gcc/cp/cp-ubsan.cc

   1 /* UndefinedBehaviorSanitizer, undefined behavior detector.
   2    Copyright (C) 2014-2022 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_trap & SANITIZE_VPTR))
  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       suppress_warning (cond, OPT_Wnonnull_compare);
  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 op, *opp;
 122
 123   tree fn = CALL_EXPR_FN (stmt);
 124   if (fn && TREE_CODE (fn) == OBJ_TYPE_REF)
 125     {
 126       /* Virtual function call: Sanitize the use of the object pointer in the
 127          OBJ_TYPE_REF, since the vtable reference will SEGV otherwise (95221).
 128          OBJ_TYPE_REF_EXPR is ptr->vptr[N] and OBJ_TYPE_REF_OBJECT is ptr.  But
 129          we can't be sure of finding OBJ_TYPE_REF_OBJECT in OBJ_TYPE_REF_EXPR
 130          if the latter has been optimized, so we use a COMPOUND_EXPR below.  */
 131       opp = &OBJ_TYPE_REF_EXPR (fn);
 132       op = OBJ_TYPE_REF_OBJECT (fn);
 133     }
 134   else
 135     {
 136       /* Non-virtual call: Sanitize the 'this' argument.  */
 137       opp = &CALL_EXPR_ARG (stmt, 0);
 138       if (*opp == error_mark_node
 139           || !INDIRECT_TYPE_P (TREE_TYPE (*opp)))
 140         return;
 141       while (TREE_CODE (*opp) == COMPOUND_EXPR)
 142         opp = &TREE_OPERAND (*opp, 1);
 143       op = *opp;
 144     }
 145   op = cp_ubsan_maybe_instrument_vptr (EXPR_LOCATION (stmt), op,
 146                                        TREE_TYPE (TREE_TYPE (op)),
 147                                        true, UBSAN_MEMBER_CALL);
 148   if (!op)
 149     /* No change.  */;
 150   else if (fn && TREE_CODE (fn) == OBJ_TYPE_REF)
 151     *opp = cp_build_compound_expr (op, *opp, tf_none);
 152   else
 153     *opp = op;
 154 }
 155
 156 /* Data passed to cp_ubsan_check_member_access_r.  */
 157
 158 struct cp_ubsan_check_member_access_data
 159 {
 160   hash_set<tree> *pset;
 161   bool is_addr;
 162 };
 163
 164 static tree cp_ubsan_check_member_access_r (tree *, int *, void *);
 165
 166 /* Instrument a member access.  */
 167
 168 static bool
 169 cp_ubsan_maybe_instrument_member_access
 170      (tree stmt, cp_ubsan_check_member_access_data *ucmd)
 171 {
 172   if (DECL_ARTIFICIAL (TREE_OPERAND (stmt, 1)))
 173     return false;
 174
 175   tree base = TREE_OPERAND (stmt, 0);
 176   if (!cp_ubsan_instrument_vptr_p (TREE_TYPE (base)))
 177     return false;
 178
 179   cp_walk_tree (&base, cp_ubsan_check_member_access_r, ucmd, ucmd->pset);
 180
 181   base = cp_ubsan_instrument_vptr (EXPR_LOCATION (stmt), base,
 182                                    TREE_TYPE (base), false,
 183                                    UBSAN_MEMBER_ACCESS);
 184   TREE_OPERAND (stmt, 0)
 185     = build_fold_indirect_ref_loc (EXPR_LOCATION (stmt), base);
 186   return true;
 187 }
 188
 189 /* Attempt to instrument member accesses inside of the function.
 190    cp_ubsan_maybe_instrument_member_access should be called on COMPONENT_REFs
 191    in the GENERIC IL, but only when the field is actually accessed, not
 192    merely when it's address is taken.  Therefore we track in is_addr field
 193    whether in the current context we are processing address taken
 194    handled components or not.  E.g. for &x->y[w->z] we want to call
 195    cp_ubsan_maybe_instrument_member_access on *w.z COMPONENT_REF, but
 196    not on *x.y.  */
 197
 198 static tree
 199 cp_ubsan_check_member_access_r (tree *stmt_p, int *walk_subtrees, void *data)
 200 {
 201   tree stmt = *stmt_p, t;
 202   cp_ubsan_check_member_access_data *ucmd
 203     = (cp_ubsan_check_member_access_data *) data;
 204   switch (TREE_CODE (stmt))
 205     {
 206     case ADDR_EXPR:
 207       t = TREE_OPERAND (stmt, 0);
 208       while ((TREE_CODE (t) == MEM_REF || INDIRECT_REF_P (t))
 209              && TREE_CODE (TREE_OPERAND (t, 0)) == ADDR_EXPR)
 210         t = TREE_OPERAND (TREE_OPERAND (t, 0), 0);
 211       if (handled_component_p (t))
 212         {
 213           *walk_subtrees = 0;
 214           ucmd->is_addr = true;
 215           cp_walk_tree (&t, cp_ubsan_check_member_access_r,
 216                         data, ucmd->pset);
 217           ucmd->is_addr = false;
 218         }
 219       break;
 220     case MEM_REF:
 221     case INDIRECT_REF:
 222       t = TREE_OPERAND (stmt, 0);
 223       if (TREE_CODE (t) == ADDR_EXPR)
 224         {
 225           *walk_subtrees = 0;
 226           t = TREE_OPERAND (t, 0);
 227           cp_walk_tree (&t, cp_ubsan_check_member_access_r, data, ucmd->pset);
 228         }
 229       break;
 230     case COMPONENT_REF:
 231       if (!ucmd->is_addr && cp_ubsan_maybe_instrument_member_access (stmt, ucmd))
 232         {
