increased structleak coverage

- And scalar and array initialization coverage
 - Refactor Kconfig to make options more clear
 - Add self-test module for testing automatic initialization
 -----BEGIN PGP SIGNATURE-----
 Comment: Kees Cook <kees@outflux.net>
 
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Merge tag 'gcc-plugins-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull gcc-plugins updates from Kees Cook:
 "This adds additional type coverage to the existing structleak plugin
  and adds a large set of selftests to help evaluate stack variable
  zero-initialization coverage.

  That can be used to test whatever instrumentation might be performing
  zero-initialization: either with the structleak plugin or with Clang's
  coming "-ftrivial-auto-var-init=zero" option.

  Summary:

   - Add scalar and array initialization coverage

   - Refactor Kconfig to make options more clear

   - Add self-test module for testing automatic initialization"

* tag 'gcc-plugins-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  lib: Introduce test_stackinit module
  gcc-plugins: structleak: Generalize to all variable types

lib/Kconfig.debug

@@ -2016,6 +2016,16 @@ config TEST_OBJAGG
 	  (or module load).
 
 
+config TEST_STACKINIT
+	tristate "Test level of stack variable initialization"
+	help
+	  Test if the kernel is zero-initializing stack variables and
+	  padding. Coverage is controlled by compiler flags,
+	  CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
+	  or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
+
+	  If unsure, say N.
+
 endif # RUNTIME_TESTING_MENU
 
 config MEMTEST

lib/Makefile

@@ -77,6 +77,7 @@ obj-$(CONFIG_TEST_KMOD) += test_kmod.o
 obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
 obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o
 obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
+obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 

