Bug Summary

File:lib/CodeGen/SafeStack.cpp
Warning:line 589, column 7
Value stored to 'Size' is never read

Annotated Source Code

Press '?' to see keyboard shortcuts

clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name SafeStack.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-eagerly-assume -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn338205/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/CodeGen -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-07-29-043837-17923-1 -x c++ /build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp -faddrsig
1//===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass splits the stack into the safe stack (kept as-is for LLVM backend)
11// and the unsafe stack (explicitly allocated and managed through the runtime
12// support library).
13//
14// http://clang.llvm.org/docs/SafeStack.html
15//
16//===----------------------------------------------------------------------===//
17
18#include "SafeStackColoring.h"
19#include "SafeStackLayout.h"
20#include "llvm/ADT/APInt.h"
21#include "llvm/ADT/ArrayRef.h"
22#include "llvm/ADT/SmallPtrSet.h"
23#include "llvm/ADT/SmallVector.h"
24#include "llvm/ADT/Statistic.h"
25#include "llvm/Analysis/AssumptionCache.h"
26#include "llvm/Analysis/BranchProbabilityInfo.h"
27#include "llvm/Analysis/InlineCost.h"
28#include "llvm/Analysis/LoopInfo.h"
29#include "llvm/Analysis/ScalarEvolution.h"
30#include "llvm/Analysis/ScalarEvolutionExpressions.h"
31#include "llvm/Analysis/TargetLibraryInfo.h"
32#include "llvm/Transforms/Utils/Local.h"
33#include "llvm/CodeGen/TargetLowering.h"
34#include "llvm/CodeGen/TargetPassConfig.h"
35#include "llvm/CodeGen/TargetSubtargetInfo.h"
36#include "llvm/IR/Argument.h"
37#include "llvm/IR/Attributes.h"
38#include "llvm/IR/CallSite.h"
39#include "llvm/IR/ConstantRange.h"
40#include "llvm/IR/Constants.h"
41#include "llvm/IR/DIBuilder.h"
42#include "llvm/IR/DataLayout.h"
43#include "llvm/IR/DerivedTypes.h"
44#include "llvm/IR/Dominators.h"
45#include "llvm/IR/Function.h"
46#include "llvm/IR/IRBuilder.h"
47#include "llvm/IR/InstIterator.h"
48#include "llvm/IR/Instruction.h"
49#include "llvm/IR/Instructions.h"
50#include "llvm/IR/IntrinsicInst.h"
51#include "llvm/IR/Intrinsics.h"
52#include "llvm/IR/MDBuilder.h"
53#include "llvm/IR/Module.h"
54#include "llvm/IR/Type.h"
55#include "llvm/IR/Use.h"
56#include "llvm/IR/User.h"
57#include "llvm/IR/Value.h"
58#include "llvm/Pass.h"
59#include "llvm/Support/Casting.h"
60#include "llvm/Support/Debug.h"
61#include "llvm/Support/ErrorHandling.h"
62#include "llvm/Support/MathExtras.h"
63#include "llvm/Support/raw_ostream.h"
64#include "llvm/Target/TargetMachine.h"
65#include "llvm/Transforms/Utils/BasicBlockUtils.h"
66#include "llvm/Transforms/Utils/Cloning.h"
67#include <algorithm>
68#include <cassert>
69#include <cstdint>
70#include <string>
71#include <utility>
72
73using namespace llvm;
74using namespace llvm::safestack;
75
76#define DEBUG_TYPE"safe-stack" "safe-stack"
77
78namespace llvm {
79
80STATISTIC(NumFunctions, "Total number of functions")static llvm::Statistic NumFunctions = {"safe-stack", "NumFunctions"
, "Total number of functions", {0}, {false}}
;
81STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack")static llvm::Statistic NumUnsafeStackFunctions = {"safe-stack"
, "NumUnsafeStackFunctions", "Number of functions with unsafe stack"
, {0}, {false}}
;
82STATISTIC(NumUnsafeStackRestorePointsFunctions,static llvm::Statistic NumUnsafeStackRestorePointsFunctions =
{"safe-stack", "NumUnsafeStackRestorePointsFunctions", "Number of functions that use setjmp or exceptions"
, {0}, {false}}
83 "Number of functions that use setjmp or exceptions")static llvm::Statistic NumUnsafeStackRestorePointsFunctions =
{"safe-stack", "NumUnsafeStackRestorePointsFunctions", "Number of functions that use setjmp or exceptions"
, {0}, {false}}
;
84
85STATISTIC(NumAllocas, "Total number of allocas")static llvm::Statistic NumAllocas = {"safe-stack", "NumAllocas"
, "Total number of allocas", {0}, {false}}
;
86STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas")static llvm::Statistic NumUnsafeStaticAllocas = {"safe-stack"
, "NumUnsafeStaticAllocas", "Number of unsafe static allocas"
, {0}, {false}}
;
87STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas")static llvm::Statistic NumUnsafeDynamicAllocas = {"safe-stack"
, "NumUnsafeDynamicAllocas", "Number of unsafe dynamic allocas"
, {0}, {false}}
;
88STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments")static llvm::Statistic NumUnsafeByValArguments = {"safe-stack"
, "NumUnsafeByValArguments", "Number of unsafe byval arguments"
, {0}, {false}}
;
89STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads")static llvm::Statistic NumUnsafeStackRestorePoints = {"safe-stack"
, "NumUnsafeStackRestorePoints", "Number of setjmps and landingpads"
, {0}, {false}}
;
90
91} // namespace llvm
92
93/// Use __safestack_pointer_address even if the platform has a faster way of
94/// access safe stack pointer.
