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   tree op1_utype = unsigned_type_for (type1);
 118   HOST_WIDE_INT op0_prec = TYPE_PRECISION (type0);
 119   tree uprecm1 = build_int_cst (op1_utype, op0_prec - 1);
 120
 121   op0 = unshare_expr (op0);
 122   op1 = unshare_expr (op1);
 123
 124   t = fold_convert_loc (loc, op1_utype, op1);
 125   t = fold_build2 (GT_EXPR, boolean_type_node, t, uprecm1);
 126
 127   /* If this is not a signed operation, don't perform overflow checks.
 128      Also punt on bit-fields.  */
 129   if (!INTEGRAL_TYPE_P (type0)
 130       || TYPE_OVERFLOW_WRAPS (type0)
 131       || GET_MODE_BITSIZE (TYPE_MODE (type0)) != TYPE_PRECISION (type0))
 132     ;
 133
 134   /* For signed x << y, in C99/C11, the following:
 135      (unsigned) x >> (uprecm1 - y)
 136      if non-zero, is undefined.  */
 137   else if (code == LSHIFT_EXPR && flag_isoc99 && cxx_dialect < cxx11)
 138     {
 139       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 140                             fold_convert (op1_utype, unshare_expr (op1)));
 141       tt = fold_convert_loc (loc, unsigned_type_for (type0), op0);
 142       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 143       tt = fold_build2 (NE_EXPR, boolean_type_node, tt,
 144                         build_int_cst (TREE_TYPE (tt), 0));
 145     }
 146
 147   /* For signed x << y, in C++11 and later, the following:
 148      x < 0 || ((unsigned) x >> (uprecm1 - y))
 149      if > 1, is undefined.  */
 150   else if (code == LSHIFT_EXPR && cxx_dialect >= cxx11)
 151     {
 152       tree x = fold_build2 (MINUS_EXPR, op1_utype, uprecm1,
 153                             fold_convert (op1_utype, unshare_expr (op1)));
 154       tt = fold_convert_loc (loc, unsigned_type_for (type0),
 155                              unshare_expr (op0));
 156       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 157       tt = fold_build2 (GT_EXPR, boolean_type_node, tt,
 158                         build_int_cst (TREE_TYPE (tt), 1));
 159       x = fold_build2 (LT_EXPR, boolean_type_node, unshare_expr (op0),
 160                        build_int_cst (type0, 0));
 161       tt = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, x, tt);
 162     }
 163
 164   /* If the condition was folded to 0, no need to instrument
 165      this expression.  */
 166   if (integer_zerop (t) && (tt == NULL_TREE || integer_zerop (tt)))
 167     return NULL_TREE;
 168
 169   /* In case we have a SAVE_EXPR in a conditional context, we need to
 170      make sure it gets evaluated before the condition.  */
 171   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), unshare_expr (op0), t);
 172   t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t,
 173                    tt ? tt : integer_zero_node);
 174
 175   if (flag_sanitize_undefined_trap_on_error)
 176     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 177   else
 178     {
 179       tree data = ubsan_create_data ("__ubsan_shift_data", 1, &loc,
 180                                      ubsan_type_descriptor (type0),
 181                                      ubsan_type_descriptor (type1), NULL_TREE,
 182                                      NULL_TREE);
 183       data = build_fold_addr_expr_loc (loc, data);
 184
 185       enum built_in_function bcode
 186         = (flag_sanitize_recover & SANITIZE_SHIFT)
 187           ? BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS
 188           : BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS_ABORT;
 189       tt = builtin_decl_explicit (bcode);