lib/test_stackinit.c

@@ -0,0 +1,378 @@
+// SPDX-Licenses: GPLv2
+/*
+ * Test cases for compiler-based stack variable zeroing via future
+ * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+/* Exfiltration buffer. */
+#define MAX_VAR_SIZE	128
+static char check_buf[MAX_VAR_SIZE];
+
+/* Character array to trigger stack protector in all functions. */
+#define VAR_BUFFER	 32
+
+/* Volatile mask to convince compiler to copy memory with 0xff. */
+static volatile u8 forced_mask = 0xff;
+
+/* Location and size tracking to validate fill and test are colocated. */
+static void *fill_start, *target_start;
+static size_t fill_size, target_size;
+
+static bool range_contains(char *haystack_start, size_t haystack_size,
+			   char *needle_start, size_t needle_size)
+{
+	if (needle_start >= haystack_start &&
+	    needle_start + needle_size <= haystack_start + haystack_size)
+		return true;
+	return false;
+}
+
+#define DO_NOTHING_TYPE_SCALAR(var_type)	var_type
+#define DO_NOTHING_TYPE_STRING(var_type)	void
+#define DO_NOTHING_TYPE_STRUCT(var_type)	void
+
+#define DO_NOTHING_RETURN_SCALAR(ptr)		*(ptr)
+#define DO_NOTHING_RETURN_STRING(ptr)		/**/
+#define DO_NOTHING_RETURN_STRUCT(ptr)		/**/
+
+#define DO_NOTHING_CALL_SCALAR(var, name)			\
+		(var) = do_nothing_ ## name(&(var))
+#define DO_NOTHING_CALL_STRING(var, name)			\
+		do_nothing_ ## name(var)
+#define DO_NOTHING_CALL_STRUCT(var, name)			\
+		do_nothing_ ## name(&(var))
+
+#define FETCH_ARG_SCALAR(var)		&var
+#define FETCH_ARG_STRING(var)		var
+#define FETCH_ARG_STRUCT(var)		&var
+
+#define FILL_SIZE_STRING		16
+
+#define INIT_CLONE_SCALAR		/**/
+#define INIT_CLONE_STRING		[FILL_SIZE_STRING]
+#define INIT_CLONE_STRUCT		/**/
+
+#define INIT_SCALAR_none		/**/
+#define INIT_SCALAR_zero		= 0
+
+#define INIT_STRING_none		[FILL_SIZE_STRING] /**/
+#define INIT_STRING_zero		[FILL_SIZE_STRING] = { }
+
+#define INIT_STRUCT_none		/**/
+#define INIT_STRUCT_zero		= { }
+#define INIT_STRUCT_static_partial	= { .two = 0, }
+#define INIT_STRUCT_static_all		= { .one = arg->one,		\
+					    .two = arg->two,		\
+					    .three = arg->three,	\
+					    .four = arg->four,		\
+					}
+#define INIT_STRUCT_dynamic_partial	= { .two = arg->two, }
+#define INIT_STRUCT_dynamic_all		= { .one = arg->one,		\
+					    .two = arg->two,		\
+					    .three = arg->three,	\
+					    .four = arg->four,		\
+					}
+#define INIT_STRUCT_runtime_partial	;				\
+					var.two = 0
+#define INIT_STRUCT_runtime_all		;				\
+					var.one = 0;			\
+					var.two = 0;			\
+					var.three = 0;			\
+					memset(&var.four, 0,		\
+					       sizeof(var.four))
+
+/*
+ * @name: unique string name for the test
+ * @var_type: type to be tested for zeroing initialization
+ * @which: is this a SCALAR, STRING, or STRUCT type?
+ * @init_level: what kind of initialization is performed
+ */
+#define DEFINE_TEST_DRIVER(name, var_type, which)		\
+/* Returns 0 on success, 1 on failure. */			\
+static noinline __init int test_ ## name (void)			\
+{								\
+	var_type zero INIT_CLONE_ ## which;			\
+	int ignored;						\
+	u8 sum = 0, i;						\
+								\
+	/* Notice when a new test is larger than expected. */	\
+	BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE);		\
+								\
+	/* Fill clone type with zero for per-field init. */	\
+	memset(&zero, 0x00, sizeof(zero));			\
+	/* Fill stack with 0xFF. */				\
+	ignored = leaf_ ##name((unsigned long)&ignored, 1,	\
+				FETCH_ARG_ ## which(zero));	\
+	/* Clear entire check buffer for later bit tests. */	\
+	memset(check_buf, 0x00, sizeof(check_buf));		\
+	/* Extract stack-defined variable contents. */		\
+	ignored = leaf_ ##name((unsigned long)&ignored, 0,	\
+				FETCH_ARG_ ## which(zero));	\
+								\
+	/* Validate that compiler lined up fill and target. */	\
+	if (!range_contains(fill_start, fill_size,		\
+			    target_start, target_size)) {	\
+		pr_err(#name ": stack fill missed target!?\n");	\
+		pr_err(#name ": fill %zu wide\n", fill_size);	\
+		pr_err(#name ": target offset by %d\n",	\
+			(int)((ssize_t)(uintptr_t)fill_start -	\
+			(ssize_t)(uintptr_t)target_start));	\
+		return 1;					\
+	}							\
+								\
+	/* Look for any set bits in the check region. */	\
+	for (i = 0; i < sizeof(check_buf); i++)			\
+		sum += (check_buf[i] != 0);			\
+								\
+	if (sum == 0)						\
+		pr_info(#name " ok\n");				\
+	else							\
+		pr_warn(#name " FAIL (uninit bytes: %d)\n",	\
+			sum);					\
+								\
+	return (sum != 0);					\
+}
+#define DEFINE_TEST(name, var_type, which, init_level)		\
+/* no-op to force compiler into ignoring "uninitialized" vars */\
+static noinline __init DO_NOTHING_TYPE_ ## which(var_type)	\
+do_nothing_ ## name(var_type *ptr)				\
+{								\
+	/* Will always be true, but compiler doesn't know. */	\
+	if ((unsigned long)ptr > 0x2)				\
+		return DO_NOTHING_RETURN_ ## which(ptr);	\
+	else							\
+		return DO_NOTHING_RETURN_ ## which(ptr + 1);	\
+}								\
+static noinline __init int leaf_ ## name(unsigned long sp,	\
+					 bool fill,		\
+					 var_type *arg)		\
+{								\
+	char buf[VAR_BUFFER];					\
+	var_type var INIT_ ## which ## _ ## init_level;		\
+								\
+	target_start = &var;					\
+	target_size = sizeof(var);				\
+	/*							\
+	 * Keep this buffer around to make sure we've got a	\
+	 * stack frame of SOME kind...				\
+	 */							\
+	memset(buf, (char)(sp && 0xff), sizeof(buf));		\
+	/* Fill variable with 0xFF. */				\
+	if (fill) {						\
+		fill_start = &var;				\
+		fill_size = sizeof(var);			\
+		memset(fill_start,				\
