dfsan: Enable 48-bit VMA support on aarch64

[zatrazz]

Summary

This patch adds 48-bits VMA support for msan on aarch64. As current
mappings for aarch64, 48-bit VMA also supports PIE executable.

Tested on 39 and 48-bit VMA kernels on aarch64.

[rengolin]

All tests pass on an APM running Ubuntu Xenial.

lib/dfsan/dfsan.cc

 // +--------------------+ 0x1200000000 (kUnusedAddr)
 // |    union table     |
 // +--------------------+ 0x8000000000 (kUnionTableAddr)
 // |   shadow memory    |
 // +--------------------+ 0x0000010000 (kShadowAddr)
 // | reserved by kernel |
 // +--------------------+ 0x0000000000
 
+// On Linux/AArch64 (48-bit VMA), memory is laid out as follow:
+//
+// +--------------------+ 0x1000000000000 (top of memory)
+// | application memory |
+// +--------------------+ 0xffff00008000 (kAppAddr)
+// |       unused       |
+// +--------------------+ 0xaaaab0000000 (top of PIE address)
+// | application PIE    |
+// +--------------------+ 0xaaaaa0000000 (top of PIE address)
+// |                    |
+// |       unused       |
+// |                    |
+// +--------------------+ 0x1200000000 (kUnusedAddr)
+// |    union table     |
+// +--------------------+ 0x8000000000 (kUnionTableAddr)
+// |   shadow memory    |
+// +--------------------+ 0x0000010000 (kShadowAddr)
+// | reserved by kernel |
+// +--------------------+ 0x0000000000
+
 typedef atomic_dfsan_label dfsan_union_table_t[kNumLabels][kNumLabels];
 
 #ifdef DFSAN_RUNTIME_VMA
 // Runtime detected VMA size.
 int __dfsan::vmaSize;
 #endif
 
 static uptr UnusedAddr() {
static void InitializeFlags() {
   if (common_flags()->help) parser.PrintFlagDescriptions();
 }
 
 static void InitializePlatformEarly() {
   AvoidCVE_2016_2143();
 #ifdef DFSAN_RUNTIME_VMA
   __dfsan::vmaSize =
     (MostSignificantSetBitIndex(GET_CURRENT_FRAME()) + 1);
-  if (__dfsan::vmaSize == 39 || __dfsan::vmaSize == 42) {
+  if (__dfsan::vmaSize == 39 || __dfsan::vmaSize == 42 ||
+      __dfsan::vmaSize == 48) {
     __dfsan_shadow_ptr_mask = ShadowMask();
   } else {
     Printf("FATAL: DataFlowSanitizer: unsupported VMA range\n");
-    Printf("FATAL: Found %d - Supported 39 and 42\n", __dfsan::vmaSize);
+    Printf("FATAL: Found %d - Supported 39, 42, and 48\n", __dfsan::vmaSize);
     Die();
   }
 #endif
 }
 
 static void dfsan_fini() {
   if (internal_strcmp(flags().dump_labels_at_exit, "") != 0) {
     fd_t fd = OpenFile(flags().dump_labels_at_exit, WrOnly);

lib/dfsan/dfsan_platform.h

 
 struct Mapping42 {
   static const uptr kShadowAddr = 0x10000;
   static const uptr kUnionTableAddr = 0x8000000000;
   static const uptr kAppAddr = 0x3ff00008000;
   static const uptr kShadowMask = ~0x3c000000000;
 };
 
+struct Mapping48 {
+  static const uptr kShadowAddr = 0x10000;
+  static const uptr kUnionTableAddr = 0x8000000000;
+  static const uptr kAppAddr = 0xffff00008000;
+  static const uptr kShadowMask = ~0xfffff0000000;
+};
+
 extern int vmaSize;
 # define DFSAN_RUNTIME_VMA 1
 #else
 # error "DFSan not supported for this platform!"
 #endif
 
 enum MappingType {
   MAPPING_SHADOW_ADDR,
switch (Type) {
     case MAPPING_APP_ADDR: return Mapping::kAppAddr;
     case MAPPING_SHADOW_MASK: return Mapping::kShadowMask;
   }
 }
 
 template<int Type>
 uptr MappingArchImpl(void) {
 #ifdef __aarch64__
-  if (vmaSize == 39)
-    return MappingImpl<Mapping39, Type>();
-  else
-    return MappingImpl<Mapping42, Type>();
+  switch (vmaSize) {
+    case 39: return MappingImpl<Mapping39, Type>();
+    case 42: return MappingImpl<Mapping42, Type>();
+    case 48: return MappingImpl<Mapping48, Type>();
+  }
   DCHECK(0);
+  return 0;
 #else
   return MappingImpl<Mapping, Type>();
 #endif
 }
 
 ALWAYS_INLINE
 uptr ShadowAddr() {
   return MappingArchImpl<MAPPING_SHADOW_ADDR>();