95static cl::opt<bool>
96 SafeStackUsePointerAddress("safestack-use-pointer-address",
97 cl::init(false), cl::Hidden);
98
99
100namespace {
101
102/// Rewrite an SCEV expression for a memory access address to an expression that
103/// represents offset from the given alloca.
104///
105/// The implementation simply replaces all mentions of the alloca with zero.
106class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
107 const Value *AllocaPtr;
108
109public:
110 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
111 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
112
113 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
114 if (Expr->getValue() == AllocaPtr)
115 return SE.getZero(Expr->getType());
116 return Expr;
117 }
118};
119
120/// The SafeStack pass splits the stack of each function into the safe
121/// stack, which is only accessed through memory safe dereferences (as
122/// determined statically), and the unsafe stack, which contains all
123/// local variables that are accessed in ways that we can't prove to
124/// be safe.
125class SafeStack {
126 Function &F;
127 const TargetLoweringBase &TL;
128 const DataLayout &DL;
129 ScalarEvolution &SE;
130
131 Type *StackPtrTy;
132 Type *IntPtrTy;
133 Type *Int32Ty;
134 Type *Int8Ty;
135
136 Value *UnsafeStackPtr = nullptr;
137
138 /// Unsafe stack alignment. Each stack frame must ensure that the stack is
139 /// aligned to this value. We need to re-align the unsafe stack if the
140 /// alignment of any object on the stack exceeds this value.
141 ///
142 /// 16 seems like a reasonable upper bound on the alignment of objects that we
143 /// might expect to appear on the stack on most common targets.
144 enum { StackAlignment = 16 };
145
146 /// Return the value of the stack canary.
147 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
148
149 /// Load stack guard from the frame and check if it has changed.
150 void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
151 AllocaInst *StackGuardSlot, Value *StackGuard);
152
153 /// Find all static allocas, dynamic allocas, return instructions and
154 /// stack restore points (exception unwind blocks and setjmp calls) in the
155 /// given function and append them to the respective vectors.
156 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
157 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
158 SmallVectorImpl<Argument *> &ByValArguments,
159 SmallVectorImpl<ReturnInst *> &Returns,
160 SmallVectorImpl<Instruction *> &StackRestorePoints);
161
162 /// Calculate the allocation size of a given alloca. Returns 0 if the
163 /// size can not be statically determined.
164 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
165
166 /// Allocate space for all static allocas in \p StaticAllocas,
167 /// replace allocas with pointers into the unsafe stack and generate code to
168 /// restore the stack pointer before all return instructions in \p Returns.
169 ///
170 /// \returns A pointer to the top of the unsafe stack after all unsafe static
171 /// allocas are allocated.
172 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
173 ArrayRef<AllocaInst *> StaticAllocas,
174 ArrayRef<Argument *> ByValArguments,
175 ArrayRef<ReturnInst *> Returns,
176 Instruction *BasePointer,
177 AllocaInst *StackGuardSlot);
178
179 /// Generate code to restore the stack after all stack restore points
180 /// in \p StackRestorePoints.
181 ///
182 /// \returns A local variable in which to maintain the dynamic top of the
183 /// unsafe stack if needed.
