lib/dfsan/dfsan.cc

//===-- dfsan.cc ----------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is a part of DataFlowSanitizer.
//
// DataFlowSanitizer runtime.  This file defines the public interface to
// DataFlowSanitizer as well as the definition of certain runtime functions
// called automatically by the compiler (specifically the instrumentation pass
// in llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp).
//
// The public interface is defined in include/sanitizer/dfsan_interface.h whose
// functions are prefixed dfsan_ while the compiler interface functions are
// prefixed __dfsan_.
//===----------------------------------------------------------------------===//

#include "sanitizer_common/sanitizer_atomic.h"
#include "sanitizer_common/sanitizer_common.h"
#include "sanitizer_common/sanitizer_flags.h"
#include "sanitizer_common/sanitizer_libc.h"

#include "dfsan/dfsan.h"

using namespace __dfsan;

typedef atomic_uint16_t atomic_dfsan_label;
static const dfsan_label kInitializingLabel = -1;

static const uptr kNumLabels = 1 << (sizeof(dfsan_label) * 8);

static atomic_dfsan_label __dfsan_last_label;
static dfsan_label_info __dfsan_label_info[kNumLabels];

Flags __dfsan::flags_data;

SANITIZER_INTERFACE_ATTRIBUTE THREADLOCAL dfsan_label __dfsan_retval_tls;
SANITIZER_INTERFACE_ATTRIBUTE THREADLOCAL dfsan_label __dfsan_arg_tls[64];

// On Linux/x86_64, memory is laid out as follows:
//
// +--------------------+ 0x800000000000 (top of memory)
// | application memory |
// +--------------------+ 0x700000008000 (kAppAddr)
// |                    |
// |       unused       |
// |                    |
// +--------------------+ 0x200200000000 (kUnusedAddr)
// |    union table     |
// +--------------------+ 0x200000000000 (kUnionTableAddr)
// |   shadow memory    |
// +--------------------+ 0x000000010000 (kShadowAddr)
// | reserved by kernel |
// +--------------------+ 0x000000000000
//
// To derive a shadow memory address from an application memory address,
// bits 44-46 are cleared to bring the address into the range
// [0x000000008000,0x100000000000).  Then the address is shifted left by 1 to
// account for the double byte representation of shadow labels and move the
// address into the shadow memory range.  See the function shadow_for below.

typedef atomic_dfsan_label dfsan_union_table_t[kNumLabels][kNumLabels];

static const uptr kShadowAddr = 0x10000;
static const uptr kUnionTableAddr = 0x200000000000;
static const uptr kUnusedAddr = kUnionTableAddr + sizeof(dfsan_union_table_t);
static const uptr kAppAddr = 0x700000008000;

static atomic_dfsan_label *union_table(dfsan_label l1, dfsan_label l2) {
  return &(*(dfsan_union_table_t *) kUnionTableAddr)[l1][l2];
}

// Resolves the union of two unequal labels.  Nonequality is a precondition for
// this function (the instrumentation pass inlines the equality test).
extern "C" SANITIZER_INTERFACE_ATTRIBUTE
dfsan_label __dfsan_union(dfsan_label l1, dfsan_label l2) {
  DCHECK_NE(l1, l2);

  if (l1 == 0)
    return l2;
  if (l2 == 0)
    return l1;

  if (l1 > l2)
    Swap(l1, l2);

  atomic_dfsan_label *table_ent = union_table(l1, l2);
  // We need to deal with the case where two threads concurrently request
  // a union of the same pair of labels.  If the table entry is uninitialized,
  // (i.e. 0) use a compare-exchange to set the entry to kInitializingLabel
  // (i.e. -1) to mark that we are initializing it.
  dfsan_label label = 0;
  if (atomic_compare_exchange_strong(table_ent, &label, kInitializingLabel,
                                     memory_order_acquire)) {
    // Check whether l2 subsumes l1.  We don't need to check whether l1
    // subsumes l2 because we are guaranteed here that l1 < l2, and (at least
    // in the cases we are interested in) a label may only subsume labels
    // created earlier (i.e. with a lower numerical value).
    if (__dfsan_label_info[l2].l1 == l1 ||
        __dfsan_label_info[l2].l2 == l1) {
      label = l2;
    } else {
      label =
        atomic_fetch_add(&__dfsan_last_label, 1, memory_order_relaxed) + 1;
      CHECK_NE(label, kInitializingLabel);
      __dfsan_label_info[label].l1 = l1;
      __dfsan_label_info[label].l2 = l2;
    }
    atomic_store(table_ent, label, memory_order_release);
  } else if (label == kInitializingLabel) {
    // Another thread is initializing the entry.  Wait until it is finished.
    do {
      internal_sched_yield();
      label = atomic_load(table_ent, memory_order_acquire);
    } while (label == kInitializingLabel);
  }
  return label;
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE
dfsan_label __dfsan_union_load(const dfsan_label *ls, uptr n) {
  dfsan_label label = ls[0];
  for (uptr i = 1; i != n; ++i) {
    dfsan_label next_label = ls[i];
    if (label != next_label)
      label = __dfsan_union(label, next_label);
  }
  return label;
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE
void __dfsan_unimplemented(char *fname) {
  if (flags().warn_unimplemented)
    Report("WARNING: DataFlowSanitizer: call to uninstrumented function %s\n",
           fname);
}

