gcc/libsanitizer/asan/asan_globals.cpp

//===-- asan_globals.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
//
//===----------------------------------------------------------------------===//
//
// This file is a part of AddressSanitizer, an address sanity checker.
//
// Handle globals.
//===----------------------------------------------------------------------===//

#include "asan_interceptors.h"
#include "asan_internal.h"
#include "asan_mapping.h"
#include "asan_poisoning.h"
#include "asan_report.h"
#include "asan_stack.h"
#include "asan_stats.h"
#include "asan_suppressions.h"
#include "asan_thread.h"
#include "sanitizer_common/sanitizer_common.h"
#include "sanitizer_common/sanitizer_dense_map.h"
#include "sanitizer_common/sanitizer_list.h"
#include "sanitizer_common/sanitizer_mutex.h"
#include "sanitizer_common/sanitizer_placement_new.h"
#include "sanitizer_common/sanitizer_stackdepot.h"
#include "sanitizer_common/sanitizer_symbolizer.h"
#include "sanitizer_common/sanitizer_thread_safety.h"

namespace __asan {

typedef __asan_global Global;

struct GlobalListNode {
  const Global *g = nullptr;
  GlobalListNode *next = nullptr;
};
typedef IntrusiveList<GlobalListNode> ListOfGlobals;

static Mutex mu_for_globals;
static ListOfGlobals list_of_all_globals SANITIZER_GUARDED_BY(mu_for_globals);

struct DynInitGlobal {
  Global g = {};
  bool initialized = false;
  DynInitGlobal *next = nullptr;
};

// We want to remember where a certain range of globals was registered.
struct GlobalRegistrationSite {
  u32 stack_id;
  Global *g_first, *g_last;
};
typedef InternalMmapVector<GlobalRegistrationSite> GlobalRegistrationSiteVector;
static GlobalRegistrationSiteVector *global_registration_site_vector;

static ListOfGlobals &GlobalsByIndicator(uptr odr_indicator)
    SANITIZER_REQUIRES(mu_for_globals) {
  using MapOfGlobals = DenseMap<uptr, ListOfGlobals>;

  static MapOfGlobals *globals_by_indicator = nullptr;
  if (!globals_by_indicator) {
    alignas(
        alignof(MapOfGlobals)) static char placeholder[sizeof(MapOfGlobals)];
    globals_by_indicator = new (placeholder) MapOfGlobals();
  }

  return (*globals_by_indicator)[odr_indicator];
}

static const char *current_dynamic_init_module_name
    SANITIZER_GUARDED_BY(mu_for_globals) = nullptr;

using DynInitGlobalsByModule =
    DenseMap<const char *, IntrusiveList<DynInitGlobal>>;

// TODO: Add a NoDestroy helper, this patter is very common in sanitizers.
static DynInitGlobalsByModule &DynInitGlobals()
    SANITIZER_REQUIRES(mu_for_globals) {
  static DynInitGlobalsByModule *globals_by_module = nullptr;
  if (!globals_by_module) {
    alignas(alignof(DynInitGlobalsByModule)) static char
        placeholder[sizeof(DynInitGlobalsByModule)];
    globals_by_module = new (placeholder) DynInitGlobalsByModule();
  }

  return *globals_by_module;
}

ALWAYS_INLINE void PoisonShadowForGlobal(const Global *g, u8 value) {
  FastPoisonShadow(g->beg, g->size_with_redzone, value);
}

ALWAYS_INLINE void PoisonRedZones(const Global &g) {
  uptr aligned_size = RoundUpTo(g.size, ASAN_SHADOW_GRANULARITY);
  FastPoisonShadow(g.beg + aligned_size, g.size_with_redzone - aligned_size,
                   kAsanGlobalRedzoneMagic);
  if (g.size != aligned_size) {
    FastPoisonShadowPartialRightRedzone(
        g.beg + RoundDownTo(g.size, ASAN_SHADOW_GRANULARITY),
        g.size % ASAN_SHADOW_GRANULARITY, ASAN_SHADOW_GRANULARITY,
        kAsanGlobalRedzoneMagic);
  }
}

const uptr kMinimalDistanceFromAnotherGlobal = 64;

static void AddGlobalToList(ListOfGlobals &list, const Global *g) {
  list.push_front(new (GetGlobalLowLevelAllocator()) GlobalListNode{g});
}

