PING^2 (C/C++): Re: [PATCH 6/6] Add __attribute__ ((tainted))

[David Malcolm <dmalcolm@redhat.com>]

On Thu, 2022-01-06 at 09:08 -0500, David Malcolm wrote:
> On Sat, 2021-11-13 at 15:37 -0500, David Malcolm wrote:
> > This patch adds a new __attribute__ ((tainted)) to the C/C++
> > frontends.
> 
> Ping for GCC C/C++ mantainers for review of the C/C++ FE parts of this
> patch (attribute registration, documentation, the name of the
> attribute, etc).
> 
> (I believe it's independent of the rest of the patch kit, in that it
> could go into trunk without needing the prior patches)
> 
> Thanks
> Dave

Getting close to end of stage 3 for GCC 12, so pinging this patch
again...

https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584376.html

Thanks
Dave

> 
> 
> > 
> > It can be used on function decls: the analyzer will treat as tainted
> > all parameters to the function and all buffers pointed to by
> > parameters
> > to the function.  Adding this in one place to the Linux kernel's
> > __SYSCALL_DEFINEx macro allows the analyzer to treat all syscalls as
> > having tainted inputs.  This gives additional testing beyond e.g.
> > __user
> > pointers added by earlier patches - an example of the use of this can
> > be
> > seen in CVE-2011-2210, where given:
> > 
> >  SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *,
> > buffer,
> >                  unsigned long, nbytes, int __user *, start, void
> > __user *, arg)
> > 
> > the analyzer will treat the nbytes param as under attacker control,
> > and
> > can complain accordingly:
> > 
> > taint-CVE-2011-2210-1.c: In function ‘sys_osf_getsysinfo’:
> > taint-CVE-2011-2210-1.c:69:21: warning: use of attacker-controlled
> > value
> >   ‘nbytes’ as size without upper-bounds checking [CWE-129] [-
> > Wanalyzer-tainted-size]
> >    69 |                 if (copy_to_user(buffer, hwrpb, nbytes) != 0)
> >       |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > Additionally, the patch allows the attribute to be used on field
> > decls:
> > specifically function pointers.  Any function used as an initializer
> > for such a field gets treated as tainted.  An example can be seen in
> > CVE-2020-13143, where adding __attribute__((tainted)) to the "store"
> > callback of configfs_attribute:
> > 
> >   struct configfs_attribute {
> >      /* [...snip...] */
> >      ssize_t (*store)(struct config_item *, const char *, size_t)
> >        __attribute__((tainted));
> >      /* [...snip...] */
> >   };
> > 
> > allows the analyzer to see:
> > 
> >  CONFIGFS_ATTR(gadget_dev_desc_, UDC);
> > 
> > and treat gadget_dev_desc_UDC_store as tainted, so that it complains:
> > 
> > taint-CVE-2020-13143-1.c: In function ‘gadget_dev_desc_UDC_store’:
> > taint-CVE-2020-13143-1.c:33:17: warning: use of attacker-controlled
> > value
> >   ‘len + 18446744073709551615’ as offset without upper-bounds
> > checking [CWE-823] [-Wanalyzer-tainted-offset]
> >    33 |         if (name[len - 1] == '\n')
> >       |             ~~~~^~~~~~~~~
> > 
> > Similarly, the attribute could be used on the ioctl callback field,
> > USB device callbacks, network-handling callbacks etc.  This
> > potentially
> > gives a lot of test coverage with relatively little code annotation,
> > and
> > without necessarily needing link-time analysis (which -fanalyzer can
> > only do at present on trivial examples).
> > 
> > I believe this is the first time we've had an attribute on a field.
> > If that's an issue, I could prepare a version of the patch that
> > merely allowed it on functions themselves.
> > 
> > As before this currently still needs -fanalyzer-checker=taint (in
> > addition to -fanalyzer).
> > 
> > gcc/analyzer/ChangeLog:
> >         * engine.cc: Include "stringpool.h", "attribs.h", and
> >         "tree-dfa.h".
> >         (mark_params_as_tainted): New.
> >         (class tainted_function_custom_event): New.
> >         (class tainted_function_info): New.
> >         (exploded_graph::add_function_entry): Handle functions with
> >         "tainted" attribute.
> >         (class tainted_field_custom_event): New.
> >         (class tainted_callback_custom_event): New.
> >         (class tainted_call_info): New.
> >         (add_tainted_callback): New.
> >         (add_any_callbacks): New.
> >         (exploded_graph::build_initial_worklist): Find callbacks that
> > are
> >         reachable from global initializers, calling add_any_callbacks
> > on
> >         them.
> > 
> > gcc/c-family/ChangeLog:
> >         * c-attribs.c (c_common_attribute_table): Add "tainted".
> >         (handle_tainted_attribute): New.
> > 
> > gcc/ChangeLog:
> >         * doc/extend.texi (Function Attributes): Note that "tainted"
> > can
> >         be used on field decls.
> >         (Common Function Attributes): Add entry on "tainted"
> > attribute.
> > 
> > gcc/testsuite/ChangeLog:
> >         * gcc.dg/analyzer/attr-tainted-1.c: New test.
> >         * gcc.dg/analyzer/attr-tainted-misuses.c: New test.
> >         * gcc.dg/analyzer/taint-CVE-2011-2210-1.c: New test.
> >         * gcc.dg/analyzer/taint-CVE-2020-13143-1.c: New test.
> >         * gcc.dg/analyzer/taint-CVE-2020-13143-2.c: New test.
> >         * gcc.dg/analyzer/taint-CVE-2020-13143.h: New test.
> >         * gcc.dg/analyzer/taint-alloc-3.c: New test.
> >         * gcc.dg/analyzer/taint-alloc-4.c: New test.
