gcc/cp/cp-ubsan.c

   1 /* UndefinedBehaviorSanitizer, undefined behavior detector.
   2    Copyright (C) 2014-2018 Free Software Foundation, Inc.
   3    Contributed by Jakub Jelinek <jakub@redhat.com>
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "cp-tree.h"
  25 #include "ubsan.h"
  26 #include "stringpool.h"
  27 #include "attribs.h"
  28 #include "asan.h"
  29
  30 /* Test if we should instrument vptr access.  */
  31
  32 static bool
  33 cp_ubsan_instrument_vptr_p (tree type)
  34 {
  35   if (!flag_rtti || flag_sanitize_undefined_trap_on_error)
  36     return false;
  37
  38   if (!sanitize_flags_p (SANITIZE_VPTR))
  39     return false;
  40
  41   if (current_function_decl == NULL_TREE)
  42     return false;
  43
  44   if (type)
  45     {
  46       type = TYPE_MAIN_VARIANT (type);
  47       if (!CLASS_TYPE_P (type) || !CLASSTYPE_VTABLES (type))
  48         return false;
  49     }
  50
  51   return true;
  52 }
  53
  54 /* Helper function for
  55    cp_ubsan_maybe_instrument_{member_{call,access},downcast}.
  56    Instrument vptr access.  */
  57
  58 static tree
  59 cp_ubsan_instrument_vptr (location_t loc, tree op, tree type, bool is_addr,
  60                           enum ubsan_null_ckind ckind)
  61 {
  62   type = TYPE_MAIN_VARIANT (type);
  63   const char *mangled = mangle_type_string (type);
  64   hashval_t str_hash1 = htab_hash_string (mangled);
  65   hashval_t str_hash2 = iterative_hash (mangled, strlen (mangled), 0);
  66   tree str_hash = wide_int_to_tree (uint64_type_node,
  67                                     wi::uhwi (((uint64_t) str_hash1 << 32)
  68                                               | str_hash2, 64));
  69   if (!is_addr)
  70     op = build_fold_addr_expr_loc (loc, op);
  71   op = save_expr (op);
  72   tree vptr = fold_build3_loc (loc, COMPONENT_REF,
  73                                TREE_TYPE (TYPE_VFIELD (type)),
  74                                build_fold_indirect_ref_loc (loc, op),
  75                                TYPE_VFIELD (type), NULL_TREE);
  76   vptr = fold_convert_loc (loc, pointer_sized_int_node, vptr);
  77   vptr = fold_convert_loc (loc, uint64_type_node, vptr);
  78   if (ckind == UBSAN_DOWNCAST_POINTER)
  79     {
  80       tree cond = build2_loc (loc, NE_EXPR, boolean_type_node, op,
  81                               build_zero_cst (TREE_TYPE (op)));
  82       /* This is a compiler generated comparison, don't emit
  83          e.g. -Wnonnull-compare warning for it.  */
  84       TREE_NO_WARNING (cond) = 1;
  85       vptr = build3_loc (loc, COND_EXPR, uint64_type_node, cond,
  86                          vptr, build_int_cst (uint64_type_node, 0));
  87     }
  88   tree ti_decl = get_tinfo_decl (type);
  89   mark_used (ti_decl);
  90   tree ptype = build_pointer_type (type);
  91   tree call
  92     = build_call_expr_internal_loc (loc, IFN_UBSAN_VPTR,
  93                                     void_type_node, 5, op, vptr, str_hash,
  94                                     build_address (ti_decl),
  95                                     build_int_cst (ptype, ckind));
  96   TREE_SIDE_EFFECTS (call) = 1;
  97   return fold_build2 (COMPOUND_EXPR, TREE_TYPE (op), call, op);
  98 }
  99
 100 /* Helper function for
 101    cp_ubsan_maybe_instrument_{member_{call,access},downcast}.
