gcc/analyzer/sm-taint.cc

/* An experimental state machine, for tracking "taint": unsanitized uses
   of data potentially under an attacker's control.

   Copyright (C) 2019-2021 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 "basic-block.h"
#include "gimple.h"
#include "options.h"
#include "diagnostic-path.h"
#include "diagnostic-metadata.h"
#include "function.h"
#include "json.h"
#include "analyzer/analyzer.h"
#include "analyzer/analyzer-logging.h"
#include "gimple-iterator.h"
#include "tristate.h"
#include "selftest.h"
#include "ordered-hash-map.h"
#include "cgraph.h"
#include "cfg.h"
#include "digraph.h"
#include "analyzer/supergraph.h"
#include "analyzer/call-string.h"
#include "analyzer/program-point.h"
#include "analyzer/store.h"
#include "analyzer/region-model.h"
#include "analyzer/sm.h"
#include "analyzer/program-state.h"
#include "analyzer/pending-diagnostic.h"

#if ENABLE_ANALYZER

namespace ana {

namespace {

/* An enum for describing tainted values.  */

enum bounds
{
  /* This tainted value has no upper or lower bound.  */
  BOUNDS_NONE,

  /* This tainted value has an upper bound but not lower bound.  */
  BOUNDS_UPPER,

  /* This tainted value has a lower bound but no upper bound.  */
  BOUNDS_LOWER
};

/* An experimental state machine, for tracking "taint": unsanitized uses
   of data potentially under an attacker's control.  */

class taint_state_machine : public state_machine
{
public:
  taint_state_machine (logger *logger);

  bool inherited_state_p () const FINAL OVERRIDE { return true; }

  state_t alt_get_inherited_state (const sm_state_map &map,
				   const svalue *sval,
				   const extrinsic_state &ext_state)
    const FINAL OVERRIDE;

  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,
		     const svalue *lhs,
		     enum tree_code op,
		     const svalue *rhs) const FINAL OVERRIDE;

  bool can_purge_p (state_t s) const FINAL OVERRIDE;

  bool get_taint (state_t s, tree type, enum bounds *out) const;

  state_t combine_states (state_t s0, state_t s1) const;

  /* State for a "tainted" value: unsanitized data potentially under an
     attacker's control.  */
  state_t m_tainted;

  /* State for a "tainted" value that has a lower bound.  */
  state_t m_has_lb;

  /* State for a "tainted" value that has an upper bound.  */
  state_t m_has_ub;

  /* Stop state, for a value we don't want to track any more.  */
  state_t m_stop;
};

/* Class for diagnostics relating to taint_state_machine.  */

class taint_diagnostic : public pending_diagnostic
{
public:
  taint_diagnostic (const taint_state_machine &sm, tree arg,
		    enum bounds has_bounds)
  : m_sm (sm), m_arg (arg), m_has_bounds (has_bounds)
  {}

  bool subclass_equal_p (const pending_diagnostic &base_other) const OVERRIDE
  {
    return same_tree_p (m_arg, ((const taint_diagnostic &)base_other).m_arg);
  }

  label_text describe_state_change (const evdesc::state_change &change)
    FINAL OVERRIDE
  {
    if (change.m_new_state == m_sm.m_tainted)
      {
	if (change.m_origin)
	  return change.formatted_print ("%qE has an unchecked value here"
					 " (from %qE)",
					 change.m_expr, change.m_origin);
	else
	  return change.formatted_print ("%qE gets an unchecked value here",
					 change.m_expr);
      }
    else if (change.m_new_state == m_sm.m_has_lb)
      return change.formatted_print ("%qE has its lower bound checked here",
				     change.m_expr);
    else if (change.m_new_state == m_sm.m_has_ub)
      return change.formatted_print ("%qE has its upper bound checked here",
				     change.m_expr);
    return label_text ();
  }
protected:
  const taint_state_machine &m_sm;
  tree m_arg;
  enum bounds m_has_bounds;
};

