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torvaldstorvalds
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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
2 parents c815f04 + a8fc576 commit b55060d

3 files changed

Lines changed: 242 additions & 87 deletions

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‎Makefile‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -841,6 +841,11 @@ endif
841841
# for the randomize_kstack_offset feature. Disable it for all compilers.
842842
KBUILD_CFLAGS += $(call cc-option, -fno-stack-clash-protection)
843843

844+
# Clear used registers at func exit (to reduce data lifetime and ROP gadgets).
845+
ifdef CONFIG_ZERO_CALL_USED_REGS
846+
KBUILD_CFLAGS += -fzero-call-used-regs=used-gpr
847+
endif
848+
844849
DEBUG_CFLAGS :=
845850

846851
# Workaround for GCC versions < 5.0

‎lib/test_stackinit.c‎

Lines changed: 186 additions & 67 deletions
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,77 @@
1-
// SPDX-License-Identifier: GPL-2.0
1+
// SPDX-License-Identifier: GPL-2.0-or-later
22
/*
3-
* Test cases for compiler-based stack variable zeroing via future
4-
* compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
3+
* Test cases for compiler-based stack variable zeroing via
4+
* -ftrivial-auto-var-init={zero,pattern} or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
5+
*
6+
* External build example:
7+
* clang -O2 -Wall -ftrivial-auto-var-init=pattern \
8+
* -o test_stackinit test_stackinit.c
59
*/
10+
#ifdef __KERNEL__
611
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
712

813
#include <linux/init.h>
914
#include <linux/kernel.h>
1015
#include <linux/module.h>
1116
#include <linux/string.h>
1217

18+
#else
19+
20+
/* Userspace headers. */
21+
#include <stdio.h>
22+
#include <stdint.h>
23+
#include <string.h>
24+
#include <stdbool.h>
25+
#include <errno.h>
26+
#include <sys/types.h>
27+
28+
/* Linux kernel-ism stubs for stand-alone userspace build. */
29+
#define KBUILD_MODNAME "stackinit"
30+
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
31+
#define pr_err(fmt, ...) fprintf(stderr, pr_fmt(fmt), ##__VA_ARGS__)
32+
#define pr_warn(fmt, ...) fprintf(stderr, pr_fmt(fmt), ##__VA_ARGS__)
33+
#define pr_info(fmt, ...) fprintf(stdout, pr_fmt(fmt), ##__VA_ARGS__)
34+
#define __init /**/
35+
#define __exit /**/
36+
#define __user /**/
37+
#define noinline __attribute__((__noinline__))
38+
#define __aligned(x) __attribute__((__aligned__(x)))
39+
#ifdef __clang__
40+
# define __compiletime_error(message) /**/
41+
#else
42+
# define __compiletime_error(message) __attribute__((__error__(message)))
43+
#endif
44+
#define __compiletime_assert(condition, msg, prefix, suffix) \
45+
do { \
46+
extern void prefix ## suffix(void) __compiletime_error(msg); \
47+
if (!(condition)) \
48+
prefix ## suffix(); \
49+
} while (0)
50+
#define _compiletime_assert(condition, msg, prefix, suffix) \
51+
__compiletime_assert(condition, msg, prefix, suffix)
52+
#define compiletime_assert(condition, msg) \
53+
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
54+
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
55+
#define BUILD_BUG_ON(condition) \
56+
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
57+
typedef uint8_t u8;
58+
typedef uint16_t u16;
59+
typedef uint32_t u32;
60+
typedef uint64_t u64;
61+
62+
#define module_init(func) static int (*do_init)(void) = func
63+
#define module_exit(func) static void (*do_exit)(void) = func
64+
#define MODULE_LICENSE(str) int main(void) { \
65+
int rc; \
66+
/* License: str */ \
67+
rc = do_init(); \
68+
if (rc == 0) \
69+
do_exit(); \
70+
return rc; \
71+
}
72+
73+
#endif /* __KERNEL__ */
74+
1375
/* Exfiltration buffer. */
1476
#define MAX_VAR_SIZE 128
1577
static u8 check_buf[MAX_VAR_SIZE];
@@ -33,6 +95,10 @@ static bool range_contains(char *haystack_start, size_t haystack_size,
3395
return false;
3496
}
3597

