gcc/c-family/c-ubsan.c

   1 /* UndefinedBehaviorSanitizer, undefined behavior detector.
   2    Copyright (C) 2013-2016 Free Software Foundation, Inc.
   3    Contributed by Marek Polacek <polacek@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 "tm.h"
  25 #include "c-family/c-common.h"
  26 #include "ubsan.h"
  27 #include "c-family/c-ubsan.h"
  28 #include "asan.h"
  29 #include "stor-layout.h"
  30 #include "builtins.h"
  31 #include "gimplify.h"
  32
  33 /* Instrument division by zero and INT_MIN / -1.  If not instrumenting,
  34    return NULL_TREE.  */
  35
  36 tree
  37 ubsan_instrument_division (location_t loc, tree op0, tree op1)
  38 {
  39   tree t, tt;
  40   tree type = TREE_TYPE (op0);
  41
  42   /* At this point both operands should have the same type,
  43      because they are already converted to RESULT_TYPE.
  44      Use TYPE_MAIN_VARIANT since typedefs can confuse us.  */
  45   gcc_assert (TYPE_MAIN_VARIANT (TREE_TYPE (op0))
  46               == TYPE_MAIN_VARIANT (TREE_TYPE (op1)));
  47
  48   op0 = unshare_expr (op0);
  49   op1 = unshare_expr (op1);
  50
  51   if (TREE_CODE (type) == INTEGER_TYPE
  52       && (flag_sanitize & SANITIZE_DIVIDE))
  53     t = fold_build2 (EQ_EXPR, boolean_type_node,
  54                      op1, build_int_cst (type, 0));
  55   else if (TREE_CODE (type) == REAL_TYPE
  56            && (flag_sanitize & SANITIZE_FLOAT_DIVIDE))
  57     t = fold_build2 (EQ_EXPR, boolean_type_node,
  58                      op1, build_real (type, dconst0));
  59   else
  60     return NULL_TREE;
  61
  62   /* We check INT_MIN / -1 only for signed types.  */
  63   if (TREE_CODE (type) == INTEGER_TYPE
  64       && (flag_sanitize & SANITIZE_DIVIDE)
  65       && !TYPE_UNSIGNED (type))
  66     {
  67       tree x;
  68       tt = fold_build2 (EQ_EXPR, boolean_type_node, unshare_expr (op1),
  69                         build_int_cst (type, -1));
  70       x = fold_build2 (EQ_EXPR, boolean_type_node, op0,
  71                        TYPE_MIN_VALUE (type));
  72       x = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, x, tt);
  73       t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, x);
  74     }
  75
  76   /* If the condition was folded to 0, no need to instrument
  77      this expression.  */
  78   if (integer_zerop (t))
  79     return NULL_TREE;
  80
  81   /* In case we have a SAVE_EXPR in a conditional context, we need to
  82      make sure it gets evaluated before the condition.  */
  83   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op0), t);
  84   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op1), t);
  85   if (flag_sanitize_undefined_trap_on_error)
  86     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
  87   else
  88     {
  89       tree data = ubsan_create_data ("__ubsan_overflow_data", 1, &loc,
  90                                      ubsan_type_descriptor (type), NULL_TREE,
  91                                      NULL_TREE);
  92       data = build_fold_addr_expr_loc (loc, data);
  93       enum built_in_function bcode
  94         = (flag_sanitize_recover & SANITIZE_DIVIDE)
  95           ? BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW
  96           : BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW_ABORT;
  97       tt = builtin_decl_explicit (bcode);
  98       op0 = unshare_expr (op0);
  99       op1 = unshare_expr (op1);
 100       tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 101                                 ubsan_encode_value (op1));
 102     }
 103   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 104
 105   return t;
 106 }
 107
 108 /* Instrument left and right shifts.  */
 109
 110 tree
 111 ubsan_instrument_shift (location_t loc, enum tree_code code,
 112                         tree op0, tree op1)
 113 {
 114   tree t, tt = NULL_TREE;
 115   tree type0 = TREE_TYPE (op0);
 116   tree type1 = TREE_TYPE (op1);
 117   if (!INTEGRAL_TYPE_P (type0))
 118     return NULL_TREE;
 119
 120   tree op1_utype = unsigned_type_for (type1);
 121   HOST_WIDE_INT op0_prec = TYPE_PRECISION (type0);
 122   tree uprecm1 = build_int_cst (op1_utype, op0_prec - 1);
 123
 124   op0 = unshare_expr (op0);
 125   op1 = unshare_expr (op1);
 126
 127   t = fold_convert_loc (loc, op1_utype, op1);
 128   t = fold_build2 (GT_EXPR, boolean_type_node, t, uprecm1);
 129
 130   /* If this is not a signed operation, don't perform overflow checks.