 190       op0 = unshare_expr (op0);
 191       op1 = unshare_expr (op1);
 192       tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 193                                 ubsan_encode_value (op1));
 194     }
 195   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 196
 197   return t;
 198 }
 199
 200 /* Instrument variable length array bound.  */
 201
 202 tree
 203 ubsan_instrument_vla (location_t loc, tree size)
 204 {
 205   tree type = TREE_TYPE (size);
 206   tree t, tt;
 207
 208   t = fold_build2 (LE_EXPR, boolean_type_node, size, build_int_cst (type, 0));
 209   if (flag_sanitize_undefined_trap_on_error)
 210     tt = build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 211   else
 212     {
 213       tree data = ubsan_create_data ("__ubsan_vla_data", 1, &loc,
 214                                      ubsan_type_descriptor (type), NULL_TREE,
 215                                      NULL_TREE);
 216       data = build_fold_addr_expr_loc (loc, data);
 217       enum built_in_function bcode
 218         = (flag_sanitize_recover & SANITIZE_VLA)
 219           ? BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE
 220           : BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE_ABORT;
 221       tt = builtin_decl_explicit (bcode);
 222       tt = build_call_expr_loc (loc, tt, 2, data, ubsan_encode_value (size));
 223     }
 224   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
 225
 226   return t;
 227 }
 228
 229 /* Instrument missing return in C++ functions returning non-void.  */
 230
 231 tree
 232 ubsan_instrument_return (location_t loc)
 233 {
 234   if (flag_sanitize_undefined_trap_on_error)
 235     return build_call_expr_loc (loc, builtin_decl_explicit (BUILT_IN_TRAP), 0);
 236   /* It is possible that PCH zapped table with definitions of sanitizer
 237      builtins.  Reinitialize them if needed.  */
 238   initialize_sanitizer_builtins ();
 239
 240   tree data = ubsan_create_data ("__ubsan_missing_return_data", 1, &loc,
 241                                  NULL_TREE, NULL_TREE);
 242   tree t = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_MISSING_RETURN);
 243   return build_call_expr_loc (loc, t, 1, build_fold_addr_expr_loc (loc, data));
 244 }
 245
 246 /* Instrument array bounds for ARRAY_REFs.  We create special builtin,
 247    that gets expanded in the sanopt pass, and make an array dimension
 248    of it.  ARRAY is the array, *INDEX is an index to the array.
 249    Return NULL_TREE if no instrumentation is emitted.
 250    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 251
 252 tree
 253 ubsan_instrument_bounds (location_t loc, tree array, tree *index,
 254                          bool ignore_off_by_one)
 255 {
 256   tree type = TREE_TYPE (array);
 257   tree domain = TYPE_DOMAIN (type);
 258
 259   if (domain == NULL_TREE || TYPE_MAX_VALUE (domain) == NULL_TREE)
 260     return NULL_TREE;
 261
 262   tree bound = TYPE_MAX_VALUE (domain);
 263   if (ignore_off_by_one)
 264     bound = fold_build2 (PLUS_EXPR, TREE_TYPE (bound), bound,
 265                          build_int_cst (TREE_TYPE (bound), 1));
 266
 267   /* Detect flexible array members and suchlike, unless
 268      -fsanitize=bounds-strict.  */
 269   tree base = get_base_address (array);
 270   if ((flag_sanitize & SANITIZE_BOUNDS_STRICT) == 0
 271       && TREE_CODE (array) == COMPONENT_REF
 272       && base && (INDIRECT_REF_P (base) || TREE_CODE (base) == MEM_REF))
 273     {
 274       tree next = NULL_TREE;
 275       tree cref = array;
 276
 277       /* Walk all structs/unions.  */
