c
===================================================================
--- clang/test/CodeGen/cfi-icall-cross-dso.c
+++ clang/test/CodeGen/cfi-icall-cross-dso.c
@@ -1,27 +1,27 @@
// RUN: %clang_cc1 -triple x86_64-unknown-linux -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK --check-prefix=CHECK-DIAG \
// RUN: --check-prefix=ITANIUM --check-prefix=ITANIUM-DIAG \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-trap=cfi-icall \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK \
// RUN: --check-prefix=ITANIUM --check-prefix=ITANIUM-TRAP \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK --check-prefix=CHECK-DIAG \
// RUN: --check-prefix=MS --check-prefix=MS-DIAG \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-trap=cfi-icall \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK \
// RUN: --check-prefix=MS --check-prefix=MS-TRAP \
// RUN: %s
Index: clang/test/CodeGen/cfi-icall-canonical-jump-tables.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/cfi-icall-canonical-jump-tables.c
@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,NOCANON %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CANON %s
+
+void ext(void);
+
+// CHECK: define void @f({{.*}} [[ATTR1:#[0-9]+]]
+void f() {
+ ext();
+}
+
+// NOCANON: declare !type {{.*}} @ext()
+// CANON: declare void @ext()
+
+// CHECK: define void @g({{.*}} [[ATTR2:#[0-9]+]]
+__attribute__((cfi_jump_table_canonical)) void g() {}
+
+// CHECK: [[ATTR1]] = {
+// CHECK-NOT: "cfi-jump-table-canonical"
+// CHECK: }
+
+// CHECK: [[ATTR2]] = { {{.*}} "cfi-jump-table-canonical" {{.*}} }
+
+// NOCANON: !{i32 4, !"CFI Canonical Jump Tables", i32 0}
+// CANON: !{i32 4, !"CFI Canonical Jump Tables", i32 1}
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -7198,6 +7198,9 @@
// Interacts with -fstack-protector options.
handleSimpleAttribute<NoStackProtectorAttr>(S, D, AL);
break;
+ case ParsedAttr::AT_CFIJumpTableCanonical:
+ handleSimpleAttribute<CFIJumpTableCanonicalAttr>(S, D, AL);
+ break;
case ParsedAttr::AT_StdCall:
case ParsedAttr::AT_CDecl:
case ParsedAttr::AT_FastCall:
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -1138,6 +1138,8 @@
Opts.SanitizeCfiCrossDso = Args.hasArg(OPT_fsanitize_cfi_cross_dso);
Opts.SanitizeCfiICallGeneralizePointers =
Args.hasArg(OPT_fsanitize_cfi_icall_generalize_pointers);
+ Opts.SanitizeCfiCanonicalJumpTables =
+ Args.hasArg(OPT_fsanitize_cfi_canonical_jump_tables);
Opts.SanitizeStats = Args.hasArg(OPT_fsanitize_stats);
if (Arg *A = Args.getLastArg(
OPT_fsanitize_address_poison_custom_array_cookie,
Index: clang/lib/Driver/SanitizerArgs.cpp
===================================================================
--- clang/lib/Driver/SanitizerArgs.cpp
+++ clang/lib/Driver/SanitizerArgs.cpp
@@ -635,6 +635,10 @@
D.Diag(diag::err_drv_argument_not_allowed_with)
<< "-fsanitize-cfi-cross-dso"
<< "-fsanitize-cfi-icall-generalize-pointers";
+
+ CfiCanonicalJumpTables =
+ Args.hasFlag(options::OPT_fsanitize_cfi_canonical_jump_tables,
+ options::OPT_fno_sanitize_cfi_canonical_jump_tables, true);
}
Stats = Args.hasFlag(options::OPT_fsanitize_stats,
@@ -969,6 +973,9 @@
if (CfiICallGeneralizePointers)
CmdArgs.push_back("-fsanitize-cfi-icall-generalize-pointers");
+ if (CfiCanonicalJumpTables)
+ CmdArgs.push_back("-fsanitize-cfi-canonical-jump-tables");
+
if (Stats)
CmdArgs.push_back("-fsanitize-stats");
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -535,6 +535,12 @@
getModule().addModuleFlag(llvm::Module::Override, "Cross-DSO CFI", 1);
}
+ if (LangOpts.Sanitize.has(SanitizerKind::CFIICall)) {
+ getModule().addModuleFlag(llvm::Module::Override,
+ "CFI Canonical Jump Tables",
+ CodeGenOpts.SanitizeCfiCanonicalJumpTables);
+ }
+
if (CodeGenOpts.CFProtectionReturn &&
Target.checkCFProtectionReturnSupported(getDiags())) {
// Indicate that we want to instrument return control flow protection.