 131      Also punt on bit-fields.  */
 132   if (TYPE_OVERFLOW_WRAPS (type0)
 133       || GET_MODE_BITSIZE (TYPE_MODE (type0)) != TYPE_PRECISION (type0))
 134     ;
 135
 136   /* For signed x << y, in C99/C11, the following:
 137      (unsigned) x >> (uprecm1 - y)
 138      if non-zero, is undefined.  */
 139   else if (code == LSHIFT_EXPR && flag_isoc99 && cxx_dialect < cxx11)
 140     {
 141       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 142                             fold_convert (op1_utype, unshare_expr (op1)));
 143       tt = fold_convert_loc (loc, unsigned_type_for (type0), op0);
 144       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 145       tt = fold_build2 (NE_EXPR, boolean_type_node, tt,
 146                         build_int_cst (TREE_TYPE (tt), 0));
 147     }
 148
 149   /* For signed x << y, in C++11 and later, the following:
 150      x < 0 || ((unsigned) x >> (uprecm1 - y))
 151      if > 1, is undefined.  */
 152   else if (code == LSHIFT_EXPR && cxx_dialect >= cxx11)
 153     {
 154       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 155                             fold_convert (op1_utype, unshare_expr (op1)));
 156       tt = fold_convert_loc (loc, unsigned_type_for (type0),
 157                              unshare_expr (op0));
 158       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 159       tt = fold_build2 (GT_EXPR, boolean_type_node, tt,
 160                         build_int_cst (TREE_TYPE (tt), 1));
 161       x = fold_build2 (LT_EXPR, boolean_type_node, unshare_expr (op0),
 162                        build_int_cst (type0, 0));
 163       tt = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, x, tt);
 164     }
 165
 166   /* If the condition was folded to 0, no need to instrument
 167      this expression.  */
 168   if (integer_zerop (t) && (tt == NULL_TREE || integer_zerop (tt)))
 169     return NULL_TREE;
 170
 171   /* In case we have a SAVE_EXPR in a conditional context, we need to
 172      make sure it gets evaluated before the condition.  */
 173   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op0), t);
 174   t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t,
 175                    tt ? tt : integer_zero_node);
 176
 177   if (flag_sanitize_undefined_trap_on_error)
 178     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 179   else
 180     {
 181       tree data = ubsan_create_data ("__ubsan_shift_data", 1, &loc,
 182                                      ubsan_type_descriptor (type0),
 183                                      ubsan_type_descriptor (type1), NULL_TREE,
 184                                      NULL_TREE);
 185       data = build_fold_addr_expr_loc (loc, data);
 186
 187       enum built_in_function bcode
 188         = (flag_sanitize_recover & SANITIZE_SHIFT)
 189           ? BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS
 190           : BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS_ABORT;
 191       tt = builtin_decl_explicit (bcode);
 192       op0 = unshare_expr (op0);
 193       op1 = unshare_expr (op1);
 194       tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 195                                 ubsan_encode_value (op1));
 196     }
 197   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 198
 199   return t;
 200 }
 201
 202 /* Instrument variable length array bound.  */
 203
 204 tree
 205 ubsan_instrument_vla (location_t loc, tree size)
 206 {
 207   tree type = TREE_TYPE (size);
 208   tree t, tt;
 209
 210   t = fold_build2 (LE_EXPR, boolean_type_node, size, build_int_cst (type, 0));
 211   if (flag_sanitize_undefined_trap_on_error)
 212     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 213   else
 214     {
 215       tree data = ubsan_create_data ("__ubsan_vla_data", 1, &loc,
 216                                      ubsan_type_descriptor (type), NULL_TREE,
 217                                      NULL_TREE);
 218       data = build_fold_addr_expr_loc (loc, data);
 219       enum built_in_function bcode
 220         = (flag_sanitize_recover & SANITIZE_VLA)
 221           ? BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE
 222           : BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE_ABORT;
 223       tt = builtin_decl_explicit (bcode);
 224       tt = build_call_expr_loc (loc, tt, 2, data, ubsan_encode_value (size));
 225     }
 226   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 227
 228   return t;
 229 }
 230
 231 /* Instrument missing return in C++ functions returning non-void.  */
 232
 233 tree
 234 ubsan_instrument_return (location_t loc)
 235 {
 236   if (flag_sanitize_undefined_trap_on_error)
 237     return build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 238
 239   tree data = ubsan_create_data ("__ubsan_missing_return_data", 1, &loc,
 240                                  NULL_TREE, NULL_TREE);
 241   tree t = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_MISSING_RETURN);
 242   return build_call_expr_loc (loc, t, 1, build_fold_addr_expr_loc (loc, data));
 243 }
 244
 245 /* Instrument array bounds for ARRAY_REFs.  We create special builtin,
 246    that gets expanded in the sanopt pass, and make an array dimension
 247    of it.  ARRAY is the array, *INDEX is an index to the array.