static void UnpoisonDynamicGlobals(IntrusiveList<DynInitGlobal> &dyn_globals,
                                   bool mark_initialized) {
  for (auto &dyn_g : dyn_globals) {
    const Global *g = &dyn_g.g;
    if (dyn_g.initialized)
      continue;
    // Unpoison the whole global.
    PoisonShadowForGlobal(g, 0);
    // Poison redzones back.
    PoisonRedZones(*g);
    if (mark_initialized)
      dyn_g.initialized = true;
  }
}

static void PoisonDynamicGlobals(
    const IntrusiveList<DynInitGlobal> &dyn_globals) {
  for (auto &dyn_g : dyn_globals) {
    const Global *g = &dyn_g.g;
    if (dyn_g.initialized)
      continue;
    PoisonShadowForGlobal(g, kAsanInitializationOrderMagic);
  }
}

static bool IsAddressNearGlobal(uptr addr, const __asan_global &g) {
  if (addr <= g.beg - kMinimalDistanceFromAnotherGlobal) return false;
  if (addr >= g.beg + g.size_with_redzone) return false;
  return true;
}

static void ReportGlobal(const Global &g, const char *prefix) {
  DataInfo info;
  bool symbolized = Symbolizer::GetOrInit()->SymbolizeData(g.beg, &info);
  Report(
      "%s Global[%p]: beg=%p size=%zu/%zu name=%s source=%s module=%s "
      "dyn_init=%zu "
      "odr_indicator=%p\n",
      prefix, (void *)&g, (void *)g.beg, g.size, g.size_with_redzone, g.name,
      g.module_name, (symbolized ? info.module : "?"), g.has_dynamic_init,
      (void *)g.odr_indicator);

  if (symbolized && info.line != 0) {
    Report("  location: name=%s, %d\n", info.file, static_cast<int>(info.line));
  } else if (g.gcc_location != 0) {
    // Fallback to Global::gcc_location
    Report("  location: name=%s, %d\n", g.gcc_location->filename, g.gcc_location->line_no);
  }
}

static u32 FindRegistrationSite(const Global *g) {
  mu_for_globals.CheckLocked();
  CHECK(global_registration_site_vector);
  for (uptr i = 0, n = global_registration_site_vector->size(); i < n; i++) {
    GlobalRegistrationSite &grs = (*global_registration_site_vector)[i];
    if (g >= grs.g_first && g <= grs.g_last)
      return grs.stack_id;
  }
  return 0;
}

int GetGlobalsForAddress(uptr addr, Global *globals, u32 *reg_sites,
                         int max_globals) {
  if (!flags()->report_globals) return 0;
  Lock lock(&mu_for_globals);
  int res = 0;
  for (const auto &l : list_of_all_globals) {
    const Global &g = *l.g;
    if (flags()->report_globals >= 2)
      ReportGlobal(g, "Search");
    if (IsAddressNearGlobal(addr, g)) {
      internal_memcpy(&globals[res], &g, sizeof(g));
      if (reg_sites)
        reg_sites[res] = FindRegistrationSite(&g);
      res++;
      if (res == max_globals)
        break;
    }
  }
  return res;
}

enum GlobalSymbolState {
  UNREGISTERED = 0,
  REGISTERED = 1
};

// Check ODR violation for given global G via special ODR indicator. We use
// this method in case compiler instruments global variables through their
// local aliases.
static void CheckODRViolationViaIndicator(const Global *g)
    SANITIZER_REQUIRES(mu_for_globals) {
  // Instrumentation requests to skip ODR check.
  if (g->odr_indicator == UINTPTR_MAX)
    return;

  ListOfGlobals &relevant_globals = GlobalsByIndicator(g->odr_indicator);

  u8 *odr_indicator = reinterpret_cast<u8 *>(g->odr_indicator);
  if (*odr_indicator == REGISTERED) {
    // If *odr_indicator is REGISTERED, some module have already registered
    // externally visible symbol with the same name. This is an ODR violation.
    for (const auto &l : relevant_globals) {
      if ((flags()->detect_odr_violation >= 2 || g->size != l.g->size) &&
          !IsODRViolationSuppressed(g->name))
        ReportODRViolation(g, FindRegistrationSite(g), l.g,
                           FindRegistrationSite(l.g));
    }
  } else {  // UNREGISTERED
    *odr_indicator = REGISTERED;
  }