> > 
> > Signed-off-by: David Malcolm <dmalcolm@redhat.com>
> > ---
> >  gcc/analyzer/engine.cc                        | 317
> > +++++++++++++++++-
> >  gcc/c-family/c-attribs.c                      |  36 ++
> >  gcc/doc/extend.texi                           |  22 +-
> >  .../gcc.dg/analyzer/attr-tainted-1.c          |  88 +++++
> >  .../gcc.dg/analyzer/attr-tainted-misuses.c    |   6 +
> >  .../gcc.dg/analyzer/taint-CVE-2011-2210-1.c   |  93 +++++
> >  .../gcc.dg/analyzer/taint-CVE-2020-13143-1.c  |  38 +++
> >  .../gcc.dg/analyzer/taint-CVE-2020-13143-2.c  |  32 ++
> >  .../gcc.dg/analyzer/taint-CVE-2020-13143.h    |  91 +++++
> >  gcc/testsuite/gcc.dg/analyzer/taint-alloc-3.c |  21 ++
> >  gcc/testsuite/gcc.dg/analyzer/taint-alloc-4.c |  31 ++
> >  11 files changed, 772 insertions(+), 3 deletions(-)
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/attr-tainted-1.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/attr-tainted-
> > misuses.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-CVE-2011-
> > 2210-1.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-
> > 13143-1.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-
> > 13143-2.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-
> > 13143.h
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-alloc-3.c
> >  create mode 100644 gcc/testsuite/gcc.dg/analyzer/taint-alloc-4.c
> > 
> > diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc
> > index 096e219392d..5fab41daf93 100644
> > --- a/gcc/analyzer/engine.cc
> > +++ b/gcc/analyzer/engine.cc
> > @@ -68,6 +68,9 @@ along with GCC; see the file COPYING3.  If not see
> >  #include "plugin.h"
> >  #include "target.h"
> >  #include <memory>
> > +#include "stringpool.h"
> > +#include "attribs.h"
> > +#include "tree-dfa.h"
> >  
> >  /* For an overview, see gcc/doc/analyzer.texi.  */
> >  
> > @@ -2276,6 +2279,116 @@ exploded_graph::~exploded_graph ()
> >      delete (*iter).second;
> >  }
> >  
> > +/* Subroutine for use when implementing __attribute__((tainted))
> > +   on functions and on function pointer fields in structs.
> > +
> > +   Called on STATE representing a call to FNDECL.
> > +   Mark all params of FNDECL in STATE as "tainted".  Mark the value
> > of all
> > +   regions pointed to by params of FNDECL as "tainted".
> > +
> > +   Return true if successful; return false if the "taint" state
> > machine
> > +   was not found.  */
> > +
> > +static bool
> > +mark_params_as_tainted (program_state *state, tree fndecl,
> > +                       const extrinsic_state &ext_state)
> > +{
> > +  unsigned taint_sm_idx;
> > +  if (!ext_state.get_sm_idx_by_name ("taint", &taint_sm_idx))
> > +    return false;
> > +  sm_state_map *smap = state->m_checker_states[taint_sm_idx];
> > +
> > +  const state_machine &sm = ext_state.get_sm (taint_sm_idx);
> > +  state_machine::state_t tainted = sm.get_state_by_name ("tainted");
> > +
> > +  region_model_manager *mgr = ext_state.get_model_manager ();
> > +
> > +  function *fun = DECL_STRUCT_FUNCTION (fndecl);
> > +  gcc_assert (fun);
> > +
> > +  for (tree iter_parm = DECL_ARGUMENTS (fndecl); iter_parm;
> > +       iter_parm = DECL_CHAIN (iter_parm))
> > +    {
> > +      tree param = iter_parm;
> > +      if (tree parm_default_ssa = ssa_default_def (fun, iter_parm))
> > +       param = parm_default_ssa;
> > +      const region *param_reg = state->m_region_model->get_lvalue
> > (param, NULL);
> > +      const svalue *init_sval = mgr->get_or_create_initial_value
> > (param_reg);
> > +      smap->set_state (state->m_region_model, init_sval,
> > +                      tainted, NULL /*origin_new_sval*/, ext_state);
> > +      if (POINTER_TYPE_P (TREE_TYPE (param)))
> > +       {
> > +         const region *pointee_reg = mgr->get_symbolic_region
> > (init_sval);
> > +         /* Mark "*param" as tainted.  */
> > +         const svalue *init_pointee_sval
> > +           = mgr->get_or_create_initial_value (pointee_reg);
> > +         smap->set_state (state->m_region_model, init_pointee_sval,
> > +                          tainted, NULL /*origin_new_sval*/,
> > ext_state);
> > +       }
> > +    }
> > +
> > +  return true;
> > +}
> > +
> > +/* Custom event for use by tainted_function_info when a function
> > +   has been marked with __attribute__((tainted)).  */
> > +
> > +class tainted_function_custom_event : public custom_event
> > +{
> > +public:
> > +  tainted_function_custom_event (location_t loc, tree fndecl, int
> > depth)
> > +  : custom_event (loc, fndecl, depth),
> > +    m_fndecl (fndecl)
> > +  {
> > +  }
> > +
> > +  label_text get_desc (bool can_colorize) const FINAL OVERRIDE
> > +  {
> > +    return make_label_text
> > +      (can_colorize,
> > +       "function %qE marked with %<__attribute__((tainted))%>",
> > +       m_fndecl);
> > +  }
> > +
> > +private:
> > +  tree m_fndecl;
> > +};
> > +
> > +/* Custom exploded_edge info for top-level calls to a function
> > +   marked with __attribute__((tainted)).  */
> > +
> > +class tainted_function_info : public custom_edge_info
> > +{
> > +public:
> > +  tainted_function_info (tree fndecl)
> > +  : m_fndecl (fndecl)
> > +  {}
> > +
> > +  void print (pretty_printer *pp) const FINAL OVERRIDE
> > +  {
> > +    pp_string (pp, "call to tainted function");
> > +  };
> > +
> > +  bool update_model (region_model *,
> > +                    const exploded_edge *,
> > +                    region_model_context *) const FINAL OVERRIDE
> > +  {
> > +    /* No-op.  */
> > +    return true;
> > +  }
> > +
> > +  void add_events_to_path (checker_path *emission_path,
> > +                          const exploded_edge &) const FINAL
> > OVERRIDE
> > +  {
> > +    emission_path->add_event
> > +      (new tainted_function_custom_event
> > +       (DECL_SOURCE_LOCATION (m_fndecl), m_fndecl, 0));
> > +  }
> > +
> > +private:
> > +  tree m_fndecl;
> > +};
> > +
> >  /* Ensure that there is an exploded_node representing an external
> > call to
> >     FUN, adding it to the worklist if creating it.