 248    Return NULL_TREE if no instrumentation is emitted.
 249    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 250
 251 tree
 252 ubsan_instrument_bounds (location_t loc, tree array, tree *index,
 253                          bool ignore_off_by_one)
 254 {
 255   tree type = TREE_TYPE (array);
 256   tree domain = TYPE_DOMAIN (type);
 257
 258   if (domain == NULL_TREE || TYPE_MAX_VALUE (domain) == NULL_TREE)
 259     return NULL_TREE;
 260
 261   tree bound = TYPE_MAX_VALUE (domain);
 262   if (ignore_off_by_one)
 263     bound = fold_build2 (PLUS_EXPR, TREE_TYPE (bound), bound,
 264                          build_int_cst (TREE_TYPE (bound), 1));
 265
 266   /* Detect flexible array members and suchlike, unless
 267      -fsanitize=bounds-strict.  */
 268   tree base = get_base_address (array);
 269   if ((flag_sanitize & SANITIZE_BOUNDS_STRICT) == 0
 270       && TREE_CODE (array) == COMPONENT_REF
 271       && base && (INDIRECT_REF_P (base) || TREE_CODE (base) == MEM_REF))
 272     {
 273       tree next = NULL_TREE;
 274       tree cref = array;
 275
 276       /* Walk all structs/unions.  */
 277       while (TREE_CODE (cref) == COMPONENT_REF)
 278         {
 279           if (TREE_CODE (TREE_TYPE (TREE_OPERAND (cref, 0))) == RECORD_TYPE)
 280             for (next = DECL_CHAIN (TREE_OPERAND (cref, 1));
 281                  next && TREE_CODE (next) != FIELD_DECL;
 282                  next = DECL_CHAIN (next))
 283               ;
 284           if (next)
 285             /* Not a last element.  Instrument it.  */
 286             break;
 287           /* Ok, this is the last field of the structure/union.  But the
 288              aggregate containing the field must be the last field too,
 289              recursively.  */
 290           cref = TREE_OPERAND (cref, 0);
 291         }
 292       if (!next)
 293         /* Don't instrument this flexible array member-like array in non-strict
 294            -fsanitize=bounds mode.  */
 295         return NULL_TREE;
 296     }
 297
 298   /* Don't emit instrumentation in the most common cases.  */
 299   tree idx = NULL_TREE;
 300   if (TREE_CODE (*index) == INTEGER_CST)
 301     idx = *index;
 302   else if (TREE_CODE (*index) == BIT_AND_EXPR
 303            && TREE_CODE (TREE_OPERAND (*index, 1)) == INTEGER_CST)
 304     idx = TREE_OPERAND (*index, 1);
 305   if (idx
 306       && TREE_CODE (bound) == INTEGER_CST
 307       && tree_int_cst_sgn (idx) >= 0
 308       && tree_int_cst_le (idx, bound))
 309     return NULL_TREE;
 310
 311   *index = save_expr (*index);
 312   /* Create a "(T *) 0" tree node to describe the array type.  */
 313   tree zero_with_type = build_int_cst (build_pointer_type (type), 0);
 314   return build_call_expr_internal_loc (loc, IFN_UBSAN_BOUNDS,
 315                                        void_type_node, 3, zero_with_type,
 316                                        *index, bound);
 317 }
 318
 319 /* Return true iff T is an array that was instrumented by SANITIZE_BOUNDS.  */
 320
 321 bool
 322 ubsan_array_ref_instrumented_p (const_tree t)
 323 {
 324   if (TREE_CODE (t) != ARRAY_REF)
 325     return false;
 326
 327   tree op1 = TREE_OPERAND (t, 1);
 328   return TREE_CODE (op1) == COMPOUND_EXPR
 329          && TREE_CODE (TREE_OPERAND (op1, 0)) == CALL_EXPR
 330          && CALL_EXPR_FN (TREE_OPERAND (op1, 0)) == NULL_TREE
 331          && CALL_EXPR_IFN (TREE_OPERAND (op1, 0)) == IFN_UBSAN_BOUNDS;
 332 }
 333
 334 /* Instrument an ARRAY_REF, if it hasn't already been instrumented.
