[PATCH] D26650: [asan] Don't assert that a target is within 2GB on 32-bit Windows

[Reid Kleckner via llvm-commits]

rnk created this revision.
rnk added a reviewer: etienneb.
rnk added a subscriber: llvm-commits.
Herald added a subscriber: mgorny.

In a 32-bit address space, PC-relative jump targets are wrapped, so a
direct branch at 0x90000001 can reach address 0x10000000 with a
displacement of 0x7FFFFFFFF. This can happen in applications, such as
Chrome, that are linked with /LARGEADDRESSAWARE.


https://reviews.llvm.org/D26650

Files:
  lib/interception/interception_win.cc
  lib/interception/tests/CMakeLists.txt
  lib/interception/tests/interception_win_test.cc


Index: lib/interception/tests/interception_win_test.cc
===================================================================
--- lib/interception/tests/interception_win_test.cc
+++ lib/interception/tests/interception_win_test.cc
@@ -204,19 +204,38 @@
 
 // A buffer holding the dynamically generated code under test.
 u8* ActiveCode;
-size_t ActiveCodeLength = 4096;
+const size_t ActiveCodeLength = 4096;
+
+int InterceptorFunction(int x);
+
+/// Allocate code memory more than 2GB away from Base.
+u8 *AllocateCode2GBAway(u8 *Base) {
+  // Find a 64K aligned location after Base plus 2GB.
+  size_t TwoGB = 0x80000000;
+  size_t AllocGranularity = 0x10000;
+  Base = (u8 *)((((uptr)Base + TwoGB + AllocGranularity)) & ~(AllocGranularity - 1));
+
+  // Check if that location is free, and if not, loop over regions until we find
+  // one that is.
+  MEMORY_BASIC_INFORMATION mbi = {0};
+  while (sizeof(mbi) == VirtualQuery(Base, &mbi, sizeof(mbi))) {
+    if (mbi.State & MEM_FREE) break;
+    Base += mbi.RegionSize;
+  }
+
+  // Allocate one RWX page at the free location.
+  return (u8 *)::VirtualAlloc(Base, ActiveCodeLength, MEM_COMMIT | MEM_RESERVE,
+                              PAGE_EXECUTE_READWRITE);
+}
 
 template<class T>
 static void LoadActiveCode(
     const T &code,
     uptr *entry_point,
     FunctionPrefixKind prefix_kind = FunctionPrefixNone) {
   if (ActiveCode == nullptr) {
-    ActiveCode =
-        (u8*)::VirtualAlloc(nullptr, ActiveCodeLength,
-                            MEM_COMMIT | MEM_RESERVE,
-                            PAGE_EXECUTE_READWRITE);
-    ASSERT_NE(ActiveCode, nullptr);
+    ActiveCode = AllocateCode2GBAway((u8*)&InterceptorFunction);
+    ASSERT_NE(ActiveCode, nullptr) << "failed to allocate RWX memory 2GB away";
   }
 
   size_t position = 0;
Index: lib/interception/tests/CMakeLists.txt
===================================================================
--- lib/interception/tests/CMakeLists.txt
+++ lib/interception/tests/CMakeLists.txt
@@ -29,6 +29,7 @@
 endif()
 if(MSVC)
   list(APPEND INTERCEPTION_TEST_CFLAGS_COMMON -gcodeview)
+  list(APPEND INTERCEPTION_TEST_LINK_FLAGS_COMMON -Wl,-largeaddressaware)
 endif()
 list(APPEND INTERCEPTION_TEST_LINK_FLAGS_COMMON -g)
 
Index: lib/interception/interception_win.cc
===================================================================
--- lib/interception/interception_win.cc
+++ lib/interception/interception_win.cc
@@ -148,10 +148,16 @@
 }
 
 static bool DistanceIsWithin2Gig(uptr from, uptr target) {
+#if SANITIZER_WINDOWS64
   if (from < target)
     return target - from <= (uptr)0x7FFFFFFFU;
   else
     return from - target <= (uptr)0x80000000U;
+#else
+  // In a 32-bit address space, the address calculation will wrap, so this check
+  // is unnecessary.
+  return true;
+#endif
 }
 
 static uptr GetMmapGranularity() {


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