 233           *walk_subtrees = 0;
 234           break;
 235         }
 236       /* FALLTHRU */
 237     default:
 238       if (ucmd->is_addr && handled_component_p (stmt))
 239         {
 240           int i, len = TREE_OPERAND_LENGTH (stmt);
 241           *walk_subtrees = 0;
 242           if (!handled_component_p (TREE_OPERAND (stmt, 0)))
 243             ucmd->is_addr = false;
 244           for (i = 0; i < len; i++)
 245             {
 246               cp_walk_tree (&TREE_OPERAND (stmt, i),
 247                             cp_ubsan_check_member_access_r, data, ucmd->pset);
 248               ucmd->is_addr = false;
 249             }
 250           ucmd->is_addr = true;
 251         }
 252       break;
 253     }
 254   return NULL_TREE;
 255 }
 256
 257 /* Instrument all member accesses inside GENERIC *T_P.  */
 258
 259 void
 260 cp_ubsan_instrument_member_accesses (tree *t_p)
 261 {
 262   if (cp_ubsan_instrument_vptr_p (NULL_TREE))
 263     {
 264       hash_set<tree> pset;
 265       cp_ubsan_check_member_access_data ucmd;
 266       ucmd.pset = &pset;
 267       ucmd.is_addr = false;
 268       cp_walk_tree (t_p, cp_ubsan_check_member_access_r, &ucmd, &pset);
 269     }
 270 }
 271
 272 /* Instrument downcast.  */
 273
 274 tree
 275 cp_ubsan_maybe_instrument_downcast (location_t loc, tree type,
 276                                     tree intype, tree op)
 277 {
 278   if (!INDIRECT_TYPE_P (type)
 279       || !INDIRECT_TYPE_P (intype)
 280       || !INDIRECT_TYPE_P (TREE_TYPE (op))
 281       || !CLASS_TYPE_P (TREE_TYPE (TREE_TYPE (op)))
 282       || !is_properly_derived_from (TREE_TYPE (type), TREE_TYPE (intype)))
 283     return NULL_TREE;
 284
 285   return cp_ubsan_maybe_instrument_vptr (loc, op, TREE_TYPE (type), true,
 286                                          TYPE_PTR_P (type)
 287                                          ? UBSAN_DOWNCAST_POINTER
 288                                          : UBSAN_DOWNCAST_REFERENCE);
 289 }
 290
 291 /* Instrument cast to virtual base.  */
 292
 293 tree
 294 cp_ubsan_maybe_instrument_cast_to_vbase (location_t loc, tree type, tree op)
 295 {
 296   return cp_ubsan_maybe_instrument_vptr (loc, op, type, true,
 297                                          UBSAN_CAST_TO_VBASE);
 298 }
 299
 300 /* Called from initialize_vtbl_ptrs via dfs_walk.  BINFO is the base
 301    which we want to initialize the vtable pointer for, DATA is
 302    TREE_LIST whose TREE_VALUE is the this ptr expression.  */
 303
 304 static tree
 305 cp_ubsan_dfs_initialize_vtbl_ptrs (tree binfo, void *data)
 306 {
 307   if (!TYPE_CONTAINS_VPTR_P (BINFO_TYPE (binfo)))
 308     return dfs_skip_bases;
 309
 310   if (!BINFO_PRIMARY_P (binfo))
 311     {
 312       tree base_ptr = TREE_VALUE ((tree) data);
 313
 314       base_ptr = build_base_path (PLUS_EXPR, base_ptr, binfo, /*nonnull=*/1,
 315                                   tf_warning_or_error);
 316
 317       /* Compute the location of the vtpr.  */
 318       tree vtbl_ptr
 319         = build_vfield_ref (cp_build_fold_indirect_ref (base_ptr),
 320                             TREE_TYPE (binfo));
 321       gcc_assert (vtbl_ptr != error_mark_node);
 322
 323       /* Assign NULL to the vptr.  */
 324       tree vtbl = build_zero_cst (TREE_TYPE (vtbl_ptr));
 325       tree stmt = cp_build_modify_expr (input_location, vtbl_ptr, NOP_EXPR,
 326                                         vtbl, tf_warning_or_error);
 327       if (vptr_via_virtual_p (binfo))
 328         /* If this vptr comes from a virtual base of the complete object, only
 329            clear it if we're in charge of virtual bases.  */
 330         stmt = build_if_in_charge (stmt);
 331       finish_expr_stmt (stmt);
 332     }
 333
 334   return NULL_TREE;
 335 }
 336
 337 /* Initialize all the vtable pointers in the object pointed to by
 338    ADDR to NULL, so that we catch invalid calls to methods before
 339    mem-initializers are completed.  */
 340
 341 void
 342 cp_ubsan_maybe_initialize_vtbl_ptrs (tree addr)
 343 {
 344   if (!cp_ubsan_instrument_vptr_p (NULL_TREE))
 345     return;
 346
 347   tree type = TREE_TYPE (TREE_TYPE (addr));
 348   tree list = build_tree_list (type, addr);
 349   /* We cannot rely on the vtable being set up.  We have to indirect via the
 350      vtt_parm.  */
 351   int save_in_base_initializer = in_base_initializer;
 352   in_base_initializer = 1;
 353
 354   /* Walk through the hierarchy, initializing the vptr in each base
 355      class to NULL.  */
 356   dfs_walk_once (TYPE_BINFO (type), cp_ubsan_dfs_initialize_vtbl_ptrs,
 357                  NULL, list);
 358
 359   in_base_initializer = save_in_base_initializer;
 360 }