/* Concrete taint_diagnostic subclass for reporting attacker-controlled
   array index.  */

class tainted_array_index : public taint_diagnostic
{
public:
  tainted_array_index (const taint_state_machine &sm, tree arg,
		       enum bounds has_bounds)
  : taint_diagnostic (sm, arg, has_bounds)
  {}

  const char *get_kind () const FINAL OVERRIDE { return "tainted_array_index"; }

  bool emit (rich_location *rich_loc) FINAL OVERRIDE
  {
    diagnostic_metadata m;
    /* CWE-129: "Improper Validation of Array Index".  */
    m.add_cwe (129);
    switch (m_has_bounds)
      {
      default:
	gcc_unreachable ();
      case BOUNDS_NONE:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_array_index,
			     "use of attacker-controlled value %qE"
			     " in array lookup without bounds checking",
			     m_arg);
	break;
      case BOUNDS_UPPER:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_array_index,
			     "use of attacker-controlled value %qE"
			     " in array lookup without checking for negative",
			     m_arg);
	break;
      case BOUNDS_LOWER:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_array_index,
			     "use of attacker-controlled value %qE"
			     " in array lookup without upper-bounds checking",
			     m_arg);
	break;
      }
  }

  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
  {
    switch (m_has_bounds)
      {
      default:
	gcc_unreachable ();
      case BOUNDS_NONE:
	return ev.formatted_print
	  ("use of attacker-controlled value %qE in array lookup"
	   " without bounds checking",
	   m_arg);
      case BOUNDS_UPPER:
	return ev.formatted_print
	  ("use of attacker-controlled value %qE"
	   " in array lookup without checking for negative",
	   m_arg);
      case BOUNDS_LOWER:
	return ev.formatted_print
	  ("use of attacker-controlled value %qE"
	   " in array lookup without upper-bounds checking",
	   m_arg);
      }
  }
};

/* Concrete taint_diagnostic subclass for reporting attacker-controlled
   pointer offset.  */

class tainted_offset : public taint_diagnostic
{
public:
  tainted_offset (const taint_state_machine &sm, tree arg,
		       enum bounds has_bounds)
  : taint_diagnostic (sm, arg, has_bounds)
  {}

  const char *get_kind () const FINAL OVERRIDE { return "tainted_offset"; }

  bool emit (rich_location *rich_loc) FINAL OVERRIDE
  {
    diagnostic_metadata m;
    /* CWE-823: "Use of Out-of-range Pointer Offset".  */
    m.add_cwe (823);
    if (m_arg)
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value %qE as offset"
			       " without bounds checking",
			       m_arg);
	  break;
	case BOUNDS_UPPER:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value %qE as offset"
			       " without lower-bounds checking",
			       m_arg);
	  break;
	case BOUNDS_LOWER:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value %qE as offset"
			       " without upper-bounds checking",
			       m_arg);
	  break;
	}
    else
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value as offset"
			       " without bounds checking");
	  break;
	case BOUNDS_UPPER:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value as offset"
			       " without lower-bounds checking");
	  break;
	case BOUNDS_LOWER:
	  return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_offset,
			       "use of attacker-controlled value as offset"
			       " without upper-bounds checking");
	  break;
	}
  }

  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
  {
    if (m_arg)
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return ev.formatted_print ("use of attacker-controlled value %qE"
				     " as offset without bounds checking",
				     m_arg);
	case BOUNDS_UPPER:
	  return ev.formatted_print ("use of attacker-controlled value %qE"
				     " as offset without lower-bounds checking",
				     m_arg);
	case BOUNDS_LOWER:
	  return ev.formatted_print ("use of attacker-controlled value %qE"
				     " as offset without upper-bounds checking",
				     m_arg);
	}
    else
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return ev.formatted_print ("use of attacker-controlled value"
				     " as offset without bounds checking");
	case BOUNDS_UPPER:
	  return ev.formatted_print ("use of attacker-controlled value"
				     " as offset without lower-bounds"
				     " checking");
	case BOUNDS_LOWER:
	  return ev.formatted_print ("use of attacker-controlled value"
				     " as offset without upper-bounds"
				     " checking");
	}
  }
};

/* Concrete taint_diagnostic subclass for reporting attacker-controlled
   size.  */

class tainted_size : public taint_diagnostic
{
public:
  tainted_size (const taint_state_machine &sm, tree arg,
		enum bounds has_bounds,
		enum access_direction dir)
  : taint_diagnostic (sm, arg, has_bounds),
    m_dir (dir)
  {}

  const char *get_kind () const FINAL OVERRIDE { return "tainted_size"; }

  bool emit (rich_location *rich_loc) FINAL OVERRIDE
  {
    diagnostic_metadata m;
    m.add_cwe (129);
    switch (m_has_bounds)
      {
      default:
	gcc_unreachable ();
      case BOUNDS_NONE:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_size,
			     "use of attacker-controlled value %qE as size"
			     " without bounds checking",
			     m_arg);
	break;
      case BOUNDS_UPPER:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_size,
			     "use of attacker-controlled value %qE as size"
			     " without lower-bounds checking",
			     m_arg);
	break;
      case BOUNDS_LOWER:
	return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_size,
			     "use of attacker-controlled value %qE as size"
			     " without upper-bounds checking",
			     m_arg);
	break;
      }
  }

