Merge tag 'hardening-v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull hardening updates from Kees Cook:

 - Expand lib/test_stackinit to include more initialization styles

 - Improve Kconfig for CLang's auto-var-init feature

 - Introduce support for GCC's zero-call-used-regs feature

* tag 'hardening-v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  lib/test_stackinit: Add assigned initializers
  lib/test_stackinit: Allow building stand-alone
  lib/test_stackinit: Fix static initializer test
  hardening: Clarify Kconfig text for auto-var-init
  hardening: Introduce CONFIG_ZERO_CALL_USED_REGS

3 files changed, 242 insertions, 87 deletions

diff --git a/Makefile b/Makefile
index 61741e9d9c6e..2af6e2f17103 100644
--- a/Makefile
+++ b/Makefile
@@ -841,6 +841,11 @@ endif
 # for the randomize_kstack_offset feature. Disable it for all compilers.
 KBUILD_CFLAGS	+= $(call cc-option, -fno-stack-clash-protection)
 
+# Clear used registers at func exit (to reduce data lifetime and ROP gadgets).
+ifdef CONFIG_ZERO_CALL_USED_REGS
+KBUILD_CFLAGS	+= -fzero-call-used-regs=used-gpr
+endif
+
 DEBUG_CFLAGS	:=
 
 # Workaround for GCC versions < 5.0
diff --git a/lib/test_stackinit.c b/lib/test_stackinit.c
index f93b1e145ada..a3c74e6a21ff 100644
--- a/lib/test_stackinit.c
+++ b/lib/test_stackinit.c
@@ -1,8 +1,13 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
- * Test cases for compiler-based stack variable zeroing via future
- * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
+ * Test cases for compiler-based stack variable zeroing via
+ * -ftrivial-auto-var-init={zero,pattern} or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
+ *
+ * External build example:
+ *	clang -O2 -Wall -ftrivial-auto-var-init=pattern \
+ *		-o test_stackinit test_stackinit.c
  */
+#ifdef __KERNEL__
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/init.h>
@@ -10,6 +15,63 @@
 #include <linux/module.h>
 #include <linux/string.h>
 
+#else
+
+/* Userspace headers. */
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <sys/types.h>
+
+/* Linux kernel-ism stubs for stand-alone userspace build. */
+#define KBUILD_MODNAME		"stackinit"
+#define pr_fmt(fmt)		KBUILD_MODNAME ": " fmt
+#define pr_err(fmt, ...)	fprintf(stderr, pr_fmt(fmt), ##__VA_ARGS__)
+#define pr_warn(fmt, ...)	fprintf(stderr, pr_fmt(fmt), ##__VA_ARGS__)
+#define pr_info(fmt, ...)	fprintf(stdout, pr_fmt(fmt), ##__VA_ARGS__)
+#define __init			/**/
+#define __exit			/**/
+#define __user			/**/
+#define noinline		__attribute__((__noinline__))
+#define __aligned(x)		__attribute__((__aligned__(x)))
+#ifdef __clang__
+# define __compiletime_error(message) /**/
+#else
+# define __compiletime_error(message) __attribute__((__error__(message)))
+#endif
+#define __compiletime_assert(condition, msg, prefix, suffix)		\
+	do {								\
+		extern void prefix ## suffix(void) __compiletime_error(msg); \
+		if (!(condition))					\
+			prefix ## suffix();				\
+	} while (0)
+#define _compiletime_assert(condition, msg, prefix, suffix) \
+	__compiletime_assert(condition, msg, prefix, suffix)
+#define compiletime_assert(condition, msg) \
+	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
+#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
+#define BUILD_BUG_ON(condition) \
+	BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
+typedef uint8_t			u8;
+typedef uint16_t		u16;
+typedef uint32_t		u32;
+typedef uint64_t		u64;
+
+#define module_init(func)	static int (*do_init)(void) = func
+#define module_exit(func)	static void (*do_exit)(void) = func
+#define MODULE_LICENSE(str)	int main(void) {		\
+					int rc;			\
+					/* License: str */	\
+					rc = do_init();		\
+					if (rc == 0)		\
+						do_exit();	\
+					return rc;		\
+				}
+
+#endif /* __KERNEL__ */
+
 /* Exfiltration buffer. */
 #define MAX_VAR_SIZE	128
 static u8 check_buf[MAX_VAR_SIZE];
@@ -33,6 +95,10 @@ static bool range_contains(char *haystack_start, size_t haystack_size,
 	return false;
 }
 
