gcc/c-family/c-ubsan.c

   1 /* UndefinedBehaviorSanitizer, undefined behavior detector.
   2    Copyright (C) 2013-2017 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 "stor-layout.h"
  29 #include "builtins.h"
  30 #include "gimplify.h"
  31 #include "stringpool.h"
  32 #include "attribs.h"
  33 #include "asan.h"
  34
  35 /* Instrument division by zero and INT_MIN / -1.  If not instrumenting,
  36    return NULL_TREE.  */
  37
  38 tree
  39 ubsan_instrument_division (location_t loc, tree op0, tree op1)
  40 {
  41   tree t, tt;
  42   tree type = TREE_TYPE (op0);
  43
  44   /* At this point both operands should have the same type,
  45      because they are already converted to RESULT_TYPE.
  46      Use TYPE_MAIN_VARIANT since typedefs can confuse us.  */
  47   gcc_assert (TYPE_MAIN_VARIANT (TREE_TYPE (op0))
  48               == TYPE_MAIN_VARIANT (TREE_TYPE (op1)));
  49
  50   op0 = unshare_expr (op0);
  51   op1 = unshare_expr (op1);
  52
  53   if (TREE_CODE (type) == INTEGER_TYPE
  54       && sanitize_flags_p (SANITIZE_DIVIDE))
  55     t = fold_build2 (EQ_EXPR, boolean_type_node,
  56                      op1, build_int_cst (type, 0));
  57   else if (TREE_CODE (type) == REAL_TYPE
  58            && sanitize_flags_p (SANITIZE_FLOAT_DIVIDE))
  59     t = fold_build2 (EQ_EXPR, boolean_type_node,
  60                      op1, build_real (type, dconst0));
  61   else
  62     return NULL_TREE;
  63
  64   /* We check INT_MIN / -1 only for signed types.  */
  65   if (TREE_CODE (type) == INTEGER_TYPE
  66       && sanitize_flags_p (SANITIZE_DIVIDE)
  67       && !TYPE_UNSIGNED (type))
  68     {
  69       tree x;
  70       tt = fold_build2 (EQ_EXPR, boolean_type_node, unshare_expr (op1),
  71                         build_int_cst (type, -1));
  72       x = fold_build2 (EQ_EXPR, boolean_type_node, op0,
  73                        TYPE_MIN_VALUE (type));
  74       x = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, x, tt);
  75       t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, x);
  76     }
  77
  78   /* If the condition was folded to 0, no need to instrument
  79      this expression.  */
  80   if (integer_zerop (t))
  81     return NULL_TREE;
  82
  83   /* In case we have a SAVE_EXPR in a conditional context, we need to
  84      make sure it gets evaluated before the condition.  */
  85   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op0), t);
  86   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op1), t);
  87   if (flag_sanitize_undefined_trap_on_error)
  88     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
  89   else
  90     {
  91       tree data = ubsan_create_data ("__ubsan_overflow_data", 1, &loc,
  92                                      ubsan_type_descriptor (type), NULL_TREE,
  93                                      NULL_TREE);
  94       data = build_fold_addr_expr_loc (loc, data);
  95       enum built_in_function bcode
  96         = (flag_sanitize_recover & SANITIZE_DIVIDE)
  97           ? BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW
  98           : BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW_ABORT;
  99       tt = builtin_decl_explicit (bcode);
 100       op0 = unshare_expr (op0);
 101       op1 = unshare_expr (op1);
 102       tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 103                                 ubsan_encode_value (op1));
 104     }
 105   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 106
 107   return t;
 108 }
 109
 110 /* Instrument left and right shifts.  */
 111
 112 tree
 113 ubsan_instrument_shift (location_t loc, enum tree_code code,
 114                         tree op0, tree op1)
 115 {
 116   tree t, tt = NULL_TREE;
 117   tree type0 = TREE_TYPE (op0);
 118   tree type1 = TREE_TYPE (op1);
 119   if (!INTEGRAL_TYPE_P (type0))
 120     return NULL_TREE;
 121
 122   tree op1_utype = unsigned_type_for (type1);
 123   HOST_WIDE_INT op0_prec = TYPE_PRECISION (type0);
 124   tree uprecm1 = build_int_cst (op1_utype, op0_prec - 1);
 125
 126   op0 = unshare_expr (op0);
 127   op1 = unshare_expr (op1);
 128
 129   t = fold_convert_loc (loc, op1_utype, op1);
 130   t = fold_build2 (GT_EXPR, boolean_type_node, t, uprecm1);
 131
 132   /* If this is not a signed operation, don't perform overflow checks.