  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
  {
    switch (m_has_bounds)
      {
      default:
	gcc_unreachable ();
      case BOUNDS_NONE:
	return ev.formatted_print ("use of attacker-controlled value %qE"
				   " as size without bounds checking",
				   m_arg);
      case BOUNDS_UPPER:
	return ev.formatted_print ("use of attacker-controlled value %qE"
				   " as size without lower-bounds checking",
				   m_arg);
      case BOUNDS_LOWER:
	return ev.formatted_print ("use of attacker-controlled value %qE"
				   " as size without upper-bounds checking",
				   m_arg);
      }
  }

private:
  enum access_direction m_dir;
};

/* Concrete taint_diagnostic subclass for reporting attacker-controlled
   divisor (so that an attacker can trigger a divide by zero).  */

class tainted_divisor : public taint_diagnostic
{
public:
  tainted_divisor (const taint_state_machine &sm, tree arg,
		   enum bounds has_bounds)
  : taint_diagnostic (sm, arg, has_bounds)
  {}

  const char *get_kind () const FINAL OVERRIDE { return "tainted_divisor"; }

  bool emit (rich_location *rich_loc) FINAL OVERRIDE
  {
    diagnostic_metadata m;
    /* CWE-369: "Divide By Zero".  */
    m.add_cwe (369);
    if (m_arg)
      return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_divisor,
			   "use of attacker-controlled value %qE as divisor"
			   " without checking for zero",
			   m_arg);
    else
      return warning_meta (rich_loc, m, OPT_Wanalyzer_tainted_divisor,
			   "use of attacker-controlled value as divisor"
			   " without checking for zero");
  }

  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
  {
    if (m_arg)
      return ev.formatted_print
	("use of attacker-controlled value %qE as divisor"
	 " without checking for zero",
	 m_arg);
    else
      return ev.formatted_print
	("use of attacker-controlled value as divisor"
	 " without checking for zero");
  }
};

/* Concrete taint_diagnostic subclass for reporting attacker-controlled
   size of a dynamic allocation.  */

class tainted_allocation_size : public taint_diagnostic
{
public:
  tainted_allocation_size (const taint_state_machine &sm, tree arg,
			   enum bounds has_bounds, enum memory_space mem_space)
  : taint_diagnostic (sm, arg, has_bounds),
    m_mem_space (mem_space)
  {
    gcc_assert (mem_space == MEMSPACE_STACK || mem_space == MEMSPACE_HEAP);
  }

  const char *get_kind () const FINAL OVERRIDE
  {
    return "tainted_allocation_size";
  }

  bool emit (rich_location *rich_loc) FINAL OVERRIDE
  {
    diagnostic_metadata m;
    /* "CWE-789: Memory Allocation with Excessive Size Value".  */
    m.add_cwe (789);
    gcc_assert (m_mem_space == MEMSPACE_STACK || m_mem_space == MEMSPACE_HEAP);
    // TODO: make use of m_mem_space
    if (m_arg)
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value %qE as"
			       " allocation size without bounds checking",
			       m_arg);
	  break;
	case BOUNDS_UPPER:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value %qE as"
			       " allocation size without lower-bounds checking",
			       m_arg);
	  break;
	case BOUNDS_LOWER:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value %qE as"
			       " allocation size without upper-bounds checking",
			     m_arg);
	  break;
	}
    else
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value as"
			       " allocation size without bounds"
			       " checking");
	  break;
	case BOUNDS_UPPER:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value as"
			       " allocation size without lower-bounds"
			       " checking");
	  break;
	case BOUNDS_LOWER:
	  return warning_meta (rich_loc, m,
			       OPT_Wanalyzer_tainted_allocation_size,
			       "use of attacker-controlled value as"
			       " allocation size without upper-bounds"
			       " checking");
	  break;
	}
  }

