check_pointer_math.c

   1 /*
   2  * Copyright (C) 2012 Oracle.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 #include "smatch.h"
  19
  20 static int my_id;
  21
  22 STATE(size_in_bytes);
  23
  24 static void set_undefined(struct sm_state *sm, struct expression *mod_expr)
  25 {
  26         if (sm->state == &size_in_bytes)
  27                 set_state(my_id, sm->name, sm->sym, &undefined);
  28 }
  29
  30 static int is_sizeof(struct expression *expr)
  31 {
  32         return (expr->type == EXPR_SIZEOF);
  33 }
  34
  35 static int is_macro(struct expression *expr, const char *macro_name)
  36 {
  37         char *name;
  38         struct expression *outside_expr;
  39
  40         /* check that we aren't inside the macro itself */
  41         outside_expr = last_ptr_list((struct ptr_list *)big_expression_stack);
  42         if (outside_expr && positions_eq(expr->pos, outside_expr->pos))
  43                 return 0;
  44
  45         name = get_macro_name(expr->pos);
  46         if (name && strcmp(name, macro_name) == 0)
  47                 return 1;
  48         return 0;
  49 }
  50
  51 static int is_size_in_bytes(struct expression *expr)
  52 {
  53         if (is_sizeof(expr))
  54                 return 1;
  55
  56         if (is_macro(expr, "offsetof"))
  57                 return 1;
  58         if (is_macro(expr, "PAGE_SIZE"))
  59                 return 1;
  60
  61         if (get_state_expr(my_id, expr) == &size_in_bytes)
  62                 return 1;
  63
  64         return 0;
  65 }
  66
  67 static void match_binop(struct expression *expr)
  68 {
  69         struct symbol *type;
  70         char *name;
  71         int size;
  72
  73         if (expr->op != '+')
  74                 return;
  75         type = get_pointer_type(expr->left);
  76         if (!type)
  77                 return;
  78         if (type_bits(type) <= 8) /* ignore void, bool and char pointers*/
  79                 return;
  80         if (!is_size_in_bytes(expr->right))
  81                 return;
  82
  83         /* if we know it's within bounds then don't complain */
  84         size = get_array_size(expr->left);
  85         if (size) {
  86                 sval_t max;
  87
  88                 get_absolute_max(expr->right, &max);
  89                 if (max.uvalue < size)
  90                         return;
  91         }
  92
  93         name = expr_to_str(expr->left);
  94         sm_msg("warn: potential pointer math issue ('%s' is a %d bit pointer)",
  95                name, type_bits(type));
  96         free_string(name);
  97 }
  98
  99 static void match_assign(struct expression *expr)
 100 {
 101         if (expr->op != '=')
 102                 return;
 103
 104         if (!is_size_in_bytes(expr->right))
 105                 return;
 106         set_state_expr(my_id, expr->left, &size_in_bytes);
 107 }
 108
 109 static void check_assign(struct expression *expr)
 110 {
 111         struct symbol *type;
 112         char *name;
 113
 114         if (expr->op != SPECIAL_ADD_ASSIGN && expr->op != SPECIAL_SUB_ASSIGN)
 115                 return;
 116
 117         type = get_pointer_type(expr->left);
 118         if (!type)
 119                 return;
 120         if (type_bits(type) == 8 || type_bits(type) == -1)
 121                 return;
 122         if (!is_size_in_bytes(expr->right))
 123                 return;
 124         name = expr_to_var(expr->left);
 125         sm_msg("warn: potential pointer math issue ('%s' is a %d bit pointer)",
 126                name, type_bits(type));
 127         free_string(name);
 128 }
 129
 130 void check_pointer_math(int id)
 131 {
 132         my_id = id;
 133         add_hook(&match_binop, BINOP_HOOK);
 134         add_hook(&match_assign, ASSIGNMENT_HOOK);
 135         add_hook(&check_assign, ASSIGNMENT_HOOK);
 136         add_modification_hook(my_id, &set_undefined);
 137 }