 278       while (TREE_CODE (cref) == COMPONENT_REF)
 279         {
 280           if (TREE_CODE (TREE_TYPE (TREE_OPERAND (cref, 0))) == RECORD_TYPE)
 281             for (next = DECL_CHAIN (TREE_OPERAND (cref, 1));
 282                  next && TREE_CODE (next) != FIELD_DECL;
 283                  next = DECL_CHAIN (next))
 284               ;
 285           if (next)
 286             /* Not a last element.  Instrument it.  */
 287             break;
 288           /* Ok, this is the last field of the structure/union.  But the
 289              aggregate containing the field must be the last field too,
 290              recursively.  */
 291           cref = TREE_OPERAND (cref, 0);
 292         }
 293       if (!next)
 294         /* Don't instrument this flexible array member-like array in non-strict
 295            -fsanitize=bounds mode.  */
 296         return NULL_TREE;
 297     }
 298
 299   /* Don't emit instrumentation in the most common cases.  */
 300   tree idx = NULL_TREE;
 301   if (TREE_CODE (*index) == INTEGER_CST)
 302     idx = *index;
 303   else if (TREE_CODE (*index) == BIT_AND_EXPR
 304            && TREE_CODE (TREE_OPERAND (*index, 1)) == INTEGER_CST)
 305     idx = TREE_OPERAND (*index, 1);
 306   if (idx
 307       && TREE_CODE (bound) == INTEGER_CST
 308       && tree_int_cst_sgn (idx) >= 0
 309       && tree_int_cst_le (idx, bound))
 310     return NULL_TREE;
 311
 312   *index = save_expr (*index);
 313   /* Create a "(T *) 0" tree node to describe the array type.  */
 314   tree zero_with_type = build_int_cst (build_pointer_type (type), 0);
 315   return build_call_expr_internal_loc (loc, IFN_UBSAN_BOUNDS,
 316                                        void_type_node, 3, zero_with_type,
 317                                        *index, bound);
 318 }
 319
 320 /* Return true iff T is an array that was instrumented by SANITIZE_BOUNDS.  */
 321
 322 bool
 323 ubsan_array_ref_instrumented_p (const_tree t)
 324 {
 325   if (TREE_CODE (t) != ARRAY_REF)
 326     return false;
 327
 328   tree op1 = TREE_OPERAND (t, 1);
 329   return TREE_CODE (op1) == COMPOUND_EXPR
 330          && TREE_CODE (TREE_OPERAND (op1, 0)) == CALL_EXPR
 331          && CALL_EXPR_FN (TREE_OPERAND (op1, 0)) == NULL_TREE
 332          && CALL_EXPR_IFN (TREE_OPERAND (op1, 0)) == IFN_UBSAN_BOUNDS;
 333 }
 334
 335 /* Instrument an ARRAY_REF, if it hasn't already been instrumented.
 336    IGNORE_OFF_BY_ONE is true if the ARRAY_REF is inside a ADDR_EXPR.  */
 337
 338 void
 339 ubsan_maybe_instrument_array_ref (tree *expr_p, bool ignore_off_by_one)
 340 {
 341   if (!ubsan_array_ref_instrumented_p (*expr_p)
 342       && do_ubsan_in_current_function ())
 343     {
 344       tree op0 = TREE_OPERAND (*expr_p, 0);
 345       tree op1 = TREE_OPERAND (*expr_p, 1);
 346       tree e = ubsan_instrument_bounds (EXPR_LOCATION (*expr_p), op0, &op1,
 347                                         ignore_off_by_one);
 348       if (e != NULL_TREE)
 349         {
 350           tree t = copy_node (*expr_p);
 351           TREE_OPERAND (t, 1) = build2 (COMPOUND_EXPR, TREE_TYPE (op1),
 352                                         e, op1);
 353           *expr_p = t;
 354         }
 355     }
 356 }
 357
 358 static tree
 359 ubsan_maybe_instrument_reference_or_call (location_t loc, tree op, tree ptype,
 360                                           enum ubsan_null_ckind ckind)
 361 {
 362   if (!do_ubsan_in_current_function ())
 363     return NULL_TREE;
 364
 365   tree type = TREE_TYPE (ptype);
 366   tree orig_op = op;
 367   bool instrument = false;
