[asan] Use dynamic shadow on 32-bit Android.

Summary:
The following kernel change has moved ET_DYN base to 0x4000000 on arm32:
https://marc.info/?l=linux-kernel&m=149825162606848&w=2

Switch to dynamic shadow base to avoid such conflicts in the future.

Reserve shadow memory in an ifunc resolver, but don't use it in the instrumentation
until PR35221 is fixed. This will eventually let use save one load per function.

Reviewers: kcc

Subscribers: aemerson, srhines, kubamracek, kristof.beyls, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D39393

llvm-svn: 317943

1 files changed, 39 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index 3d50007..33e0206 100644
--- a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -136,8 +136,8 @@ static const char *const kAsanUnregisterElfGlobalsName =
 static const char *const kAsanPoisonGlobalsName = "__asan_before_dynamic_init";
 static const char *const kAsanUnpoisonGlobalsName = "__asan_after_dynamic_init";
 static const char *const kAsanInitName = "__asan_init";
-static const char *const kAsanVersionCheckName =
-    "__asan_version_mismatch_check_v8";
+static const char *const kAsanVersionCheckNamePrefix =
+    "__asan_version_mismatch_check_v";
 static const char *const kAsanPtrCmp = "__sanitizer_ptr_cmp";
 static const char *const kAsanPtrSub = "__sanitizer_ptr_sub";
 static const char *const kAsanHandleNoReturnName = "__asan_handle_no_return";
@@ -207,6 +207,12 @@ static cl::opt<bool> ClForceDynamicShadow(
     cl::desc("Load shadow address into a local variable for each function"),
     cl::Hidden, cl::init(false));
 
+static cl::opt<bool>
+    ClWithIfunc("asan-with-ifunc",
+                cl::desc("Access dynamic shadow through an ifunc global on "
+                         "platforms that support this"),
+                cl::Hidden, cl::init(false));
+
 // This flag limits the number of instructions to be instrumented
 // in any given BB. Normally, this should be set to unlimited (INT_MAX),
 // but due to http://llvm.org/bugs/show_bug.cgi?id=12652 we temporary
@@ -447,10 +453,14 @@ private:
 
 /// This struct defines the shadow mapping using the rule:
 ///   shadow = (mem >> Scale) ADD-or-OR Offset.
+/// If InGlobal is true, then
+///   extern char __asan_shadow[];
+///   shadow = (mem >> Scale) + &__asan_shadow
 struct ShadowMapping {
   int Scale;
   uint64_t Offset;
   bool OrShadowOffset;
+  bool InGlobal;
 };
 
 } // end anonymous namespace
@@ -472,6 +482,7 @@ static ShadowMapping getShadowMapping(Triple &TargetTriple, int LongSize,
                   TargetTriple.getArch() == Triple::mipsel;
   bool IsMIPS64 = TargetTriple.getArch() == Triple::mips64 ||
                   TargetTriple.getArch() == Triple::mips64el;
+  bool IsArmOrThumb = TargetTriple.isARM() || TargetTriple.isThumb();
   bool IsAArch64 = TargetTriple.getArch() == Triple::aarch64;
   bool IsWindows = TargetTriple.isOSWindows();
   bool IsFuchsia = TargetTriple.isOSFuchsia();
@@ -479,10 +490,8 @@ static ShadowMapping getShadowMapping(Triple &TargetTriple, int LongSize,
   ShadowMapping Mapping;
 
   if (LongSize == 32) {
-    // Android is always PIE, which means that the beginning of the address
-    // space is always available.
     if (IsAndroid)
-      Mapping.Offset = 0;
+      Mapping.Offset = kDynamicShadowSentinel;
     else if (IsMIPS32)
       Mapping.Offset = kMIPS32_ShadowOffset32;
     else if (IsFreeBSD)
@@ -550,6 +559,7 @@ static ShadowMapping getShadowMapping(Triple &TargetTriple, int LongSize,
   Mapping.OrShadowOffset = !IsAArch64 && !IsPPC64 && !IsSystemZ && !IsPS4CPU &&
                            !(Mapping.Offset & (Mapping.Offset - 1)) &&
                            Mapping.Offset != kDynamicShadowSentinel;
+  Mapping.InGlobal = ClWithIfunc && IsAndroid && IsArmOrThumb;
 
   return Mapping;
 }
@@ -672,6 +682,7 @@ private:
   DominatorTree *DT;
   Function *AsanHandleNoReturnFunc;
   Function *AsanPtrCmpFunction, *AsanPtrSubFunction;
+  Constant *AsanShadowGlobal;
 
