gcc/analyzer/sm-sensitive.cc

   1 /* An experimental state machine, for tracking exposure of sensitive
   2    data (e.g. through logging).
   3    Copyright (C) 2019-2023 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 #define INCLUDE_MEMORY
  24 #include "system.h"
  25 #include "coretypes.h"
  26 #include "make-unique.h"
  27 #include "tree.h"
  28 #include "function.h"
  29 #include "basic-block.h"
  30 #include "gimple.h"
  31 #include "options.h"
  32 #include "diagnostic-path.h"
  33 #include "analyzer/analyzer.h"
  34 #include "diagnostic-event-id.h"
  35 #include "analyzer/analyzer-logging.h"
  36 #include "analyzer/sm.h"
  37 #include "analyzer/pending-diagnostic.h"
  38
  39 #if ENABLE_ANALYZER
  40
  41 namespace ana {
  42
  43 namespace {
  44
  45 /* An experimental state machine, for tracking exposure of sensitive
  46    data (e.g. through logging).  */
  47
  48 class sensitive_state_machine : public state_machine
  49 {
  50 public:
  51   sensitive_state_machine (logger *logger);
  52
  53   bool inherited_state_p () const final override { return true; }
  54
  55   bool on_stmt (sm_context *sm_ctxt,
  56                 const supernode *node,
  57                 const gimple *stmt) const final override;
  58
  59   bool can_purge_p (state_t s) const final override;
  60
  61   /* State for "sensitive" data, such as a password.  */
  62   state_t m_sensitive;
  63
  64   /* Stop state, for a value we don't want to track any more.  */
  65   state_t m_stop;
  66
  67 private:
  68   void warn_for_any_exposure (sm_context *sm_ctxt,
  69                               const supernode *node,
  70                               const gimple *stmt,
  71                               tree arg) const;
  72 };
  73
  74 class exposure_through_output_file
  75   : public pending_diagnostic_subclass<exposure_through_output_file>
  76 {
  77 public:
  78   exposure_through_output_file (const sensitive_state_machine &sm, tree arg)
  79   : m_sm (sm), m_arg (arg)
  80   {}
  81
  82   const char *get_kind () const final override
  83   {
  84     return "exposure_through_output_file";
  85   }
  86
  87   bool operator== (const exposure_through_output_file &other) const
  88   {
  89     return same_tree_p (m_arg, other.m_arg);
  90   }
  91
  92   int get_controlling_option () const final override
  93   {
  94     return OPT_Wanalyzer_exposure_through_output_file;
  95   }
  96
  97   bool emit (diagnostic_emission_context &ctxt) final override
  98   {
  99     /* CWE-532: Information Exposure Through Log Files */
 100     ctxt.add_cwe (532);
 101     return ctxt.warn ("sensitive value %qE written to output file",
 102                       m_arg);
 103   }
 104
 105   label_text describe_state_change (const evdesc::state_change &change)
 106     final override
 107   {
 108     if (change.m_new_state == m_sm.m_sensitive)
 109       {
 110         m_first_sensitive_event = change.m_event_id;
 111         return change.formatted_print ("sensitive value acquired here");
 112       }
 113     return label_text ();
 114   }
 115
 116   diagnostic_event::meaning
 117   get_meaning_for_state_change (const evdesc::state_change &change)
 118     const final override
 119   {
 120     if (change.m_new_state == m_sm.m_sensitive)
 121       return diagnostic_event::meaning (diagnostic_event::VERB_acquire,
 122                                         diagnostic_event::NOUN_sensitive);
 123     return diagnostic_event::meaning ();
 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   m_sensitive (add_state ("sensitive")),
 166   m_stop (add_state ("stop"))
 167 {
 168 }
 169
 170 /* Warn about an exposure at NODE and STMT if ARG is in the "sensitive"
 171    state.  */
 172
 173 void
 174 sensitive_state_machine::warn_for_any_exposure (sm_context *sm_ctxt,
 175                                                 const supernode *node,
 176                                                 const gimple *stmt,
 177                                                 tree arg) const
 178 {
 179   if (sm_ctxt->get_state (stmt, arg) == m_sensitive)
 180     {
 181       tree diag_arg = sm_ctxt->get_diagnostic_tree (arg);
 182       sm_ctxt->warn (node, stmt, arg,
 183                      make_unique<exposure_through_output_file> (*this,
 184                                                                 diag_arg));
 185     }
 186 }
 187
 188 /* Implementation of state_machine::on_stmt vfunc for
 189    sensitive_state_machine.  */
 190
 191 bool
 192 sensitive_state_machine::on_stmt (sm_context *sm_ctxt,
 193                                   const supernode *node,
 194                                   const gimple *stmt) const
 195 {
 196   if (const gcall *call = dyn_cast <const gcall *> (stmt))
 197     if (tree callee_fndecl = sm_ctxt->get_fndecl_for_call (call))
 198       {
 199         if (is_named_call_p (callee_fndecl, "getpass", call, 1))
 200           {
 201             tree lhs = gimple_call_lhs (call);
 202             if (lhs)
 203               sm_ctxt->on_transition (node, stmt, lhs, m_start, m_sensitive);
 204             return true;
 205           }
 206         else if (is_named_call_p (callee_fndecl, "fprintf")
 207                  || is_named_call_p (callee_fndecl, "printf"))
 208           {
 209             /* Handle a match at any position in varargs.  */
 210             for (unsigned idx = 1; idx < gimple_call_num_args (call); idx++)
 211               {
 212                 tree arg = gimple_call_arg (call, idx);
 213                 warn_for_any_exposure (sm_ctxt, node, stmt, arg);
 214               }
 215             return true;
 216           }
 217         else if (is_named_call_p (callee_fndecl, "fwrite", call, 4))
 218           {
 219             tree arg = gimple_call_arg (call, 0);
 220             warn_for_any_exposure (sm_ctxt, node, stmt, arg);
 221             return true;
 222           }
 223         // TODO: ...etc.  This is just a proof-of-concept at this point.
 224       }
 225   return false;
 226 }
 227
 228 bool
 229 sensitive_state_machine::can_purge_p (state_t s ATTRIBUTE_UNUSED) const
 230 {
 231   return true;
 232 }
 233
 234 } // anonymous namespace
 235
 236 /* Internal interface to this file. */
 237
 238 state_machine *
 239 make_sensitive_state_machine (logger *logger)
 240 {
 241   return new sensitive_state_machine (logger);
 242 }
 243
 244 } // namespace ana
 245
 246 #endif /* #if ENABLE_ANALYZER */