  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
  {
    if (m_arg)
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return ev.formatted_print
	    ("use of attacker-controlled value %qE as allocation size"
	     " without bounds checking",
	     m_arg);
	case BOUNDS_UPPER:
	  return ev.formatted_print
	    ("use of attacker-controlled value %qE as allocation size"
	     " without lower-bounds checking",
	     m_arg);
	case BOUNDS_LOWER:
	  return ev.formatted_print
	    ("use of attacker-controlled value %qE as allocation size"
	     " without upper-bounds checking",
	     m_arg);
	}
    else
      switch (m_has_bounds)
	{
	default:
	  gcc_unreachable ();
	case BOUNDS_NONE:
	  return ev.formatted_print
	    ("use of attacker-controlled value as allocation size"
	     " without bounds checking");
	case BOUNDS_UPPER:
	  return ev.formatted_print
	    ("use of attacker-controlled value as allocation size"
	     " without lower-bounds checking");
	case BOUNDS_LOWER:
	  return ev.formatted_print
	    ("use of attacker-controlled value as allocation size"
	     " without upper-bounds checking");
	}
  }

private:
  enum memory_space m_mem_space;
};

/* taint_state_machine's ctor.  */

taint_state_machine::taint_state_machine (logger *logger)
: state_machine ("taint", logger)
{
  m_tainted = add_state ("tainted");
  m_has_lb = add_state ("has_lb");
  m_has_ub = add_state ("has_ub");
  m_stop = add_state ("stop");
}

state_machine::state_t
taint_state_machine::alt_get_inherited_state (const sm_state_map &map,
					      const svalue *sval,
					      const extrinsic_state &ext_state)
  const
{
  switch (sval->get_kind ())
    {
    default:
      break;
    case SK_UNARYOP:
      {
	const unaryop_svalue *unaryop_sval
	  = as_a <const unaryop_svalue *> (sval);
	enum tree_code op = unaryop_sval->get_op ();
	const svalue *arg = unaryop_sval->get_arg ();
	switch (op)
	  {
	  case NOP_EXPR:
	    {
	      state_t arg_state = map.get_state (arg, ext_state);
	      return arg_state;
	    }
	  default:
	    gcc_unreachable ();
	    break;
	  }
      }
      break;
    case SK_BINOP:
      {
	const binop_svalue *binop_sval = as_a <const binop_svalue *> (sval);
	enum tree_code op = binop_sval->get_op ();
	const svalue *arg0 = binop_sval->get_arg0 ();
	const svalue *arg1 = binop_sval->get_arg1 ();
	switch (op)
	  {
	  default:
	    break;
	  case PLUS_EXPR:
	  case MINUS_EXPR:
	  case MULT_EXPR:
	  case POINTER_PLUS_EXPR:
	  case TRUNC_DIV_EXPR:
	  case TRUNC_MOD_EXPR:
	    {
	      state_t arg0_state = map.get_state (arg0, ext_state);
	      state_t arg1_state = map.get_state (arg1, ext_state);
	      return combine_states (arg0_state, arg1_state);
	    }
	    break;

	  case EQ_EXPR:
	  case GE_EXPR:
	  case LE_EXPR:
	  case NE_EXPR:
	  case GT_EXPR:
	  case LT_EXPR:
	  case UNORDERED_EXPR:
	  case ORDERED_EXPR:
	    /* Comparisons are just booleans.  */
	    return m_start;

	  case BIT_AND_EXPR:
	  case RSHIFT_EXPR:
	    return NULL;
	  }
      }
      break;
    }
  return NULL;
}

/* Implementation of state_machine::on_stmt vfunc for taint_state_machine.  */

bool
taint_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, "fread", call, 4))
	  {
	    tree arg = gimple_call_arg (call, 0);

	    sm_ctxt->on_transition (node, stmt, arg, m_start, m_tainted);

