Index: llvm/trunk/include/llvm/ProfileData/InstrProfReader.h
===================================================================
--- llvm/trunk/include/llvm/ProfileData/InstrProfReader.h
+++ llvm/trunk/include/llvm/ProfileData/InstrProfReader.h
@@ -268,8 +268,14 @@
       return (const char *)ValueDataStart;
   }
 
-  const uint64_t *getCounter(IntPtrT CounterPtr) const {
-    ptrdiff_t Offset = (swap(CounterPtr) - CountersDelta) / sizeof(uint64_t);
+  /// Get the offset of \p CounterPtr from the start of the counters section of
+  /// the profile. The offset has units of "number of counters", i.e. increasing
+  /// the offset by 1 corresponds to an increase in the *byte offset* by 8.
+  ptrdiff_t getCounterOffset(IntPtrT CounterPtr) const {
+    return (swap(CounterPtr) - CountersDelta) / sizeof(uint64_t);
+  }
+
+  const uint64_t *getCounter(ptrdiff_t Offset) const {
     return CountersStart + Offset;
   }
 
Index: llvm/trunk/lib/ProfileData/InstrProfReader.cpp
===================================================================
--- llvm/trunk/lib/ProfileData/InstrProfReader.cpp
+++ llvm/trunk/lib/ProfileData/InstrProfReader.cpp
@@ -413,13 +413,19 @@
   if (NumCounters == 0)
     return error(instrprof_error::malformed);
 
-  auto RawCounts = makeArrayRef(getCounter(CounterPtr), NumCounters);
   auto *NamesStartAsCounter = reinterpret_cast<const uint64_t *>(NamesStart);
+  ptrdiff_t MaxNumCounters = NamesStartAsCounter - CountersStart;
 
-  // Check bounds.
-  if (RawCounts.data() < CountersStart ||
-      RawCounts.data() + RawCounts.size() > NamesStartAsCounter)
+  // Check bounds. Note that the counter pointer embedded in the data record
+  // may itself be corrupt.
+  if (NumCounters > MaxNumCounters)
     return error(instrprof_error::malformed);
+  ptrdiff_t CounterOffset = getCounterOffset(CounterPtr);
+  if (CounterOffset < 0 || CounterOffset > MaxNumCounters ||
+      (CounterOffset + NumCounters) > MaxNumCounters)
+    return error(instrprof_error::malformed);
+
+  auto RawCounts = makeArrayRef(getCounter(CounterOffset), NumCounters);
 
   if (ShouldSwapBytes) {
     Record.Counts.clear();
Index: llvm/trunk/test/tools/llvm-profdata/malformed-ptr-to-counter-array.test
===================================================================
--- llvm/trunk/test/tools/llvm-profdata/malformed-ptr-to-counter-array.test
+++ llvm/trunk/test/tools/llvm-profdata/malformed-ptr-to-counter-array.test
@@ -0,0 +1,5 @@
+REQUIRES: zlib
+
+RUN: not llvm-profdata merge -o /dev/null %p/Inputs/malformed-ptr-to-counter-array.profraw 2>&1 | FileCheck %s
+
+CHECK: Malformed instrumentation profile data