@@ -1605,10 +1611,17 @@
F->setAlignment(2);
}
- // In the cross-dso CFI mode, we want !type attributes on definitions only.
- if (CodeGenOpts.SanitizeCfiCrossDso)
- if (auto *FD = dyn_cast<FunctionDecl>(D))
- CreateFunctionTypeMetadataForIcall(FD, F);
+ // In the cross-dso CFI mode with canonical jump tables, we want !type
+ // attributes on definitions only.
+ if (CodeGenOpts.SanitizeCfiCrossDso &&
+ CodeGenOpts.SanitizeCfiCanonicalJumpTables) {
+ if (auto *FD = dyn_cast<FunctionDecl>(D)) {
+ // Skip available_externally functions. They won't be codegen'ed in the
+ // current module anyway.
+ if (getContext().GetGVALinkageForFunction(FD) != GVA_AvailableExternally)
+ CreateFunctionTypeMetadataForIcall(FD, F);
+ }
+ }
// Emit type metadata on member functions for member function pointer checks.
// These are only ever necessary on definitions; we're guaranteed that the
@@ -1765,14 +1778,6 @@
if (isa<CXXMethodDecl>(FD) && !cast<CXXMethodDecl>(FD)->isStatic())
return;
- // Additionally, if building with cross-DSO support...
- if (CodeGenOpts.SanitizeCfiCrossDso) {
- // Skip available_externally functions. They won't be codegen'ed in the
- // current module anyway.
- if (getContext().GetGVALinkageForFunction(FD) == GVA_AvailableExternally)
- return;
- }
-
llvm::Metadata *MD = CreateMetadataIdentifierForType(FD->getType());
F->addTypeMetadata(0, MD);
F->addTypeMetadata(0, CreateMetadataIdentifierGeneralized(FD->getType()));
@@ -1849,8 +1854,11 @@
F->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
// Don't emit entries for function declarations in the cross-DSO mode. This
- // is handled with better precision by the receiving DSO.
- if (!CodeGenOpts.SanitizeCfiCrossDso)
+ // is handled with better precision by the receiving DSO. But if jump tables
+ // are non-canonical then we need type metadata in order to produce the local
+ // jump table.
+ if (!CodeGenOpts.SanitizeCfiCrossDso ||
+ !CodeGenOpts.SanitizeCfiCanonicalJumpTables)
CreateFunctionTypeMetadataForIcall(FD, F);
if (getLangOpts().OpenMP && FD->hasAttr<OMPDeclareSimdDeclAttr>())
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -762,6 +762,9 @@
if (CGM.getCodeGenOpts().ProfileSampleAccurate)
Fn->addFnAttr("profile-sample-accurate");
+ if (D && D->hasAttr<CFIJumpTableCanonicalAttr>())
+ Fn->addFnAttr("cfi-jump-table-canonical");
+
if (getLangOpts().OpenCL) {
// Add metadata for a kernel function.
if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
Index: clang/include/clang/Driver/SanitizerArgs.h
===================================================================
--- clang/include/clang/Driver/SanitizerArgs.h
+++ clang/include/clang/Driver/SanitizerArgs.h
@@ -32,6 +32,7 @@
bool MsanUseAfterDtor = true;
bool CfiCrossDso = false;
bool CfiICallGeneralizePointers = false;
+ bool CfiCanonicalJumpTables = false;
int AsanFieldPadding = 0;
bool SharedRuntime = false;
bool AsanUseAfterScope = true;
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1055,6 +1055,13 @@
def fsanitize_cfi_icall_generalize_pointers : Flag<["-"], "fsanitize-cfi-icall-generalize-pointers">,
Group<f_clang_Group>,
HelpText<"Generalize pointers in CFI indirect call type signature checks">;
+def fsanitize_cfi_canonical_jump_tables : Flag<["-"], "fsanitize-cfi-canonical-jump-tables">,
+ Group<f_clang_Group>,
+ HelpText<"Make the jump table addresses canonical in the symbol table">;
+def fno_sanitize_cfi_canonical_jump_tables : Flag<["-"], "fno-sanitize-cfi-canonical-jump-tables">,
+ Group<f_clang_Group>,
+ Flags<[CoreOption, DriverOption]>,
+ HelpText<"Do not make the jump table addresses canonical in the symbol table">;
def fsanitize_stats : Flag<["-"], "fsanitize-stats">,
Group<f_clang_Group>,
HelpText<"Enable sanitizer statistics gathering.">;
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -194,6 +194,8 @@
///< diagnostics.
