smatch_param_limit.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 /*
  19  * This is almost the same as smatch_param_filter.c.  The difference is that
  20  * this only deals with values passed on the stack and param filter only deals
  21  * with values changed so that the caller sees the new value.  It other words
  22  * the key for these should always be "$" and the key for param_filter should
  23  * never be "$".  Also smatch_param_set() should never use "$" as the key.
  24  * Param set should work together with param_filter to determine the value that
  25  * the caller sees at the end.
  26  *
  27  * This is for functions like this:
  28  *
  29  * int foo(int a)
  30  * {
  31  *        if (a >= 0 && a < 10) {
  32  *                 a = 42;
  33  *                 return 1;
  34  *        }
  35  *        return 0;
  36  * }
  37  *
  38  * If we pass in 5, it returns 1.
  39  *
  40  * It's a bit complicated because we can't just consider the final value, we
  41  * have to always consider the passed in value.
  42  *
  43  */
  44
  45 #include "smatch.h"
  46 #include "smatch_extra.h"
  47 #include "smatch_slist.h"
  48
  49 static int my_id;
  50
  51 static struct stree *limit_states;
  52 static struct stree *ignore_states;
  53
  54 int __no_limits;
  55
  56 static struct smatch_state *unmatched_state(struct sm_state *sm)
  57 {
  58         struct smatch_state *state;
  59
  60         if (!param_was_set_var_sym(sm->name, sm->sym)) {
  61                 state = __get_state(SMATCH_EXTRA, sm->name, sm->sym);
  62                 if (state)
  63                         return state;
  64         }
  65         return alloc_estate_whole(estate_type(sm->state));
  66 }
  67
  68 struct smatch_state *get_orig_estate(const char *name, struct symbol *sym)
  69 {
  70         struct smatch_state *state;
  71
  72         state = get_state(my_id, name, sym);
  73         if (state)
  74                 return state;
  75
  76         state = get_state(SMATCH_EXTRA, name, sym);
  77         if (state)
  78                 return state;
  79         return alloc_estate_rl(alloc_whole_rl(get_real_base_type(sym)));
  80 }
  81
  82 static struct range_list *generify_mtag_range(struct smatch_state *state)
  83 {
  84         struct range_list *rl;
  85         struct data_range *drange;
  86
  87         if (!estate_type(state) || estate_type(state)->type != SYM_PTR)
  88                 return estate_rl(state);
  89
  90         /*
  91          * The problem is that we get too specific on our param limits when we
  92          * know exactly what pointers are passed to a function.  It gets to the
  93          * point where we say "pointer x will succeed, but everything else will
  94          * fail."  And then we introduce a new caller which passes a different
  95          * pointer and it's like, "Sorry bro, that's not possible."
  96          *
  97          */
  98         rl = estate_rl(state);
  99         FOR_EACH_PTR(rl, drange) {
 100                 if (drange->min.value != drange->max.value)
 101                         continue;
 102                 if (drange->min.value == 0)
 103                         continue;
 104                 if (is_err_ptr(drange->min))
 105                         continue;
 106                 return rl_union(valid_ptr_rl, rl);
 107         } END_FOR_EACH_PTR(drange);
 108
 109         return estate_rl(state);
 110 }
 111
 112 static bool sm_was_set(struct sm_state *sm)
 113 {
 114         struct relation *rel;
 115
 116         if (!estate_related(sm->state))
 117                 return param_was_set_var_sym(sm->name, sm->sym);
 118
 119         FOR_EACH_PTR(estate_related(sm->state), rel) {
 120                 if (param_was_set_var_sym(sm->name, sm->sym))
 121                         return true;
 122         } END_FOR_EACH_PTR(rel);
 123         return false;
 124 }
 125
 126 static bool is_boring_pointer_info(const char *name, struct range_list *rl)
 127 {
 128         char *rl_str;
 129
 130         /* addresses are always boring */
 131         if (name[0] == '&')
 132                 return true;
 133
 134         /*
 135          * One way that PARAM_LIMIT can be set is by dereferencing pointers.
 136          * It's not necessarily very valuable to track that a pointer must
 137          * be non-NULL.  It's even less valuable to know that it's either NULL
 138          * or valid.  It can be nice to know that it's not an error pointer, I
 139          * suppose.  But let's not pass that data back to all the callers
 140          * forever.
 141          *
 142          */
 143
 144         if (strlen(name) < 40)
 145                 return false;
 146
 147         rl_str = show_rl(rl);
 148         if (!rl_str)
 149                 return false;
 150
 151         if (strcmp(rl_str, "4096-ptr_max") == 0 ||
 152             strcmp(rl_str, "0,4096-ptr_max") == 0)
 153                 return true;
 154
 155         return false;
 156 }
 157
 158 static void print_return_value_param(int return_id, char *return_ranges, struct expression *expr)
 159 {
 160         struct smatch_state *state, *old;
 161         struct sm_state *tmp;
 162         struct range_list *rl;
 163         const char *param_name;
 164         int param;
 165
 166         FOR_EACH_MY_SM(SMATCH_EXTRA, __get_cur_stree(), tmp) {
 167                 if (tmp->name[0] == '&')
 168                         continue;
 169
 170                 if (!get_state_stree(limit_states, my_id, tmp->name, tmp->sym) &&
 171                     get_state_stree(ignore_states, my_id, tmp->name, tmp->sym))
 172                         continue;
 173
 174                 param = get_param_num_from_sym(tmp->sym);
 175                 if (param < 0)
 176                         continue;
 177
 178                 param_name = get_param_name(tmp);
 179                 if (!param_name)
 180                         continue;
 181
 182                 state = __get_state(my_id, tmp->name, tmp->sym);
 183                 if (!state) {
 184                         if (sm_was_set(tmp))
 185                                 continue;
 186                         state = tmp->state;
 187                 }
 188
 189                 if (estate_is_whole(state) || estate_is_empty(state))
 190                         continue;
 191                 old = get_state_stree(get_start_states(), SMATCH_EXTRA, tmp->name, tmp->sym);
 192                 if (old && rl_equiv(estate_rl(old), estate_rl(state)))
 193                         continue;
 194
 195                 if (is_ignored_kernel_data(param_name))
 196                         continue;
 197
 198                 rl = generify_mtag_range(state);
 199                 if (is_boring_pointer_info(param_name, rl))
 200                         continue;
 201
 202                 sql_insert_return_states(return_id, return_ranges, PARAM_LIMIT,
 203                                          param, param_name, show_rl(rl));
 204         } END_FOR_EACH_SM(tmp);
 205 }
 206
 207 static void extra_mod_hook(const char *name, struct symbol *sym, struct expression *expr, struct smatch_state *state)
 208 {
 209         struct smatch_state *orig;
 210         struct symbol *param_sym;
 211         char *param_name;
 212
 213         if (expr && expr->smatch_flags & Fake)
 214                 return;
 215
 216         param_name = get_param_var_sym_var_sym(name, sym, NULL, &param_sym);
 217         if (!param_name || !param_sym)
 218                 goto free;
 219         if (get_param_num_from_sym(param_sym) < 0)
 220                 goto free;
 221
 222         /* already saved */
 223         if (get_state(my_id, param_name, param_sym))
 224                 goto free;
 225
 226         if (__in_buf_clear)
 227                 return;
 228
 229         orig = get_state(SMATCH_EXTRA, param_name, param_sym);
 230         if (!orig)
 231                 orig = alloc_estate_whole(estate_type(state));
 232
 233         set_state(my_id, param_name, param_sym, orig);
 234 free:
 235         free_string(param_name);
 236 }
 237
 238 static void extra_nomod_hook(const char *name, struct symbol *sym, struct expression *expr, struct smatch_state *state)
 239 {
 240         if (__no_limits) {
 241                 set_state_stree(&ignore_states, my_id, name, sym, &undefined);
 242                 return;
 243         }
 244         set_state_stree(&limit_states, my_id, name, sym, &undefined);
 245 }
 246
 247 static void match_end_func(struct symbol *sym)
 248 {
 249         free_stree(&ignore_states);
 250         free_stree(&limit_states);
 251 }
 252
 253 void register_param_limit(int id)
 254 {
 255         my_id = id;
 256
 257         add_function_data((unsigned long *)&limit_states);
 258         add_function_data((unsigned long *)&ignore_states);
 259         add_hook(&match_end_func, END_FUNC_HOOK);
 260
 261         db_ignore_states(my_id);
 262         set_dynamic_states(my_id);
 263
 264         add_extra_mod_hook(&extra_mod_hook);
 265         add_extra_nomod_hook(&extra_nomod_hook);
 266         add_unmatched_state_hook(my_id, &unmatched_state);
 267         add_merge_hook(my_id, &merge_estates);
 268
 269         add_split_return_callback(&print_return_value_param);
 270 }
 271