+/* Whether the test is expected to fail. */
+#define WANT_SUCCESS				0
+#define XFAIL					1
+
 #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
@@ -58,34 +124,73 @@ static bool range_contains(char *haystack_start, size_t haystack_size,
 #define INIT_CLONE_STRING		[FILL_SIZE_STRING]
 #define INIT_CLONE_STRUCT		/**/
 
-#define INIT_SCALAR_none		/**/
-#define INIT_SCALAR_zero		= 0
+#define ZERO_CLONE_SCALAR(zero)		memset(&(zero), 0x00, sizeof(zero))
+#define ZERO_CLONE_STRING(zero)		memset(&(zero), 0x00, sizeof(zero))
+/*
+ * For the struct, intentionally poison padding to see if it gets
+ * copied out in direct assignments.
+ * */
+#define ZERO_CLONE_STRUCT(zero)				\
+	do {						\
+		memset(&(zero), 0xFF, sizeof(zero));	\
+		zero.one = 0;				\
+		zero.two = 0;				\
+		zero.three = 0;				\
+		zero.four = 0;				\
+	} while (0)
+
+#define INIT_SCALAR_none(var_type)	/**/
+#define INIT_SCALAR_zero(var_type)	= 0
 
-#define INIT_STRING_none		[FILL_SIZE_STRING] /**/
-#define INIT_STRING_zero		[FILL_SIZE_STRING] = { }
+#define INIT_STRING_none(var_type)	[FILL_SIZE_STRING] /**/
+#define INIT_STRING_zero(var_type)	[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_none(var_type)	/**/
+#define INIT_STRUCT_zero(var_type)	= { }
+
+
+#define __static_partial		{ .two = 0, }
+#define __static_all			{ .one = 0,			\
+					  .two = 0,			\
+					  .three = 0,			\
+					  .four = 0,			\
 					}
-#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 __dynamic_partial		{ .two = arg->two, }
+#define __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;			\
+#define __runtime_partial		var.two = 0
+#define __runtime_all			var.one = 0;			\
 					var.two = 0;			\
 					var.three = 0;			\
-					memset(&var.four, 0,		\
-					       sizeof(var.four))
+					var.four = 0
+
+#define INIT_STRUCT_static_partial(var_type)				\
+					= __static_partial
+#define INIT_STRUCT_static_all(var_type)				\
+					= __static_all
+#define INIT_STRUCT_dynamic_partial(var_type)				\
+					= __dynamic_partial
+#define INIT_STRUCT_dynamic_all(var_type)				\
+					= __dynamic_all
+#define INIT_STRUCT_runtime_partial(var_type)				\
+					; __runtime_partial
+#define INIT_STRUCT_runtime_all(var_type)				\
+					; __runtime_all
+
+#define INIT_STRUCT_assigned_static_partial(var_type)			\
+					; var = (var_type)__static_partial
+#define INIT_STRUCT_assigned_static_all(var_type)			\
+					; var = (var_type)__static_all
+#define INIT_STRUCT_assigned_dynamic_partial(var_type)			\
+					; var = (var_type)__dynamic_partial
+#define INIT_STRUCT_assigned_dynamic_all(var_type)			\
+					; var = (var_type)__dynamic_all
+
+#define INIT_STRUCT_assigned_copy(var_type)				\
+					; var = *(arg)
 