> >  
> > @@ -2302,14 +2415,25 @@ exploded_graph::add_function_entry (function
> > *fun)
> >    program_state state (m_ext_state);
> >    state.push_frame (m_ext_state, fun);
> >  
> > +  custom_edge_info *edge_info = NULL;
> > +
> > +  if (lookup_attribute ("tainted", DECL_ATTRIBUTES (fun->decl)))
> > +    {
> > +      if (mark_params_as_tainted (&state, fun->decl, m_ext_state))
> > +       edge_info = new tainted_function_info (fun->decl);
> > +    }
> > +
> >    if (!state.m_valid)
> >      return NULL;
> >  
> >    exploded_node *enode = get_or_create_node (point, state, NULL);
> >    if (!enode)
> > -    return NULL;
> > +    {
> > +      delete edge_info;
> > +      return NULL;
> > +    }
> >  
> > -  add_edge (m_origin, enode, NULL);
> > +  add_edge (m_origin, enode, NULL, edge_info);
> >  
> >    m_functions_with_enodes.add (fun);
> >  
> > @@ -2623,6 +2747,184 @@ toplevel_function_p (function *fun, logger
> > *logger)
> >    return true;
> >  }
> >  
> > +/* Custom event for use by tainted_call_info when a callback field
> > has been
> > +   marked with __attribute__((tainted)), for labelling the field. 
> > */
> > +
> > +class tainted_field_custom_event : public custom_event
> > +{
> > +public:
> > +  tainted_field_custom_event (tree field)
> > +  : custom_event (DECL_SOURCE_LOCATION (field), NULL_TREE, 0),
> > +    m_field (field)
> > +  {
> > +  }
> > +
> > +  label_text get_desc (bool can_colorize) const FINAL OVERRIDE
> > +  {
> > +    return make_label_text (can_colorize,
> > +                           "field %qE of %qT"
> > +                           " is marked with
> > %<__attribute__((tainted))%>",
> > +                           m_field, DECL_CONTEXT (m_field));
> > +  }
> > +
> > +private:
> > +  tree m_field;
> > +};
> > +
> > +/* Custom event for use by tainted_call_info when a callback field
> > has been
> > +   marked with __attribute__((tainted)), for labelling the function
> > used
> > +   in that callback.  */
> > +
> > +class tainted_callback_custom_event : public custom_event
> > +{
> > +public:
> > +  tainted_callback_custom_event (location_t loc, tree fndecl, int
> > depth,
> > +                                tree field)
> > +  : custom_event (loc, fndecl, depth),
> > +    m_field (field)
> > +  {
> > +  }
> > +
> > +  label_text get_desc (bool can_colorize) const FINAL OVERRIDE
> > +  {
> > +    return make_label_text (can_colorize,
> > +                           "function %qE used as initializer for
> > field %qE"
> > +                           " marked with
> > %<__attribute__((tainted))%>",
> > +                           m_fndecl, m_field);
> > +  }
> > +
> > +private:
> > +  tree m_field;
> > +};
> > +
> > +/* Custom edge info for use when adding a function used by a
> > callback field
> > +   marked with '__attribute__((tainted))'.   */
> > +
> > +class tainted_call_info : public custom_edge_info
> > +{
> > +public:
> > +  tainted_call_info (tree field, tree fndecl, location_t loc)
> > +  : m_field (field), m_fndecl (fndecl), m_loc (loc)
> > +  {}
> > +
> > +  void print (pretty_printer *pp) const FINAL OVERRIDE
> > +  {
> > +    pp_string (pp, "call to tainted field");
> > +  };
> > +
> > +  bool update_model (region_model *,
> > +                    const exploded_edge *,
> > +                    region_model_context *) const FINAL OVERRIDE
> > +  {
> > +    /* No-op.  */
> > +    return true;
> > +  }
> > +
> > +  void add_events_to_path (checker_path *emission_path,
> > +                          const exploded_edge &) const FINAL
> > OVERRIDE
> > +  {
> > +    /* Show the field in the struct declaration
> > +       e.g. "(1) field 'store' is marked with
> > '__attribute__((tainted))'"  */
> > +    emission_path->add_event
> > +      (new tainted_field_custom_event (m_field));
> > +
> > +    /* Show the callback in the initializer
> > +       e.g.
> > +       "(2) function 'gadget_dev_desc_UDC_store' used as initializer
> > +       for field 'store' marked with '__attribute__((tainted))'". 