184 AllocaInst *
185 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
186 ArrayRef<Instruction *> StackRestorePoints,
187 Value *StaticTop, bool NeedDynamicTop);
188
189 /// Replace all allocas in \p DynamicAllocas with code to allocate
190 /// space dynamically on the unsafe stack and store the dynamic unsafe stack
191 /// top to \p DynamicTop if non-null.
192 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
193 AllocaInst *DynamicTop,
194 ArrayRef<AllocaInst *> DynamicAllocas);
195
196 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
197
198 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
199 const Value *AllocaPtr, uint64_t AllocaSize);
200 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
201 uint64_t AllocaSize);
202
203 bool ShouldInlinePointerAddress(CallSite &CS);
204 void TryInlinePointerAddress();
205
206public:
207 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
208 ScalarEvolution &SE)
209 : F(F), TL(TL), DL(DL), SE(SE),
210 StackPtrTy(Type::getInt8PtrTy(F.getContext())),
211 IntPtrTy(DL.getIntPtrType(F.getContext())),
212 Int32Ty(Type::getInt32Ty(F.getContext())),
213 Int8Ty(Type::getInt8Ty(F.getContext())) {}
214
215 // Run the transformation on the associated function.
216 // Returns whether the function was changed.
217 bool run();
218};
219
220uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
221 uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
222 if (AI->isArrayAllocation()) {
223 auto C = dyn_cast<ConstantInt>(AI->getArraySize());
224 if (!C)
225 return 0;
226 Size *= C->getZExtValue();
227 }
228 return Size;
229}
230
231bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
232 const Value *AllocaPtr, uint64_t AllocaSize) {
233 AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
234 const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
235
236 uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
237 ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
238 ConstantRange SizeRange =
239 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
240 ConstantRange AccessRange = AccessStartRange.add(SizeRange);
241 ConstantRange AllocaRange =
242 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
243 bool Safe = AllocaRange.contains(AccessRange);
244
245 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
246 dbgs() << "[SafeStack] "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
247 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
248 << *AllocaPtr << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
249 << " Access " << *Addr << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
250 << " SCEV " << *Exprdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
251 << " U: " << SE.getUnsignedRange(Expr)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
252 << ", S: " << SE.getSignedRange(Expr) << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
253 << " Range " << AccessRange << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
254 << " AllocaRange " << AllocaRange << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
255 << " " << (Safe ? "safe" : "unsafe") << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
;
256
257 return Safe;
258}
259
260bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
261 const Value *AllocaPtr,
262 uint64_t AllocaSize) {
263 // All MemIntrinsics have destination address in Arg0 and size in Arg2.
264 if (MI->getRawDest() != U) return true;
265 const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
266 // Non-constant size => unsafe. FIXME: try SCEV getRange.
267 if (!Len) return false;
268 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
269}
270
271/// Check whether a given allocation must be put on the safe
272/// stack or not. The function analyzes all uses of AI and checks whether it is
273/// only accessed in a memory safe way (as decided statically).
274bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
275 // Go through all uses of this alloca and check whether all accesses to the
276 // allocated object are statically known to be memory safe and, hence, the
277 // object can be placed on the safe stack.
278 SmallPtrSet<const Value *, 16> Visited;
279 SmallVector<const Value *, 8> WorkList;
280 WorkList.push_back(AllocaPtr);
281
282 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
283 while (!WorkList.empty()) {
284 const Value *V = WorkList.pop_back_val();
285 for (const Use &UI : V->uses()) {
286 auto I = cast<const Instruction>(UI.getUser());
287 assert(V == UI.get())(static_cast <bool> (V == UI.get()) ? void (0) : __assert_fail
("V == UI.get()", "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 287, __extension__ __PRETTY_FUNCTION__))
;
288
289 switch (I->getOpcode()) {
290 case Instruction::Load:
291 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
292 AllocaSize))
293 return false;
294 break;
295
296 case Instruction::VAArg:
297 // "va-arg" from a pointer is safe.
298 break;
299 case Instruction::Store:
300 if (V == I->getOperand(0)) {
301 // Stored the pointer - conservatively assume it may be unsafe.
302 LLVM_DEBUG(dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
303 << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
304 << "\n store of address: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
;
305 return false;
306 }
307
308 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
309 AllocaPtr, AllocaSize))
310 return false;
311 break;
312
313 case Instruction::Ret:
314 // Information leak.
