check_impossible_compare.c

   1 /*
   2  * Copyright 2023 Linaro Ltd.
   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 #include "smatch_extra.h"
  20
  21 static int my_id;
  22
  23 static const char *okay_macros[] = {
  24         "ULONG_MAX",
  25 };
  26
  27 static const char *kernel_macros[] = {
  28         "DP_FFE_PRESET_MAX_LEVEL",
  29         "FSMC_THOLD_MASK",
  30         "FSMC_TSET_MASK",
  31         "FSMC_TWAIT_MASK",
  32         "L2CAP_CID_DYN_END",
  33         "LOGICVC_DIMENSIONS_MAX",
  34         "MAXREFCEXTLEN",
  35         "MAXREFCOUNT",
  36         "NLM4_OFFSET_MAX",
  37         "TIPC_MAX_PORT",
  38         "TSL2591_ALS_MAX_VALUE",
  39         "UBIFS_COMPR_TYPES_CNT",
  40         "XFS_MAX_CRC_AG_BLOCKS",
  41         NULL
  42 };
  43
  44 static const char **allowed_macros;
  45
  46 static bool is_lt_zero(int op, sval_t known)
  47 {
  48         if (op != '<' && op != SPECIAL_UNSIGNED_LT)
  49                 return false;
  50         if (known.value != 0)
  51                 return false;
  52         return true;
  53 }
  54
  55 static bool check_is_ulong_max_recursive(struct expression *expr)
  56 {
  57         sval_t sval;
  58
  59         expr = strip_expr(expr);
  60
  61         if (!get_value(expr, &sval))
  62                 return false;
  63
  64         if (expr->type == EXPR_BINOP) {
  65                 if (check_is_ulong_max_recursive(expr->left))
  66                         return true;
  67                 return false;
  68         }
  69
  70         if (sval_cmp(sval, sval_type_max(&ulong_ctype)) == 0)
  71                 return true;
  72         return false;
  73 }
  74
  75 static bool is_u64_vs_ulongmax(struct expression *expr)
  76 {
  77         struct symbol *left, *right;
  78
  79         if (expr->op != '>' && expr->op != SPECIAL_UNSIGNED_GT)
  80                 return false;
  81         if (!check_is_ulong_max_recursive(expr->right))
  82                 return false;
  83
  84         left = get_type(expr->left);
  85         right = get_type(expr->right);
  86
  87         if (left == right)
  88                 return true;
  89         if (type_positive_bits(left) < type_positive_bits(right))
  90                 return true;
  91
  92         if (type_bits(left) != 64)
  93                 return false;
  94         if (right != &ulong_ctype && right != &uint_ctype)
  95                 return false;
  96
  97         return true;
  98 }
  99
 100 static bool is_long_vs_UINTMAX(struct range_list *rl, int op, sval_t known)
 101 {
 102         if (op != '>' && op != SPECIAL_UNSIGNED_GT)
 103                 return false;
 104         if (rl_type(rl) != &long_ctype && rl_type(rl) != &ulong_ctype)
 105                 return false;
 106         if (known.value == UINT_MAX)
 107                 return true;
 108         return false;
 109 }
 110
 111 static bool is_allowed_impossible_limit(struct expression *expr)
 112 {
 113         char *macro;
 114         int i;
 115
 116         if (!allowed_macros)
 117                 return false;
 118
 119         macro = get_macro_name(expr->pos);
 120         if (!macro) {
 121                 macro = pos_ident(expr->pos);
 122                 if (!macro)
 123                         return false;
 124         }
 125         i = -1;
 126         while (allowed_macros[++i]) {
 127                 if (strcmp(macro, allowed_macros[i]) == 0)
 128                         return true;
 129         }
 130         return false;
 131 }
 132
 133 static void match_condition(struct expression *expr)
 134 {
 135         struct symbol *type;
 136         sval_t known, dummy;
 137         struct range_list *var_rl, *known_rl, *rl_right, *rl_left;
 138         char *name;
 139         int op;
 140
 141         if (expr->type != EXPR_COMPARE)
 142                 return;
 143
 144         type = get_type(expr);
 145         if (!type)
 146                 return;
 147
 148         if (get_macro_name(expr->pos))
 149                 return;
 150
 151         op = expr->op;
 152         if (get_value(expr->right, &known)) {
 153                 /* check that one and only one side is known */
 154                 if (get_value(expr->left, &dummy))
 155                         return;
 156
 157                 var_rl = alloc_whole_rl(get_type(expr->left));
 158         } else if (get_value(expr->left, &known)) {
 159                 op = flip_comparison(op);
 160                 var_rl = alloc_whole_rl(get_type(expr->right));
 161         } else {
 162                 return;
 163         }
 164         known = sval_cast(type, known);
 165         known_rl = alloc_rl(known, known);
 166         var_rl = cast_rl(type, var_rl);
 167
 168         /* handled by check_unsigned_lt_zero.c */
 169         if (is_lt_zero(op, known))
 170                 return;
 171
 172         if (possibly_true_rl(var_rl, op, known_rl))
 173                 return;
 174         if (is_u64_vs_ulongmax(expr))
 175                 return;
 176         if (is_long_vs_UINTMAX(var_rl, op, known))
 177                 return;
 178         if (is_allowed_impossible_limit(expr->right))
 179                 return;
 180
 181         name = expr_to_str(expr);
 182         get_absolute_rl(expr->left, &rl_left);
 183         get_absolute_rl(expr->right, &rl_right);
 184         sm_warning("impossible condition '(%s) => (%s %s %s)'", name,
 185                    show_rl(rl_left), show_special(expr->op), show_rl(rl_right));
 186         free_string(name);
 187 }
 188
 189 void check_impossible_compare(int id)
 190 {
 191         my_id = id;
 192
 193         allowed_macros = okay_macros;
 194         if (option_project == PROJ_KERNEL)
 195                 allowed_macros = kernel_macros;
 196
 197         add_hook(&match_condition, CONDITION_HOOK);
 198 }