+		       (char)((sp && 0xff) | forced_mask),	\
+		       fill_size);				\
+	}							\
+								\
+	/* Silence "never initialized" warnings. */		\
+	DO_NOTHING_CALL_ ## which(var, name);			\
+								\
+	/* Exfiltrate "var". */					\
+	memcpy(check_buf, target_start, target_size);		\
+								\
+	return (int)buf[0] | (int)buf[sizeof(buf) - 1];		\
+}								\
+DEFINE_TEST_DRIVER(name, var_type, which)
+
+/* Structure with no padding. */
+struct test_packed {
+	unsigned long one;
+	unsigned long two;
+	unsigned long three;
+	unsigned long four;
+};
+
+/* Simple structure with padding likely to be covered by compiler. */
+struct test_small_hole {
+	size_t one;
+	char two;
+	/* 3 byte padding hole here. */
+	int three;
+	unsigned long four;
+};
+
+/* Try to trigger unhandled padding in a structure. */
+struct test_aligned {
+	u32 internal1;
+	u64 internal2;
+} __aligned(64);
+
+struct test_big_hole {
+	u8 one;
+	u8 two;
+	u8 three;
+	/* 61 byte padding hole here. */
+	struct test_aligned four;
+} __aligned(64);
+
+struct test_trailing_hole {
+	char *one;
+	char *two;
+	char *three;
+	char four;
+	/* "sizeof(unsigned long) - 1" byte padding hole here. */
+};
+
+/* Test if STRUCTLEAK is clearing structs with __user fields. */
+struct test_user {
+	u8 one;
+	unsigned long two;
+	char __user *three;
+	unsigned long four;
+};
+
+#define DEFINE_SCALAR_TEST(name, init)				\
+		DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
+
+#define DEFINE_SCALAR_TESTS(init)				\
+		DEFINE_SCALAR_TEST(u8, init);			\
+		DEFINE_SCALAR_TEST(u16, init);			\
+		DEFINE_SCALAR_TEST(u32, init);			\
+		DEFINE_SCALAR_TEST(u64, init);			\
+		DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
+
+#define DEFINE_STRUCT_TEST(name, init)				\
+		DEFINE_TEST(name ## _ ## init,			\
+			    struct test_ ## name, STRUCT, init)
+
+#define DEFINE_STRUCT_TESTS(init)				\
+		DEFINE_STRUCT_TEST(small_hole, init);		\
+		DEFINE_STRUCT_TEST(big_hole, init);		\
+		DEFINE_STRUCT_TEST(trailing_hole, init);	\
+		DEFINE_STRUCT_TEST(packed, init)
+
+/* These should be fully initialized all the time! */
+DEFINE_SCALAR_TESTS(zero);
+DEFINE_STRUCT_TESTS(zero);
+/* Static initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(static_partial);
+DEFINE_STRUCT_TESTS(static_all);
+/* Dynamic initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(dynamic_partial);
+DEFINE_STRUCT_TESTS(dynamic_all);
+/* Runtime initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(runtime_partial);
+DEFINE_STRUCT_TESTS(runtime_all);
+/* No initialization without compiler instrumentation. */
+DEFINE_SCALAR_TESTS(none);
+DEFINE_STRUCT_TESTS(none);
+DEFINE_TEST(user, struct test_user, STRUCT, none);
+
+/*
+ * Check two uses through a variable declaration outside either path,
+ * which was noticed as a special case in porting earlier stack init
+ * compiler logic.
+ */
+static int noinline __leaf_switch_none(int path, bool fill)
+{
+	switch (path) {
+		uint64_t var;
+
+	case 1:
+		target_start = &var;
+		target_size = sizeof(var);
+		if (fill) {
+			fill_start = &var;
+			fill_size = sizeof(var);
+
+			memset(fill_start, forced_mask | 0x55, fill_size);
+		}
+		memcpy(check_buf, target_start, target_size);
+		break;
+	case 2:
+		target_start = &var;
+		target_size = sizeof(var);
+		if (fill) {
+			fill_start = &var;
+			fill_size = sizeof(var);
+
+			memset(fill_start, forced_mask | 0xaa, fill_size);
+		}
+		memcpy(check_buf, target_start, target_size);
+		break;
+	default:
+		var = 5;
+		return var & forced_mask;
+	}
+	return 0;
+}
+
+static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
+					      uint64_t *arg)
+{
+	return __leaf_switch_none(1, fill);
+}
+
+static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
+					      uint64_t *arg)
+{
+	return __leaf_switch_none(2, fill);
+}
+
+DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR);
+DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR);
+
+static int __init test_stackinit_init(void)
+{
+	unsigned int failures = 0;
+
+#define test_scalars(init)	do {				\
+		failures += test_u8_ ## init ();		\
+		failures += test_u16_ ## init ();		\
+		failures += test_u32_ ## init ();		\
+		failures += test_u64_ ## init ();		\
+		failures += test_char_array_ ## init ();	\
+	} while (0)
+
+#define test_structs(init)	do {				\
+		failures += test_small_hole_ ## init ();	\
+		failures += test_big_hole_ ## init ();		\
+		failures += test_trailing_hole_ ## init ();	\
+		failures += test_packed_ ## init ();		\
+	} while (0)
+
+	/* These are explicitly initialized and should always pass. */
+	test_scalars(zero);
+	test_structs(zero);
+	/* Padding here appears to be accidentally always initialized? */
+	test_structs(dynamic_partial);
+	/* Padding initialization depends on compiler behaviors. */
+	test_structs(static_partial);
+	test_structs(static_all);
+	test_structs(dynamic_all);
+	test_structs(runtime_partial);
+	test_structs(runtime_all);
+
+	/* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
+	test_scalars(none);
+	failures += test_switch_1_none();
+	failures += test_switch_2_none();
+
+	/* STRUCTLEAK_BYREF should cover from here down. */
+	test_structs(none);
+
+	/* STRUCTLEAK will only cover this. */
+	failures += test_user();
+
+	if (failures == 0)
+		pr_info("all tests passed!\n");
+	else
+		pr_err("failures: %u\n", failures);
+
+	return failures ? -EINVAL : 0;
+}
+module_init(test_stackinit_init);
+
+static void __exit test_stackinit_exit(void)
+{ }
+module_exit(test_stackinit_exit);
+
+MODULE_LICENSE("GPL");