315 return false;
316
317 case Instruction::Call:
318 case Instruction::Invoke: {
319 ImmutableCallSite CS(I);
320
321 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
322 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
323 II->getIntrinsicID() == Intrinsic::lifetime_end)
324 continue;
325 }
326
327 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
328 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
329 LLVM_DEBUG(dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
330 << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
331 << "\n unsafe memintrinsic: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
;
332 return false;
333 }
334 continue;
335 }
336
337 // LLVM 'nocapture' attribute is only set for arguments whose address
338 // is not stored, passed around, or used in any other non-trivial way.
339 // We assume that passing a pointer to an object as a 'nocapture
340 // readnone' argument is safe.
341 // FIXME: a more precise solution would require an interprocedural
342 // analysis here, which would look at all uses of an argument inside
343 // the function being called.
344 ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
345 for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
346 if (A->get() == V)
347 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
348 CS.doesNotAccessMemory()))) {
349 LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe call: " <<
*I << "\n"; } } while (false)
350 << "\n unsafe call: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe call: " <<
*I << "\n"; } } while (false)
;
351 return false;
352 }
353 continue;
354 }
355
356 default:
357 if (Visited.insert(I).second)
358 WorkList.push_back(cast<const Instruction>(I));
359 }
360 }
361 }
362
363 // All uses of the alloca are safe, we can place it on the safe stack.
364 return true;
365}
366
367Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
368 Value *StackGuardVar = TL.getIRStackGuard(IRB);
369 if (!StackGuardVar)
370 StackGuardVar =
371 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
372 return IRB.CreateLoad(StackGuardVar, "StackGuard");
373}
374
375void SafeStack::findInsts(Function &F,
376 SmallVectorImpl<AllocaInst *> &StaticAllocas,
377 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
378 SmallVectorImpl<Argument *> &ByValArguments,
379 SmallVectorImpl<ReturnInst *> &Returns,
380 SmallVectorImpl<Instruction *> &StackRestorePoints) {
381 for (Instruction &I : instructions(&F)) {
382 if (auto AI = dyn_cast<AllocaInst>(&I)) {
383 ++NumAllocas;
384
385 uint64_t Size = getStaticAllocaAllocationSize(AI);
386 if (IsSafeStackAlloca(AI, Size))
387 continue;
388
389 if (AI->isStaticAlloca()) {
390 ++NumUnsafeStaticAllocas;
391 StaticAllocas.push_back(AI);
392 } else {
393 ++NumUnsafeDynamicAllocas;
394 DynamicAllocas.push_back(AI);
395 }
396 } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
397 Returns.push_back(RI);
398 } else if (auto CI = dyn_cast<CallInst>(&I)) {
399 // setjmps require stack restore.
400 if (CI->getCalledFunction() && CI->canReturnTwice())
401 StackRestorePoints.push_back(CI);
402 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
403 // Exception landing pads require stack restore.
404 StackRestorePoints.push_back(LP);
405 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
406 if (II->getIntrinsicID() == Intrinsic::gcroot)
407 report_fatal_error(
408 "gcroot intrinsic not compatible with safestack attribute");
409 }
410 }
411 for (Argument &Arg : F.args()) {
412 if (!Arg.hasByValAttr())
413 continue;
414 uint64_t Size =
415 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
416 if (IsSafeStackAlloca(&Arg, Size))
417 continue;
418
419 ++NumUnsafeByValArguments;
420 ByValArguments.push_back(&Arg);
421 }
422}
423
424AllocaInst *
425SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
426 ArrayRef<Instruction *> StackRestorePoints,
427 Value *StaticTop, bool NeedDynamicTop) {
428 assert(StaticTop && "The stack top isn't set.")(static_cast <bool> (StaticTop && "The stack top isn't set."
) ? void (0) : __assert_fail ("StaticTop && \"The stack top isn't set.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 428, __extension__ __PRETTY_FUNCTION__))
;
429
430 if (StackRestorePoints.empty())
431 return nullptr;
432
433 // We need the current value of the shadow stack pointer to restore
434 // after longjmp or exception catching.
435
436 // FIXME: On some platforms this could be handled by the longjmp/exception
437 // runtime itself.
438
439 AllocaInst *DynamicTop = nullptr;
440 if (NeedDynamicTop) {
441 // If we also have dynamic alloca's, the stack pointer value changes
442 // throughout the function. For now we store it in an alloca.
443 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
444 "unsafe_stack_dynamic_ptr");
445 IRB.CreateStore(StaticTop, DynamicTop);
446 }
447
448 // Restore current stack pointer after longjmp/exception catch.
