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-rw-r--r--llvm/lib/CodeGen/StackProtector.cpp126
1 files changed, 103 insertions, 23 deletions
diff --git a/llvm/lib/CodeGen/StackProtector.cpp b/llvm/lib/CodeGen/StackProtector.cpp
index 049efc1c861..f3be37c9ee6 100644
--- a/llvm/lib/CodeGen/StackProtector.cpp
+++ b/llvm/lib/CodeGen/StackProtector.cpp
@@ -16,6 +16,8 @@
#define DEBUG_TYPE "stack-protector"
#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/IR/Attributes.h"
@@ -32,6 +34,10 @@
#include "llvm/Target/TargetOptions.h"
using namespace llvm;
+STATISTIC(NumFunProtected, "Number of functions protected");
+STATISTIC(NumAddrTaken, "Number of local variables that have their address"
+ " taken.");
+
namespace {
class StackProtector : public FunctionPass {
/// TLI - Keep a pointer of a TargetLowering to consult for determining
@@ -43,6 +49,12 @@ namespace {
DominatorTree *DT;
+ /// VisitedPHIs - The set of PHI nodes visited when determining
+ /// if a variable's reference has been taken. This set
+ /// is maintained to ensure we don't visit the same PHI node multiple
+ /// times.
+ SmallPtrSet<const PHINode*, 16> VisitedPHIs;
+
/// InsertStackProtectors - Insert code into the prologue and epilogue of
/// the function.
///
@@ -58,11 +70,15 @@ namespace {
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains an array of sufficient size so that we need stack protectors
/// for it.
- bool ContainsProtectableArray(Type *Ty, bool InStruct = false) const;
+ bool ContainsProtectableArray(Type *Ty, bool Strong = false,
+ bool InStruct = false) const;
+
+ /// \brief Check whether a stack allocation has its address taken.
+ bool HasAddressTaken(const Instruction *AI);
/// RequiresStackProtector - Check whether or not this function needs a
/// stack protector based upon the stack protector level.
- bool RequiresStackProtector() const;
+ bool RequiresStackProtector();
public:
static char ID; // Pass identification, replacement for typeid.
StackProtector() : FunctionPass(ID), TLI(0) {
@@ -96,15 +112,21 @@ bool StackProtector::runOnFunction(Function &Fn) {
if (!RequiresStackProtector()) return false;
+ ++NumFunProtected;
return InsertStackProtectors();
}
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains a char array of sufficient size so that we need stack protectors
/// for it.
-bool StackProtector::ContainsProtectableArray(Type *Ty, bool InStruct) const {
+bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
+ bool InStruct) const {
if (!Ty) return false;
if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+ // In strong mode any array, regardless of type and size, triggers a
+ // protector
+ if (Strong)
+ return true;
const TargetMachine &TM = TLI->getTargetMachine();
if (!AT->getElementType()->isIntegerTy(8)) {
Triple Trip(TM.getTargetTriple());
@@ -126,45 +148,103 @@ bool StackProtector::ContainsProtectableArray(Type *Ty, bool InStruct) const {
for (StructType::element_iterator I = ST->element_begin(),
E = ST->element_end(); I != E; ++I)
- if (ContainsProtectableArray(*I, true))
+ if (ContainsProtectableArray(*I, Strong, true))
return true;
return false;
}
-/// RequiresStackProtector - Check whether or not this function needs a stack
-/// protector based upon the stack protector level. The heuristic we use is to
-/// add a guard variable to functions that call alloca, and functions with
-/// buffers larger than SSPBufferSize bytes.
-bool StackProtector::RequiresStackProtector() const {
- if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
- Attribute::StackProtectReq))
- return true;
+bool StackProtector::HasAddressTaken(const Instruction *AI) {
+ for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE; ++UI) {
+ const User *U = *UI;
+ if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
+ if (AI == SI->getValueOperand())
+ return true;
+ } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
+ if (AI == SI->getOperand(0))
+ return true;
+ } else if (isa<CallInst>(U)) {
+ return true;
+ } else if (isa<InvokeInst>(U)) {
+ return true;
+ } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
+ if (HasAddressTaken(SI))
+ return true;
+ } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
+ // Keep track of what PHI nodes we have already visited to ensure
+ // they are only visited once.
+ if (VisitedPHIs.insert(PN))
+ if (HasAddressTaken(PN))
+ return true;
+ } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
+ if (HasAddressTaken(GEP))
+ return true;
+ } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
+ if (HasAddressTaken(BI))
+ return true;
+ }
+ }
+ return false;
+}
- // FIXME: Dummy SSP-strong implementation. Default to required until
- // strong heuristic is implemented.
+/// \brief Check whether or not this function needs a stack protector based
+/// upon the stack protector level.
+///
+/// We use two heuristics: a standard (ssp) and strong (sspstrong).
+/// The standard heuristic which will add a guard variable to functions that
+/// call alloca with a either a variable size or a size >= SSPBufferSize,
+/// functions with character buffers larger than SSPBufferSize, and functions
+/// with aggregates containing character buffers larger than SSPBufferSize. The
+/// strong heuristic will add a guard variables to functions that call alloca
+/// regardless of size, functions with any buffer regardless of type and size,
+/// functions with aggregates that contain any buffer regardless of type and
+/// size, and functions that contain stack-based variables that have had their
+/// address taken.
+bool StackProtector::RequiresStackProtector() {
+ bool Strong = false;
if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
- Attribute::StackProtectStrong))
+ Attribute::StackProtectReq))
return true;
-
- if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
- Attribute::StackProtect))
+ else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::StackProtectStrong))
+ Strong = true;
+ else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::StackProtect))
return false;
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
BasicBlock *BB = I;
for (BasicBlock::iterator
- II = BB->begin(), IE = BB->end(); II != IE; ++II)
+ II = BB->begin(), IE = BB->end(); II != IE; ++II) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
- if (AI->isArrayAllocation())
- // This is a call to alloca with a variable size. Emit stack
- // protectors.
+ if (AI->isArrayAllocation()) {
+ // SSP-Strong: Enable protectors for any call to alloca, regardless
+ // of size.
+ if (Strong)
+ return true;
+
+ if (const ConstantInt *CI =
+ dyn_cast<ConstantInt>(AI->getArraySize())) {
+ unsigned BufferSize = TLI->getTargetMachine().Options.SSPBufferSize;
+ if (CI->getLimitedValue(BufferSize) >= BufferSize)
+ // A call to alloca with size >= SSPBufferSize requires
+ // stack protectors.
+ return true;
+ } else // A call to alloca with a variable size requires protectors.
+ return true;
+ }
+
+ if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
return true;
- if (ContainsProtectableArray(AI->getAllocatedType()))
+ if (Strong && HasAddressTaken(AI)) {
+ ++NumAddrTaken;
return true;
+ }
}
+ }
}
return false;
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