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Commit c61f13ea authored by Kees Cook's avatar Kees Cook
Browse files

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: default avatarKees Cook <keescook@chromium.org>
parent 8d4973a1

arch/Kconfig

+22 −0
Original line number Diff line number Diff line
@@ -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 forcefully 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

include/linux/compiler.h

+5 −1
Original line number Diff line number Diff line
@@ -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__ */

# ifdef STRUCTLEAK_PLUGIN

#  define __user __attribute__((user))

# else

#  define __user

# endif

# define __kernel

# define __safe

# define __force

scripts/Makefile.gcc-plugins

+4 −0
Original line number Diff line number Diff line
@@ -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

scripts/gcc-plugins/structleak_plugin.c

0 → 100644
+246 −0
Original line number Diff line number Diff line 
/*

 * 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;

}