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/*
* Copyright 2013-2017 by PaX Team <pageexec@freemail.hu>
* Licensed under the GPL v2
*
* Note: the choice of the license means that the compilation process is
* NOT 'eligible' as defined by gcc's library exception to the GPL v3,
* but for the kernel it doesn't matter since it doesn't link against
* any of the gcc libraries
*
* gcc plugin to forcibly initialize certain local variables that could
* otherwise leak kernel stack to userland if they aren't properly initialized
* by later code
*
* Homepage: http://pax.grsecurity.net/
*
* Options:
* -fplugin-arg-structleak_plugin-disable
* -fplugin-arg-structleak_plugin-verbose
*
* Usage:
* $ # for 4.5/4.6/C based 4.7
* $ gcc -I`gcc -print-file-name=plugin`/include -I`gcc -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o structleak_plugin.so structleak_plugin.c
* $ # for C++ based 4.7/4.8+
* $ g++ -I`g++ -print-file-name=plugin`/include -I`g++ -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o structleak_plugin.so structleak_plugin.c
* $ gcc -fplugin=./structleak_plugin.so test.c -O2
*
* TODO: eliminate redundant initializers
* increase type coverage
*/
#include "gcc-common.h"
/* unused C type flag in all versions 4.5-6 */
#define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE)
__visible int plugin_is_GPL_compatible;
static struct plugin_info structleak_plugin_info = {
.version = "201607271510vanilla",
.help = "disable\tdo not activate plugin\n"
"verbose\tprint all initialized variables\n",
};
static bool verbose;
static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs)
{
*no_add_attrs = true;
/* check for types? for now accept everything linux has to offer */
if (TREE_CODE(*node) != FIELD_DECL)
return NULL_TREE;
*no_add_attrs = false;
return NULL_TREE;
}
static struct attribute_spec user_attr = {
.name = "user",
.min_length = 0,
.max_length = 0,
.decl_required = false,
.type_required = false,
.function_type_required = false,
.handler = handle_user_attribute,
#if BUILDING_GCC_VERSION >= 4007
.affects_type_identity = true
#endif
};
static void register_attributes(void *event_data, void *data)
{
register_attribute(&user_attr);
}
static tree get_field_type(tree field)
{
return strip_array_types(TREE_TYPE(field));
}
static bool is_userspace_type(tree type)
{
tree field;
for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) {
tree fieldtype = get_field_type(field);
enum tree_code code = TREE_CODE(fieldtype);
if (code == RECORD_TYPE || code == UNION_TYPE)
if (is_userspace_type(fieldtype))
return true;
if (lookup_attribute("user", DECL_ATTRIBUTES(field)))
return true;
}
return false;
}
static void finish_type(void *event_data, void *data)
{
tree type = (tree)event_data;
if (type == NULL_TREE || type == error_mark_node)
return;
#if BUILDING_GCC_VERSION >= 5000
if (TREE_CODE(type) == ENUMERAL_TYPE)
return;
#endif
if (TYPE_USERSPACE(type))
return;
if (is_userspace_type(type))
TYPE_USERSPACE(type) = 1;
}
static void initialize(tree var)
{
basic_block bb;
gimple_stmt_iterator gsi;
tree initializer;
gimple init_stmt;
/* this is the original entry bb before the forced split */
bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
/* first check if variable is already initialized, warn otherwise */
for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
gimple stmt = gsi_stmt(gsi);
tree rhs1;
/* we're looking for an assignment of a single rhs... */
if (!gimple_assign_single_p(stmt))
continue;
rhs1 = gimple_assign_rhs1(stmt);
#if BUILDING_GCC_VERSION >= 4007
/* ... of a non-clobbering expression... */
if (TREE_CLOBBER_P(rhs1))
continue;
#endif
/* ... to our variable... */
if (gimple_get_lhs(stmt) != var)
continue;
/* if it's an initializer then we're good */
if (TREE_CODE(rhs1) == CONSTRUCTOR)
return;
}
/* these aren't the 0days you're looking for */
if (verbose)
inform(DECL_SOURCE_LOCATION(var),
"userspace variable will be forcibly initialized");
/* build the initializer expression */
initializer = build_constructor(TREE_TYPE(var), NULL);
/* build the initializer stmt */
init_stmt = gimple_build_assign(var, initializer);
gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT);
update_stmt(init_stmt);
}
static unsigned int structleak_execute(void)
{
basic_block bb;
unsigned int ret = 0;
tree var;
unsigned int i;
/* split the first bb where we can put the forced initializers */
gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
if (!single_pred_p(bb)) {
split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
}
/* enumerate all local variables and forcibly initialize our targets */
FOR_EACH_LOCAL_DECL(cfun, i, var) {
tree type = TREE_TYPE(var);
gcc_assert(DECL_P(var));
if (!auto_var_in_fn_p(var, current_function_decl))
continue;
/* only care about structure types */
if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
continue;
/* if the type is of interest, examine the variable */
if (TYPE_USERSPACE(type))
initialize(var);
}
return ret;
}
#define PASS_NAME structleak
#define NO_GATE
#define PROPERTIES_REQUIRED PROP_cfg
#define TODO_FLAGS_FINISH TODO_verify_il | TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func | TODO_remove_unused_locals | TODO_update_ssa | TODO_ggc_collect | TODO_verify_flow
#include "gcc-generate-gimple-pass.h"
__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
{
int i;
const char * const plugin_name = plugin_info->base_name;
const int argc = plugin_info->argc;
const struct plugin_argument * const argv = plugin_info->argv;
bool enable = true;
PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE);
if (!plugin_default_version_check(version, &gcc_version)) {
error(G_("incompatible gcc/plugin versions"));
return 1;
}
if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) {
inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name);
enable = false;
}
for (i = 0; i < argc; ++i) {
if (!strcmp(argv[i].key, "disable")) {
enable = false;
continue;
}
if (!strcmp(argv[i].key, "verbose")) {
verbose = true;
continue;
}
error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
}
register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info);
if (enable) {
register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info);
register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL);
}
register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL);
return 0;
}
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