Add red zones to BumpPtrAllocator under ASan

To help catch buffer overruns, this patch changes BumpPtrAllocator to
insert an extra unused byte between allocations when building with
ASan. SpecificBumpPtrAllocator opts out of this behavior, since it
needs to destroy its items later by walking the allocated memory.

Reviewed by Pete Cooper.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297310 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/Allocator.h

@@ -155,7 +155,7 @@ public:
   BumpPtrAllocatorImpl(BumpPtrAllocatorImpl &&Old)
       : CurPtr(Old.CurPtr), End(Old.End), Slabs(std::move(Old.Slabs)),
         CustomSizedSlabs(std::move(Old.CustomSizedSlabs)),
-        BytesAllocated(Old.BytesAllocated),
+        BytesAllocated(Old.BytesAllocated), RedZoneSize(Old.RedZoneSize),
         Allocator(std::move(Old.Allocator)) {
     Old.CurPtr = Old.End = nullptr;
     Old.BytesAllocated = 0;
@@ -175,6 +175,7 @@ public:
     CurPtr = RHS.CurPtr;
     End = RHS.End;
     BytesAllocated = RHS.BytesAllocated;
+    RedZoneSize = RHS.RedZoneSize;
     Slabs = std::move(RHS.Slabs);
     CustomSizedSlabs = std::move(RHS.CustomSizedSlabs);
     Allocator = std::move(RHS.Allocator);
@@ -217,10 +218,16 @@ public:
     size_t Adjustment = alignmentAdjustment(CurPtr, Alignment);
     assert(Adjustment + Size >= Size && "Adjustment + Size must not overflow");
 
+    size_t SizeToAllocate = Size;
+#if LLVM_ADDRESS_SANITIZER_BUILD
+    // Add trailing bytes as a "red zone" under ASan.
+    SizeToAllocate += RedZoneSize;
+#endif
+
     // Check if we have enough space.
-    if (Adjustment + Size <= size_t(End - CurPtr)) {
+    if (Adjustment + SizeToAllocate <= size_t(End - CurPtr)) {
       char *AlignedPtr = CurPtr + Adjustment;
-      CurPtr = AlignedPtr + Size;
+      CurPtr = AlignedPtr + SizeToAllocate;
       // Update the allocation point of this memory block in MemorySanitizer.
       // Without this, MemorySanitizer messages for values originated from here
       // will point to the allocation of the entire slab.
@@ -231,7 +238,7 @@ public:
     }
 
     // If Size is really big, allocate a separate slab for it.
-    size_t PaddedSize = Size + Alignment - 1;
+    size_t PaddedSize = SizeToAllocate + Alignment - 1;
     if (PaddedSize > SizeThreshold) {
       void *NewSlab = Allocator.Allocate(PaddedSize, 0);
       // We own the new slab and don't want anyone reading anyting other than
@@ -250,10 +257,10 @@ public:
     // Otherwise, start a new slab and try again.
     StartNewSlab();
     uintptr_t AlignedAddr = alignAddr(CurPtr, Alignment);
-    assert(AlignedAddr + Size <= (uintptr_t)End &&
+    assert(AlignedAddr + SizeToAllocate <= (uintptr_t)End &&
            "Unable to allocate memory!");
     char *AlignedPtr = (char*)AlignedAddr;
-    CurPtr = AlignedPtr + Size;
+    CurPtr = AlignedPtr + SizeToAllocate;
     __msan_allocated_memory(AlignedPtr, Size);
     __asan_unpoison_memory_region(AlignedPtr, Size);
     return AlignedPtr;
@@ -282,6 +289,10 @@ public:
 
   size_t getBytesAllocated() const { return BytesAllocated; }
 
+  void setRedZoneSize(size_t NewSize) {
+    RedZoneSize = NewSize;
+  }
+
   void PrintStats() const {
     detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
                                        getTotalMemory());
@@ -307,6 +318,10 @@ private:
   /// Used so that we can compute how much space was wasted.
   size_t BytesAllocated = 0;
 
+  /// \brief The number of bytes to put between allocations when running under
+  /// a sanitizer.
+  size_t RedZoneSize = 1;
+
   /// \brief The allocator instance we use to get slabs of memory.
   AllocatorT Allocator;
 
@@ -368,7 +383,11 @@ template <typename T> class SpecificBumpPtrAllocator {
   BumpPtrAllocator Allocator;
 
 public:
-  SpecificBumpPtrAllocator() = default;
+  SpecificBumpPtrAllocator() {
+    // Because SpecificBumpPtrAllocator walks the memory to call destructors,
+    // it can't have red zones between allocations.
+    Allocator.setRedZoneSize(0);
+  }
   SpecificBumpPtrAllocator(SpecificBumpPtrAllocator &&Old)
       : Allocator(std::move(Old.Allocator)) {}
   ~SpecificBumpPtrAllocator() { DestroyAll(); }