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
  25 static int is_sizeof(struct expression *expr)
  26 {
  27         return (expr->type == EXPR_SIZEOF);
  28 }
  29
  30 static int is_macro(struct expression *expr, const char *macro_name)
  31 {
  32         char *name;
  33         struct expression *outside_expr;
  34
  35         /* check that we aren't inside the macro itself */
  36         outside_expr = last_ptr_list((struct ptr_list *)big_expression_stack);
  37         if (outside_expr && positions_eq(expr->pos, outside_expr->pos))
  38                 return 0;
  39
  40         name = get_macro_name(expr->pos);
  41         if (name && strcmp(name, macro_name) == 0)
  42                 return 1;
  43         return 0;
  44 }
  45
  46 static int is_size_in_bytes(struct expression *expr)
  47 {
  48         if (is_sizeof(expr))
  49                 return 1;
  50
  51         if (is_macro(expr, "offsetof"))
  52                 return 1;
  53         if (is_macro(expr, "PAGE_SIZE"))
  54                 return 1;
  55
  56         if (get_state_expr(my_id, expr) == &size_in_bytes)
  57                 return 1;
  58
  59         return 0;
  60 }
  61
  62 static void match_binop(struct expression *expr)
  63 {
  64         struct symbol *type;
  65         char *name;
  66         int size;
  67
  68         if (expr->op != '+')
  69                 return;
  70         type = get_pointer_type(expr->left);
  71         if (!type)
  72                 return;
  73         if (type_bits(type) <= 8) /* ignore void, bool and char pointers*/
  74                 return;
  75         if (!is_size_in_bytes(expr->right))
  76                 return;
  77
  78         /* if we know it's within bounds then don't complain */
  79         size = get_array_size(expr->left);
  80         if (size) {
  81                 sval_t max;
  82
  83                 get_absolute_max(expr->right, &max);
  84                 if (max.uvalue < size)
  85                         return;
  86         }
  87
  88         name = expr_to_str(expr->left);
  89         sm_warning("potential pointer math issue ('%s' is a %d bit pointer)",
  90                name, type_bits(type));
  91         free_string(name);
  92 }
  93
  94 static void match_assign(struct expression *expr)
  95 {
  96         if (expr->op != '=')
  97                 return;
  98
  99         if (!is_size_in_bytes(expr->right))
 100                 return;
 101         set_state_expr(my_id, expr->left, &size_in_bytes);
 102 }
 103
 104 static void check_assign(struct expression *expr)
 105 {
 106         struct symbol *type;
 107         char *name;
 108
 109         if (expr->op != SPECIAL_ADD_ASSIGN && expr->op != SPECIAL_SUB_ASSIGN)
 110                 return;
 111
 112         type = get_pointer_type(expr->left);
 113         if (!type)
 114                 return;
 115         if (type_bits(type) == 8 || type_bits(type) == -1)
 116                 return;
 117         if (!is_size_in_bytes(expr->right))
 118                 return;
 119         name = expr_to_var(expr->left);
 120         sm_warning("potential pointer math issue ('%s' is a %d bit pointer)",
 121                name, type_bits(type));
 122         free_string(name);
 123 }
 124
 125 void check_pointer_math(int id)
 126 {
 127         my_id = id;
 128         add_hook(&match_binop, BINOP_HOOK);
 129         add_hook(&match_assign, ASSIGNMENT_HOOK);
 130         add_hook(&check_assign, ASSIGNMENT_HOOK);
 131         add_modification_hook(my_id, &set_undefined);
 132 }