[RFC/RFT] gcc-plugins: force initialize auto variables whose addresses are taken

Message ID	20170706101317.10382-1-ard.biesheuvel@linaro.org (mailing list archive)
State	New, archived
Headers	show Return-Path: <kernel-hardening-return-8875-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com> Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk From: Ard Biesheuvel <ard.biesheuvel@linaro.org> To: kernel-hardening@lists.openwall.com Cc: arnd@arndb.de, keescook@chromium.org, torvalds@linux-foundation.org, Ard Biesheuvel <ard.biesheuvel@linaro.org> Date: Thu, 6 Jul 2017 11:13:17 +0100 Message-Id: <20170706101317.10382-1-ard.biesheuvel@linaro.org> Subject: [kernel-hardening] [RFC/RFT PATCH] gcc-plugins: force initialize auto variables whose addresses are taken

diff --git a/arch/Kconfig b/arch/Kconfig index 6c00e5b00f8b..273b66749ad8 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -443,6 +443,15 @@ config GCC_PLUGIN_STRUCTLEAK_VERBOSE initialized. Since not all existing initializers are detected by the plugin, this can produce false positive warnings. +config GCC_PLUGIN_INITAUTOBYREF + bool "Force initialization of auto variables that have their address taken" + depends on GCC_PLUGINS + help + +config GCC_PLUGIN_INITAUTOBYREF_VERBOSE + bool "Report uninitialized auto variables that have their address taken" + depends on GCC_PLUGIN_INITAUTOBYREF + config HAVE_CC_STACKPROTECTOR bool help diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins index 82335533620e..90f30622f86d 100644 --- a/scripts/Makefile.gcc-plugins +++ b/scripts/Makefile.gcc-plugins @@ -29,6 +29,9 @@ ifdef CONFIG_GCC_PLUGINS gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE) += -fplugin-arg-structleak_plugin-verbose gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += -DSTRUCTLEAK_PLUGIN + gcc-plugin-$(CONFIG_GCC_PLUGIN_INITAUTOBYREF) += initautobyref_plugin.so + gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_INITAUTOBYREF_VERBOSE) += -fplugin-arg-initautobyref_plugin-verbose + 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/initautobyref_plugin.c b/scripts/gcc-plugins/initautobyref_plugin.c new file mode 100644 index 000000000000..afc8b8f22056 --- /dev/null +++ b/scripts/gcc-plugins/initautobyref_plugin.c @@ -0,0 +1,159 @@ +/* + * Copyright 2013-2017 by PaX Team <pageexec@freemail.hu> + * Copyright 2017 by Ard Biesheuvel <ard.biesheuvel@linaro.org> + * 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 local variables that have their address + * taken, to prevent leaking data if the variable is never initialized (which + * may be difficult to decide for the compiler if the address is passed outside + * of the compilation unit) + * + * Options: + * -fplugin-arg-initautobyref_plugin-disable + * -fplugin-arg-initautobyref_plugin-verbose + */ + +#include "gcc-common.h" + +__visible int plugin_is_GPL_compatible; + +static struct plugin_info initautobyref_plugin_info = { + .version = "0.1", + .help = "disable\tdo not activate plugin\n" + "verbose\tprint all initialized variables\n", +}; + +static bool verbose; + +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), + "auto 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 initautobyref_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; + + /* initialize the variable if its address is taken */ + if (TREE_ADDRESSABLE (var)) + initialize(var); + } + + return ret; +} + +#define PASS_NAME initautobyref +#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(initautobyref, "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, &initautobyref_plugin_info); + if (enable) { + register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &initautobyref_pass_info); + } + + return 0; +}

[RFC/RFT] gcc-plugins: force initialize auto variables whose addresses are taken

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