 368   unsigned int mina = 0;
 369
 370   if (flag_sanitize & SANITIZE_ALIGNMENT)
 371     {
 372       mina = min_align_of_type (type);
 373       if (mina <= 1)
 374         mina = 0;
 375     }
 376   while ((TREE_CODE (op) == NOP_EXPR
 377           || TREE_CODE (op) == NON_LVALUE_EXPR)
 378          && TREE_CODE (TREE_TYPE (op)) == POINTER_TYPE)
 379     op = TREE_OPERAND (op, 0);
 380   if (TREE_CODE (op) == NOP_EXPR
 381       && TREE_CODE (TREE_TYPE (op)) == REFERENCE_TYPE)
 382     {
 383       if (mina && mina > min_align_of_type (TREE_TYPE (TREE_TYPE (op))))
 384         instrument = true;
 385     }
 386   else
 387     {
 388       if ((flag_sanitize & SANITIZE_NULL) && TREE_CODE (op) == ADDR_EXPR)
 389         {
 390           bool strict_overflow_p = false;
 391           /* tree_single_nonzero_warnv_p will not return true for non-weak
 392              non-automatic decls with -fno-delete-null-pointer-checks,
 393              which is disabled during -fsanitize=null.  We don't want to
 394              instrument those, just weak vars though.  */
 395           int save_flag_delete_null_pointer_checks
 396             = flag_delete_null_pointer_checks;
 397           flag_delete_null_pointer_checks = 1;
 398           if (!tree_single_nonzero_warnv_p (op, &strict_overflow_p)
 399               || strict_overflow_p)
 400             instrument = true;
 401           flag_delete_null_pointer_checks
 402             = save_flag_delete_null_pointer_checks;
 403         }
 404       else if (flag_sanitize & SANITIZE_NULL)
 405         instrument = true;
 406       if (mina && mina > 1)
 407         {
 408           if (!POINTER_TYPE_P (TREE_TYPE (op))
 409               || mina > get_pointer_alignment (op) / BITS_PER_UNIT)
 410             instrument = true;
 411         }
 412     }
 413   if (!instrument)
 414     return NULL_TREE;
 415   op = save_expr (orig_op);
 416   gcc_assert (POINTER_TYPE_P (ptype));
 417   if (TREE_CODE (ptype) == REFERENCE_TYPE)
 418     ptype = build_pointer_type (TREE_TYPE (ptype));
 419   tree kind = build_int_cst (ptype, ckind);
 420   tree align = build_int_cst (pointer_sized_int_node, mina);
 421   tree call
 422     = build_call_expr_internal_loc (loc, IFN_UBSAN_NULL, void_type_node,
 423                                     3, op, kind, align);
 424   TREE_SIDE_EFFECTS (call) = 1;
 425   return fold_build2 (COMPOUND_EXPR, TREE_TYPE (op), call, op);
 426 }
 427
 428 /* Instrument a NOP_EXPR to REFERENCE_TYPE if needed.  */
 429
 430 void
 431 ubsan_maybe_instrument_reference (tree stmt)
 432 {
 433   tree op = TREE_OPERAND (stmt, 0);
 434   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 435                                                  TREE_TYPE (stmt),
 436                                                  UBSAN_REF_BINDING);
 437   if (op)
 438     TREE_OPERAND (stmt, 0) = op;
 439 }
 440
 441 /* Instrument a CALL_EXPR to a method if needed.  */
 442
 443 void
 444 ubsan_maybe_instrument_member_call (tree stmt, bool is_ctor)
 445 {
 446   if (call_expr_nargs (stmt) == 0)
 447     return;
 448   tree op = CALL_EXPR_ARG (stmt, 0);
 449   if (op == error_mark_node
 450       || !POINTER_TYPE_P (TREE_TYPE (op)))
 451     return;
 452   op = ubsan_maybe_instrument_reference_or_call (EXPR_LOCATION (stmt), op,
 453                                                  TREE_TYPE (op),
 454                                                  is_ctor ? UBSAN_CTOR_CALL
 455                                                  : UBSAN_MEMBER_CALL);
 456   if (op)
 457     CALL_EXPR_ARG (stmt, 0) = op;
 458 }