 /*
  * @name: unique string name for the test
@@ -106,7 +211,7 @@ static noinline __init int test_ ## name (void)			\
 	BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE);		\
 								\
 	/* Fill clone type with zero for per-field init. */	\
-	memset(&zero, 0x00, sizeof(zero));			\
+	ZERO_CLONE_ ## which(zero);				\
 	/* Clear entire check buffer for 0xFF overlap test. */	\
 	memset(check_buf, 0x00, sizeof(check_buf));		\
 	/* Fill stack with 0xFF. */				\
@@ -149,7 +254,7 @@ static noinline __init int test_ ## name (void)			\
 		return (xfail) ? 0 : 1;				\
 	}							\
 }
-#define DEFINE_TEST(name, var_type, which, init_level)		\
+#define DEFINE_TEST(name, var_type, which, init_level, xfail)	\
 /* no-op to force compiler into ignoring "uninitialized" vars */\
 static noinline __init DO_NOTHING_TYPE_ ## which(var_type)	\
 do_nothing_ ## name(var_type *ptr)				\
@@ -165,7 +270,8 @@ static noinline __init int leaf_ ## name(unsigned long sp,	\
 					 var_type *arg)		\
 {								\
 	char buf[VAR_BUFFER];					\
-	var_type var INIT_ ## which ## _ ## init_level;		\
+	var_type var						\
+		INIT_ ## which ## _ ## init_level(var_type);	\
 								\
 	target_start = &var;					\
 	target_size = sizeof(var);				\
@@ -191,7 +297,7 @@ static noinline __init int leaf_ ## name(unsigned long sp,	\
 								\
 	return (int)buf[0] | (int)buf[sizeof(buf) - 1];		\
 }								\
-DEFINE_TEST_DRIVER(name, var_type, which, 0)
+DEFINE_TEST_DRIVER(name, var_type, which, xfail)
 
 /* Structure with no padding. */
 struct test_packed {
@@ -210,18 +316,13 @@ struct test_small_hole {
 	unsigned long four;
 };
 
-/* Try to trigger unhandled padding in a structure. */
-struct test_aligned {
-	u32 internal1;
-	u64 internal2;
-} __aligned(64);
-
+/* Trigger unhandled padding in a structure. */
 struct test_big_hole {
 	u8 one;
 	u8 two;
 	u8 three;
 	/* 61 byte padding hole here. */
-	struct test_aligned four;
+	u8 four __aligned(64);
 } __aligned(64);
 
 struct test_trailing_hole {
@@ -240,42 +341,50 @@ struct test_user {
 	unsigned long four;
 };
 
-#define DEFINE_SCALAR_TEST(name, init)				\
-		DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
+#define DEFINE_SCALAR_TEST(name, init, xfail)			\
+		DEFINE_TEST(name ## _ ## init, name, SCALAR,	\
+			    init, xfail)
 
-#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_SCALAR_TESTS(init, xfail)			\
+		DEFINE_SCALAR_TEST(u8, init, xfail);		\
+		DEFINE_SCALAR_TEST(u16, init, xfail);		\
+		DEFINE_SCALAR_TEST(u32, init, xfail);		\
+		DEFINE_SCALAR_TEST(u64, init, xfail);		\
+		DEFINE_TEST(char_array_ ## init, unsigned char,	\
+			    STRING, init, xfail)
 
-#define DEFINE_STRUCT_TEST(name, init)				\
+#define DEFINE_STRUCT_TEST(name, init, xfail)			\
 		DEFINE_TEST(name ## _ ## init,			\
-			    struct test_ ## name, STRUCT, init)
+			    struct test_ ## name, STRUCT, init, \
+			    xfail)
+
+#define DEFINE_STRUCT_TESTS(init, xfail)			\
+		DEFINE_STRUCT_TEST(small_hole, init, xfail);	\
+		DEFINE_STRUCT_TEST(big_hole, init, xfail);	\
+		DEFINE_STRUCT_TEST(trailing_hole, init, xfail);	\
+		DEFINE_STRUCT_TEST(packed, init, xfail)
 
