[hwasan] Allow optional early shadow setup.

[eugenis]

Summary

Provide __hwasan_shadow_init that can be used to initialize shadow w/o touching libc.
It can be used to bootstrap an unusual case of fully-static executable with
hwasan-instrumented libc, which needs to run hwasan code before it is ready to serve
user calls like madvise().

compiler-rt/include/sanitizer/hwasan_interface.h

 #ifndef SANITIZER_HWASAN_INTERFACE_H
 #define SANITIZER_HWASAN_INTERFACE_H
 
 #include <sanitizer/common_interface_defs.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
+  // Initialize shadow but not the rest of the runtime.
+  // Does not call libc unless there is an error.
+  // Can be called multiple times, or not at all (in which case shadow will
+  // be initialized in compiler-inserted __hwasan_init() call).
+  void __hwasan_shadow_init(void);
+
   // This function may be optionally provided by user and should return
   // a string containing HWASan runtime options. See asan_flags.h for details.
   const char* __hwasan_default_options(void);
 
   void __hwasan_enable_allocator_tagging(void);
   void __hwasan_disable_allocator_tagging(void);
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // SANITIZER_HWASAN_INTERFACE_H

compiler-rt/lib/hwasan/hwasan.h

 namespace __hwasan {
 
 extern int hwasan_inited;
 extern bool hwasan_init_is_running;
 extern int hwasan_report_count;
 
 bool ProtectRange(uptr beg, uptr end);
 bool InitShadow();
+void MadviseShadow();
 char *GetProcSelfMaps();
 void InitializeInterceptors();
 
 void HwasanAllocatorInit();
 void HwasanAllocatorThreadFinish();
 void HwasanDeallocate(StackTrace *stack, void *ptr);
 
 void *hwasan_malloc(uptr size, StackTrace *stack);

compiler-rt/lib/hwasan/hwasan.cc

 
 static Flags hwasan_flags;
 
 Flags *flags() {
   return &hwasan_flags;
 }
 
 int hwasan_inited = 0;
+int hwasan_shadow_inited = 0;
 bool hwasan_init_is_running;
 
 int hwasan_report_count = 0;
 
 void Flags::SetDefaults() {
 #define HWASAN_FLAG(Type, Name, DefaultValue, Description) Name = DefaultValue;
 #include "hwasan_flags.inc"
 #undef HWASAN_FLAG

 } // namespace __hwasan
 
 // Interface.
 
 using namespace __hwasan;
 
 uptr __hwasan_shadow_memory_dynamic_address;  // Global interface symbol.
 
+void __hwasan_shadow_init() {
+  if (hwasan_shadow_inited) return;
+  if (!InitShadow()) {
+    Printf("FATAL: HWAddressSanitizer cannot mmap the shadow memory.\n");
+    if (HWASAN_FIXED_MAPPING) {
+      Printf("FATAL: Make sure to compile with -fPIE and to link with -pie.\n");
+      Printf("FATAL: Disabling ASLR is known to cause this error.\n");
+      Printf("FATAL: If running under GDB, try "
+             "'set disable-randomization off'.\n");
+    }
+    DumpProcessMap();
+    Die();
+  }
+  hwasan_shadow_inited = 1;
+}
+
 void __hwasan_init() {
   CHECK(!hwasan_init_is_running);
   if (hwasan_inited) return;
   hwasan_init_is_running = 1;
   SanitizerToolName = "HWAddressSanitizer";
 
   InitTlsSize();
 
   CacheBinaryName();
   InitializeFlags();
 
   // Install tool-specific callbacks in sanitizer_common.
   SetCheckFailedCallback(HWAsanCheckFailed);
 
   __sanitizer_set_report_path(common_flags()->log_path);
 
   DisableCoreDumperIfNecessary();
-  if (!InitShadow()) {
-    Printf("FATAL: HWAddressSanitizer cannot mmap the shadow memory.\n");
-    if (HWASAN_FIXED_MAPPING) {
-      Printf("FATAL: Make sure to compile with -fPIE and to link with -pie.\n");
-      Printf("FATAL: Disabling ASLR is known to cause this error.\n");
-      Printf("FATAL: If running under GDB, try "
-             "'set disable-randomization off'.\n");
-    }
-    DumpProcessMap();
-    Die();
-  }
+  __hwasan_shadow_init();
+  MadviseShadow();
 
   InitializeInterceptors();
   InstallDeadlySignalHandlers(HwasanOnDeadlySignal);
   InstallAtExitHandler(); // Needs __cxa_atexit interceptor.
 
   Symbolizer::GetOrInit()->AddHooks(EnterSymbolizer, ExitSymbolizer);
 
   InitializeCoverage(common_flags()->coverage, common_flags()->coverage_dir);

compiler-rt/lib/hwasan/hwasan_interface_internal.h

 #ifndef HWASAN_INTERFACE_INTERNAL_H
 #define HWASAN_INTERFACE_INTERNAL_H
 
 #include "sanitizer_common/sanitizer_internal_defs.h"
 
 extern "C" {
 
 SANITIZER_INTERFACE_ATTRIBUTE
+void __hwasan_shadow_init();
+
+SANITIZER_INTERFACE_ATTRIBUTE
 void __hwasan_init();
 
 using __sanitizer::uptr;
 using __sanitizer::sptr;
 using __sanitizer::uu64;
 using __sanitizer::uu32;
 using __sanitizer::uu16;
 using __sanitizer::u64;

compiler-rt/lib/hwasan/hwasan_linux.cc

static void ReserveShadowMemoryRange(uptr beg, uptr end, const char *name) {
   DecreaseTotalMmap(size);  // Don't count the shadow against mmap_limit_mb.
   if (!MmapFixedNoReserve(beg, size, name)) {
     Report(
         "ReserveShadowMemoryRange failed while trying to map 0x%zx bytes. "
         "Perhaps you're using ulimit -v\n",
         size);
     Abort();
   }
-  if (common_flags()->no_huge_pages_for_shadow) NoHugePagesInRegion(beg, size);
-  if (common_flags()->use_madv_dontdump) DontDumpShadowMemory(beg, size);
 }
 
 static void ProtectGap(uptr addr, uptr size) {
   if (!size)
     return;
   void *res = MmapFixedNoAccess(addr, size, "shadow gap");
   if (addr == (uptr)res)
     return;
if (kLowMemEnd + 1 < kHighShadowStart)
       ProtectGap(kLowMemEnd + 1, kHighShadowStart - kLowMemEnd - 1);
   }
   if (kHighShadowEnd + 1 < kHighMemStart)
     ProtectGap(kHighShadowEnd + 1, kHighMemStart - kHighShadowEnd - 1);
 
   return true;
 }
 
+static void MadviseShadowRegion(uptr beg, uptr end) {
+  uptr size = end - beg + 1;
+  if (common_flags()->no_huge_pages_for_shadow)
+    NoHugePagesInRegion(beg, size);
+  if (common_flags()->use_madv_dontdump)
+    DontDumpShadowMemory(beg, size);
+}
+
+void MadviseShadow() {
+  MadviseShadowRegion(kLowShadowStart, kLowShadowEnd);
+  MadviseShadowRegion(kHighShadowStart, kHighShadowEnd);
+}
+
 bool MemIsApp(uptr p) {
   CHECK(GetTagFromPointer(p) == 0);
   return p >= kHighMemStart || (p >= kLowMemStart && p <= kLowMemEnd);
 }
 
 static void HwasanAtExit(void) {
   if (flags()->print_stats && (flags()->atexit || hwasan_report_count > 0))
     ReportStats();