[PATCH] gcc-plugins: Add structleak for more stack initialization
From: Kees Cook
Date: Fri Jan 13 2017 - 17:03:04 EST
This plugin detects any structures that contain __user attributes and
makes sure it is being fulling initialized so that a specific class of
information exposure is eliminated. (For example, the exposure of siginfo
in CVE-2013-2141 would have been blocked by this plugin.)
Ported from grsecurity/PaX. This version adds a verbose option to the
plugin and the Kconfig.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/Kconfig | 22 +++
include/linux/compiler.h | 6 +-
scripts/Makefile.gcc-plugins | 4 +
scripts/gcc-plugins/structleak_plugin.c | 246 ++++++++++++++++++++++++++++++++
4 files changed, 277 insertions(+), 1 deletion(-)
create mode 100644 scripts/gcc-plugins/structleak_plugin.c
diff --git a/arch/Kconfig b/arch/Kconfig
index 99839c23d453..f1250ba0b06f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -410,6 +410,28 @@ config GCC_PLUGIN_LATENT_ENTROPY
* https://grsecurity.net/
* https://pax.grsecurity.net/
+config GCC_PLUGIN_STRUCTLEAK
+ bool "Force initialization of variables containing userspace addresses"
+ depends on GCC_PLUGINS
+ help
+ This plugin zero-initializes any structures that containing a
+ __user attribute. This can prevent some classes of information
+ exposures.
+
+ This plugin was ported from grsecurity/PaX. More information at:
+ * https://grsecurity.net/
+ * https://pax.grsecurity.net/
+
+config GCC_PLUGIN_STRUCTLEAK_VERBOSE
+ bool "Report initialized variables"
+ depends on GCC_PLUGIN_STRUCTLEAK
+ depends on !COMPILE_TEST
+ help
+ This option will cause a warning to be printed each time the
+ structleak plugin finds a variable it thinks needs to be
+ initialized. Since not all existing initializers are detected
+ by the plugin, this can produce false positive warnings.
+
config HAVE_CC_STACKPROTECTOR
bool
help
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index cf0fa5d86059..91c30cba984e 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -27,7 +27,11 @@ extern void __chk_user_ptr(const volatile void __user *);
extern void __chk_io_ptr(const volatile void __iomem *);
# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
#else /* __CHECKER__ */
-# define __user
+# ifdef STRUCTLEAK_PLUGIN
+# define __user __attribute__((user))
+# else
+# define __user
+# endif
# define __kernel
# define __safe
# define __force
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 060d2cb373db..a084f7a511d8 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -25,6 +25,10 @@ ifdef CONFIG_GCC_PLUGINS
endif
endif
+ gcc-plugin-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += structleak_plugin.so
+ gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE) += -fplugin-arg-structleak_plugin-verbose
+ gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += -DSTRUCTLEAK_PLUGIN
+
GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR
diff --git a/scripts/gcc-plugins/structleak_plugin.c b/scripts/gcc-plugins/structleak_plugin.c
new file mode 100644
index 000000000000..deddb7291a26
--- /dev/null
+++ b/scripts/gcc-plugins/structleak_plugin.c
@@ -0,0 +1,246 @@
+/*
+ * Copyright 2013-2017 by PaX Team <pageexec@xxxxxxxxxxx>
+ * 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)));
+ }
+
+ /* enumarate 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;
+}
--
2.7.4
--
Kees Cook
Nexus Security