scripts/Makefile.gcc-plugins

@@ -15,6 +15,8 @@ gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV)		+= sancov_plugin.so
 gcc-plugin-$(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_BYREF)		\
+		+= -fplugin-arg-structleak_plugin-byref
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL)	\
 		+= -fplugin-arg-structleak_plugin-byref-all
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK)		\

scripts/gcc-plugins/Kconfig

@@ -67,23 +67,59 @@ config GCC_PLUGIN_LATENT_ENTROPY
 	   * https://pax.grsecurity.net/
 
 config GCC_PLUGIN_STRUCTLEAK
-	bool "Force initialization of variables containing userspace addresses"
+	bool "Zero initialize stack variables"
 	help
-	  This plugin zero-initializes any structures containing a
+	  While the kernel is built with warnings enabled for any missed
-	  __user attribute. This can prevent some classes of information
+	  stack variable initializations, this warning is silenced for
-	  exposures.
+	  anything passed by reference to another function, under the
+	  occasionally misguided assumption that the function will do
+	  the initialization. As this regularly leads to exploitable
+	  flaws, this plugin is available to identify and zero-initialize
+	  such variables, depending on the chosen level of coverage.
 
-	  This plugin was ported from grsecurity/PaX. More information at:
+	  This plugin was originally ported from grsecurity/PaX. More
+	  information at:
 	   * https://grsecurity.net/
 	   * https://pax.grsecurity.net/
 