	    /* Dereference an ADDR_EXPR.  */
	    // TODO: should the engine do this?
	    if (TREE_CODE (arg) == ADDR_EXPR)
	      sm_ctxt->on_transition (node, stmt, TREE_OPERAND (arg, 0),
				      m_start, m_tainted);
	    return true;
	  }
      }
  // TODO: ...etc; many other sources of untrusted data

  if (const gassign *assign = dyn_cast <const gassign *> (stmt))
    {
      enum tree_code op = gimple_assign_rhs_code (assign);

      switch (op)
	{
	default:
	  break;
	case TRUNC_DIV_EXPR:
	case CEIL_DIV_EXPR:
	case FLOOR_DIV_EXPR:
	case ROUND_DIV_EXPR:
	case TRUNC_MOD_EXPR:
	case CEIL_MOD_EXPR:
	case FLOOR_MOD_EXPR:
	case ROUND_MOD_EXPR:
	case RDIV_EXPR:
	case EXACT_DIV_EXPR:
	  {
	    tree divisor = gimple_assign_rhs2 (assign);;
	    state_t state = sm_ctxt->get_state (stmt, divisor);
	    enum bounds b;
	    if (get_taint (state, TREE_TYPE (divisor), &b))
	      {
		tree diag_divisor = sm_ctxt->get_diagnostic_tree (divisor);
		sm_ctxt->warn  (node, stmt, divisor,
				new tainted_divisor (*this, diag_divisor, b));
		sm_ctxt->set_next_state (stmt, divisor, m_stop);
	      }
	  }
	  break;
	}
    }

  return false;
}

/* Implementation of state_machine::on_condition vfunc for taint_state_machine.
   Potentially transition state 'tainted' to 'has_ub' or 'has_lb',
   and states 'has_ub' and 'has_lb' to 'stop'.  */

void
taint_state_machine::on_condition (sm_context *sm_ctxt,
				   const supernode *node,
				   const gimple *stmt,
				   const svalue *lhs,
				   enum tree_code op,
				   const svalue *rhs ATTRIBUTE_UNUSED) const
{
  if (stmt == NULL)
    return;

  // TODO: this doesn't use the RHS; should we make it symmetric?

  // TODO
  switch (op)
    {
      //case NE_EXPR:
      //case EQ_EXPR:
    case GE_EXPR:
    case GT_EXPR:
      {
	sm_ctxt->on_transition (node, stmt, lhs, m_tainted,
				m_has_lb);
	sm_ctxt->on_transition (node, stmt, lhs, m_has_ub,
				m_stop);
      }
      break;
    case LE_EXPR:
    case LT_EXPR:
      {
	sm_ctxt->on_transition (node, stmt, lhs, m_tainted,
				m_has_ub);
	sm_ctxt->on_transition (node, stmt, lhs, m_has_lb,
				m_stop);
      }
      break;
    default:
      break;
    }
}

bool
taint_state_machine::can_purge_p (state_t s ATTRIBUTE_UNUSED) const
{
  return true;
}

/* If STATE is a tainted state, write the bounds to *OUT and return true.
   Otherwise return false.
   Use the signedness of TYPE to determine if "has_ub" is tainted.  */

bool
taint_state_machine::get_taint (state_t state, tree type,
				enum bounds *out) const
{
  /* Unsigned types have an implicit lower bound.  */
  bool is_unsigned = false;
  if (type)
    if (INTEGRAL_TYPE_P (type))
      is_unsigned = TYPE_UNSIGNED (type);

  /* Can't use a switch as the states are non-const.  */
  if (state == m_tainted)
    {
      *out = is_unsigned ? BOUNDS_LOWER : BOUNDS_NONE;
      return true;
    }
  else if (state == m_has_lb)
    {
      *out = BOUNDS_LOWER;
      return true;
    }
  else if (state == m_has_ub && !is_unsigned)
    {
      /* Missing lower bound.  */
      *out = BOUNDS_UPPER;
      return true;
    }
  return false;
}

/* Find the most tainted state of S0 and S1.  */

state_machine::state_t
taint_state_machine::combine_states (state_t s0, state_t s1) const
{
  gcc_assert (s0);
  gcc_assert (s1);
  if (s0 == s1)
    return s0;
  if (s0 == m_tainted || s1 == m_tainted)
    return m_tainted;
  if (s0 == m_stop)
    return s1;
  if (s1 == m_stop)
    return s0;
  if (s0 == m_start)
    return s1;
  if (s1 == m_start)
    return s0;
  gcc_unreachable ();
}

} // anonymous namespace

/* Internal interface to this file. */

state_machine *
make_taint_state_machine (logger *logger)
{
  return new taint_state_machine (logger);
}

/* Complain to CTXT if accessing REG leads could lead to arbitrary
   memory access under an attacker's control (due to taint).  */

void
region_model::check_region_for_taint (const region *reg,
				      enum access_direction dir,
				      region_model_context *ctxt) const
{
  gcc_assert (reg);
  gcc_assert (ctxt);

