gcc-plugins: Add structleak for more stack initialization

This plugin detects any structures that contain __user attributes and
makes sure it is being fully initialized so that a specific class of
information exposure is eliminated. (This plugin was originally designed
to block the exposure of siginfo in CVE-2013-2141.)

Ported from grsecurity/PaX. This version adds a verbose option to the
plugin and the Kconfig.

Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 246 insertions, 0 deletions

diff --git a/scripts/gcc-plugins/structleak_plugin.c b/scripts/gcc-plugins/structleak_plugin.c
new file mode 100644
index 000000000000..fa3d7a4b26f2
--- /dev/null
+++ b/scripts/gcc-plugins/structleak_plugin.c
@@ -0,0 +1,246 @@
+/*
+ * 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;
+}