-config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
+choice
-	bool "Force initialize all struct type variables passed by reference"
+	prompt "Coverage"
 	depends on GCC_PLUGIN_STRUCTLEAK
-	depends on !COMPILE_TEST
+	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 	help
-	  Zero initialize any struct type local variable that may be passed by
+	  This chooses the level of coverage over classes of potentially
-	  reference without having been initialized.
+	  uninitialized variables. The selected class will be
+	  zero-initialized before use.
+
+	config GCC_PLUGIN_STRUCTLEAK_USER
+		bool "structs marked for userspace"
+		help
+		  Zero-initialize any structures on the stack containing
+		  a __user attribute. This can prevent some classes of
+		  uninitialized stack variable exploits and information
+		  exposures, like CVE-2013-2141:
+		  https://git.kernel.org/linus/b9e146d8eb3b9eca
+
+	config GCC_PLUGIN_STRUCTLEAK_BYREF
+		bool "structs passed by reference"
+		help
+		  Zero-initialize any structures on the stack that may
+		  be passed by reference and had not already been
+		  explicitly initialized. This can prevent most classes
+		  of uninitialized stack variable exploits and information
+		  exposures, like CVE-2017-1000410:
+		  https://git.kernel.org/linus/06e7e776ca4d3654
+
+	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
+		bool "anything passed by reference"
+		help
+		  Zero-initialize any stack variables that may be passed
+		  by reference and had not already been explicitly
+		  initialized. This is intended to eliminate all classes
+		  of uninitialized stack variable exploits and information
+		  exposures.
+
+endchoice
 
 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 	bool "Report forcefully initialized variables"

scripts/gcc-plugins/structleak_plugin.c

@@ -16,6 +16,7 @@
  * Options:
  * -fplugin-arg-structleak_plugin-disable
  * -fplugin-arg-structleak_plugin-verbose
+ * -fplugin-arg-structleak_plugin-byref
  * -fplugin-arg-structleak_plugin-byref-all
  *
  * Usage:
@@ -26,7 +27,6 @@
  * $ gcc -fplugin=./structleak_plugin.so test.c -O2
  *
  * TODO: eliminate redundant initializers
- *       increase type coverage
  */
 
 #include "gcc-common.h"
@@ -37,13 +37,18 @@
 __visible int plugin_is_GPL_compatible;
 
 static struct plugin_info structleak_plugin_info = {
-	.version	= "201607271510vanilla",
+	.version	= "20190125vanilla",
 	.help		= "disable\tdo not activate plugin\n"
+			  "byref\tinit structs passed by reference\n"
+			  "byref-all\tinit anything passed by reference\n"
 			  "verbose\tprint all initialized variables\n",
 };
 
+#define BYREF_STRUCT	1
+#define BYREF_ALL	2
+
 static bool verbose;
-static bool byref_all;
+static int byref;
 
 static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs)
 {
@@ -118,6 +123,7 @@ static void initialize(tree var)
 	gimple_stmt_iterator gsi;
 	tree initializer;
 	gimple init_stmt;
+	tree type;
 
 	/* this is the original entry bb before the forced split */
 	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
@@ -148,11 +154,15 @@ static void initialize(tree var)
 	if (verbose)
 		inform(DECL_SOURCE_LOCATION(var),
 			"%s variable will be forcibly initialized",
-			(byref_all && TREE_ADDRESSABLE(var)) ? "byref"
+			(byref && TREE_ADDRESSABLE(var)) ? "byref"
 							 : "userspace");
 
 	/* build the initializer expression */
-	initializer = build_constructor(TREE_TYPE(var), NULL);
+	type = TREE_TYPE(var);
+	if (AGGREGATE_TYPE_P(type))
+		initializer = build_constructor(type, NULL);
+	else
+		initializer = fold_convert(type, integer_zero_node);
 
 	/* build the initializer stmt */
 	init_stmt = gimple_build_assign(var, initializer);
@@ -184,13 +194,13 @@ static unsigned int structleak_execute(void)
 		if (!auto_var_in_fn_p(var, current_function_decl))
 			continue;
 
-		/* only care about structure types */
+		/* only care about structure types unless byref-all */
-		if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
+		if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
 			continue;
 
 		/* if the type is of interest, examine the variable */
 		if (TYPE_USERSPACE(type) ||
-		    (byref_all && TREE_ADDRESSABLE(var)))
+		    (byref && TREE_ADDRESSABLE(var)))
 			initialize(var);
 	}
 
@@ -232,8 +242,12 @@ __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gc
 			verbose = true;
 			continue;
 		}
+		if (!strcmp(argv[i].key, "byref")) {
+			byref = BYREF_STRUCT;
+			continue;
+		}
 		if (!strcmp(argv[i].key, "byref-all")) {
-			byref_all = true;
+			byref = BYREF_ALL;
 			continue;
 		}
 		error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);