 133      Also punt on bit-fields.  */
 134   if (TYPE_OVERFLOW_WRAPS (type0)
 135       || GET_MODE_BITSIZE (TYPE_MODE (type0)) != TYPE_PRECISION (type0)
 136       || !sanitize_flags_p (SANITIZE_SHIFT_BASE))
 137     ;
 138
 139   /* For signed x << y, in C99/C11, the following:
 140      (unsigned) x >> (uprecm1 - y)
 141      if non-zero, is undefined.  */
 142   else if (code == LSHIFT_EXPR && flag_isoc99 && cxx_dialect < cxx11)
 143     {
 144       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 145                             fold_convert (op1_utype, unshare_expr (op1)));
 146       tt = fold_convert_loc (loc, unsigned_type_for (type0), op0);
 147       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 148       tt = fold_build2 (NE_EXPR, boolean_type_node, tt,
 149                         build_int_cst (TREE_TYPE (tt), 0));
 150     }
 151
 152   /* For signed x << y, in C++11 and later, the following:
 153      x < 0 || ((unsigned) x >> (uprecm1 - y))
 154      if > 1, is undefined.  */
 155   else if (code == LSHIFT_EXPR && cxx_dialect >= cxx11)
 156     {
 157       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 158                             fold_convert (op1_utype, unshare_expr (op1)));
 159       tt = fold_convert_loc (loc, unsigned_type_for (type0),
 160                              unshare_expr (op0));
 161       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 162       tt = fold_build2 (GT_EXPR, boolean_type_node, tt,
 163                         build_int_cst (TREE_TYPE (tt), 1));
 164       x = fold_build2 (LT_EXPR, boolean_type_node, unshare_expr (op0),
 165                        build_int_cst (type0, 0));
 166       tt = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, x, tt);
 167     }
 168
 169   /* If the condition was folded to 0, no need to instrument
 170      this expression.  */
 171   if (integer_zerop (t) && (tt == NULL_TREE || integer_zerop (tt)))
 172     return NULL_TREE;
 173
 174   /* In case we have a SAVE_EXPR in a conditional context, we need to
 175      make sure it gets evaluated before the condition.  */
 176   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op0), t);
 177   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op1), t);
 178
 179   enum sanitize_code recover_kind = SANITIZE_SHIFT_EXPONENT;
 180   tree else_t = void_node;
 181   if (tt)
 182     {
 183       if (!sanitize_flags_p (SANITIZE_SHIFT_EXPONENT))
 184         {
 185           t = fold_build1 (TRUTH_NOT_EXPR, boolean_type_node, t);
 186           t = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, t, tt);
 187           recover_kind = SANITIZE_SHIFT_BASE;
 188         }
 189       else
 190         {
 191           if (flag_sanitize_undefined_trap_on_error
 192               || ((!(flag_sanitize_recover & SANITIZE_SHIFT_EXPONENT))
 193                   == (!(flag_sanitize_recover & SANITIZE_SHIFT_BASE))))
 194             t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, tt);
 195           else
 196             else_t = tt;
 197         }
 198     }
 199
 200   if (flag_sanitize_undefined_trap_on_error)
 201     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 202   else
 203     {
 204       tree data = ubsan_create_data ("__ubsan_shift_data", 1, &loc,
 205                                      ubsan_type_descriptor (type0),
 206                                      ubsan_type_descriptor (type1), NULL_TREE,
 207                                      NULL_TREE);
 208       data = build_fold_addr_expr_loc (loc, data);
 209
 210       enum built_in_function bcode
 211         = (flag_sanitize_recover & recover_kind)
 212           ? BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS
 213           : BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS_ABORT;
 214       tt = builtin_decl_explicit (bcode);
 215       op0 = unshare_expr (op0);