 102    Instrument vptr access if it should be instrumented, otherwise return
 103    NULL_TREE.  */
 104
 105 static tree
 106 cp_ubsan_maybe_instrument_vptr (location_t loc, tree op, tree type,
 107                                 bool is_addr, enum ubsan_null_ckind ckind)
 108 {
 109   if (!cp_ubsan_instrument_vptr_p (type))
 110     return NULL_TREE;
 111   return cp_ubsan_instrument_vptr (loc, op, type, is_addr, ckind);
 112 }
 113
 114 /* Instrument a member call (but not constructor call) if needed.  */
 115
 116 void
 117 cp_ubsan_maybe_instrument_member_call (tree stmt)
 118 {
 119   if (call_expr_nargs (stmt) == 0)
 120     return;
 121   tree *opp = &CALL_EXPR_ARG (stmt, 0);
 122   tree op = *opp;
 123   if (op == error_mark_node
 124       || !POINTER_TYPE_P (TREE_TYPE (op)))
 125     return;
 126   while (TREE_CODE (op) == COMPOUND_EXPR)
 127     {
 128       opp = &TREE_OPERAND (op, 1);
 129       op = *opp;
 130     }
 131   op = cp_ubsan_maybe_instrument_vptr (EXPR_LOCATION (stmt), op,
 132                                        TREE_TYPE (TREE_TYPE (op)),
 133                                        true, UBSAN_MEMBER_CALL);
 134   if (op)
 135     *opp = op;
 136 }
 137
 138 /* Data passed to cp_ubsan_check_member_access_r.  */
 139
 140 struct cp_ubsan_check_member_access_data
 141 {
 142   hash_set<tree> *pset;
 143   bool is_addr;
 144 };
 145
 146 static tree cp_ubsan_check_member_access_r (tree *, int *, void *);
 147
 148 /* Instrument a member access.  */
 149
 150 static bool
 151 cp_ubsan_maybe_instrument_member_access
 152      (tree stmt, cp_ubsan_check_member_access_data *ucmd)
 153 {
 154   if (DECL_ARTIFICIAL (TREE_OPERAND (stmt, 1)))
 155     return false;
 156
 157   tree base = TREE_OPERAND (stmt, 0);
 158   if (!cp_ubsan_instrument_vptr_p (TREE_TYPE (base)))
 159     return false;
 160
 161   cp_walk_tree (&base, cp_ubsan_check_member_access_r, ucmd, ucmd->pset);
 162
 163   base = cp_ubsan_instrument_vptr (EXPR_LOCATION (stmt), base,
 164                                    TREE_TYPE (base), false,
 165                                    UBSAN_MEMBER_ACCESS);
 166   TREE_OPERAND (stmt, 0)
 167     = build_fold_indirect_ref_loc (EXPR_LOCATION (stmt), base);
 168   return true;
 169 }
 170
 171 /* Attempt to instrument member accesses inside of the function.
 172    cp_ubsan_maybe_instrument_member_access should be called on COMPONENT_REFs
 173    in the GENERIC IL, but only when the field is actually accessed, not
 174    merely when it's address is taken.  Therefore we track in is_addr field
 175    whether in the current context we are processing address taken
 176    handled components or not.  E.g. for &x->y[w->z] we want to call
 177    cp_ubsan_maybe_instrument_member_access on *w.z COMPONENT_REF, but
 178    not on *x.y.  */
 179
 180 static tree
 181 cp_ubsan_check_member_access_r (tree *stmt_p, int *walk_subtrees, void *data)
 182 {
 183   tree stmt = *stmt_p, t;
 184   cp_ubsan_check_member_access_data *ucmd
 185     = (cp_ubsan_check_member_access_data *) data;
 186   switch (TREE_CODE (stmt))
 187     {
 188     case ADDR_EXPR:
 189       t = TREE_OPERAND (stmt, 0);
 190       while ((TREE_CODE (t) == MEM_REF || INDIRECT_REF_P (t))
 191              && TREE_CODE (TREE_OPERAND (t, 0)) == ADDR_EXPR)
 192         t = TREE_OPERAND (TREE_OPERAND (t, 0), 0);
 193       if (handled_component_p (t))
 194         {
 195           *walk_subtrees = 0;
 196           ucmd->is_addr = true;
 197           cp_walk_tree (&t, cp_ubsan_check_member_access_r,
 198                         data, ucmd->pset);
 199           ucmd->is_addr = false;
 200         }
 201       break;
 202     case MEM_REF:
 203     case INDIRECT_REF:
 204       t = TREE_OPERAND (stmt, 0);
 205       if (TREE_CODE (t) == ADDR_EXPR)
 206         {
 207           *walk_subtrees = 0;
 208           t = TREE_OPERAND (t, 0);
 209           cp_walk_tree (&t, cp_ubsan_check_member_access_r, data, ucmd->pset);
 210         }
 211       break;
 212     case COMPONENT_REF:
 213       if (!ucmd->is_addr && cp_ubsan_maybe_instrument_member_access (stmt, ucmd))
 214         {
 215           *walk_subtrees = 0;
 216           break;
 217         }
 218       /* FALLTHRU */
 219     default:
 220       if (ucmd->is_addr && handled_component_p (stmt))
 221         {
 222           int i, len = TREE_OPERAND_LENGTH (stmt);
 223           *walk_subtrees = 0;