98+
/* Whether the test is expected to fail. */
99+
#define WANT_SUCCESS 0
100+
#define XFAIL 1
101+
36102
#define DO_NOTHING_TYPE_SCALAR(var_type) var_type
37103
#define DO_NOTHING_TYPE_STRING(var_type) void
38104
#define DO_NOTHING_TYPE_STRUCT(var_type) void
@@ -58,34 +124,73 @@ static bool range_contains(char *haystack_start, size_t haystack_size,
58124
#define INIT_CLONE_STRING [FILL_SIZE_STRING]
59125
#define INIT_CLONE_STRUCT /**/
60126

61-
#define INIT_SCALAR_none /**/
62-
#define INIT_SCALAR_zero = 0
127+
#define ZERO_CLONE_SCALAR(zero) memset(&(zero), 0x00, sizeof(zero))
128+
#define ZERO_CLONE_STRING(zero) memset(&(zero), 0x00, sizeof(zero))
129+
/*
130+
* For the struct, intentionally poison padding to see if it gets
131+
* copied out in direct assignments.
132+
* */
133+
#define ZERO_CLONE_STRUCT(zero) \
134+
do { \
135+
memset(&(zero), 0xFF, sizeof(zero)); \
136+
zero.one = 0; \
137+
zero.two = 0; \
138+
zero.three = 0; \
139+
zero.four = 0; \
140+
} while (0)
141+
142+
#define INIT_SCALAR_none(var_type) /**/
143+
#define INIT_SCALAR_zero(var_type) = 0
63144

64-
#define INIT_STRING_none [FILL_SIZE_STRING] /**/
65-
#define INIT_STRING_zero [FILL_SIZE_STRING] = { }
145+
#define INIT_STRING_none(var_type) [FILL_SIZE_STRING] /**/
146+
#define INIT_STRING_zero(var_type) [FILL_SIZE_STRING] = { }
66147

67-
#define INIT_STRUCT_none /**/
68-
#define INIT_STRUCT_zero = { }
69-
#define INIT_STRUCT_static_partial = { .two = 0, }
70-
#define INIT_STRUCT_static_all = { .one = arg->one, \
71-
.two = arg->two, \
72-
.three = arg->three, \
73-
.four = arg->four, \
148+
#define INIT_STRUCT_none(var_type) /**/
149+
#define INIT_STRUCT_zero(var_type) = { }
150+
151+
152+
#define __static_partial { .two = 0, }
153+
#define __static_all { .one = 0, \
154+
.two = 0, \
155+
.three = 0, \
156+
.four = 0, \
74157
}
75-
#define INIT_STRUCT_dynamic_partial = { .two = arg->two, }
76-
#define INIT_STRUCT_dynamic_all = { .one = arg->one, \
77-
.two = arg->two, \
78-
.three = arg->three, \
79-
.four = arg->four, \
158+
#define __dynamic_partial { .two = arg->two, }
159+
#define __dynamic_all { .one = arg->one, \
160+
.two = arg->two, \
161+
.three = arg->three, \
162+
.four = arg->four, \
80163
}
81-
#define INIT_STRUCT_runtime_partial ; \
82-
var.two = 0
83-
#define INIT_STRUCT_runtime_all ; \
84-
var.one = 0; \
164+
#define __runtime_partial var.two = 0
165+
#define __runtime_all var.one = 0; \
85166
var.two = 0; \
86167
var.three = 0; \
87-
memset(&var.four, 0, \
88-
sizeof(var.four))
168+
var.four = 0
169+
170+
#define INIT_STRUCT_static_partial(var_type) \
171+
= __static_partial
172+
#define INIT_STRUCT_static_all(var_type) \
173+
= __static_all
174+
#define INIT_STRUCT_dynamic_partial(var_type) \
175+
= __dynamic_partial
176+
#define INIT_STRUCT_dynamic_all(var_type) \
177+
= __dynamic_all
178+
#define INIT_STRUCT_runtime_partial(var_type) \
179+
; __runtime_partial
180+
#define INIT_STRUCT_runtime_all(var_type) \
181+
; __runtime_all
182+
183+
#define INIT_STRUCT_assigned_static_partial(var_type) \
184+
; var = (var_type)__static_partial
185+
#define INIT_STRUCT_assigned_static_all(var_type) \
186+
; var = (var_type)__static_all
187+
#define INIT_STRUCT_assigned_dynamic_partial(var_type) \
188+
; var = (var_type)__dynamic_partial
189+
#define INIT_STRUCT_assigned_dynamic_all(var_type) \
190+
; var = (var_type)__dynamic_all
191+
192+
#define INIT_STRUCT_assigned_copy(var_type) \
193+
; var = *(arg)
89194

