[PATCH 32/45] analyzer: new file: sm-sensitive.cc
David Malcolm
dmalcolm@redhat.com
Fri Dec 13 18:12:00 GMT 2019
Changed in v4:
- Remove include of gcc-plugin.h, reworking includes accordingly.
- Wrap everything in #if ENABLE_ANALYZER
- Remove /// comment lines
- Rework on_leak vfunc:
https://gcc.gnu.org/ml/gcc-patches/2019-11/msg02028.html
- Rework for changes to is_named_call_p, resolving function pointers:
https://gcc.gnu.org/ml/gcc-patches/2019-12/msg00178.html
- Implement precision-of-wording vfuncs
This patch adds a state machine checker for tracking exposure of
sensitive data (e.g. writing passwords to log files).
This checker isn't ready for production, and is presented as a
proof-of-concept of the sm-based approach.
gcc/ChangeLog:
* analyzer/sm-sensitive.cc: New file.
---
gcc/analyzer/sm-sensitive.cc | 245 +++++++++++++++++++++++++++++++++++
1 file changed, 245 insertions(+)
create mode 100644 gcc/analyzer/sm-sensitive.cc
diff --git a/gcc/analyzer/sm-sensitive.cc b/gcc/analyzer/sm-sensitive.cc
new file mode 100644
index 000000000000..37219b915da3
--- /dev/null
+++ b/gcc/analyzer/sm-sensitive.cc
@@ -0,0 +1,245 @@
+/* An experimental state machine, for tracking exposure of sensitive
+ data (e.g. through logging).
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ Contributed by David Malcolm <dmalcolm@redhat.com>.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tree.h"
+#include "function.h"
+#include "function.h"
+#include "basic-block.h"
+#include "gimple.h"
+#include "options.h"
+#include "diagnostic-path.h"
+#include "diagnostic-metadata.h"
+#include "analyzer/analyzer.h"
+#include "analyzer/pending-diagnostic.h"
+#include "analyzer/sm.h"
+
+#if ENABLE_ANALYZER
+
+namespace {
+
+/* An experimental state machine, for tracking exposure of sensitive
+ data (e.g. through logging). */
+
+class sensitive_state_machine : public state_machine
+{
+public:
+ sensitive_state_machine (logger *logger);
+
+ bool inherited_state_p () const FINAL OVERRIDE { return true; }
+
+ bool on_stmt (sm_context *sm_ctxt,
+ const supernode *node,
+ const gimple *stmt) const FINAL OVERRIDE;
+
+ void on_condition (sm_context *sm_ctxt,
+ const supernode *node,
+ const gimple *stmt,
+ tree lhs,
+ enum tree_code op,
+ tree rhs) const FINAL OVERRIDE;
+
+ bool can_purge_p (state_t s) const FINAL OVERRIDE;
+
+ /* Start state. */
+ state_t m_start;
+
+ /* State for "sensitive" data, such as a password. */
+ state_t m_sensitive;
+
+ /* Stop state, for a value we don't want to track any more. */
+ state_t m_stop;
+
+private:
+ void warn_for_any_exposure (sm_context *sm_ctxt,
+ const supernode *node,
+ const gimple *stmt,
+ tree arg) const;
+};
+
+class exposure_through_output_file
+ : public pending_diagnostic_subclass<exposure_through_output_file>
+{
+public:
+ exposure_through_output_file (const sensitive_state_machine &sm, tree arg)
+ : m_sm (sm), m_arg (arg)
+ {}
+
+ const char *get_kind () const FINAL OVERRIDE
+ {
+ return "exposure_through_output_file";
+ }
+
+ bool operator== (const exposure_through_output_file &other) const
+ {
+ return m_arg == other.m_arg;
+ }
+
+ bool emit (rich_location *rich_loc) FINAL OVERRIDE
+ {
+ diagnostic_metadata m;
+ /* CWE-532: Information Exposure Through Log Files */
+ m.add_cwe (532);
+ return warning_at (rich_loc, m, OPT_Wanalyzer_exposure_through_output_file,
+ "sensitive value %qE written to output file",
+ m_arg);
+ }
+
+ label_text describe_state_change (const evdesc::state_change &change)
+ FINAL OVERRIDE
+ {
+ if (change.m_new_state == m_sm.m_sensitive)
+ {
+ m_first_sensitive_event = change.m_event_id;