   // These arrays is indexed by AccessIsWrite, Experiment and log2(AccessSize).
   Function *AsanErrorCallback[2][2][kNumberOfAccessSizes];
@@ -744,6 +755,7 @@ private:
   size_t MinRedzoneSizeForGlobal() const {
     return RedzoneSizeForScale(Mapping.Scale);
   }
+  int GetAsanVersion(const Module &M) const;
 
   GlobalsMetadata GlobalsMD;
   bool CompileKernel;
@@ -1109,6 +1121,11 @@ Value *AddressSanitizer::memToShadow(Value *Shadow, IRBuilder<> &IRB) {
   if (Mapping.Offset == 0) return Shadow;
   // (Shadow >> scale) | offset
   Value *ShadowBase;
+  if (Mapping.InGlobal)
+    return IRB.CreatePtrToInt(
+        IRB.CreateGEP(AsanShadowGlobal,
+                      {ConstantInt::get(IntptrTy, 0), Shadow}),
+        IntptrTy);
   if (LocalDynamicShadow)
     ShadowBase = LocalDynamicShadow;
   else
@@ -2156,6 +2173,16 @@ bool AddressSanitizerModule::InstrumentGlobals(IRBuilder<> &IRB, Module &M, bool
   return true;
 }
 
+int AddressSanitizerModule::GetAsanVersion(const Module &M) const {
+  int LongSize = M.getDataLayout().getPointerSizeInBits();
+  bool isAndroid = Triple(M.getTargetTriple()).isAndroid();
+  int Version = 8;
+  // 32-bit Android is one version ahead because of the switch to dynamic
+  // shadow.
+  Version += (LongSize == 32 && isAndroid);
+  return Version;
+}
+
 bool AddressSanitizerModule::runOnModule(Module &M) {
   C = &(M.getContext());
   int LongSize = M.getDataLayout().getPointerSizeInBits();
@@ -2169,9 +2196,11 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
 
   // Create a module constructor. A destructor is created lazily because not all
   // platforms, and not all modules need it.
+  std::string VersionCheckName =
+      kAsanVersionCheckNamePrefix + std::to_string(GetAsanVersion(M));
   std::tie(AsanCtorFunction, std::ignore) = createSanitizerCtorAndInitFunctions(
       M, kAsanModuleCtorName, kAsanInitName, /*InitArgTypes=*/{},
-      /*InitArgs=*/{}, kAsanVersionCheckName);
+      /*InitArgs=*/{}, VersionCheckName);
 
   bool CtorComdat = true;
   bool Changed = false;
@@ -2270,6 +2299,9 @@ void AddressSanitizer::initializeCallbacks(Module &M) {
   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
                             StringRef(""), StringRef(""),
                             /*hasSideEffects=*/true);
+  if (Mapping.InGlobal)
+    AsanShadowGlobal = M.getOrInsertGlobal("__asan_shadow",
+                                           ArrayType::get(IRB.getInt8Ty(), 0));
 }
 
 // virtual
@@ -2311,7 +2343,7 @@ bool AddressSanitizer::maybeInsertAsanInitAtFunctionEntry(Function &F) {
 
 void AddressSanitizer::maybeInsertDynamicShadowAtFunctionEntry(Function &F) {
   // Generate code only when dynamic addressing is needed.
-  if (Mapping.Offset != kDynamicShadowSentinel)
+  if (Mapping.Offset != kDynamicShadowSentinel || Mapping.InGlobal)
     return;
 
   IRBuilder<> IRB(&F.front().front());