  AddGlobalToList(relevant_globals, g);
}

// Clang provides two different ways for global variables protection:
// it can poison the global itself or its private alias. In former
// case we may poison same symbol multiple times, that can help us to
// cheaply detect ODR violation: if we try to poison an already poisoned
// global, we have ODR violation error.
// In latter case, we poison each symbol exactly once, so we use special
// indicator symbol to perform similar check.
// In either case, compiler provides a special odr_indicator field to Global
// structure, that can contain two kinds of values:
//   1) Non-zero value. In this case, odr_indicator is an address of
//      corresponding indicator variable for given global.
//   2) Zero. This means that we don't use private aliases for global variables
//      and can freely check ODR violation with the first method.
//
// This routine chooses between two different methods of ODR violation
// detection.
static inline bool UseODRIndicator(const Global *g) {
  return g->odr_indicator > 0;
}

// Register a global variable.
// This function may be called more than once for every global
// so we store the globals in a map.
static void RegisterGlobal(const Global *g) SANITIZER_REQUIRES(mu_for_globals) {
  CHECK(AsanInited());
  if (flags()->report_globals >= 2)
    ReportGlobal(*g, "Added");
  CHECK(flags()->report_globals);
  CHECK(AddrIsInMem(g->beg));
  if (!AddrIsAlignedByGranularity(g->beg)) {
    Report("The following global variable is not properly aligned.\n");
    Report("This may happen if another global with the same name\n");
    Report("resides in another non-instrumented module.\n");
    Report("Or the global comes from a C file built w/o -fno-common.\n");
    Report("In either case this is likely an ODR violation bug,\n");
    Report("but AddressSanitizer can not provide more details.\n");
    ReportODRViolation(g, FindRegistrationSite(g), g, FindRegistrationSite(g));
    CHECK(AddrIsAlignedByGranularity(g->beg));
  }
  CHECK(AddrIsAlignedByGranularity(g->size_with_redzone));
  if (flags()->detect_odr_violation) {
    // Try detecting ODR (One Definition Rule) violation, i.e. the situation
    // where two globals with the same name are defined in different modules.
    if (UseODRIndicator(g))
      CheckODRViolationViaIndicator(g);
  }
  if (CanPoisonMemory())
    PoisonRedZones(*g);

  AddGlobalToList(list_of_all_globals, g);

  if (g->has_dynamic_init) {
    DynInitGlobals()[g->module_name].push_back(
        new (GetGlobalLowLevelAllocator()) DynInitGlobal{*g, false});
  }
}

static void UnregisterGlobal(const Global *g)
    SANITIZER_REQUIRES(mu_for_globals) {
  CHECK(AsanInited());
  if (flags()->report_globals >= 2)
    ReportGlobal(*g, "Removed");
  CHECK(flags()->report_globals);
  CHECK(AddrIsInMem(g->beg));
  CHECK(AddrIsAlignedByGranularity(g->beg));
  CHECK(AddrIsAlignedByGranularity(g->size_with_redzone));
  if (CanPoisonMemory())
    PoisonShadowForGlobal(g, 0);
  // We unpoison the shadow memory for the global but we do not remove it from
  // the list because that would require O(n^2) time with the current list
  // implementation. It might not be worth doing anyway.

  // Release ODR indicator.
  if (UseODRIndicator(g) && g->odr_indicator != UINTPTR_MAX) {
    u8 *odr_indicator = reinterpret_cast<u8 *>(g->odr_indicator);
    *odr_indicator = UNREGISTERED;
  }
}

void StopInitOrderChecking() {
  if (!flags()->check_initialization_order)
    return;
  Lock lock(&mu_for_globals);
  flags()->check_initialization_order = false;
  DynInitGlobals().forEach([&](auto &kv) {
    UnpoisonDynamicGlobals(kv.second, /*mark_initialized=*/false);
    return true;
  });
}

static bool IsASCII(unsigned char c) { return /*0x00 <= c &&*/ c <= 0x7F; }

const char *MaybeDemangleGlobalName(const char *name) {
  // We can spoil names of globals with C linkage, so use an heuristic
  // approach to check if the name should be demangled.
  bool should_demangle = false;
  if (name[0] == '_' && name[1] == 'Z')
    should_demangle = true;
  else if (SANITIZER_WINDOWS && name[0] == '\01' && name[1] == '?')
    should_demangle = true;

  return should_demangle ? Symbolizer::GetOrInit()->Demangle(name) : name;
}

// Check if the global is a zero-terminated ASCII string. If so, print it.
void PrintGlobalNameIfASCII(InternalScopedString *str, const __asan_global &g) {
  for (uptr p = g.beg; p < g.beg + g.size - 1; p++) {
    unsigned char c = *(unsigned char *)p;
    if (c == '\0' || !IsASCII(c)) return;
  }
  if (*(char *)(g.beg + g.size - 1) != '\0') return;
  str->AppendF("  '%s' is ascii string '%s'\n", MaybeDemangleGlobalName(g.name),
               (char *)g.beg);
}