  LOG_SCOPE (ctxt->get_logger ());

  sm_state_map *smap;
  const state_machine *sm;
  unsigned sm_idx;
  if (!ctxt->get_taint_map (&smap, &sm, &sm_idx))
    return;

  gcc_assert (smap);
  gcc_assert (sm);

  const taint_state_machine &taint_sm = (const taint_state_machine &)*sm;

  const extrinsic_state *ext_state = ctxt->get_ext_state ();
  if (!ext_state)
    return;

  const region *iter_region = reg;
  while (iter_region)
    {
      switch (iter_region->get_kind ())
	{
	default:
	  break;

	case RK_ELEMENT:
	  {
	    const element_region *element_reg
	      = (const element_region *)iter_region;
	    const svalue *index = element_reg->get_index ();
	    const state_machine::state_t
	      state = smap->get_state (index, *ext_state);
	    gcc_assert (state);
	    enum bounds b;
	    if (taint_sm.get_taint (state, index->get_type (), &b))
	    {
	      tree arg = get_representative_tree (index);
	      ctxt->warn (new tainted_array_index (taint_sm, arg, b));
	    }
	  }
	  break;

	case RK_OFFSET:
	  {
	    const offset_region *offset_reg
	      = (const offset_region *)iter_region;
	    const svalue *offset = offset_reg->get_byte_offset ();
	    const state_machine::state_t
	      state = smap->get_state (offset, *ext_state);
	    gcc_assert (state);
	    /* Handle implicit cast to sizetype.  */
	    tree effective_type = offset->get_type ();
	    if (const svalue *cast = offset->maybe_undo_cast ())
	      if (cast->get_type ())
		effective_type = cast->get_type ();
	    enum bounds b;
	    if (taint_sm.get_taint (state, effective_type, &b))
	      {
		tree arg = get_representative_tree (offset);
		ctxt->warn (new tainted_offset (taint_sm, arg, b));
	      }
	  }
	  break;

	case RK_CAST:
	  {
	    const cast_region *cast_reg
	      = as_a <const cast_region *> (iter_region);
	    iter_region = cast_reg->get_original_region ();
	    continue;
	  }

	case RK_SIZED:
	  {
	    const sized_region *sized_reg
	      = (const sized_region *)iter_region;
	    const svalue *size_sval = sized_reg->get_byte_size_sval (m_mgr);
	    const state_machine::state_t
	      state = smap->get_state (size_sval, *ext_state);
	    gcc_assert (state);
	    enum bounds b;
	    if (taint_sm.get_taint (state, size_sval->get_type (), &b))
	      {
		tree arg = get_representative_tree (size_sval);
		ctxt->warn (new tainted_size (taint_sm, arg, b, dir));
	      }
	  }
	  break;
	}

      iter_region = iter_region->get_parent_region ();
    }
}

/* Complain to CTXT about a tainted allocation size if SIZE_IN_BYTES is
   under an attacker's control (due to taint), where the allocation
   is happening within MEM_SPACE.  */

void
region_model::check_dynamic_size_for_taint (enum memory_space mem_space,
					    const svalue *size_in_bytes,
					    region_model_context *ctxt) const
{
  gcc_assert (mem_space == MEMSPACE_STACK || mem_space == MEMSPACE_HEAP);
  gcc_assert (size_in_bytes);
  gcc_assert (ctxt);

  LOG_SCOPE (ctxt->get_logger ());

  sm_state_map *smap;
  const state_machine *sm;
  unsigned sm_idx;
  if (!ctxt->get_taint_map (&smap, &sm, &sm_idx))
    return;

  gcc_assert (smap);
  gcc_assert (sm);

  const taint_state_machine &taint_sm = (const taint_state_machine &)*sm;

  const extrinsic_state *ext_state = ctxt->get_ext_state ();
  if (!ext_state)
    return;

  const state_machine::state_t
    state = smap->get_state (size_in_bytes, *ext_state);
  gcc_assert (state);
  enum bounds b;
  if (taint_sm.get_taint (state, size_in_bytes->get_type (), &b))
    {
      tree arg = get_representative_tree (size_in_bytes);
      ctxt->warn (new tainted_allocation_size (taint_sm, arg, b, mem_space));
    }
}

} // namespace ana

#endif /* #if ENABLE_ANALYZER */