 335    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 336
 337 void
 338 ubsan_maybe_instrument_array_ref (tree *expr_p, bool ignore_off_by_one)
 339 {
 340   if (!ubsan_array_ref_instrumented_p (*expr_p)
 341       && do_ubsan_in_current_function ())
 342     {
 343       tree op0 = TREE_OPERAND (*expr_p, 0);
 344       tree op1 = TREE_OPERAND (*expr_p, 1);
 345       tree e = ubsan_instrument_bounds (EXPR_LOCATION (*expr_p), op0, &op1,
 346                                         ignore_off_by_one);
 347       if (e != NULL_TREE)
 348         {
 349           tree t = copy_node (*expr_p);
 350           TREE_OPERAND (t, 1) = build2 (COMPOUND_EXPR, TREE_TYPE (op1),
 351                                         e, op1);
 352           *expr_p = t;
 353         }
 354     }
 355 }
 356
 357 static tree
 358 ubsan_maybe_instrument_reference_or_call (location_t loc, tree op, tree ptype,
 359                                           enum ubsan_null_ckind ckind)
 360 {
 361   if (!do_ubsan_in_current_function ())
 362     return NULL_TREE;
 363
 364   tree type = TREE_TYPE (ptype);
 365   tree orig_op = op;
 366   bool instrument = false;
 367   unsigned int mina = 0;
 368
 369   if (flag_sanitize & SANITIZE_ALIGNMENT)
 370     {
 371       mina = min_align_of_type (type);
 372       if (mina <= 1)
 373         mina = 0;
 374     }
 375   while ((TREE_CODE (op) == NOP_EXPR
 376           || TREE_CODE (op) == NON_LVALUE_EXPR)
 377          && TREE_CODE (TREE_TYPE (op)) == POINTER_TYPE)
 378     op = TREE_OPERAND (op, 0);
 379   if (TREE_CODE (op) == NOP_EXPR
 380       && TREE_CODE (TREE_TYPE (op)) == REFERENCE_TYPE)
 381     {
 382       if (mina && mina > min_align_of_type (TREE_TYPE (TREE_TYPE (op))))
 383         instrument = true;
 384     }
 385   else
 386     {
 387       if ((flag_sanitize & SANITIZE_NULL) && TREE_CODE (op) == ADDR_EXPR)
 388         {
 389           bool strict_overflow_p = false;
 390           /* tree_single_nonzero_warnv_p will not return true for non-weak
 391              non-automatic decls with -fno-delete-null-pointer-checks,
 392              which is disabled during -fsanitize=null.  We don't want to
 393              instrument those, just weak vars though.  */
 394           int save_flag_delete_null_pointer_checks
 395             = flag_delete_null_pointer_checks;
 396           flag_delete_null_pointer_checks = 1;
 397           if (!tree_single_nonzero_warnv_p (op, &strict_overflow_p)
 398               || strict_overflow_p)
 399             instrument = true;
 400           flag_delete_null_pointer_checks
 401             = save_flag_delete_null_pointer_checks;
 402         }
 403       else if (flag_sanitize & SANITIZE_NULL)
 404         instrument = true;
 405       if (mina && mina > 1)
 406         {
 407           if (!POINTER_TYPE_P (TREE_TYPE (op))
 408               || mina > get_pointer_alignment (op) / BITS_PER_UNIT)
 409             instrument = true;
 410         }
 411     }
 412   if (!instrument)
 413     return NULL_TREE;
 414   op = save_expr (orig_op);
 415   gcc_assert (POINTER_TYPE_P (ptype));
 416   if (TREE_CODE (ptype) == REFERENCE_TYPE)
 417     ptype = build_pointer_type (TREE_TYPE (ptype));
 418   tree kind = build_int_cst (ptype, ckind);
 419   tree align = build_int_cst (pointer_sized_int_node, mina);
 420   tree call
 421     = build_call_expr_internal_loc (loc, IFN_UBSAN_NULL, void_type_node,
 422                                     3, op, kind, align);
 423   TREE_SIDE_EFFECTS (call) = 1;
 424   return fold_build2 (COMPOUND_EXPR, TREE_TYPE (op), call, op);
 425 }
 426
 427 /* Instrument a NOP_EXPR to REFERENCE_TYPE if needed.  */
 428
 429 void
 430 ubsan_maybe_instrument_reference (tree stmt)
 431 {
 432   tree op = TREE_OPERAND (stmt, 0);
 433   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 434                                                  TREE_TYPE (stmt),
 435                                                  UBSAN_REF_BINDING);
 436   if (op)
 437     TREE_OPERAND (stmt, 0) = op;
 438 }
 439
 440 /* Instrument a CALL_EXPR to a method if needed.  */
 441
 442 void
 443 ubsan_maybe_instrument_member_call (tree stmt, bool is_ctor)
 444 {
 445   if (call_expr_nargs (stmt) == 0)
 446     return;
 447   tree op = CALL_EXPR_ARG (stmt, 0);
 448   if (op == error_mark_node
 449       || !POINTER_TYPE_P (TREE_TYPE (op)))
 450     return;
 451   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 452                                                  TREE_TYPE (op),
 453                                                  is_ctor ? UBSAN_CTOR_CALL
 454                                                  : UBSAN_MEMBER_CALL);
 455   if (op)
 456     CALL_EXPR_ARG (stmt, 0) = op;
 457 }