449 for (Instruction *I : StackRestorePoints) {
450 ++NumUnsafeStackRestorePoints;
451
452 IRB.SetInsertPoint(I->getNextNode());
453 Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
454 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
455 }
456
457 return DynamicTop;
458}
459
460void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
461 AllocaInst *StackGuardSlot, Value *StackGuard) {
462 Value *V = IRB.CreateLoad(StackGuardSlot);
463 Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
464
465 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
466 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
467 MDNode *Weights = MDBuilder(F.getContext())
468 .createBranchWeights(SuccessProb.getNumerator(),
469 FailureProb.getNumerator());
470 Instruction *CheckTerm =
471 SplitBlockAndInsertIfThen(Cmp, &RI,
472 /* Unreachable */ true, Weights);
473 IRBuilder<> IRBFail(CheckTerm);
474 // FIXME: respect -fsanitize-trap / -ftrap-function here?
475 Constant *StackChkFail = F.getParent()->getOrInsertFunction(
476 "__stack_chk_fail", IRB.getVoidTy());
477 IRBFail.CreateCall(StackChkFail, {});
478}
479
480/// We explicitly compute and set the unsafe stack layout for all unsafe
481/// static alloca instructions. We save the unsafe "base pointer" in the
482/// prologue into a local variable and restore it in the epilogue.
483Value *SafeStack::moveStaticAllocasToUnsafeStack(
484 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
485 ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
486 Instruction *BasePointer, AllocaInst *StackGuardSlot) {
487 if (StaticAllocas.empty() && ByValArguments.empty())
488 return BasePointer;
489
490 DIBuilder DIB(*F.getParent());
491
492 StackColoring SSC(F, StaticAllocas);
493 SSC.run();
494 SSC.removeAllMarkers();
495
496 // Unsafe stack always grows down.
497 StackLayout SSL(StackAlignment);
498 if (StackGuardSlot) {
499 Type *Ty = StackGuardSlot->getAllocatedType();
500 unsigned Align =
501 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
502 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
503 Align, SSC.getFullLiveRange());
504 }
505
506 for (Argument *Arg : ByValArguments) {
507 Type *Ty = Arg->getType()->getPointerElementType();
508 uint64_t Size = DL.getTypeStoreSize(Ty);
509 if (Size == 0)
510 Size = 1; // Don't create zero-sized stack objects.
511
512 // Ensure the object is properly aligned.
513 unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
514 Arg->getParamAlignment());
515 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
516 }
517
518 for (AllocaInst *AI : StaticAllocas) {
519 Type *Ty = AI->getAllocatedType();
520 uint64_t Size = getStaticAllocaAllocationSize(AI);
521 if (Size == 0)
522 Size = 1; // Don't create zero-sized stack objects.
523
524 // Ensure the object is properly aligned.
525 unsigned Align =
526 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
527
528 SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
529 }
530
531 SSL.computeLayout();
532 unsigned FrameAlignment = SSL.getFrameAlignment();
533
534 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
535 // (AlignmentSkew).
536 if (FrameAlignment > StackAlignment) {
537 // Re-align the base pointer according to the max requested alignment.
538 assert(isPowerOf2_32(FrameAlignment))(static_cast <bool> (isPowerOf2_32(FrameAlignment)) ? void
(0) : __assert_fail ("isPowerOf2_32(FrameAlignment)", "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 538, __extension__ __PRETTY_FUNCTION__))
;
539 IRB.SetInsertPoint(BasePointer->getNextNode());
540 BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
541 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
542 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
543 StackPtrTy));
544 }
545
546 IRB.SetInsertPoint(BasePointer->getNextNode());
547
548 if (StackGuardSlot) {
549 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
550 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
551 ConstantInt::get(Int32Ty, -Offset));
552 Value *NewAI =
553 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
554
555 // Replace alloc with the new location.
556 StackGuardSlot->replaceAllUsesWith(NewAI);
557 StackGuardSlot->eraseFromParent();
558 }
559
560 for (Argument *Arg : ByValArguments) {
561 unsigned Offset = SSL.getObjectOffset(Arg);
562 unsigned Align = SSL.getObjectAlignment(Arg);
563 Type *Ty = Arg->getType()->getPointerElementType();
564
565 uint64_t Size = DL.getTypeStoreSize(Ty);
566 if (Size == 0)
567 Size = 1; // Don't create zero-sized stack objects.
568
569 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
570 ConstantInt::get(Int32Ty, -Offset));
571 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
572 Arg->getName() + ".unsafe-byval");
573
574 // Replace alloc with the new location.