> > */
> > +    emission_path->add_event
> > +      (new tainted_callback_custom_event (m_loc, m_fndecl, 0,
> > m_field));
> > +  }
> > +
> > +private:
> > +  tree m_field;
> > +  tree m_fndecl;
> > +  location_t m_loc;
> > +};
> > +
> > +/* Given an initializer at LOC for FIELD marked with
> > '__attribute__((tainted))'
> > +   initialized with FNDECL, add an entrypoint to FNDECL to EG (and
> > to its
> > +   worklist) where the params to FNDECL are marked as tainted.  */
> > +
> > +static void
> > +add_tainted_callback (exploded_graph *eg, tree field, tree fndecl,
> > +                     location_t loc)
> > +{
> > +  logger *logger = eg->get_logger ();
> > +
> > +  LOG_SCOPE (logger);
> > +
> > +  if (!gimple_has_body_p (fndecl))
> > +    return;
> > +
> > +  const extrinsic_state &ext_state = eg->get_ext_state ();
> > +
> > +  function *fun = DECL_STRUCT_FUNCTION (fndecl);
> > +  gcc_assert (fun);
> > +
> > +  program_point point
> > +    = program_point::from_function_entry (eg->get_supergraph (),
> > fun);
> > +  program_state state (ext_state);
> > +  state.push_frame (ext_state, fun);
> > +
> > +  if (!mark_params_as_tainted (&state, fndecl, ext_state))
> > +    return;
> > +
> > +  if (!state.m_valid)
> > +    return;
> > +
> > +  exploded_node *enode = eg->get_or_create_node (point, state,
> > NULL);
> > +  if (logger)
> > +    {
> > +      if (enode)
> > +       logger->log ("created EN %i for tainted %qE entrypoint",
> > +                    enode->m_index, fndecl);
> > +      else
> > +       {
> > +         logger->log ("did not create enode for tainted %qE
> > entrypoint",
> > +                      fndecl);
> > +         return;
> > +       }
> > +    }
> > +
> > +  tainted_call_info *info = new tainted_call_info (field, fndecl,
> > loc);
> > +  eg->add_edge (eg->get_origin (), enode, NULL, info);
> > +}
> > +
> > +/* Callback for walk_tree for finding callbacks within initializers;
> > +   ensure that any callback initializer where the corresponding
> > field is
> > +   marked with '__attribute__((tainted))' is treated as an
> > entrypoint to the
> > +   analysis, special-casing that the inputs to the callback are
> > +   untrustworthy.  */
> > +
> > +static tree
> > +add_any_callbacks (tree *tp, int *, void *data)
> > +{
> > +  exploded_graph *eg = (exploded_graph *)data;
> > +  if (TREE_CODE (*tp) == CONSTRUCTOR)
> > +    {
> > +      /* Find fields with the "tainted" attribute.
> > +        walk_tree only walks the values, not the index values;
> > +        look at the index values.  */
> > +      unsigned HOST_WIDE_INT idx;
> > +      constructor_elt *ce;
> > +
> > +      for (idx = 0; vec_safe_iterate (CONSTRUCTOR_ELTS (*tp), idx,
> > &ce);
> > +          idx++)
> > +       if (ce->index && TREE_CODE (ce->index) == FIELD_DECL)
> > +         if (lookup_attribute ("tainted", DECL_ATTRIBUTES (ce-
> > > index)))
> > +           {
> > +             tree value = ce->value;
> > +             if (TREE_CODE (value) == ADDR_EXPR
> > +                 && TREE_CODE (TREE_OPERAND (value, 0)) ==
> > FUNCTION_DECL)
> > +               add_tainted_callback (eg, ce->index, TREE_OPERAND
> > (value, 0),
> > +                                     EXPR_LOCATION (value));
> > +           }
> > +    }
> > +
> > +  return NULL_TREE;
> > +}
> > +
> >  /* Add initial nodes to EG, with entrypoints for externally-callable
> >     functions.  */
> >  
> > @@ -2648,6 +2950,17 @@ exploded_graph::build_initial_worklist ()
> >           logger->log ("did not create enode for %qE entrypoint",
> > fun->decl);
> >        }
> >    }
> > +
> > +  /* Find callbacks that are reachable from global initializers.  */
> > +  varpool_node *vpnode;
> > +  FOR_EACH_VARIABLE (vpnode)
> > +    {
> > +      tree decl = vpnode->decl;
> > +      tree init = DECL_INITIAL (decl);
> > +      if (!init)
> > +       continue;
> > +      walk_tree (&init, add_any_callbacks, this, NULL);
> > +    }
> >  }
> >  
> >  /* The main loop of the analysis.
> > diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
> > index 9e03156de5e..835ba6e0e8c 100644
> > --- a/gcc/c-family/c-attribs.c
> > +++ b/gcc/c-family/c-attribs.c
> > @@ -117,6 +117,7 @@ static tree
> > handle_no_profile_instrument_function_attribute (tree *, tree,
> >                                                              tree,
> > int, bool *);
> >  static tree handle_malloc_attribute (tree *, tree, tree, int, bool
> > *);
> >  static tree handle_dealloc_attribute (tree *, tree, tree, int, bool
> > *);
> > +static tree handle_tainted_attribute (tree *, tree, tree, int, bool
> > *);
> >  static tree handle_returns_twice_attribute (tree *, tree, tree, int,
> > bool *);
> >  static tree handle_no_limit_stack_attribute (tree *, tree, tree,
> > int,
> >                                              bool *);
> > @@ -569,6 +570,8 @@ const struct attribute_spec
> > c_common_attribute_table[] =
> >                               handle_objc_nullability_attribute, NULL
> > },
> >    { "*dealloc",                1, 2, true, false, false, false,
> >                               handle_dealloc_attribute, NULL },
> > +  { "tainted",               0, 0, true,  false, false, false,
> > +                             handle_tainted_attribute, NULL },
> >    { NULL,                     0, 0, false, false, false, false,
> > NULL, NULL }
> >  };
> >  
> > @@ -5857,6 +5860,39 @@ handle_objc_nullability_attribute (tree *node,
> > tree name, tree args,
> >    return NULL_TREE;
> >  }
> >  
> > +/* Handle a "tainted" attribute; arguments as in
> > +   struct attribute_spec.handler.  */
> > +
> > +static tree
> > +handle_tainted_attribute (tree *node, tree name, tree, int,
> > +                         bool *no_add_attrs)
> > +{
> > +  if (TREE_CODE (*node) != FUNCTION_DECL
> > +      && TREE_CODE (*node) != FIELD_DECL)
> > +    {
> > +      warning (OPT_Wattributes, "%qE attribute ignored; valid only "
> > +              "for functions and function pointer fields",
> > +              name);
> > +      *no_add_attrs = true;
> > +      return NULL_TREE;
> > +    }
> > +
> > +  if (TREE_CODE (*node) == FIELD_DECL
> > +      && !(TREE_CODE (TREE_TYPE (*node)) == POINTER_TYPE
> > +          && TREE_CODE (TREE_TYPE (TREE_TYPE (*node))) ==
> > FUNCTION_TYPE))
> > +    {
> > +      warning (OPT_Wattributes, "%qE attribute ignored;"
> > +              " field must be a function pointer",
> > +              name);
> > +      *no_add_attrs = true;
> > +      return NULL_TREE;
> > +    }
> > +
> > +  *no_add_attrs = false; /* OK */
> > +
> > +  return NULL_TREE;
> > +}
> > +
> >  /* Attempt to partially validate a single attribute ATTR as if
> >     it were to be applied to an entity OPER.  */
> >  
> > diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> > index 5a6ef464779..826bbd48e7e 100644
> > --- a/gcc/doc/extend.texi
> > +++ b/gcc/doc/extend.texi
> > @@ -2465,7 +2465,8 @@ variable declarations (@pxref{Variable
> > Attributes}),
> >  labels (@pxref{Label Attributes}),
> >  enumerators (@pxref{Enumerator Attributes}),
> >  statements (@pxref{Statement Attributes}),
> > -and types (@pxref{Type Attributes}).
> > +types (@pxref{Type Attributes}),
> > +and on field declarations (for @code{tainted}).
> >  
> >  There is some overlap between the purposes of attributes and pragmas
> >  (@pxref{Pragmas,,Pragmas Accepted by GCC}).  It has been
> > @@ -3977,6 +3978,25 @@ addition to creating a symbol version (as if
> >  @code{"@var{name2}@@@var{nodename}"} was used) the version will be
> > also used
> >  to resolve @var{name2} by the linker.
> >  
> > +@item tainted
> > +@cindex @code{tainted} function attribute
> > +The @code{tainted} attribute is used to specify that a function is
> > called
> > +in a way that requires sanitization of its arguments, such as a
> > system
> > +call in an operating system kernel.  Such a function can be
> > considered part
> > +of the ``attack surface'' of the program.  The attribute can be used
> > both
> > +on function declarations, and on field declarations containing
> > function
> > +pointers.  In the latter case, any function used as an initializer
> > of
> > +such a callback field will be treated as tainted.
> > +
> > +The analyzer will pay particular attention to such functions when
> > both
> > +@option{-fanalyzer} and @option{-fanalyzer-checker=taint} are
> > supplied,
> > +potentially issuing warnings guarded by
> > +@option{-Wanalyzer-exposure-through-uninit-copy},
> > +@option{-Wanalyzer-tainted-allocation-size},
> > +@option{-Wanalyzer-tainted-array-index},
> > +@option{Wanalyzer-tainted-offset},
> > +and @option{Wanalyzer-tainted-size}.
> > +
> >  @item target_clones (@var{options})
> >  @cindex @code{target_clones} function attribute
> >  The @code{target_clones} attribute is used to specify that a
> > function
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/attr-tainted-1.c
> > b/gcc/testsuite/gcc.dg/analyzer/attr-tainted-1.c
> > new file mode 100644
> > index 00000000000..cc4d5900372
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/attr-tainted-1.c
> > @@ -0,0 +1,88 @@
> > +// TODO: remove need for this option
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +#include "analyzer-decls.h"
> > +
> > +struct arg_buf
> > +{
> > +  int i;
> > +  int j;
> > +};
> > +
> > +/* Example of marking a function as tainted.  */
> > +
> > +void __attribute__((tainted))
> > +test_1 (int i, void *p, char *q)
> > +{
> > +  /* There should be a single enode,
> > +     for the "tainted" entry to the function.  */
> > +  __analyzer_dump_exploded_nodes (0); /* { dg-warning "1 processed
> > enode" } */
> > +
> > +  __analyzer_dump_state ("taint", i); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", p); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", q); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", *q); /* { dg-warning "state:
> > 'tainted'" } */
> > +
> > +  struct arg_buf *args = p;
> > +  __analyzer_dump_state ("taint", args->i); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", args->j); /* { dg-warning "state:
> > 'tainted'" } */  
> > +}
> > +
> > +/* Example of marking a callback field as tainted.  */
> > +
> > +struct s2
> > +{
> > +  void (*cb) (int, void *, char *)
> > +    __attribute__((tainted));
> > +};
> > +
> > +/* Function not marked as tainted.  */
> > +
> > +void
> > +test_2a (int i, void *p, char *q)
> > +{
> > +  /* There should be a single enode,
> > +     for the normal entry to the function.  */
> > +  __analyzer_dump_exploded_nodes (0); /* { dg-warning "1 processed
> > enode" } */
> > +
> > +  __analyzer_dump_state ("taint", i); /* { dg-warning "state:
> > 'start'" } */
> > +  __analyzer_dump_state ("taint", p); /* { dg-warning "state:
> > 'start'" } */
> > +  __analyzer_dump_state ("taint", q); /* { dg-warning "state:
> > 'start'" } */
> > +
> > +  struct arg_buf *args = p;
> > +  __analyzer_dump_state ("taint", args->i); /* { dg-warning "state:
> > 'start'" } */
> > +  __analyzer_dump_state ("taint", args->j); /* { dg-warning "state:
> > 'start'" } */  
> > +}
> > +
> > +/* Function referenced via t2b.cb, marked as "tainted".  */
> > +
> > +void
> > +test_2b (int i, void *p, char *q)
> > +{
> > +  /* There should be two enodes
> > +     for the direct call, and the "tainted" entry to the function. 