void PrintGlobalLocation(InternalScopedString *str, const __asan_global &g,
                         bool print_module_name) {
  DataInfo info;
  if (Symbolizer::GetOrInit()->SymbolizeData(g.beg, &info) && info.line != 0) {
    str->AppendF("%s:%d", info.file, static_cast<int>(info.line));
  } else if (g.gcc_location != 0) {
    // Fallback to Global::gcc_location
    str->AppendF("%s", g.gcc_location->filename ? g.gcc_location->filename
                                                : g.module_name);
    if (g.gcc_location->line_no)
      str->AppendF(":%d", g.gcc_location->line_no);
    if (g.gcc_location->column_no)
      str->AppendF(":%d", g.gcc_location->column_no);
  } else {
    str->AppendF("%s", g.module_name);
  }
  if (print_module_name && info.module)
    str->AppendF(" in %s", info.module);
}

} // namespace __asan

// ---------------------- Interface ---------------- {{{1
using namespace __asan;

// Apply __asan_register_globals to all globals found in the same loaded
// executable or shared library as `flag'. The flag tracks whether globals have
// already been registered or not for this image.
void __asan_register_image_globals(uptr *flag) {
  if (*flag)
    return;
  AsanApplyToGlobals(__asan_register_globals, flag);
  *flag = 1;
}

// This mirrors __asan_register_image_globals.
void __asan_unregister_image_globals(uptr *flag) {
  if (!*flag)
    return;
  AsanApplyToGlobals(__asan_unregister_globals, flag);
  *flag = 0;
}

void __asan_register_elf_globals(uptr *flag, void *start, void *stop) {
  if (*flag || start == stop)
    return;
  CHECK_EQ(0, ((uptr)stop - (uptr)start) % sizeof(__asan_global));
  __asan_global *globals_start = (__asan_global*)start;
  __asan_global *globals_stop = (__asan_global*)stop;
  __asan_register_globals(globals_start, globals_stop - globals_start);
  *flag = 1;
}

void __asan_unregister_elf_globals(uptr *flag, void *start, void *stop) {
  if (!*flag || start == stop)
    return;
  CHECK_EQ(0, ((uptr)stop - (uptr)start) % sizeof(__asan_global));
  __asan_global *globals_start = (__asan_global*)start;
  __asan_global *globals_stop = (__asan_global*)stop;
  __asan_unregister_globals(globals_start, globals_stop - globals_start);
  *flag = 0;
}

// Register an array of globals.
void __asan_register_globals(__asan_global *globals, uptr n) {
  if (!flags()->report_globals) return;
  GET_STACK_TRACE_MALLOC;
  u32 stack_id = StackDepotPut(stack);
  Lock lock(&mu_for_globals);
  if (!global_registration_site_vector) {
    global_registration_site_vector =
        new (GetGlobalLowLevelAllocator()) GlobalRegistrationSiteVector;
    global_registration_site_vector->reserve(128);
  }
  GlobalRegistrationSite site = {stack_id, &globals[0], &globals[n - 1]};
  global_registration_site_vector->push_back(site);
  if (flags()->report_globals >= 2) {
    PRINT_CURRENT_STACK();
    Printf("=== ID %d; %p %p\n", stack_id, (void *)&globals[0],
           (void *)&globals[n - 1]);
  }
  for (uptr i = 0; i < n; i++) {
    if (SANITIZER_WINDOWS && globals[i].beg == 0) {
      // The MSVC incremental linker may pad globals out to 256 bytes. As long
      // as __asan_global is less than 256 bytes large and its size is a power
      // of two, we can skip over the padding.
      static_assert(
          sizeof(__asan_global) < 256 &&
              (sizeof(__asan_global) & (sizeof(__asan_global) - 1)) == 0,
          "sizeof(__asan_global) incompatible with incremental linker padding");
      // If these are padding bytes, the rest of the global should be zero.
      CHECK(globals[i].size == 0 && globals[i].size_with_redzone == 0 &&
            globals[i].name == nullptr && globals[i].module_name == nullptr &&
            globals[i].odr_indicator == 0);
      continue;
    }
    RegisterGlobal(&globals[i]);
  }

  // Poison the metadata. It should not be accessible to user code.
  PoisonShadow(reinterpret_cast<uptr>(globals), n * sizeof(__asan_global),
               kAsanGlobalRedzoneMagic);
}