 216       op1 = unshare_expr (op1);
 217       tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 218                                 ubsan_encode_value (op1));
 219       if (else_t != void_node)
 220         {
 221           bcode = (flag_sanitize_recover & SANITIZE_SHIFT_BASE)
 222                   ? BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS
 223                   : BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS_ABORT;
 224           tree else_tt = builtin_decl_explicit (bcode);
 225           op0 = unshare_expr (op0);
 226           op1 = unshare_expr (op1);
 227           else_tt = build_call_expr_loc (loc, else_tt, 3, data,
 228                                          ubsan_encode_value (op0),
 229                                          ubsan_encode_value (op1));
 230           else_t = fold_build3 (COND_EXPR, void_type_node, else_t,
 231                                 else_tt, void_node);
 232         }
 233     }
 234   t = fold_build3 (COND_EXPR, void_type_node, t, tt, else_t);
 235
 236   return t;
 237 }
 238
 239 /* Instrument variable length array bound.  */
 240
 241 tree
 242 ubsan_instrument_vla (location_t loc, tree size)
 243 {
 244   tree type = TREE_TYPE (size);
 245   tree t, tt;
 246
 247   t = fold_build2 (LE_EXPR, boolean_type_node, size, build_int_cst (type, 0));
 248   if (flag_sanitize_undefined_trap_on_error)
 249     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 250   else
 251     {
 252       tree data = ubsan_create_data ("__ubsan_vla_data", 1, &loc,
 253                                      ubsan_type_descriptor (type), NULL_TREE,
 254                                      NULL_TREE);
 255       data = build_fold_addr_expr_loc (loc, data);
 256       enum built_in_function bcode
 257         = (flag_sanitize_recover & SANITIZE_VLA)
 258           ? BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE
 259           : BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE_ABORT;
 260       tt = builtin_decl_explicit (bcode);
 261       tt = build_call_expr_loc (loc, tt, 2, data, ubsan_encode_value (size));
 262     }
 263   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 264
 265   return t;
 266 }
 267
 268 /* Instrument missing return in C++ functions returning non-void.  */
 269
 270 tree
 271 ubsan_instrument_return (location_t loc)
 272 {
 273   if (flag_sanitize_undefined_trap_on_error)
 274     return build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 275
 276   tree data = ubsan_create_data ("__ubsan_missing_return_data", 1, &loc,
 277                                  NULL_TREE, NULL_TREE);
 278   tree t = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_MISSING_RETURN);
 279   return build_call_expr_loc (loc, t, 1, build_fold_addr_expr_loc (loc, data));
 280 }
 281
 282 /* Instrument array bounds for ARRAY_REFs.  We create special builtin,
 283    that gets expanded in the sanopt pass, and make an array dimension
 284    of it.  ARRAY is the array, *INDEX is an index to the array.
 285    Return NULL_TREE if no instrumentation is emitted.
 286    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 287
 288 tree
 289 ubsan_instrument_bounds (location_t loc, tree array, tree *index,
 290                          bool ignore_off_by_one)
 291 {
 292   tree type = TREE_TYPE (array);
 293   tree domain = TYPE_DOMAIN (type);
 294
 295   if (domain == NULL_TREE || TYPE_MAX_VALUE (domain) == NULL_TREE)
 296     return NULL_TREE;
 297
 298   tree bound = TYPE_MAX_VALUE (domain);
 299   if (ignore_off_by_one)
 300     bound = fold_build2 (PLUS_EXPR, TREE_TYPE (bound), bound,
 301                          build_int_cst (TREE_TYPE (bound), 1));
 302
 303   /* Detect flexible array members and suchlike, unless
 304      -fsanitize=bounds-strict.  */
 305   tree base = get_base_address (array);
 306   if (!sanitize_flags_p (SANITIZE_BOUNDS_STRICT)