575 replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
576 DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
577 Arg->replaceAllUsesWith(NewArg);
578 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
579 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
580 }
581
582 // Allocate space for every unsafe static AllocaInst on the unsafe stack.
583 for (AllocaInst *AI : StaticAllocas) {
584 IRB.SetInsertPoint(AI);
585 unsigned Offset = SSL.getObjectOffset(AI);
586
587 uint64_t Size = getStaticAllocaAllocationSize(AI);
588 if (Size == 0)
589 Size = 1; // Don't create zero-sized stack objects.
Value stored to 'Size' is never read
590
591 replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::NoDeref,
592 -Offset, DIExpression::NoDeref);
593 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
594
595 // Replace uses of the alloca with the new location.
596 // Insert address calculation close to each use to work around PR27844.
597 std::string Name = std::string(AI->getName()) + ".unsafe";
598 while (!AI->use_empty()) {
599 Use &U = *AI->use_begin();
600 Instruction *User = cast<Instruction>(U.getUser());
601
602 Instruction *InsertBefore;
603 if (auto *PHI = dyn_cast<PHINode>(User))
604 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
605 else
606 InsertBefore = User;
607
608 IRBuilder<> IRBUser(InsertBefore);
609 Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
610 ConstantInt::get(Int32Ty, -Offset));
611 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
612
613 if (auto *PHI = dyn_cast<PHINode>(User)) {
614 // PHI nodes may have multiple incoming edges from the same BB (why??),
615 // all must be updated at once with the same incoming value.
616 auto *BB = PHI->getIncomingBlock(U);
617 for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
618 if (PHI->getIncomingBlock(I) == BB)
619 PHI->setIncomingValue(I, Replacement);
620 } else {
621 U.set(Replacement);
622 }
623 }
624
625 AI->eraseFromParent();
626 }
627
628 // Re-align BasePointer so that our callees would see it aligned as
629 // expected.
630 // FIXME: no need to update BasePointer in leaf functions.
631 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
632
633 // Update shadow stack pointer in the function epilogue.
634 IRB.SetInsertPoint(BasePointer->getNextNode());
635
636 Value *StaticTop =
637 IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
638 "unsafe_stack_static_top");
639 IRB.CreateStore(StaticTop, UnsafeStackPtr);
640 return StaticTop;
641}
642
643void SafeStack::moveDynamicAllocasToUnsafeStack(
644 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
645 ArrayRef<AllocaInst *> DynamicAllocas) {
646 DIBuilder DIB(*F.getParent());
647
648 for (AllocaInst *AI : DynamicAllocas) {
649 IRBuilder<> IRB(AI);
650
651 // Compute the new SP value (after AI).
652 Value *ArraySize = AI->getArraySize();
653 if (ArraySize->getType() != IntPtrTy)
654 ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
655
656 Type *Ty = AI->getAllocatedType();
657 uint64_t TySize = DL.getTypeAllocSize(Ty);
658 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
659
660 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
661 SP = IRB.CreateSub(SP, Size);
662
663 // Align the SP value to satisfy the AllocaInst, type and stack alignments.
664 unsigned Align = std::max(
665 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
666 (unsigned)StackAlignment);
667
668 assert(isPowerOf2_32(Align))(static_cast <bool> (isPowerOf2_32(Align)) ? void (0) :
__assert_fail ("isPowerOf2_32(Align)", "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 668, __extension__ __PRETTY_FUNCTION__))
;
669 Value *NewTop = IRB.CreateIntToPtr(
670 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
671 StackPtrTy);
672
673 // Save the stack pointer.
674 IRB.CreateStore(NewTop, UnsafeStackPtr);
675 if (DynamicTop)
676 IRB.CreateStore(NewTop, DynamicTop);
677
678 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
679 if (AI->hasName() && isa<Instruction>(NewAI))
680 NewAI->takeName(AI);
681
682 replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::NoDeref, 0,
683 DIExpression::NoDeref);
684 AI->replaceAllUsesWith(NewAI);
685 AI->eraseFromParent();
686 }
687
688 if (!DynamicAllocas.empty()) {
689 // Now go through the instructions again, replacing stacksave/stackrestore.