-#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)
+#define DEFINE_STRUCT_INITIALIZER_TESTS(base)			\
+		DEFINE_STRUCT_TESTS(base ## _ ## partial,	\
+				    WANT_SUCCESS);		\
+		DEFINE_STRUCT_TESTS(base ## _ ## all,		\
+				    WANT_SUCCESS)
 
 /* 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);
+DEFINE_SCALAR_TESTS(zero, WANT_SUCCESS);
+DEFINE_STRUCT_TESTS(zero, WANT_SUCCESS);
+/* Struct initializers: padding may be left uninitialized. */
+DEFINE_STRUCT_INITIALIZER_TESTS(static);
+DEFINE_STRUCT_INITIALIZER_TESTS(dynamic);
+DEFINE_STRUCT_INITIALIZER_TESTS(runtime);
+DEFINE_STRUCT_INITIALIZER_TESTS(assigned_static);
+DEFINE_STRUCT_INITIALIZER_TESTS(assigned_dynamic);
+DEFINE_STRUCT_TESTS(assigned_copy, XFAIL);
 /* No initialization without compiler instrumentation. */
-DEFINE_SCALAR_TESTS(none);
-DEFINE_STRUCT_TESTS(none);
-DEFINE_TEST(user, struct test_user, STRUCT, none);
+DEFINE_SCALAR_TESTS(none, WANT_SUCCESS);
+DEFINE_STRUCT_TESTS(none, WANT_SUCCESS);
+/* Initialization of members with __user attribute. */
+DEFINE_TEST(user, struct test_user, STRUCT, none, WANT_SUCCESS);
 
 /*
  * Check two uses through a variable declaration outside either path,
@@ -285,6 +394,10 @@ DEFINE_TEST(user, struct test_user, STRUCT, none);
 static int noinline __leaf_switch_none(int path, bool fill)
 {
 	switch (path) {
+		/*
+		 * This is intentionally unreachable. To silence the
+		 * warning, build with -Wno-switch-unreachable
+		 */
 		uint64_t var;
 
 	case 1:
@@ -334,8 +447,8 @@ static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
  * non-code areas (i.e. in a switch statement before the first "case").
  * https://bugs.llvm.org/show_bug.cgi?id=44916
  */
-DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
-DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
+DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, XFAIL);
+DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, XFAIL);
 
 static int __init test_stackinit_init(void)
 {
@@ -361,12 +474,18 @@ static int __init test_stackinit_init(void)
 	test_structs(zero);
 	/* Padding here appears to be accidentally always initialized? */
 	test_structs(dynamic_partial);
+	test_structs(assigned_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);
+	test_structs(assigned_static_partial);
+	test_structs(assigned_static_all);
+	test_structs(assigned_dynamic_all);
+	/* Everything fails this since it effectively performs a memcpy(). */
+	test_structs(assigned_copy);
 
 	/* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
 	test_scalars(none);
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index a56c36470cb1..90cbaff86e13 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -29,6 +29,7 @@ choice
 	prompt "Initialize kernel stack variables at function entry"
 	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
 	default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
+	default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_PATTERN
 	default INIT_STACK_NONE
 	help
 	  This option enables initialization of stack variables at
@@ -39,11 +40,11 @@ choice
 	  syscalls.
 
 	  This chooses the level of coverage over classes of potentially
-	  uninitialized variables. The selected class will be
+	  uninitialized variables. The selected class of variable will be
 	  initialized before use in a function.
 
 	config INIT_STACK_NONE
-		bool "no automatic initialization (weakest)"
+		bool "no automatic stack variable initialization (weakest)"
 		help
 		  Disable automatic stack variable initialization.
 		  This leaves the kernel vulnerable to the standard
@@ -80,7 +81,7 @@ choice
 		  and is disallowed.
 
