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author | Linus Torvalds <torvalds@linux-foundation.org> | 2021-09-02 12:35:34 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-09-02 12:35:34 -0700 |
commit | b55060d796c5300ad7a410cb5faec36582925570 (patch) | |
tree | 7711068e1cfdb3cb87541d42678272314bf9e4e1 | |
parent | c815f04ba94940fbc303a6ea9669e7da87f8e77d (diff) | |
parent | a8fc576d4af2f23a87a586424252df97f0ad0b06 (diff) | |
download | linux-b55060d796c5300ad7a410cb5faec36582925570.tar.bz2 |
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-- | Makefile | 5 | ||||
-rw-r--r-- | lib/test_stackinit.c | 253 | ||||
-rw-r--r-- | security/Kconfig.hardening | 71 |
3 files changed, 242 insertions, 87 deletions
@@ -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 |