90195
/*
91196
* @name: unique string name for the test
@@ -106,7 +211,7 @@ static noinline __init int test_ ## name (void) \
106211
BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE); \
107212
\
108213
/* Fill clone type with zero for per-field init. */ \
109-
memset(&zero, 0x00, sizeof(zero)); \
214+
ZERO_CLONE_ ## which(zero); \
110215
/* Clear entire check buffer for 0xFF overlap test. */ \
111216
memset(check_buf, 0x00, sizeof(check_buf)); \
112217
/* Fill stack with 0xFF. */ \
@@ -149,7 +254,7 @@ static noinline __init int test_ ## name (void) \
149254
return (xfail) ? 0 : 1; \
150255
} \
151256
}
152-
#define DEFINE_TEST(name, var_type, which, init_level) \
257+
#define DEFINE_TEST(name, var_type, which, init_level, xfail) \
153258
/* no-op to force compiler into ignoring "uninitialized" vars */\
154259
static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \
155260
do_nothing_ ## name(var_type *ptr) \
@@ -165,7 +270,8 @@ static noinline __init int leaf_ ## name(unsigned long sp, \
165270
var_type *arg) \
166271
{ \
167272
char buf[VAR_BUFFER]; \
168-
var_type var INIT_ ## which ## _ ## init_level; \
273+
var_type var \
274+
INIT_ ## which ## _ ## init_level(var_type); \
169275
\
170276
target_start = &var; \
171277
target_size = sizeof(var); \
@@ -191,7 +297,7 @@ static noinline __init int leaf_ ## name(unsigned long sp, \
191297
\
192298
return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \
193299
} \
194-
DEFINE_TEST_DRIVER(name, var_type, which, 0)
300+
DEFINE_TEST_DRIVER(name, var_type, which, xfail)
195301

196302
/* Structure with no padding. */
197303
struct test_packed {
@@ -210,18 +316,13 @@ struct test_small_hole {
210316
unsigned long four;
211317
};
212318

213-
/* Try to trigger unhandled padding in a structure. */
214-
struct test_aligned {
215-
u32 internal1;
216-
u64 internal2;
217-
} __aligned(64);
218-
319+
/* Trigger unhandled padding in a structure. */
219320
struct test_big_hole {
220321
u8 one;
221322
u8 two;
222323
u8 three;
223324
/* 61 byte padding hole here. */
224-
struct test_aligned four;
325+
u8 four __aligned(64);
225326
} __aligned(64);
226327

227328
struct test_trailing_hole {
@@ -240,42 +341,50 @@ struct test_user {
240341
unsigned long four;
241342
};
242343

243-
#define DEFINE_SCALAR_TEST(name, init) \
244-
DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
344+
#define DEFINE_SCALAR_TEST(name, init, xfail) \
345+
DEFINE_TEST(name ## _ ## init, name, SCALAR, \
346+
init, xfail)
245347

246-
#define DEFINE_SCALAR_TESTS(init) \
247-
DEFINE_SCALAR_TEST(u8, init); \
248-
DEFINE_SCALAR_TEST(u16, init); \
249-
DEFINE_SCALAR_TEST(u32, init); \
250-
DEFINE_SCALAR_TEST(u64, init); \
251-
DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
348+
#define DEFINE_SCALAR_TESTS(init, xfail) \
349+
DEFINE_SCALAR_TEST(u8, init, xfail); \
350+
DEFINE_SCALAR_TEST(u16, init, xfail); \
351+
DEFINE_SCALAR_TEST(u32, init, xfail); \
352+
DEFINE_SCALAR_TEST(u64, init, xfail); \
353+
DEFINE_TEST(char_array_ ## init, unsigned char, \
354+
STRING, init, xfail)
252355

253-
#define DEFINE_STRUCT_TEST(name, init) \
356+
#define DEFINE_STRUCT_TEST(name, init, xfail) \
254357
DEFINE_TEST(name ## _ ## init, \
255-
struct test_ ## name, STRUCT, init)
358+
struct test_ ## name, STRUCT, init, \
359+
xfail)
360+
361+
#define DEFINE_STRUCT_TESTS(init, xfail) \
362+
DEFINE_STRUCT_TEST(small_hole, init, xfail); \
363+
DEFINE_STRUCT_TEST(big_hole, init, xfail); \
364+
DEFINE_STRUCT_TEST(trailing_hole, init, xfail); \
365+
DEFINE_STRUCT_TEST(packed, init, xfail)
256366