CODEGENOPT(SanitizeCfiICallGeneralizePointers, 1, 0) ///< Generalize pointer types in
///< CFI icall function signatures
+CODEGENOPT(SanitizeCfiCanonicalJumpTables, 1, 0) ///< Make jump table symbols canonical
+ ///< instead of creating a local jump table.
CODEGENOPT(SanitizeCoverageType, 2, 0) ///< Type of sanitizer coverage
///< instrumentation.
CODEGENOPT(SanitizeCoverageIndirectCalls, 1, 0) ///< Enable sanitizer coverage
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -2221,6 +2221,18 @@
}];
}
+def CFIJumpTableCanonicalDocs : Documentation {
+ let Category = DocCatFunction;
+ let Heading = "cfi_jump_table_canonical";
+ let Content = [{
+.. _langext-cfi_jump_table_canonical:
+
+Use ``__attribute__((cfi_jump_table_canonical))`` on a function declaration to
+make the function's CFI jump table canonical. See :ref:`the CFI documentation
+<cfi-canonical-jump-tables>` for more details.
+ }];
+}
+
def DocCatTypeSafety : DocumentationCategory<"Type Safety Checking"> {
let Content = [{
Clang supports additional attributes to enable checking type safety properties
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2436,6 +2436,12 @@
let ASTNode = 0;
}
+def CFIJumpTableCanonical : InheritableAttr {
+ let Spellings = [Clang<"cfi_jump_table_canonical">];
+ let Subjects = SubjectList<[Function], ErrorDiag>;
+ let Documentation = [CFIJumpTableCanonicalDocs];
+}
+
// C/C++ Thread safety attributes (e.g. for deadlock, data race checking)
// Not all of these attributes will be given a [[]] spelling. The attributes
// which require access to function parameter names cannot use the [[]] spelling
Index: clang/docs/ControlFlowIntegrity.rst
===================================================================
--- clang/docs/ControlFlowIntegrity.rst
+++ clang/docs/ControlFlowIntegrity.rst
@@ -235,6 +235,54 @@
``-fsanitize-cfi-icall-generalize-pointers`` is not compatible with
``-fsanitize-cfi-cross-dso``.
+.. _cfi-canonical-jump-tables:
+
+``-fsanitize-cfi-canonical-jump-tables``
+----------------------------------------
+
+The default behavior of Clang's indirect function call checker will replace
+the address of each CFI-checked function in the output file's symbol table
+with the address of a jump table entry which will pass CFI checks. We refer
+to this as making the jump table `canonical`. This property allows code that
+was not compiled with ``-fsanitize=cfi-icall`` to take a CFI-valid address
+of a function, but it comes with a couple of caveats that are especially
+relevant for users of cross-DSO CFI:
+
+- There is a performance and code size overhead associated with each
+ exported function, because each such function must have an associated
+ jump table entry, which must be emitted even in the common case where the
+ function is never address-taken anywhere in the program, and must be used
+ even for direct calls between DSOs, in addition to the PLT overhead.
+
+- There is no good way to take a CFI-valid address of a function written in
+ assembly or a language not supported by Clang. The reason is that the code
+ generator would need to insert a jump table in order to form a CFI-valid
+ address for assembly functions, but there is no way in general for the
+ code generator to determine the language of the function. This may be
+ possible with LTO in the intra-DSO case, but in the cross-DSO case the only
+ information available is the function declaration. One possible solution
+ is to add a C wrapper for each assembly function, but these wrappers can
+ present a significant maintenance burden for heavy users of assembly in
+ addition to adding runtime overhead.
+
+For these reasons, we provide the option of making the jump table non-canonical
+with the flag ``-fno-sanitize-cfi-canonical-jump-tables``. When the jump
+table is made non-canonical, symbol table entries point directly to the
+function body. Any instances of a function's address being taken in C will
+be replaced with a jump table address.
+
+This scheme does have its own caveats, however. It does end up breaking
+function address equality more aggressively than the default behavior,
+especially in cross-DSO mode which normally preserves function address
+equality entirely.
+
+Furthermore, it is occasionally necessary for code not compiled with
+``-fsanitize=cfi-icall`` to take a function address that is valid
+for CFI. For example, this is necessary when a function's address
+is taken by assembly code and then called by CFI-checking C code. The
+``__attribute__((cfi_jump_table_canonical))`` attribute may be used to make
+the jump table entry of a specific function canonical so that the external
+code will end up taking a address for the function that will pass CFI checks.
``-fsanitize=cfi-icall`` and ``-fsanitize=function``
----------------------------------------------------
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