 307       && TREE_CODE (array) == COMPONENT_REF
 308       && base && (INDIRECT_REF_P (base) || TREE_CODE (base) == MEM_REF))
 309     {
 310       tree next = NULL_TREE;
 311       tree cref = array;
 312
 313       /* Walk all structs/unions.  */
 314       while (TREE_CODE (cref) == COMPONENT_REF)
 315         {
 316           if (TREE_CODE (TREE_TYPE (TREE_OPERAND (cref, 0))) == RECORD_TYPE)
 317             for (next = DECL_CHAIN (TREE_OPERAND (cref, 1));
 318                  next && TREE_CODE (next) != FIELD_DECL;
 319                  next = DECL_CHAIN (next))
 320               ;
 321           if (next)
 322             /* Not a last element.  Instrument it.  */
 323             break;
 324           /* Ok, this is the last field of the structure/union.  But the
 325              aggregate containing the field must be the last field too,
 326              recursively.  */
 327           cref = TREE_OPERAND (cref, 0);
 328         }
 329       if (!next)
 330         /* Don't instrument this flexible array member-like array in non-strict
 331            -fsanitize=bounds mode.  */
 332         return NULL_TREE;
 333     }
 334
 335   /* Don't emit instrumentation in the most common cases.  */
 336   tree idx = NULL_TREE;
 337   if (TREE_CODE (*index) == INTEGER_CST)
 338     idx = *index;
 339   else if (TREE_CODE (*index) == BIT_AND_EXPR
 340            && TREE_CODE (TREE_OPERAND (*index, 1)) == INTEGER_CST)
 341     idx = TREE_OPERAND (*index, 1);
 342   if (idx
 343       && TREE_CODE (bound) == INTEGER_CST
 344       && tree_int_cst_sgn (idx) >= 0
 345       && tree_int_cst_le (idx, bound))
 346     return NULL_TREE;
 347
 348   *index = save_expr (*index);
 349   /* Create a "(T *) 0" tree node to describe the array type.  */
 350   tree zero_with_type = build_int_cst (build_pointer_type (type), 0);
 351   return build_call_expr_internal_loc (loc, IFN_UBSAN_BOUNDS,
 352                                        void_type_node, 3, zero_with_type,
 353                                        *index, bound);
 354 }
 355
 356 /* Return true iff T is an array that was instrumented by SANITIZE_BOUNDS.  */
 357
 358 bool
 359 ubsan_array_ref_instrumented_p (const_tree t)
 360 {
 361   if (TREE_CODE (t) != ARRAY_REF)
 362     return false;
 363
 364   tree op1 = TREE_OPERAND (t, 1);
 365   return TREE_CODE (op1) == COMPOUND_EXPR
 366          && TREE_CODE (TREE_OPERAND (op1, 0)) == CALL_EXPR
 367          && CALL_EXPR_FN (TREE_OPERAND (op1, 0)) == NULL_TREE
 368          && CALL_EXPR_IFN (TREE_OPERAND (op1, 0)) == IFN_UBSAN_BOUNDS;
 369 }
 370
 371 /* Instrument an ARRAY_REF, if it hasn't already been instrumented.
 372    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 373
 374 void
 375 ubsan_maybe_instrument_array_ref (tree *expr_p, bool ignore_off_by_one)
 376 {
 377   if (!ubsan_array_ref_instrumented_p (*expr_p)
 378       && sanitize_flags_p (SANITIZE_BOUNDS | SANITIZE_BOUNDS_STRICT)
 379       && current_function_decl != NULL_TREE)
 380     {
 381       tree op0 = TREE_OPERAND (*expr_p, 0);
 382       tree op1 = TREE_OPERAND (*expr_p, 1);
 383       tree e = ubsan_instrument_bounds (EXPR_LOCATION (*expr_p), op0, &op1,
 384                                         ignore_off_by_one);
 385       if (e != NULL_TREE)
 386         {
 387           tree t = copy_node (*expr_p);
 388           TREE_OPERAND (t, 1) = build2 (COMPOUND_EXPR, TREE_TYPE (op1),
 389                                         e, op1);
 390           *expr_p = t;
 391         }
 392     }
 393 }
 394
 395 static tree
 396 ubsan_maybe_instrument_reference_or_call (location_t loc, tree op, tree ptype,
 397                                           enum ubsan_null_ckind ckind)
 398 {
 399   if (!sanitize_flags_p (SANITIZE_ALIGNMENT | SANITIZE_NULL)
 400       || current_function_decl == NULL_TREE)
 401     return NULL_TREE;
 402
 403   tree type = TREE_TYPE (ptype);
