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Merge tag 'hardening-v5.15-rc1' of git://git.kernel.org/pub/scm/linux…
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…/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
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@torvalds
torvalds committed Sep 2, 2021
2 parents c815f04 + a8fc576 commit b55060d
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5 changes: 5 additions & 0 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down
253 changes: 186 additions & 67 deletions lib/test_stackinit.c
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Original file line number Diff line number Diff line change
@@ -1,15 +1,77 @@
// 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>
#include <linux/kernel.h>
#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];
Expand All @@ -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
Expand All @@ -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
Expand All @@ -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. */ \
Expand Down Expand Up @@ -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) \
Expand All @@ -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); \
Expand All @@ -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 {
Expand All @@ -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 {
Expand All @@ -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,
Expand All @@ -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:
Expand Down Expand Up @@ -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)
{
Expand All @@ -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);
Expand Down
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