gcc/analyzer/sm-sensitive.cc

   1 /* An experimental state machine, for tracking exposure of sensitive
   2    data (e.g. through logging).
   3    Copyright (C) 2019-2020 Free Software Foundation, Inc.
   4    Contributed by David Malcolm <dmalcolm@redhat.com>.
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it
   9 under the terms of the GNU General Public License as published by
  10 the Free Software Foundation; either version 3, or (at your option)
  11 any later version.
  12
  13 GCC is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of
  15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16 General Public License for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING3.  If not see
  20 <http://www.gnu.org/licenses/>.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tree.h"
  26 #include "function.h"
  27 #include "function.h"
  28 #include "basic-block.h"
  29 #include "gimple.h"
  30 #include "options.h"
  31 #include "diagnostic-path.h"
  32 #include "diagnostic-metadata.h"
  33 #include "function.h"
  34 #include "analyzer/analyzer.h"
  35 #include "diagnostic-event-id.h"
  36 #include "analyzer/analyzer-logging.h"
  37 #include "analyzer/sm.h"
  38 #include "analyzer/pending-diagnostic.h"
  39
  40 #if ENABLE_ANALYZER
  41
  42 namespace ana {
  43
  44 namespace {
  45
  46 /* An experimental state machine, for tracking exposure of sensitive
  47    data (e.g. through logging).  */
  48
  49 class sensitive_state_machine : public state_machine
  50 {
  51 public:
  52   sensitive_state_machine (logger *logger);
  53
  54   bool inherited_state_p () const FINAL OVERRIDE { return true; }
  55
  56   bool on_stmt (sm_context *sm_ctxt,
  57                 const supernode *node,
  58                 const gimple *stmt) const FINAL OVERRIDE;
  59
  60   void on_condition (sm_context *sm_ctxt,
  61                      const supernode *node,
  62                      const gimple *stmt,
  63                      tree lhs,
  64                      enum tree_code op,
  65                      tree rhs) const FINAL OVERRIDE;
  66
  67   bool can_purge_p (state_t s) const FINAL OVERRIDE;
  68
  69   /* Start state.  */
  70   state_t m_start;
  71
  72   /* State for "sensitive" data, such as a password.  */
  73   state_t m_sensitive;
  74
  75   /* Stop state, for a value we don't want to track any more.  */
  76   state_t m_stop;
  77
  78 private:
  79   void warn_for_any_exposure (sm_context *sm_ctxt,
  80                               const supernode *node,
  81                               const gimple *stmt,
  82                               tree arg) const;
  83 };
  84
  85 class exposure_through_output_file
  86   : public pending_diagnostic_subclass<exposure_through_output_file>
  87 {
  88 public:
  89   exposure_through_output_file (const sensitive_state_machine &sm, tree arg)
  90   : m_sm (sm), m_arg (arg)
  91   {}
  92
  93   const char *get_kind () const FINAL OVERRIDE
  94   {
  95     return "exposure_through_output_file";
  96   }
  97
  98   bool operator== (const exposure_through_output_file &other) const
  99   {
 100     return same_tree_p (m_arg, other.m_arg);
 101   }
 102
 103   bool emit (rich_location *rich_loc) FINAL OVERRIDE
 104   {
 105     diagnostic_metadata m;
 106     /* CWE-532: Information Exposure Through Log Files */
 107     m.add_cwe (532);
 108     return warning_meta (rich_loc, m,
 109                          OPT_Wanalyzer_exposure_through_output_file,
 110                          "sensitive value %qE written to output file",
 111                          m_arg);
 112   }
 113
 114   label_text describe_state_change (const evdesc::state_change &change)
 115     FINAL OVERRIDE
 116   {
 117     if (change.m_new_state == m_sm.m_sensitive)
 118       {
 119         m_first_sensitive_event = change.m_event_id;
 120         return change.formatted_print ("sensitive value acquired here");
 121       }
 122     return label_text ();
 123   }
 124
 125   label_text describe_call_with_state (const evdesc::call_with_state &info)
 126     FINAL OVERRIDE
 127   {
 128     if (info.m_state == m_sm.m_sensitive)
 129       return info.formatted_print
 130         ("passing sensitive value %qE in call to %qE from %qE",
 131          info.m_expr, info.m_callee_fndecl, info.m_caller_fndecl);
 132     return label_text ();
 133   }
 134
 135   label_text describe_return_of_state (const evdesc::return_of_state &info)