// Unregister an array of globals.
// We must do this when a shared objects gets dlclosed.
void __asan_unregister_globals(__asan_global *globals, uptr n) {
  if (!flags()->report_globals) return;
  Lock lock(&mu_for_globals);
  for (uptr i = 0; i < n; i++) {
    if (SANITIZER_WINDOWS && globals[i].beg == 0) {
      // Skip globals that look like padding from the MSVC incremental linker.
      // See comment in __asan_register_globals.
      continue;
    }
    UnregisterGlobal(&globals[i]);
  }

  // Unpoison the metadata.
  PoisonShadow(reinterpret_cast<uptr>(globals), n * sizeof(__asan_global), 0);
}

// This method runs immediately prior to dynamic initialization in each TU,
// when all dynamically initialized globals are unpoisoned.  This method
// poisons all global variables not defined in this TU, so that a dynamic
// initializer can only touch global variables in the same TU.
void __asan_before_dynamic_init(const char *module_name) {
  if (!flags()->check_initialization_order || !CanPoisonMemory())
    return;
  bool strict_init_order = flags()->strict_init_order;
  CHECK(module_name);
  CHECK(AsanInited());
  Lock lock(&mu_for_globals);
  if (current_dynamic_init_module_name == module_name)
    return;
  if (flags()->report_globals >= 3)
    Printf("DynInitPoison module: %s\n", module_name);

  if (current_dynamic_init_module_name == nullptr) {
    // First call, poison all globals from other modules.
    DynInitGlobals().forEach([&](auto &kv) {
      if (kv.first != module_name) {
        PoisonDynamicGlobals(kv.second);
      } else {
        UnpoisonDynamicGlobals(kv.second,
                               /*mark_initialized=*/!strict_init_order);
      }
      return true;
    });
  } else {
    // Module changed.
    PoisonDynamicGlobals(DynInitGlobals()[current_dynamic_init_module_name]);
    UnpoisonDynamicGlobals(DynInitGlobals()[module_name],
                           /*mark_initialized=*/!strict_init_order);
  }
  current_dynamic_init_module_name = module_name;
}

// Maybe SANITIZER_CAN_USE_PREINIT_ARRAY is to conservative for `.init_array`,
// however we should not make mistake here. If `UnpoisonBeforeMain` was not
// executed at all we will have false reports on globals.
#if SANITIZER_CAN_USE_PREINIT_ARRAY
// This optimization aims to reduce the overhead of `__asan_after_dynamic_init`
// calls by leveraging incremental unpoisoning/poisoning in
// `__asan_before_dynamic_init`. We expect most `__asan_after_dynamic_init
// calls` to be no-ops. However, to ensure all globals are unpoisoned before the
// `main`, we force `UnpoisonBeforeMain` to fully execute
// `__asan_after_dynamic_init`.

// With lld, `UnpoisonBeforeMain` runs after standard `.init_array`, making it
// the final `__asan_after_dynamic_init` call for the static runtime. In
// contrast, GNU ld executes it earlier, causing subsequent
// `__asan_after_dynamic_init` calls to perform full unpoisoning, losing the
// optimization.
bool allow_after_dynamic_init SANITIZER_GUARDED_BY(mu_for_globals) = false;

static void UnpoisonBeforeMain(void) {
  {
    Lock lock(&mu_for_globals);
    if (allow_after_dynamic_init)
      return;
    allow_after_dynamic_init = true;
  }
  if (flags()->report_globals >= 3)
    Printf("UnpoisonBeforeMain\n");
  __asan_after_dynamic_init();
}

__attribute__((section(".init_array.65537"), used)) static void (
    *asan_after_init_array)(void) = UnpoisonBeforeMain;
#else
// Incremental poisoning is disabled, unpoison globals immediately.
static constexpr bool allow_after_dynamic_init = true;
#endif  // SANITIZER_CAN_USE_PREINIT_ARRAY

// This method runs immediately after dynamic initialization in each TU, when
// all dynamically initialized globals except for those defined in the current
// TU are poisoned.  It simply unpoisons all dynamically initialized globals.
void __asan_after_dynamic_init() {
  if (!flags()->check_initialization_order || !CanPoisonMemory())
    return;
  CHECK(AsanInited());
  Lock lock(&mu_for_globals);
  if (!allow_after_dynamic_init)
    return;
  if (!current_dynamic_init_module_name)
    return;

  if (flags()->report_globals >= 3)
    Printf("DynInitUnpoison\n");

  DynInitGlobals().forEach([&](auto &kv) {
    UnpoisonDynamicGlobals(kv.second, /*mark_initialized=*/false);
    return true;
  });

  current_dynamic_init_module_name = nullptr;
}