257-
#define DEFINE_STRUCT_TESTS(init) \
258-
DEFINE_STRUCT_TEST(small_hole, init); \
259-
DEFINE_STRUCT_TEST(big_hole, init); \
260-
DEFINE_STRUCT_TEST(trailing_hole, init); \
261-
DEFINE_STRUCT_TEST(packed, init)
367+
#define DEFINE_STRUCT_INITIALIZER_TESTS(base) \
368+
DEFINE_STRUCT_TESTS(base ## _ ## partial, \
369+
WANT_SUCCESS); \
370+
DEFINE_STRUCT_TESTS(base ## _ ## all, \
371+
WANT_SUCCESS)
262372

263373
/* These should be fully initialized all the time! */
264-
DEFINE_SCALAR_TESTS(zero);
265-
DEFINE_STRUCT_TESTS(zero);
266-
/* Static initialization: padding may be left uninitialized. */
267-
DEFINE_STRUCT_TESTS(static_partial);
268-
DEFINE_STRUCT_TESTS(static_all);
269-
/* Dynamic initialization: padding may be left uninitialized. */
270-
DEFINE_STRUCT_TESTS(dynamic_partial);
271-
DEFINE_STRUCT_TESTS(dynamic_all);
272-
/* Runtime initialization: padding may be left uninitialized. */
273-
DEFINE_STRUCT_TESTS(runtime_partial);
274-
DEFINE_STRUCT_TESTS(runtime_all);
374+
DEFINE_SCALAR_TESTS(zero, WANT_SUCCESS);
375+
DEFINE_STRUCT_TESTS(zero, WANT_SUCCESS);
376+
/* Struct initializers: padding may be left uninitialized. */
377+
DEFINE_STRUCT_INITIALIZER_TESTS(static);
378+
DEFINE_STRUCT_INITIALIZER_TESTS(dynamic);
379+
DEFINE_STRUCT_INITIALIZER_TESTS(runtime);
380+
DEFINE_STRUCT_INITIALIZER_TESTS(assigned_static);
381+
DEFINE_STRUCT_INITIALIZER_TESTS(assigned_dynamic);
382+
DEFINE_STRUCT_TESTS(assigned_copy, XFAIL);
275383
/* No initialization without compiler instrumentation. */
276-
DEFINE_SCALAR_TESTS(none);
277-
DEFINE_STRUCT_TESTS(none);
278-
DEFINE_TEST(user, struct test_user, STRUCT, none);
384+
DEFINE_SCALAR_TESTS(none, WANT_SUCCESS);
385+
DEFINE_STRUCT_TESTS(none, WANT_SUCCESS);
386+
/* Initialization of members with __user attribute. */
387+
DEFINE_TEST(user, struct test_user, STRUCT, none, WANT_SUCCESS);
279388

280389
/*
281390
* Check two uses through a variable declaration outside either path,
@@ -285,6 +394,10 @@ DEFINE_TEST(user, struct test_user, STRUCT, none);
285394
static int noinline __leaf_switch_none(int path, bool fill)
286395
{
287396
switch (path) {
397+
/*
398+
* This is intentionally unreachable. To silence the
399+
* warning, build with -Wno-switch-unreachable
400+
*/
288401
uint64_t var;
289402

290403
case 1:
@@ -334,8 +447,8 @@ static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
334447
* non-code areas (i.e. in a switch statement before the first "case").
335448
* https://bugs.llvm.org/show_bug.cgi?id=44916
336449
*/
337-
DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
338-
DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
450+
DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, XFAIL);
451+
DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, XFAIL);
339452

340453
static int __init test_stackinit_init(void)
341454
{
@@ -361,12 +474,18 @@ static int __init test_stackinit_init(void)
361474
test_structs(zero);
362475
/* Padding here appears to be accidentally always initialized? */
363476
test_structs(dynamic_partial);
477+
test_structs(assigned_dynamic_partial);
364478
/* Padding initialization depends on compiler behaviors. */
365479
test_structs(static_partial);
366480
test_structs(static_all);
367481
test_structs(dynamic_all);
368482
test_structs(runtime_partial);
369483
test_structs(runtime_all);
484+
test_structs(assigned_static_partial);
485+
test_structs(assigned_static_all);
486+
test_structs(assigned_dynamic_all);
487+
/* Everything fails this since it effectively performs a memcpy(). */
488+
test_structs(assigned_copy);
370489

371490
/* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
372491
test_scalars(none);

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