> > */
> > +  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed
> > enodes" } */
> > +}
> > +
> > +/* Callback used via t2c.cb, marked as "tainted".  */
> > +void
> > +__analyzer_test_2c (int i, void *p, char *q)
> > +{
> > +  /* There should be a single enode,
> > +     for the "tainted" entry to the function.  */
> > +  __analyzer_dump_exploded_nodes (0); /* { dg-warning "1 processed
> > enode" } */
> > +
> > +  __analyzer_dump_state ("taint", i); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", p); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", q); /* { dg-warning "state:
> > 'tainted'" } */
> > +}
> > +
> > +struct s2 t2b =
> > +{
> > +  .cb = test_2b
> > +};
> > +
> > +struct s2 t2c =
> > +{
> > +  .cb = __analyzer_test_2c
> > +};
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/attr-tainted-misuses.c
> > b/gcc/testsuite/gcc.dg/analyzer/attr-tainted-misuses.c
> > new file mode 100644
> > index 00000000000..6f4cbc82efb
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/attr-tainted-misuses.c
> > @@ -0,0 +1,6 @@
> > +int not_a_fn __attribute__ ((tainted)); /* { dg-warning "'tainted'
> > attribute ignored; valid only for functions and function pointer
> > fields" } */
> > +
> > +struct s
> > +{
> > +  int f __attribute__ ((tainted)); /* { dg-warning "'tainted'
> > attribute ignored; field must be a function pointer" } */
> > +};
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2011-2210-1.c
> > b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2011-2210-1.c
> > new file mode 100644
> > index 00000000000..fe6c7ebbb1f
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2011-2210-1.c
> > @@ -0,0 +1,93 @@
> > +/* "The osf_getsysinfo function in arch/alpha/kernel/osf_sys.c in
> > the
> > +   Linux kernel before 2.6.39.4 on the Alpha platform does not
> > properly
> > +   restrict the data size for GSI_GET_HWRPB operations, which allows
> > +   local users to obtain sensitive information from kernel memory
> > via
> > +   a crafted call."
> > +
> > +   Fixed in 3d0475119d8722798db5e88f26493f6547a4bb5b on linux-
> > 2.6.39.y
> > +   in linux-stable.  */
> > +
> > +// TODO: remove need for this option:
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +#include "analyzer-decls.h"
> > +#include "test-uaccess.h"
> > +
> > +/* Adapted from include/linux/linkage.h.  */
> > +
> > +#define asmlinkage
> > +
> > +/* Adapted from include/linux/syscalls.h.  */
> > +
> > +#define __SC_DECL1(t1, a1)     t1 a1
> > +#define __SC_DECL2(t2, a2, ...) t2 a2, __SC_DECL1(__VA_ARGS__)
> > +#define __SC_DECL3(t3, a3, ...) t3 a3, __SC_DECL2(__VA_ARGS__)
> > +#define __SC_DECL4(t4, a4, ...) t4 a4, __SC_DECL3(__VA_ARGS__)
> > +#define __SC_DECL5(t5, a5, ...) t5 a5, __SC_DECL4(__VA_ARGS__)
> > +#define __SC_DECL6(t6, a6, ...) t6 a6, __SC_DECL5(__VA_ARGS__)
> > +
> > +#define SYSCALL_DEFINEx(x, sname, ...)                         \
> > +       __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
> > +
> > +#define SYSCALL_DEFINE(name) asmlinkage long sys_##name
> > +#define __SYSCALL_DEFINEx(x, name,
> > ...)                                        \
> > +       asmlinkage __attribute__((tainted)) \
> > +       long sys##name(__SC_DECL##x(__VA_ARGS__))
> > +
> > +#define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name,
> > __VA_ARGS__)
> > +
> > +/* Adapted from arch/alpha/include/asm/hwrpb.h.  */
> > +
> > +struct hwrpb_struct {
> > +       unsigned long phys_addr;        /* check: physical address of
> > the hwrpb */
> > +       unsigned long id;               /* check: "HWRPB\0\0\0" */
> > +       unsigned long revision;
> > +       unsigned long size;             /* size of hwrpb */
> > +       /* [...snip...] */
> > +};
> > +
> > +extern struct hwrpb_struct *hwrpb;
> > +
> > +/* Adapted from arch/alpha/kernel/osf_sys.c.  */
> > +
> > +SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *,
> > buffer,
> > +               unsigned long, nbytes, int __user *, start, void
> > __user *, arg)
> > +{
> > +       /* [...snip...] */
> > +
> > +       __analyzer_dump_state ("taint", nbytes);  /* { dg-warning
> > "tainted" } */
> > +
> > +       /* TODO: should have an event explaining why "nbytes" is
> > treated as
> > +          attacker-controlled.  */
> > +
> > +       /* case GSI_GET_HWRPB: */
> > +               if (nbytes < sizeof(*hwrpb))
> > +                       return -1;
> > +
> > +               __analyzer_dump_state ("taint", nbytes);  /* { dg-
> > warning "has_lb" } */
> > +
> > +               if (copy_to_user(buffer, hwrpb, nbytes) != 0) /* {
> > dg-warning "use of attacker-controlled value 'nbytes' as size without
> > upper-bounds checking" } */
> > +                       return -2;
> > +
> > +               return 1;
> > +
> > +       /* [...snip...] */
> > +}
> > +
> > +/* With the fix for the sense of the size comparison.  */
> > +
> > +SYSCALL_DEFINE5(osf_getsysinfo_fixed, unsigned long, op, void __user
> > *, buffer,
> > +               unsigned long, nbytes, int __user *, start, void