 404   tree orig_op = op;
 405   bool instrument = false;
 406   unsigned int mina = 0;
 407
 408   if (sanitize_flags_p (SANITIZE_ALIGNMENT))
 409     {
 410       mina = min_align_of_type (type);
 411       if (mina <= 1)
 412         mina = 0;
 413     }
 414   while ((TREE_CODE (op) == NOP_EXPR
 415           || TREE_CODE (op) == NON_LVALUE_EXPR)
 416          && TREE_CODE (TREE_TYPE (op)) == POINTER_TYPE)
 417     op = TREE_OPERAND (op, 0);
 418   if (TREE_CODE (op) == NOP_EXPR
 419       && TREE_CODE (TREE_TYPE (op)) == REFERENCE_TYPE)
 420     {
 421       if (mina && mina > min_align_of_type (TREE_TYPE (TREE_TYPE (op))))
 422         instrument = true;
 423     }
 424   else
 425     {
 426       if (sanitize_flags_p (SANITIZE_NULL) && TREE_CODE (op) == ADDR_EXPR)
 427         {
 428           bool strict_overflow_p = false;
 429           /* tree_single_nonzero_warnv_p will not return true for non-weak
 430              non-automatic decls with -fno-delete-null-pointer-checks,
 431              which is disabled during -fsanitize=null.  We don't want to
 432              instrument those, just weak vars though.  */
 433           int save_flag_delete_null_pointer_checks
 434             = flag_delete_null_pointer_checks;
 435           flag_delete_null_pointer_checks = 1;
 436           if (!tree_single_nonzero_warnv_p (op, &strict_overflow_p)
 437               || strict_overflow_p)
 438             instrument = true;
 439           flag_delete_null_pointer_checks
 440             = save_flag_delete_null_pointer_checks;
 441         }
 442       else if (sanitize_flags_p (SANITIZE_NULL))
 443         instrument = true;
 444       if (mina && mina > 1)
 445         {
 446           if (!POINTER_TYPE_P (TREE_TYPE (op))
 447               || mina > get_pointer_alignment (op) / BITS_PER_UNIT)
 448             instrument = true;
 449         }
 450     }
 451   if (!instrument)
 452     return NULL_TREE;
 453   op = save_expr (orig_op);
 454   gcc_assert (POINTER_TYPE_P (ptype));
 455   if (TREE_CODE (ptype) == REFERENCE_TYPE)
 456     ptype = build_pointer_type (TREE_TYPE (ptype));
 457   tree kind = build_int_cst (ptype, ckind);
 458   tree align = build_int_cst (pointer_sized_int_node, mina);
 459   tree call
 460     = build_call_expr_internal_loc (loc, IFN_UBSAN_NULL, void_type_node,
 461                                     3, op, kind, align);
 462   TREE_SIDE_EFFECTS (call) = 1;
 463   return fold_build2 (COMPOUND_EXPR, TREE_TYPE (op), call, op);
 464 }
 465
 466 /* Instrument a NOP_EXPR to REFERENCE_TYPE or INTEGER_CST with REFERENCE_TYPE
 467    type if needed.  */
 468
 469 void
 470 ubsan_maybe_instrument_reference (tree *stmt_p)
 471 {
 472   tree stmt = *stmt_p;
 473   tree op = stmt;
 474   if (TREE_CODE (stmt) == NOP_EXPR)
 475     op = TREE_OPERAND (stmt, 0);
 476   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 477                                                  TREE_TYPE (stmt),
 478                                                  UBSAN_REF_BINDING);
 479   if (op)
 480     {
 481       if (TREE_CODE (stmt) == NOP_EXPR)
 482         TREE_OPERAND (stmt, 0) = op;
 483       else
 484         *stmt_p = op;
 485     }
 486 }
 487
 488 /* Instrument a CALL_EXPR to a method if needed.  */
 489
 490 void
 491 ubsan_maybe_instrument_member_call (tree stmt, bool is_ctor)
 492 {
 493   if (call_expr_nargs (stmt) == 0)
 494     return;
 495   tree op = CALL_EXPR_ARG (stmt, 0);
 496   if (op == error_mark_node
 497       || !POINTER_TYPE_P (TREE_TYPE (op)))
 498     return;
 499   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 500                                                  TREE_TYPE (op),
 501                                                  is_ctor ? UBSAN_CTOR_CALL
 502                                                  : UBSAN_MEMBER_CALL);
 503   if (op)
 504     CALL_EXPR_ARG (stmt, 0) = op;
 505 }