+ return change.formatted_print ("sensitive value acquired here");
+ }
+ return label_text ();
+ }
+
+ label_text describe_call_with_state (const evdesc::call_with_state &info)
+ FINAL OVERRIDE
+ {
+ if (info.m_state == m_sm.m_sensitive)
+ return info.formatted_print
+ ("passing sensitive value %qE in call to %qE from %qE",
+ info.m_expr, info.m_callee_fndecl, info.m_caller_fndecl);
+ return label_text ();
+ }
+
+ label_text describe_return_of_state (const evdesc::return_of_state &info)
+ FINAL OVERRIDE
+ {
+ if (info.m_state == m_sm.m_sensitive)
+ return info.formatted_print ("returning sensitive value to %qE from %qE",
+ info.m_caller_fndecl, info.m_callee_fndecl);
+ return label_text ();
+ }
+
+ label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+ {
+ if (m_first_sensitive_event.known_p ())
+ return ev.formatted_print ("sensitive value %qE written to output file"
+ "; acquired at %@",
+ m_arg, &m_first_sensitive_event);
+ else
+ return ev.formatted_print ("sensitive value %qE written to output file",
+ m_arg);
+ }
+
+private:
+ const sensitive_state_machine &m_sm;
+ tree m_arg;
+ diagnostic_event_id_t m_first_sensitive_event;
+};
+
+/* sensitive_state_machine's ctor. */
+
+sensitive_state_machine::sensitive_state_machine (logger *logger)
+: state_machine ("sensitive", logger)
+{
+ m_start = add_state ("start");
+ m_sensitive = add_state ("sensitive");
+ m_stop = add_state ("stop");
+}
+
+/* Warn about an exposure at NODE and STMT if ARG is in the "sensitive"
+ state. */
+
+void
+sensitive_state_machine::warn_for_any_exposure (sm_context *sm_ctxt,
+ const supernode *node,
+ const gimple *stmt,
+ tree arg) const
+{
+ sm_ctxt->warn_for_state (node, stmt, arg, m_sensitive,
+ new exposure_through_output_file (*this, arg));
+}
+
+/* Implementation of state_machine::on_stmt vfunc for
+ sensitive_state_machine. */
+
+bool
+sensitive_state_machine::on_stmt (sm_context *sm_ctxt,
+ const supernode *node,
+ const gimple *stmt) const
+{
+ if (const gcall *call = dyn_cast <const gcall *> (stmt))
+ if (tree callee_fndecl = sm_ctxt->get_fndecl_for_call (call))
+ {
+ if (is_named_call_p (callee_fndecl, "getpass", call, 1))
+ {
+ tree lhs = gimple_call_lhs (call);
+ if (lhs)
+ sm_ctxt->on_transition (node, stmt, lhs, m_start, m_sensitive);
+ return true;
+ }
+ else if (is_named_call_p (callee_fndecl, "fprintf")
+ || is_named_call_p (callee_fndecl, "printf"))
+ {
+ /* Handle a match at any position in varargs. */
+ for (unsigned idx = 1; idx < gimple_call_num_args (call); idx++)
+ {
+ tree arg = gimple_call_arg (call, idx);
+ warn_for_any_exposure (sm_ctxt, node, stmt, arg);
+ }
+ return true;
+ }
+ else if (is_named_call_p (callee_fndecl, "fwrite", call, 4))
+ {
+ tree arg = gimple_call_arg (call, 0);
+ warn_for_any_exposure (sm_ctxt, node, stmt, arg);
+ return true;
+ }
+ // TODO: ...etc. This is just a proof-of-concept at this point.
+ }
+ return false;
+}
+
+void
+sensitive_state_machine::on_condition (sm_context *sm_ctxt ATTRIBUTE_UNUSED,
+ const supernode *node ATTRIBUTE_UNUSED,
+ const gimple *stmt ATTRIBUTE_UNUSED,
+ tree lhs ATTRIBUTE_UNUSED,
+ enum tree_code op ATTRIBUTE_UNUSED,
+ tree rhs ATTRIBUTE_UNUSED) const
+{
+ /* Empty. */
+}
+
+bool
+sensitive_state_machine::can_purge_p (state_t s ATTRIBUTE_UNUSED) const
+{
+ return true;
+}
+
+} // anonymous namespace
+
+/* Internal interface to this file. */
+
+state_machine *
+make_sensitive_state_machine (logger *logger)
+{
+ return new sensitive_state_machine (logger);
+}
+
+#endif /* #if ENABLE_ANALYZER */
--
2.21.0
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