> > __user *, arg)
> > +{
> > +       /* [...snip...] */
> > +
> > +       /* case GSI_GET_HWRPB: */
> > +               if (nbytes > sizeof(*hwrpb))
> > +                       return -1;
> > +               if (copy_to_user(buffer, hwrpb, nbytes) != 0) /* {
> > dg-bogus "attacker-controlled" } */
> > +                       return -2;
> > +
> > +               return 1;
> > +
> > +       /* [...snip...] */
> > +}
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-1.c
> > b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-1.c
> > new file mode 100644
> > index 00000000000..0b9a94a8d6c
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-1.c
> > @@ -0,0 +1,38 @@
> > +/* See notes in this header.  */
> > +#include "taint-CVE-2020-13143.h"
> > +
> > +// TODO: remove need for this option
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +struct configfs_attribute {
> > +       /* [...snip...] */
> > +       ssize_t (*store)(struct config_item *, const char *, size_t)
> > /* { dg-message "\\(1\\) field 'store' of 'struct configfs_attribute'
> > is marked with '__attribute__\\(\\(tainted\\)\\)'" } */
> > +               __attribute__((tainted)); /* (this is added).  */
> > +};
> > +static inline struct gadget_info *to_gadget_info(struct config_item
> > *item)
> > +{
> > +        return container_of(to_config_group(item), struct
> > gadget_info, group);
> > +}
> > +
> > +static ssize_t gadget_dev_desc_UDC_store(struct config_item *item,
> > +               const char *page, size_t len)
> > +{
> > +       struct gadget_info *gi = to_gadget_info(item);
> > +       char *name;
> > +       int ret;
> > +
> > +#if 0
> > +       /* FIXME: this is the fix.  */
> > +       if (strlen(page) < len)
> > +               return -EOVERFLOW;
> > +#endif
> > +
> > +       name = kstrdup(page, GFP_KERNEL);
> > +       if (!name)
> > +               return -ENOMEM;
> > +       if (name[len - 1] == '\n') /* { dg-warning "use of attacker-
> > controlled value 'len \[^\n\r\]+' as offset without upper-bounds
> > checking" } */
> > +               name[len - 1] = '\0'; /* { dg-warning "use of
> > attacker-controlled value 'len \[^\n\r\]+' as offset without upper-
> > bounds checking" } */
> > +       /* [...snip...] */                              \
> > +}
> > +
> > +CONFIGFS_ATTR(gadget_dev_desc_, UDC); /* { dg-message "\\(2\\)
> > function 'gadget_dev_desc_UDC_store' used as initializer for field
> > 'store' marked with '__attribute__\\(\\(tainted\\)\\)'" } */
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-2.c
> > b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-2.c
> > new file mode 100644
> > index 00000000000..e05da9276c1
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143-2.c
> > @@ -0,0 +1,32 @@
> > +/* See notes in this header.  */
> > +#include "taint-CVE-2020-13143.h"
> > +
> > +// TODO: remove need for this option
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +struct configfs_attribute {
> > +       /* [...snip...] */
> > +       ssize_t (*store)(struct config_item *, const char *, size_t)
> > /* { dg-message "\\(1\\) field 'store' of 'struct configfs_attribute'
> > is marked with '__attribute__\\(\\(tainted\\)\\)'" } */
> > +               __attribute__((tainted)); /* (this is added).  */
> > +};
> > +
> > +/* Highly simplified version.  */
> > +
> > +static ssize_t gadget_dev_desc_UDC_store(struct config_item *item,
> > +               const char *page, size_t len)
> > +{
> > +       /* TODO: ought to have state_change_event talking about where
> > the tainted value comes from.  */
> > +
> > +       char *name;
> > +       /* [...snip...] */
> > +
> > +       name = kstrdup(page, GFP_KERNEL);
> > +       if (!name)
> > +               return -ENOMEM;
> > +       if (name[len - 1] == '\n') /* { dg-warning "use of attacker-
> > controlled value 'len \[^\n\r\]+' as offset without upper-bounds
> > checking" } */
> > +               name[len - 1] = '\0';  /* { dg-warning "use of
> > attacker-controlled value 'len \[^\n\r\]+' as offset without upper-
> > bounds checking" } */
> > +       /* [...snip...] */
> > +       return 0;
> > +}
> > +
> > +CONFIGFS_ATTR(gadget_dev_desc_, UDC); /* { dg-message "\\(2\\)
> > function 'gadget_dev_desc_UDC_store' used as initializer for field
> > 'store' marked with '__attribute__\\(\\(tainted\\)\\)'" } */
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143.h
> > b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143.h
> > new file mode 100644
> > index 00000000000..0ba023539af
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-CVE-2020-13143.h
> > @@ -0,0 +1,91 @@
> > +/* Shared header for the various taint-CVE-2020-13143.h tests.
> > +   
> > +   "gadget_dev_desc_UDC_store in drivers/usb/gadget/configfs.c in
> > the
> > +   Linux kernel 3.16 through 5.6.13 relies on kstrdup without
> > considering
> > +   the possibility of an internal '\0' value, which allows attackers
> > to
> > +   trigger an out-of-bounds read, aka CID-15753588bcd4."