 224           if (!handled_component_p (TREE_OPERAND (stmt, 0)))
 225             ucmd->is_addr = false;
 226           for (i = 0; i < len; i++)
 227             {
 228               cp_walk_tree (&TREE_OPERAND (stmt, i),
 229                             cp_ubsan_check_member_access_r, data, ucmd->pset);
 230               ucmd->is_addr = false;
 231             }
 232           ucmd->is_addr = true;
 233         }
 234       break;
 235     }
 236   return NULL_TREE;
 237 }
 238
 239 /* Instrument all member accesses inside GENERIC *T_P.  */
 240
 241 void
 242 cp_ubsan_instrument_member_accesses (tree *t_p)
 243 {
 244   if (cp_ubsan_instrument_vptr_p (NULL_TREE))
 245     {
 246       hash_set<tree> pset;
 247       cp_ubsan_check_member_access_data ucmd;
 248       ucmd.pset = &pset;
 249       ucmd.is_addr = false;
 250       cp_walk_tree (t_p, cp_ubsan_check_member_access_r, &ucmd, &pset);
 251     }
 252 }
 253
 254 /* Instrument downcast.  */
 255
 256 tree
 257 cp_ubsan_maybe_instrument_downcast (location_t loc, tree type,
 258                                     tree intype, tree op)
 259 {
 260   if (!POINTER_TYPE_P (type)
 261       || !POINTER_TYPE_P (intype)
 262       || !POINTER_TYPE_P (TREE_TYPE (op))
 263       || !CLASS_TYPE_P (TREE_TYPE (TREE_TYPE (op)))
 264       || !is_properly_derived_from (TREE_TYPE (type), TREE_TYPE (intype)))
 265     return NULL_TREE;
 266
 267   return cp_ubsan_maybe_instrument_vptr (loc, op, TREE_TYPE (type), true,
 268                                          TYPE_PTR_P (type)
 269                                          ? UBSAN_DOWNCAST_POINTER
 270                                          : UBSAN_DOWNCAST_REFERENCE);
 271 }
 272
 273 /* Instrument cast to virtual base.  */
 274
 275 tree
 276 cp_ubsan_maybe_instrument_cast_to_vbase (location_t loc, tree type, tree op)
 277 {
 278   return cp_ubsan_maybe_instrument_vptr (loc, op, type, true,
 279                                          UBSAN_CAST_TO_VBASE);
 280 }
 281
 282 /* Called from initialize_vtbl_ptrs via dfs_walk.  BINFO is the base
 283    which we want to initialize the vtable pointer for, DATA is
 284    TREE_LIST whose TREE_VALUE is the this ptr expression.  */
 285
 286 static tree
 287 cp_ubsan_dfs_initialize_vtbl_ptrs (tree binfo, void *data)
 288 {
 289   if (!TYPE_CONTAINS_VPTR_P (BINFO_TYPE (binfo)))
 290     return dfs_skip_bases;
 291
 292   if (!BINFO_PRIMARY_P (binfo))
 293     {
 294       tree base_ptr = TREE_VALUE ((tree) data);
 295
 296       base_ptr = build_base_path (PLUS_EXPR, base_ptr, binfo, /*nonnull=*/1,
 297                                   tf_warning_or_error);
 298
 299       /* Compute the location of the vtpr.  */
 300       tree vtbl_ptr
 301         = build_vfield_ref (cp_build_fold_indirect_ref (base_ptr),
 302                             TREE_TYPE (binfo));
 303       gcc_assert (vtbl_ptr != error_mark_node);
 304
 305       /* Assign NULL to the vptr.  */
 306       tree vtbl = build_zero_cst (TREE_TYPE (vtbl_ptr));
 307       tree stmt = cp_build_modify_expr (input_location, vtbl_ptr, NOP_EXPR,
 308                                         vtbl, tf_warning_or_error);
 309       if (vptr_via_virtual_p (binfo))
 310         /* If this vptr comes from a virtual base of the complete object, only
 311            clear it if we're in charge of virtual bases.  */
 312         stmt = build_if_in_charge (stmt);
 313       finish_expr_stmt (stmt);
 314     }
 315
 316   return NULL_TREE;
 317 }
 318
 319 /* Initialize all the vtable pointers in the object pointed to by
 320    ADDR to NULL, so that we catch invalid calls to methods before
 321    mem-initializers are completed.  */
 322
 323 void
 324 cp_ubsan_maybe_initialize_vtbl_ptrs (tree addr)
 325 {
 326   if (!cp_ubsan_instrument_vptr_p (NULL_TREE))
 327     return;
 328
 329   tree type = TREE_TYPE (TREE_TYPE (addr));
 330   tree list = build_tree_list (type, addr);
 331   /* We cannot rely on the vtable being set up.  We have to indirect via the
 332      vtt_parm.  */
 333   int save_in_base_initializer = in_base_initializer;
 334   in_base_initializer = 1;
 335
 336   /* Walk through the hierarchy, initializing the vptr in each base
 337      class to NULL.  */
 338   dfs_walk_once (TYPE_BINFO (type), cp_ubsan_dfs_initialize_vtbl_ptrs,
 339                  NULL, list);
 340
 341   in_base_initializer = save_in_base_initializer;
 342 }