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authorLinus Torvalds <torvalds@linux-foundation.org>2021-09-02 12:35:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-02 12:35:34 -0700
commitb55060d796c5300ad7a410cb5faec36582925570 (patch)
tree7711068e1cfdb3cb87541d42678272314bf9e4e1
parentc815f04ba94940fbc303a6ea9669e7da87f8e77d (diff)
parenta8fc576d4af2f23a87a586424252df97f0ad0b06 (diff)
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
-rw-r--r--Makefile5
-rw-r--r--lib/test_stackinit.c253
-rw-r--r--security/Kconfig.hardening71
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
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