> > +
> > +   Fixed by 15753588bcd4bbffae1cca33c8ced5722477fe1f on linux-5.7.y
> > +   in linux-stable.  */
> > +
> > +// TODO: remove need for this option
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +#include <stddef.h>
> > +
> > +/* Adapted from include/uapi/asm-generic/posix_types.h  */
> > +
> > +typedef unsigned int     __kernel_size_t;
> > +typedef int              __kernel_ssize_t;
> > +
> > +/* Adapted from include/linux/types.h  */
> > +
> > +//typedef __kernel_size_t              size_t;
> > +typedef __kernel_ssize_t       ssize_t;
> > +
> > +/* Adapted from include/linux/kernel.h  */
> > +
> > +#define container_of(ptr, type, member)
> > ({                             \
> > +       void *__mptr = (void
> > *)(ptr);                                   \
> > +       /* [...snip...]
> > */                                              \
> > +       ((type *)(__mptr - offsetof(type, member))); })
> > +
> > +/* Adapted from include/linux/configfs.h  */
> > +
> > +struct config_item {
> > +       /* [...snip...] */
> > +};
> > +
> > +struct config_group {
> > +       struct config_item              cg_item;
> > +       /* [...snip...] */
> > +};
> > +
> > +static inline struct config_group *to_config_group(struct
> > config_item *item)
> > +{
> > +       return item ? container_of(item,struct config_group,cg_item)
> > : NULL;
> > +}
> > +
> > +#define CONFIGFS_ATTR(_pfx, _name)                             \
> > +static struct configfs_attribute _pfx##attr_##_name = {        \
> > +       /* [...snip...] */                              \
> > +       .store          = _pfx##_name##_store,          \
> > +}
> > +
> > +/* Adapted from include/linux/compiler.h  */
> > +
> > +#define __force
> > +
> > +/* Adapted from include/asm-generic/errno-base.h  */
> > +
> > +#define        ENOMEM          12      /* Out of memory */
> > +
> > +/* Adapted from include/linux/types.h  */
> > +
> > +#define __bitwise__
> > +typedef unsigned __bitwise__ gfp_t;
> > +
> > +/* Adapted from include/linux/gfp.h  */
> > +
> > +#define ___GFP_WAIT            0x10u
> > +#define ___GFP_IO              0x40u
> > +#define ___GFP_FS              0x80u
> > +#define __GFP_WAIT     ((__force gfp_t)___GFP_WAIT)
> > +#define __GFP_IO       ((__force gfp_t)___GFP_IO)
> > +#define __GFP_FS       ((__force gfp_t)___GFP_FS)
> > +#define GFP_KERNEL  (__GFP_WAIT | __GFP_IO | __GFP_FS)
> > +
> > +/* Adapted from include/linux/compiler_attributes.h  */
> > +
> > +#define __malloc                        __attribute__((__malloc__))
> > +
> > +/* Adapted from include/linux/string.h  */
> > +
> > +extern char *kstrdup(const char *s, gfp_t gfp) __malloc;
> > +
> > +/* Adapted from drivers/usb/gadget/configfs.c  */
> > +
> > +struct gadget_info {
> > +       struct config_group group;
> > +       /* [...snip...] */                              \
> > +};
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-alloc-3.c
> > b/gcc/testsuite/gcc.dg/analyzer/taint-alloc-3.c
> > new file mode 100644
> > index 00000000000..4c567b2ffdf
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-alloc-3.c
> > @@ -0,0 +1,21 @@
> > +// TODO: remove need for this option:
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +#include "analyzer-decls.h"
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +
> > +/* malloc with tainted size from a syscall.  */
> > +
> > +void *p;
> > +
> > +void __attribute__((tainted))
> > +test_1 (size_t sz) /* { dg-message "\\(1\\) function 'test_1' marked
> > with '__attribute__\\(\\(tainted\\)\\)'" } */
> > +{
> > +  /* TODO: should have a message saying why "sz" is tainted, e.g.
> > +     "treating 'sz' as attacker-controlled because 'test_1' is
> > marked with '__attribute__((tainted))'"  */
> > +
> > +  p = malloc (sz); /* { dg-warning "use of attacker-controlled value
> > 'sz' as allocation size without upper-bounds checking" "warning" } */
> > +  /* { dg-message "\\(\[0-9\]+\\) use of attacker-controlled value
> > 'sz' as allocation size without upper-bounds checking" "final event"
> > { target *-*-* } .-1 } */
> > +}
> > diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-alloc-4.c
> > b/gcc/testsuite/gcc.dg/analyzer/taint-alloc-4.c
> > new file mode 100644
> > index 00000000000..f52cafcd71d
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/analyzer/taint-alloc-4.c
> > @@ -0,0 +1,31 @@
> > +// TODO: remove need for this option:
> > +/* { dg-additional-options "-fanalyzer-checker=taint" } */
> > +
> > +#include "analyzer-decls.h"
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +
> > +/* malloc with tainted size from a syscall.  */
> > +
> > +struct arg_buf
> > +{
> > +  size_t sz;
> > +};
> > +
> > +void *p;
> > +
> > +void __attribute__((tainted))
> > +test_1 (void *data) /* { dg-message "\\(1\\) function 'test_1'
> > marked with '__attribute__\\(\\(tainted\\)\\)'" } */
> > +{
> > +  /* we should treat pointed-to-structs as tainted.  */
> > +  __analyzer_dump_state ("taint", data); /* { dg-warning "state:
> > 'tainted'" } */
> > +  
> > +  struct arg_buf *args = data;
> > +
> > +  __analyzer_dump_state ("taint", args); /* { dg-warning "state:
> > 'tainted'" } */
> > +  __analyzer_dump_state ("taint", args->sz); /* { dg-warning "state:
> > 'tainted'" } */
> > +  
> > +  p = malloc (args->sz); /* { dg-warning "use of attacker-controlled
> > value '\\*args.sz' as allocation size without upper-bounds checking"
> > "warning" } */
> > +  /* { dg-message "\\(\[0-9\]+\\) use of attacker-controlled value
> > '\\*args.sz' as allocation size without upper-bounds checking" "final
> > event" { target *-*-* } .-1 } */
> > +}
>