 	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
-		bool "zero-init anything passed by reference (very strong)"
+		bool "zero-init everything passed by reference (very strong)"
 		depends on GCC_PLUGINS
 		depends on !(KASAN && KASAN_STACK)
 		select GCC_PLUGIN_STRUCTLEAK
@@ -91,33 +92,44 @@ choice
 		  of uninitialized stack variable exploits and information
 		  exposures.
 
+		  As a side-effect, this keeps a lot of variables on the
+		  stack that can otherwise be optimized out, so combining
+		  this with CONFIG_KASAN_STACK can lead to a stack overflow
+		  and is disallowed.
+
 	config INIT_STACK_ALL_PATTERN
-		bool "0xAA-init everything on the stack (strongest)"
+		bool "pattern-init everything (strongest)"
 		depends on CC_HAS_AUTO_VAR_INIT_PATTERN
 		help
-		  Initializes everything on the stack with a 0xAA
-		  pattern. This is intended to eliminate all classes
-		  of uninitialized stack variable exploits and information
-		  exposures, even variables that were warned to have been
-		  left uninitialized.
+		  Initializes everything on the stack (including padding)
+		  with a specific debug value. This is intended to eliminate
+		  all classes of uninitialized stack variable exploits and
+		  information exposures, even variables that were warned about
+		  having been left uninitialized.
 
 		  Pattern initialization is known to provoke many existing bugs
 		  related to uninitialized locals, e.g. pointers receive
-		  non-NULL values, buffer sizes and indices are very big.
+		  non-NULL values, buffer sizes and indices are very big. The
+		  pattern is situation-specific; Clang on 64-bit uses 0xAA
+		  repeating for all types and padding except float and double
+		  which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
+		  repeating for all types and padding.
 
 	config INIT_STACK_ALL_ZERO
-		bool "zero-init everything on the stack (strongest and safest)"
+		bool "zero-init everything (strongest and safest)"
 		depends on CC_HAS_AUTO_VAR_INIT_ZERO
 		help
-		  Initializes everything on the stack with a zero
-		  value. This is intended to eliminate all classes
-		  of uninitialized stack variable exploits and information
-		  exposures, even variables that were warned to have been
-		  left uninitialized.
-
-		  Zero initialization provides safe defaults for strings,
-		  pointers, indices and sizes, and is therefore
-		  more suitable as a security mitigation measure.
+		  Initializes everything on the stack (including padding)
+		  with a zero value. This is intended to eliminate all
+		  classes of uninitialized stack variable exploits and
+		  information exposures, even variables that were warned
+		  about having been left uninitialized.
+
+		  Zero initialization provides safe defaults for strings
+		  (immediately NUL-terminated), pointers (NULL), indices
+		  (index 0), and sizes (0 length), so it is therefore more
+		  suitable as a production security mitigation than pattern
+		  initialization.
 
 endchoice
 
@@ -217,6 +229,25 @@ config INIT_ON_FREE_DEFAULT_ON
 	  touching "cold" memory areas. Most cases see 3-5% impact. Some
 	  synthetic workloads have measured as high as 8%.
 
+config CC_HAS_ZERO_CALL_USED_REGS
+	def_bool $(cc-option,-fzero-call-used-regs=used-gpr)
+
+config ZERO_CALL_USED_REGS
+	bool "Enable register zeroing on function exit"
+	depends on CC_HAS_ZERO_CALL_USED_REGS
+	help
+	  At the end of functions, always zero any caller-used register
+	  contents. This helps ensure that temporary values are not
+	  leaked beyond the function boundary. This means that register
+	  contents are less likely to be available for side channels
+	  and information exposures. Additionally, this helps reduce the
+	  number of useful ROP gadgets by about 20% (and removes compiler
+	  generated "write-what-where" gadgets) in the resulting kernel
+	  image. This has a less than 1% performance impact on most
+	  workloads. Image size growth depends on architecture, and should
+	  be evaluated for suitability. For example, x86_64 grows by less
+	  than 1%, and arm64 grows by about 5%.
+
 endmenu
 
 endmenu