690 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
691 Instruction *I = &*(It++);
692 auto II = dyn_cast<IntrinsicInst>(I);
693 if (!II)
694 continue;
695
696 if (II->getIntrinsicID() == Intrinsic::stacksave) {
697 IRBuilder<> IRB(II);
698 Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
699 LI->takeName(II);
700 II->replaceAllUsesWith(LI);
701 II->eraseFromParent();
702 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
703 IRBuilder<> IRB(II);
704 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
705 SI->takeName(II);
706 assert(II->use_empty())(static_cast <bool> (II->use_empty()) ? void (0) : __assert_fail
("II->use_empty()", "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 706, __extension__ __PRETTY_FUNCTION__))
;
707 II->eraseFromParent();
708 }
709 }
710 }
711}
712
713bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
714 Function *Callee = CS.getCalledFunction();
715 if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
716 return true;
717 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
718 CS.isNoInline())
719 return false;
720 return true;
721}
722
723void SafeStack::TryInlinePointerAddress() {
724 if (!isa<CallInst>(UnsafeStackPtr))
725 return;
726
727 if(F.hasFnAttribute(Attribute::OptimizeNone))
728 return;
729
730 CallSite CS(UnsafeStackPtr);
731 Function *Callee = CS.getCalledFunction();
732 if (!Callee || Callee->isDeclaration())
733 return;
734
735 if (!ShouldInlinePointerAddress(CS))
736 return;
737
738 InlineFunctionInfo IFI;
739 InlineFunction(CS, IFI);
740}
741
742bool SafeStack::run() {
743 assert(F.hasFnAttribute(Attribute::SafeStack) &&(static_cast <bool> (F.hasFnAttribute(Attribute::SafeStack
) && "Can't run SafeStack on a function without the attribute"
) ? void (0) : __assert_fail ("F.hasFnAttribute(Attribute::SafeStack) && \"Can't run SafeStack on a function without the attribute\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 744, __extension__ __PRETTY_FUNCTION__))
744 "Can't run SafeStack on a function without the attribute")(static_cast <bool> (F.hasFnAttribute(Attribute::SafeStack
) && "Can't run SafeStack on a function without the attribute"
) ? void (0) : __assert_fail ("F.hasFnAttribute(Attribute::SafeStack) && \"Can't run SafeStack on a function without the attribute\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 744, __extension__ __PRETTY_FUNCTION__))
;
745 assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration")(static_cast <bool> (!F.isDeclaration() && "Can't run SafeStack on a function declaration"
) ? void (0) : __assert_fail ("!F.isDeclaration() && \"Can't run SafeStack on a function declaration\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 745, __extension__ __PRETTY_FUNCTION__))
;
746
747 ++NumFunctions;
748
749 SmallVector<AllocaInst *, 16> StaticAllocas;
750 SmallVector<AllocaInst *, 4> DynamicAllocas;
751 SmallVector<Argument *, 4> ByValArguments;
752 SmallVector<ReturnInst *, 4> Returns;
753
754 // Collect all points where stack gets unwound and needs to be restored
755 // This is only necessary because the runtime (setjmp and unwind code) is
756 // not aware of the unsafe stack and won't unwind/restore it properly.
757 // To work around this problem without changing the runtime, we insert
758 // instrumentation to restore the unsafe stack pointer when necessary.
759 SmallVector<Instruction *, 4> StackRestorePoints;
760
761 // Find all static and dynamic alloca instructions that must be moved to the
762 // unsafe stack, all return instructions and stack restore points.
763 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
764 StackRestorePoints);
765
766 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
767 ByValArguments.empty() && StackRestorePoints.empty())
768 return false; // Nothing to do in this function.
769
770 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
771 !ByValArguments.empty())
772 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
773
774 if (!StackRestorePoints.empty())
775 ++NumUnsafeStackRestorePointsFunctions;
776
777 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
778 if (SafeStackUsePointerAddress) {
779 Value *Fn = F.getParent()->getOrInsertFunction(
780 "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
781 UnsafeStackPtr = IRB.CreateCall(Fn);
782 } else {
783 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
784 }
785
786 // Load the current stack pointer (we'll also use it as a base pointer).
787 // FIXME: use a dedicated register for it ?
788 Instruction *BasePointer =
789 IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
790 assert(BasePointer->getType() == StackPtrTy)(static_cast <bool> (BasePointer->getType() == StackPtrTy
) ? void (0) : __assert_fail ("BasePointer->getType() == StackPtrTy"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/CodeGen/SafeStack.cpp"
, 790, __extension__ __PRETTY_FUNCTION__))
;
791
792 AllocaInst *StackGuardSlot = nullptr;
793 // FIXME: implement weaker forms of stack protector.
