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+//===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass inserts stack protectors into functions which need them. A variable
+// with a random value in it is stored onto the stack before the local variables
+// are allocated. Upon exiting the block, the stored value is checked. If it's
+// changed, then there was some sort of violation and the program aborts.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "stack-protector"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Attributes.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetLowering.h"
+using namespace llvm;
+
+// SSPBufferSize - The lower bound for a buffer to be considered for stack
+// smashing protection.
+static cl::opt<unsigned>
+SSPBufferSize("stack-protector-buffer-size", cl::init(8),
+ cl::desc("Lower bound for a buffer to be considered for "
+ "stack protection"));
+
+namespace {
+ class VISIBILITY_HIDDEN StackProtector : public FunctionPass {
+ /// TLI - Keep a pointer of a TargetLowering to consult for determining
+ /// target type sizes.
+ const TargetLowering *TLI;
+
+ Function *F;
+ Module *M;
+
+ /// InsertStackProtectors - Insert code into the prologue and epilogue of
+ /// the function.
+ ///
+ /// - The prologue code loads and stores the stack guard onto the stack.
+ /// - The epilogue checks the value stored in the prologue against the
+ /// original value. It calls __stack_chk_fail if they differ.
+ bool InsertStackProtectors();
+
+ /// CreateFailBB - Create a basic block to jump to when the stack protector
+ /// check fails.
+ BasicBlock *CreateFailBB();
+
+ /// RequiresStackProtector - Check whether or not this function needs a
+ /// stack protector based upon the stack protector level.
+ bool RequiresStackProtector() const;
+ public:
+ static char ID; // Pass identification, replacement for typeid.
+ StackProtector() : FunctionPass(&ID), TLI(0) {}
+ StackProtector(const TargetLowering *tli)
+ : FunctionPass(&ID), TLI(tli) {}
+
+ virtual bool runOnFunction(Function &Fn);
+ };
+} // end anonymous namespace
+
+char StackProtector::ID = 0;
+static RegisterPass<StackProtector>
+X("stack-protector", "Insert stack protectors");
+
+FunctionPass *llvm::createStackProtectorPass(const TargetLowering *tli) {
+ return new StackProtector(tli);
+}
+
+bool StackProtector::runOnFunction(Function &Fn) {
+ F = &Fn;
+ M = F->getParent();
+
+ if (!RequiresStackProtector()) return false;
+
+ return InsertStackProtectors();
+}
+
+/// 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->hasFnAttr(Attribute::StackProtectReq))
+ return true;
+
+ if (!F->hasFnAttr(Attribute::StackProtect))
+ return false;
+
+ const TargetData *TD = TLI->getTargetData();
+
+ 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)
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
+ if (AI->isArrayAllocation())
+ // This is a call to alloca with a variable size. Emit stack
+ // protectors.
+ return true;
+
+ if (const ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType()))
+ // If an array has more than SSPBufferSize bytes of allocated space,
+ // then we emit stack protectors.
+ if (SSPBufferSize <= TD->getTypeAllocSize(AT))
+ return true;
+ }
+ }
+
+ return false;
+}
+
+/// InsertStackProtectors - Insert code into the prologue and epilogue of the
+/// function.
+///
+/// - The prologue code loads and stores the stack guard onto the stack.
+/// - The epilogue checks the value stored in the prologue against the original
+/// value. It calls __stack_chk_fail if they differ.
+bool StackProtector::InsertStackProtectors() {
+ BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
+ AllocaInst *AI = 0; // Place on stack that stores the stack guard.
+ Constant *StackGuardVar = 0; // The stack guard variable.
+
+ for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
+ BasicBlock *BB = I++;
+
+ ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
+ if (!RI) continue;
+
+ if (!FailBB) {
+ // Insert code into the entry block that stores the __stack_chk_guard
+ // variable onto the stack:
+ //
+ // entry:
+ // StackGuardSlot = alloca i8*
+ // StackGuard = load __stack_chk_guard
+ // call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
+ //
+ PointerType *PtrTy = PointerType::getUnqual(Type::Int8Ty);
+ StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
+
+ BasicBlock &Entry = F->getEntryBlock();
+ Instruction *InsPt = &Entry.front();
+
+ AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
+ LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
+
+ Value *Args[] = { LI, AI };
+ CallInst::
+ Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
+ &Args[0], array_endof(Args), "", InsPt);
+
+ // Create the basic block to jump to when the guard check fails.
+ FailBB = CreateFailBB();
+ }
+
+ // For each block with a return instruction, convert this:
+ //
+ // return:
+ // ...
+ // ret ...
+ //
+ // into this:
+ //
+ // return:
+ // ...
+ // %1 = load __stack_chk_guard
+ // %2 = load StackGuardSlot
+ // %3 = cmp i1 %1, %2
+ // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
+ //
+ // SP_return:
+ // ret ...
+ //
+ // CallStackCheckFailBlk:
+ // call void @__stack_chk_fail()
+ // unreachable
+
+ // Split the basic block before the return instruction.
+ BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
+
+ // Remove default branch instruction to the new BB.
+ BB->getTerminator()->eraseFromParent();
+
+ // Move the newly created basic block to the point right after the old basic
+ // block so that it's in the "fall through" position.
+ NewBB->moveAfter(BB);
+
+ // Generate the stack protector instructions in the old basic block.
+ LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
+ LoadInst *LI2 = new LoadInst(AI, "", true, BB);
+ ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, LI1, LI2, "", BB);
+ BranchInst::Create(NewBB, FailBB, Cmp, BB);
+ }
+
+ // Return if we didn't modify any basic blocks. I.e., there are no return
+ // statements in the function.
+ if (!FailBB) return false;
+
+ return true;
+}
+
+/// CreateFailBB - Create a basic block to jump to when the stack protector
+/// check fails.
+BasicBlock *StackProtector::CreateFailBB() {
+ BasicBlock *FailBB = BasicBlock::Create("CallStackCheckFailBlk", F);
+ Constant *StackChkFail =
+ M->getOrInsertFunction("__stack_chk_fail", Type::VoidTy, NULL);
+ CallInst::Create(StackChkFail, "", FailBB);
+ new UnreachableInst(FailBB);
+ return FailBB;
+}
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