[lldb/DataFormatter] Check for overflow when finding NSDate epoch

Summary:
Fixes UBSan-reported issues where the date value inside of an
uninitialized NSDate overflows the 64-bit epoch.

rdar://61774575

Reviewers: JDevlieghere, mib, teemperor

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D80150

lldb/include/lldb/DataFormatters/Mock.h

@@ -0,0 +1,26 @@
+//===-- Mock.h --------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_DATAFORMATTERS_MOCK_H
+#define LLDB_DATAFORMATTERS_MOCK_H
+
+namespace lldb_private {
+
+class Stream;
+
+namespace formatters {
+namespace NSDate {
+
+/// Format the date_value field of a NSDate.
+bool FormatDateValue(double date_value, Stream &stream);
+
+} // namespace NSDate
+} // namespace formatters
+} // namespace lldb_private
+
+#endif // LLDB_DATAFORMATTERS_MOCK_H

lldb/source/Plugins/Language/ObjC/Cocoa.cpp

@@ -13,6 +13,7 @@
 #include "lldb/Core/ValueObject.h"
 #include "lldb/Core/ValueObjectConstResult.h"
 #include "lldb/DataFormatters/FormattersHelpers.h"
+#include "lldb/DataFormatters/Mock.h"
 #include "lldb/DataFormatters/StringPrinter.h"
 #include "lldb/DataFormatters/TypeSummary.h"
 #include "lldb/Host/Time.h"
@@ -27,6 +28,7 @@
 
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/bit.h"
+#include "llvm/Support/CheckedArithmetic.h"
 
 #include "Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.h"
 
@@ -785,6 +787,34 @@ static double decodeTaggedTimeInterval(uint64_t encodedTimeInterval) {
   return llvm::bit_cast<double>(decodedBits);
 }
 
+bool lldb_private::formatters::NSDate::FormatDateValue(double date_value,
+                                                       Stream &stream) {
+  if (date_value == -63114076800) {
+    stream.Printf("0001-12-30 00:00:00 +0000");
+    return true;
+  }
+
+  if (date_value > std::numeric_limits<time_t>::max() ||
+      date_value < std::numeric_limits<time_t>::min())
+    return false;
+
+  time_t epoch = GetOSXEpoch();
+  if (auto osx_epoch = llvm::checkedAdd(epoch, (time_t)date_value))
+    epoch = *osx_epoch;
+  else
+    return false;
+  tm *tm_date = gmtime(&epoch);
+  if (!tm_date)
+    return false;
+  std::string buffer(1024, 0);
+  if (strftime(&buffer[0], 1023, "%Z", tm_date) == 0)
+    return false;
+  stream.Printf("%04d-%02d-%02d %02d:%02d:%02d %s", tm_date->tm_year + 1900,
+                tm_date->tm_mon + 1, tm_date->tm_mday, tm_date->tm_hour,
+                tm_date->tm_min, tm_date->tm_sec, buffer.c_str());
+  return true;
+}
+
 bool lldb_private::formatters::NSDateSummaryProvider(
     ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
   ProcessSP process_sp = valobj.GetProcessSP();
@@ -828,6 +858,16 @@ bool lldb_private::formatters::NSDateSummaryProvider(
     if (descriptor->GetTaggedPointerInfo(&info_bits, &value_bits)) {
       date_value_bits = ((value_bits << 8) | (info_bits << 4));
       memcpy(&date_value, &date_value_bits, sizeof(date_value_bits));
+
+      // Accomodate the __NSTaggedDate format introduced in Foundation 1600.
+      if (class_name == g___NSTaggedDate) {
+        auto *apple_runtime = llvm::dyn_cast_or_null<AppleObjCRuntime>(
+            ObjCLanguageRuntime::Get(*process_sp));
+        if (!apple_runtime)
+          return false;
+        if (apple_runtime->GetFoundationVersion() >= 1600)
+          date_value = decodeTaggedTimeInterval(value_bits << 4);
+      }
     } else {
       llvm::Triple triple(
           process_sp->GetTarget().GetArchitecture().GetTriple());
@@ -850,34 +890,7 @@ bool lldb_private::formatters::NSDateSummaryProvider(
   } else
     return false;
 
-  if (date_value == -63114076800) {
-    stream.Printf("0001-12-30 00:00:00 +0000");
-    return true;
-  }
-
-  // Accomodate for the __NSTaggedDate format introduced in Foundation 1600.
-  if (class_name == g___NSTaggedDate) {
-    auto *runtime = llvm::dyn_cast_or_null<AppleObjCRuntime>(
-        ObjCLanguageRuntime::Get(*process_sp));
-    if (runtime && runtime->GetFoundationVersion() >= 1600)
-      date_value = decodeTaggedTimeInterval(value_bits << 4);
-  }
-
-  // this snippet of code assumes that time_t == seconds since Jan-1-1970 this
-  // is generally true and POSIXly happy, but might break if a library vendor
-  // decides to get creative
-  time_t epoch = GetOSXEpoch();
-  epoch = epoch + (time_t)date_value;
-  tm *tm_date = gmtime(&epoch);
-  if (!tm_date)
-    return false;
-  std::string buffer(1024, 0);
-  if (strftime(&buffer[0], 1023, "%Z", tm_date) == 0)
-    return false;
-  stream.Printf("%04d-%02d-%02d %02d:%02d:%02d %s", tm_date->tm_year + 1900,
-                tm_date->tm_mon + 1, tm_date->tm_mday, tm_date->tm_hour,
-                tm_date->tm_min, tm_date->tm_sec, buffer.c_str());
-  return true;
+  return NSDate::FormatDateValue(date_value, stream);
 }
 
 bool lldb_private::formatters::ObjCClassSummaryProvider(

lldb/unittests/DataFormatter/CMakeLists.txt

@@ -1,5 +1,6 @@
 add_lldb_unittest(LLDBFormatterTests
   FormatManagerTests.cpp
+  MockTests.cpp
   StringPrinterTests.cpp
 
   LINK_LIBS

lldb/unittests/DataFormatter/MockTests.cpp

@@ -0,0 +1,40 @@
+//===-- MockTests.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/DataFormatters/Mock.h"
+#include "lldb/Utility/StreamString.h"
+#include "llvm/ADT/Optional.h"
+#include "gtest/gtest.h"
+#include <string>
+
+using namespace lldb_private;
+
+// Try to format the date_value field of a NSDate.
+static llvm::Optional<std::string> formatDateValue(double date_value) {
+  StreamString s;
+  bool succcess = formatters::NSDate::FormatDateValue(date_value, s);
+  if (succcess)
+    return std::string(s.GetData());
+  return llvm::None;
+}
+
+TEST(DataFormatterMockTest, NSDate) {
+  EXPECT_EQ(*formatDateValue(-63114076800), "0001-12-30 00:00:00 +0000");
+
+  // Can't convert the date_value to a time_t.
+  EXPECT_EQ(formatDateValue(std::numeric_limits<time_t>::max() + 1),
+            llvm::None);
+  EXPECT_EQ(formatDateValue(std::numeric_limits<time_t>::min() - 1),
+            llvm::None);
+
+  // Can't add the macOS epoch to the converted date_value (the add overflows).
+  EXPECT_EQ(formatDateValue(std::numeric_limits<time_t>::max()), llvm::None);
+  EXPECT_EQ(formatDateValue(std::numeric_limits<time_t>::min()), llvm::None);
+
+  EXPECT_EQ(*formatDateValue(0), "2001-01-01 00:00:00 UTC");
+}