794 if (F.hasFnAttribute(Attribute::StackProtect) ||
795 F.hasFnAttribute(Attribute::StackProtectStrong) ||
796 F.hasFnAttribute(Attribute::StackProtectReq)) {
797 Value *StackGuard = getStackGuard(IRB, F);
798 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
799 IRB.CreateStore(StackGuard, StackGuardSlot);
800
801 for (ReturnInst *RI : Returns) {
802 IRBuilder<> IRBRet(RI);
803 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
804 }
805 }
806
807 // The top of the unsafe stack after all unsafe static allocas are
808 // allocated.
809 Value *StaticTop =
810 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
811 Returns, BasePointer, StackGuardSlot);
812
813 // Safe stack object that stores the current unsafe stack top. It is updated
814 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
815 // This is only needed if we need to restore stack pointer after longjmp
816 // or exceptions, and we have dynamic allocations.
817 // FIXME: a better alternative might be to store the unsafe stack pointer
818 // before setjmp / invoke instructions.
819 AllocaInst *DynamicTop = createStackRestorePoints(
820 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
821
822 // Handle dynamic allocas.
823 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
824 DynamicAllocas);
825
826 // Restore the unsafe stack pointer before each return.
827 for (ReturnInst *RI : Returns) {
828 IRB.SetInsertPoint(RI);
829 IRB.CreateStore(BasePointer, UnsafeStackPtr);
830 }
831
832 TryInlinePointerAddress();
833
834 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack applied\n"
; } } while (false)
;
835 return true;
836}
837
838class SafeStackLegacyPass : public FunctionPass {
839 const TargetMachine *TM = nullptr;
840
841public:
842 static char ID; // Pass identification, replacement for typeid..
843
844 SafeStackLegacyPass() : FunctionPass(ID) {
845 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
846 }
847
848 void getAnalysisUsage(AnalysisUsage &AU) const override {
849 AU.addRequired<TargetPassConfig>();
850 AU.addRequired<TargetLibraryInfoWrapperPass>();
851 AU.addRequired<AssumptionCacheTracker>();
852 }
853
854 bool runOnFunction(Function &F) override {
855 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Function: " <<
F.getName() << "\n"; } } while (false)
;
856
857 if (!F.hasFnAttribute(Attribute::SafeStack)) {
858 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack is not requested"
" for this function\n"; } } while (false)
859 " for this function\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack is not requested"
" for this function\n"; } } while (false)
;
860 return false;
861 }
862
863 if (F.isDeclaration()) {
864 LLVM_DEBUG(dbgs() << "[SafeStack] function definition"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] function definition"
" is not available\n"; } } while (false)
865 " is not available\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] function definition"
" is not available\n"; } } while (false)
;
866 return false;
867 }
868
869 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
870 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
871 if (!TL)
872 report_fatal_error("TargetLowering instance is required");
873
874 auto *DL = &F.getParent()->getDataLayout();
875 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
876 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
877
878 // Compute DT and LI only for functions that have the attribute.
879 // This is only useful because the legacy pass manager doesn't let us
880 // compute analyzes lazily.
881 // In the backend pipeline, nothing preserves DT before SafeStack, so we
882 // would otherwise always compute it wastefully, even if there is no
883 // function with the safestack attribute.
884 DominatorTree DT(F);
885 LoopInfo LI(DT);
886
887 ScalarEvolution SE(F, TLI, ACT, DT, LI);
888
889 return SafeStack(F, *TL, *DL, SE).run();
890 }
891};
892
893} // end anonymous namespace
894
895char SafeStackLegacyPass::ID = 0;
896
897INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,static void *initializeSafeStackLegacyPassPassOnce(PassRegistry
&Registry) {
898 "Safe Stack instrumentation pass", false, false)static void *initializeSafeStackLegacyPassPassOnce(PassRegistry
&Registry) {
899INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)initializeTargetPassConfigPass(Registry);
900INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,PassInfo *PI = new PassInfo( "Safe Stack instrumentation pass"
, "safe-stack", &SafeStackLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SafeStackLegacyPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeSafeStackLegacyPassPassFlag; void llvm::initializeSafeStackLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeSafeStackLegacyPassPassFlag
, initializeSafeStackLegacyPassPassOnce, std::ref(Registry));
}
901 "Safe Stack instrumentation pass", false, false)PassInfo *PI = new PassInfo( "Safe Stack instrumentation pass"
, "safe-stack", &SafeStackLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SafeStackLegacyPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeSafeStackLegacyPassPassFlag; void llvm::initializeSafeStackLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeSafeStackLegacyPassPassFlag
, initializeSafeStackLegacyPassPassOnce, std::ref(Registry));
}
902
903FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }