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 "scope.h"
  46 #include "smatch.h"
  47 #include "smatch_extra.h"
  48 #include "smatch_slist.h"
  49
  50 static int my_id;
  51
  52 static struct stree *limit_states;
  53 static struct stree *ignore_states;
  54
  55 int __no_limits;
  56
  57 static struct smatch_state *unmatched_state(struct sm_state *sm)
  58 {
  59         struct smatch_state *state;
  60
  61         if (!param_was_set_var_sym(sm->name, sm->sym)) {
  62                 state = __get_state(SMATCH_EXTRA, sm->name, sm->sym);
  63                 if (state)
  64                         return state;
  65         }
  66         return alloc_estate_whole(estate_type(sm->state));
  67 }
  68
  69 struct smatch_state *get_orig_estate(const char *name, struct symbol *sym)
  70 {
  71         struct smatch_state *state;
  72
  73         state = get_state(my_id, name, sym);
  74         if (state)
  75                 return state;
  76
  77         state = get_state(SMATCH_EXTRA, name, sym);
  78         if (state)
  79                 return state;
  80         return alloc_estate_rl(alloc_whole_rl(get_real_base_type(sym)));
  81 }
  82
  83 static struct range_list *generify_mtag_range(struct smatch_state *state)
  84 {
  85         struct range_list *rl;
  86         struct data_range *drange;
  87
  88         if (!estate_type(state) || estate_type(state)->type != SYM_PTR)
  89                 return estate_rl(state);
  90
  91         /*
  92          * The problem is that we get too specific on our param limits when we
  93          * know exactly what pointers are passed to a function.  It gets to the
  94          * point where we say "pointer x will succeed, but everything else will
  95          * fail."  And then we introduce a new caller which passes a different
  96          * pointer and it's like, "Sorry bro, that's not possible."
  97          *
  98          */
  99         rl = estate_rl(state);
 100         FOR_EACH_PTR(rl, drange) {
 101                 if (drange->min.value != drange->max.value)
 102                         continue;
 103                 if (drange->min.value == 0)
 104                         continue;
 105                 if (is_err_ptr(drange->min))
 106                         continue;
 107                 return rl_union(valid_ptr_rl, rl);
 108         } END_FOR_EACH_PTR(drange);
 109
 110         return estate_rl(state);
 111 }
 112
 113 static bool sm_was_set(struct sm_state *sm)
 114 {
 115         struct relation *rel;
 116
 117         if (!estate_related(sm->state))
 118                 return param_was_set_var_sym(sm->name, sm->sym);
 119
 120         FOR_EACH_PTR(estate_related(sm->state), rel) {
 121                 if (param_was_set_var_sym(sm->name, sm->sym))
 122                         return true;
 123         } END_FOR_EACH_PTR(rel);
 124         return false;
 125 }
 126
 127 static bool is_boring_pointer_info(const char *name, struct range_list *rl)
 128 {
 129         char *rl_str;
 130
 131         /*
 132          * One way that PARAM_LIMIT can be set is by dereferencing pointers.
 133          * It's not necessarily very valuable to track that a pointer must
 134          * be non-NULL.  It's even less valuable to know that it's either NULL
 135          * or valid.  It can be nice to know that it's not an error pointer, I
 136          * suppose.  But let's not pass that data back to all the callers
 137          * forever.
 138          *
 139          */
 140
 141         if (strlen(name) < 40)
 142                 return false;
 143
 144         rl_str = show_rl(rl);
 145         if (!rl_str)
 146                 return false;
 147
 148         if (strcmp(rl_str, "4096-ptr_max") == 0 ||
 149             strcmp(rl_str, "0,4096-ptr_max") == 0)
 150                 return true;
 151
 152         return false;
 153 }
 154
 155 static void print_return_value_param(int return_id, char *return_ranges, struct expression *expr)
 156 {
 157         struct smatch_state *state, *old;
 158         struct sm_state *tmp;
 159         struct range_list *rl;
 160         const char *param_name;
 161         int param;
 162
 163         FOR_EACH_MY_SM(SMATCH_EXTRA, __get_cur_stree(), tmp) {
 164                 if (tmp->name[0] == '&')
 165                         continue;
 166
 167                 if (!get_state_stree(limit_states, my_id, tmp->name, tmp->sym) &&
 168                     get_state_stree(ignore_states, my_id, tmp->name, tmp->sym))
 169                         continue;
 170
 171                 param = get_param_num_from_sym(tmp->sym);
 172                 if (param < 0)
 173                         continue;
 174
 175                 param_name = get_param_name(tmp);
 176                 if (!param_name)
 177                         continue;
 178
 179                 state = __get_state(my_id, tmp->name, tmp->sym);
 180                 if (!state) {
 181                         if (sm_was_set(tmp))
 182                                 continue;
 183                         state = tmp->state;
 184                 }
 185
 186                 if (estate_is_whole(state) || estate_is_empty(state))
 187                         continue;
 188                 old = get_state_stree(get_start_states(), SMATCH_EXTRA, tmp->name, tmp->sym);
 189                 if (old && rl_equiv(estate_rl(old), estate_rl(state)))
 190                         continue;
 191
 192                 if (is_ignored_kernel_data(param_name))
 193                         continue;
 194
 195                 rl = generify_mtag_range(state);
 196                 if (is_boring_pointer_info(param_name, rl))
 197                         continue;
 198
 199                 sql_insert_return_states(return_id, return_ranges, PARAM_LIMIT,
 200                                          param, param_name, show_rl(rl));
 201         } END_FOR_EACH_SM(tmp);
 202 }
 203
 204 static void extra_mod_hook(const char *name, struct symbol *sym, struct expression *expr, struct smatch_state *state)
 205 {
 206         struct smatch_state *orig;
 207         struct symbol *param_sym;
 208         char *param_name;
 209
 210         if (expr && expr->smatch_flags & Fake)
 211                 return;
 212
 213         param_name = get_param_var_sym_var_sym(name, sym, NULL, &param_sym);
 214         if (!param_name || !param_sym)
 215                 goto free;
 216         if (get_param_num_from_sym(param_sym) < 0)
 217                 goto free;
 218
 219         /* already saved */
 220         if (get_state(my_id, param_name, param_sym))
 221                 goto free;
 222
 223         orig = get_state(SMATCH_EXTRA, param_name, param_sym);
 224         if (!orig)
 225                 orig = alloc_estate_whole(estate_type(state));
 226
 227         set_state(my_id, param_name, param_sym, orig);
 228 free:
 229         free_string(param_name);
 230 }
 231
 232 static void extra_nomod_hook(const char *name, struct symbol *sym, struct expression *expr, struct smatch_state *state)
 233 {
 234         if (__no_limits) {
 235                 set_state_stree(&ignore_states, my_id, name, sym, &undefined);
 236                 return;
 237         }
 238         set_state_stree(&limit_states, my_id, name, sym, &undefined);
 239 }
 240
 241 static void match_end_func(struct symbol *sym)
 242 {
 243         free_stree(&ignore_states);
 244         free_stree(&limit_states);
 245 }
 246
 247 void register_param_limit(int id)
 248 {
 249         my_id = id;
 250
 251         add_function_data((unsigned long *)&limit_states);
 252         add_function_data((unsigned long *)&ignore_states);
 253         add_hook(&match_end_func, END_FUNC_HOOK);
 254
 255         db_ignore_states(my_id);
 256         set_dynamic_states(my_id);
 257
 258         add_extra_mod_hook(&extra_mod_hook);
 259         add_extra_nomod_hook(&extra_nomod_hook);
 260         add_unmatched_state_hook(my_id, &unmatched_state);
 261         add_merge_hook(my_id, &merge_estates);
 262
 263         add_split_return_callback(&print_return_value_param);
 264 }
 265