 136     FINAL OVERRIDE
 137   {
 138     if (info.m_state == m_sm.m_sensitive)
 139       return info.formatted_print ("returning sensitive value to %qE from %qE",
 140                                    info.m_caller_fndecl, info.m_callee_fndecl);
 141     return label_text ();
 142   }
 143
 144   label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
 145   {
 146     if (m_first_sensitive_event.known_p ())
 147       return ev.formatted_print ("sensitive value %qE written to output file"
 148                                  "; acquired at %@",
 149                                  m_arg, &m_first_sensitive_event);
 150     else
 151       return ev.formatted_print ("sensitive value %qE written to output file",
 152                                  m_arg);
 153   }
 154
 155 private:
 156   const sensitive_state_machine &m_sm;
 157   tree m_arg;
 158   diagnostic_event_id_t m_first_sensitive_event;
 159 };
 160
 161 /* sensitive_state_machine's ctor.  */
 162
 163 sensitive_state_machine::sensitive_state_machine (logger *logger)
 164 : state_machine ("sensitive", logger)
 165 {
 166   m_start = add_state ("start");
 167   m_sensitive = add_state ("sensitive");
 168   m_stop = add_state ("stop");
 169 }
 170
 171 /* Warn about an exposure at NODE and STMT if ARG is in the "sensitive"
 172    state.  */
 173
 174 void
 175 sensitive_state_machine::warn_for_any_exposure (sm_context *sm_ctxt,
 176                                                 const supernode *node,
 177                                                 const gimple *stmt,
 178                                                 tree arg) const
 179 {
 180   sm_ctxt->warn_for_state (node, stmt, arg, m_sensitive,
 181                            new exposure_through_output_file (*this, arg));
 182 }
 183
 184 /* Implementation of state_machine::on_stmt vfunc for
 185    sensitive_state_machine.  */
 186
 187 bool
 188 sensitive_state_machine::on_stmt (sm_context *sm_ctxt,
 189                                   const supernode *node,
 190                                   const gimple *stmt) const
 191 {
 192   if (const gcall *call = dyn_cast <const gcall *> (stmt))
 193     if (tree callee_fndecl = sm_ctxt->get_fndecl_for_call (call))
 194       {
 195         if (is_named_call_p (callee_fndecl, "getpass", call, 1))
 196           {
 197             tree lhs = gimple_call_lhs (call);
 198             if (lhs)
 199               sm_ctxt->on_transition (node, stmt, lhs, m_start, m_sensitive);
 200             return true;
 201           }
 202         else if (is_named_call_p (callee_fndecl, "fprintf")
 203                  || is_named_call_p (callee_fndecl, "printf"))
 204           {
 205             /* Handle a match at any position in varargs.  */
 206             for (unsigned idx = 1; idx < gimple_call_num_args (call); idx++)
 207               {
 208                 tree arg = gimple_call_arg (call, idx);
 209                 warn_for_any_exposure (sm_ctxt, node, stmt, arg);
 210               }
 211             return true;
 212           }
 213         else if (is_named_call_p (callee_fndecl, "fwrite", call, 4))
 214           {
 215             tree arg = gimple_call_arg (call, 0);
 216             warn_for_any_exposure (sm_ctxt, node, stmt, arg);
 217             return true;
 218           }
 219         // TODO: ...etc.  This is just a proof-of-concept at this point.
 220       }
 221   return false;
 222 }
 223
 224 void
 225 sensitive_state_machine::on_condition (sm_context *sm_ctxt ATTRIBUTE_UNUSED,
 226                                        const supernode *node ATTRIBUTE_UNUSED,
 227                                        const gimple *stmt ATTRIBUTE_UNUSED,
 228                                        tree lhs ATTRIBUTE_UNUSED,
 229                                        enum tree_code op ATTRIBUTE_UNUSED,
 230                                        tree rhs ATTRIBUTE_UNUSED) const
 231 {
 232   /* Empty.  */
 233 }
 234
 235 bool
 236 sensitive_state_machine::can_purge_p (state_t s ATTRIBUTE_UNUSED) const
 237 {
 238   return true;
 239 }
 240
 241 } // anonymous namespace
 242
 243 /* Internal interface to this file. */
 244
 245 state_machine *
 246 make_sensitive_state_machine (logger *logger)
 247 {
 248   return new sensitive_state_machine (logger);
 249 }
 250
 251 } // namespace ana
 252
 253 #endif /* #if ENABLE_ANALYZER */