1 files changed, 283 insertions, 0 deletions
diff --git a/lib/CodeGen/StackProtector.cpp b/lib/CodeGen/StackProtector.cpp
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+++ b/lib/CodeGen/StackProtector.cpp
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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/Analysis/Dominators.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"
+#include "llvm/Target/TargetOptions.h"
+#include "llvm/ADT/Triple.h"
+using namespace llvm;
+
+namespace {
+  class StackProtector : public FunctionPass {
+    /// TLI - Keep a pointer of a TargetLowering to consult for determining
+    /// target type sizes.
+    const TargetLowering *TLI;
+
+    Function *F;
+    Module *M;
+
+    DominatorTree *DT;
+
+    /// 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();
+
+    /// 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;
+
+    /// 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) {
+      initializeStackProtectorPass(*PassRegistry::getPassRegistry());
+    }
+    StackProtector(const TargetLowering *tli)
+      : FunctionPass(ID), TLI(tli) {
+      initializeStackProtectorPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addPreserved<DominatorTree>();
+    }
+
+    virtual bool runOnFunction(Function &Fn);
+  };
+} // end anonymous namespace
+
+char StackProtector::ID = 0;
+INITIALIZE_PASS(StackProtector, "stack-protector",
+                "Insert stack protectors", false, false)
+
+FunctionPass *llvm::createStackProtectorPass(const TargetLowering *tli) {
+  return new StackProtector(tli);
+}
+
+bool StackProtector::runOnFunction(Function &Fn) {
+  F = &Fn;
+  M = F->getParent();
+  DT = getAnalysisIfAvailable<DominatorTree>();
+
+  if (!RequiresStackProtector()) return false;
+
+  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 {
+  if (!Ty) return false;
+  if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+    const TargetMachine &TM = TLI->getTargetMachine();
+    if (!AT->getElementType()->isIntegerTy(8)) {
+      Triple Trip(TM.getTargetTriple());
+
+      // If we're on a non-Darwin platform or we're inside of a structure, don't
+      // add stack protectors unless the array is a character array.
+      if (InStruct || !Trip.isOSDarwin())
+          return false;
+    }
+
+    // If an array has more than SSPBufferSize bytes of allocated space, then we
+    // emit stack protectors.
+    if (TM.Options.SSPBufferSize <= TLI->getTargetData()->getTypeAllocSize(AT))
+      return true;
+  }
+
+  const StructType *ST = dyn_cast<StructType>(Ty);
+  if (!ST) return false;
+
+  for (StructType::element_iterator I = ST->element_begin(),
+         E = ST->element_end(); I != E; ++I)
+    if (ContainsProtectableArray(*I, 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->hasFnAttr(Attribute::StackProtectReq))
+    return true;
+
+  if (!F->hasFnAttr(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)
+      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 (ContainsProtectableArray(AI->getAllocatedType()))
+          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.
+  BasicBlock *FailBBDom = 0;    // FailBB's dominator.
+  AllocaInst *AI = 0;           // Place on stack that stores the stack guard.
+  Value *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 = Type::getInt8PtrTy(RI->getContext());
+      unsigned AddressSpace, Offset;
+      if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
+        Constant *OffsetVal =
+          ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
+
+        StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
+                                      PointerType::get(PtrTy, AddressSpace));
+      } else {
+        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, "", 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");
+
+    if (DT && DT->isReachableFromEntry(BB)) {
+      DT->addNewBlock(NewBB, BB);
+      FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
+    }
+
+    // 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(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
+    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;
+
+  if (DT && FailBBDom)
+    DT->addNewBlock(FailBB, FailBBDom);
+
+  return true;
+}
+
+/// CreateFailBB - Create a basic block to jump to when the stack protector
+/// check fails.
+BasicBlock *StackProtector::CreateFailBB() {
+  BasicBlock *FailBB = BasicBlock::Create(F->getContext(),
+                                          "CallStackCheckFailBlk", F);
+  Constant *StackChkFail =
+    M->getOrInsertFunction("__stack_chk_fail",
+                           Type::getVoidTy(F->getContext()), NULL);
+  CallInst::Create(StackChkFail, "", FailBB);
+  new UnreachableInst(F->getContext(), FailBB);
+  return FailBB;
+}