// Use '-mllvm -dfsan-debug-nonzero-labels' and break on this function
// to try to figure out where labels are being introduced in a nominally
// label-free program.
extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __dfsan_nonzero_label() {
  if (flags().warn_nonzero_labels)
    Report("WARNING: DataFlowSanitizer: saw nonzero label\n");
}

// Like __dfsan_union, but for use from the client or custom functions.  Hence
// the equality comparison is done here before calling __dfsan_union.
SANITIZER_INTERFACE_ATTRIBUTE dfsan_label
dfsan_union(dfsan_label l1, dfsan_label l2) {
  if (l1 == l2)
    return l1;
  return __dfsan_union(l1, l2);
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE
dfsan_label dfsan_create_label(const char *desc, void *userdata) {
  dfsan_label label =
    atomic_fetch_add(&__dfsan_last_label, 1, memory_order_relaxed) + 1;
  CHECK_NE(label, kInitializingLabel);
  __dfsan_label_info[label].l1 = __dfsan_label_info[label].l2 = 0;
  __dfsan_label_info[label].desc = desc;
  __dfsan_label_info[label].userdata = userdata;
  return label;
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE
void __dfsan_set_label(dfsan_label label, void *addr, uptr size) {
  for (dfsan_label *labelp = shadow_for(addr); size != 0; --size, ++labelp)
    *labelp = label;
}

SANITIZER_INTERFACE_ATTRIBUTE
void dfsan_set_label(dfsan_label label, void *addr, uptr size) {
  __dfsan_set_label(label, addr, size);
}

SANITIZER_INTERFACE_ATTRIBUTE
void dfsan_add_label(dfsan_label label, void *addr, uptr size) {
  for (dfsan_label *labelp = shadow_for(addr); size != 0; --size, ++labelp)
    if (*labelp != label)
      *labelp = __dfsan_union(*labelp, label);
}

// Unlike the other dfsan interface functions the behavior of this function
// depends on the label of one of its arguments.  Hence it is implemented as a
// custom function.
extern "C" SANITIZER_INTERFACE_ATTRIBUTE dfsan_label
__dfsw_dfsan_get_label(long data, dfsan_label data_label,
                       dfsan_label *ret_label) {
  *ret_label = 0;
  return data_label;
}

SANITIZER_INTERFACE_ATTRIBUTE dfsan_label
dfsan_read_label(const void *addr, uptr size) {
  if (size == 0)
    return 0;
  return __dfsan_union_load(shadow_for(addr), size);
}

SANITIZER_INTERFACE_ATTRIBUTE
const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label) {
  return &__dfsan_label_info[label];
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE int
dfsan_has_label(dfsan_label label, dfsan_label elem) {
  if (label == elem)
    return true;
  const dfsan_label_info *info = dfsan_get_label_info(label);
  if (info->l1 != 0) {
    return dfsan_has_label(info->l1, elem) || dfsan_has_label(info->l2, elem);
  } else {
    return false;
  }
}

extern "C" SANITIZER_INTERFACE_ATTRIBUTE dfsan_label
dfsan_has_label_with_desc(dfsan_label label, const char *desc) {
  const dfsan_label_info *info = dfsan_get_label_info(label);
  if (info->l1 != 0) {
    return dfsan_has_label_with_desc(info->l1, desc) ||
           dfsan_has_label_with_desc(info->l2, desc);
  } else {
    return internal_strcmp(desc, info->desc) == 0;
  }
}

static void InitializeFlags(Flags &f, const char *env) {
  f.warn_unimplemented = true;
  f.warn_nonzero_labels = false;

  ParseFlag(env, &f.warn_unimplemented, "warn_unimplemented");
  ParseFlag(env, &f.warn_nonzero_labels, "warn_nonzero_labels");
}

#ifdef DFSAN_NOLIBC
extern "C" void dfsan_init() {
#else
static void dfsan_init(int argc, char **argv, char **envp) {
#endif
  MmapFixedNoReserve(kShadowAddr, kUnusedAddr - kShadowAddr);

  // Protect the region of memory we don't use, to preserve the one-to-one
  // mapping from application to shadow memory. But if ASLR is disabled, Linux
  // will load our executable in the middle of our unused region. This mostly
  // works so long as the program doesn't use too much memory. We support this
  // case by disabling memory protection when ASLR is disabled.
  uptr init_addr = (uptr)&dfsan_init;
  if (!(init_addr >= kUnusedAddr && init_addr < kAppAddr))
    Mprotect(kUnusedAddr, kAppAddr - kUnusedAddr);

  InitializeFlags(flags(), GetEnv("DFSAN_OPTIONS"));

  InitializeInterceptors();
}

#ifndef DFSAN_NOLIBC
__attribute__((section(".preinit_array"), used))
static void (*dfsan_init_ptr)(int, char **, char **) = dfsan_init;
#endif