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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This is for all the tests relating directly to Control Flow Integrity.
4 */
5#include "lkdtm.h"
6#include <asm/page.h>
7
8static int called_count;
9
10/* Function taking one argument, without a return value. */
11static noinline void lkdtm_increment_void(int *counter)
12{
13 (*counter)++;
14}
15
16/* Function taking one argument, returning int. */
17static noinline int lkdtm_increment_int(int *counter)
18{
19 (*counter)++;
20
21 return *counter;
22}
23
24/* Don't allow the compiler to inline the calls. */
25static noinline void lkdtm_indirect_call(void (*func)(int *))
26{
27 func(&called_count);
28}
29
30/*
31 * This tries to call an indirect function with a mismatched prototype.
32 */
33static void lkdtm_CFI_FORWARD_PROTO(void)
34{
35 /*
36 * Matches lkdtm_increment_void()'s prototype, but not
37 * lkdtm_increment_int()'s prototype.
38 */
39 pr_info("Calling matched prototype ...\n");
40 lkdtm_indirect_call(lkdtm_increment_void);
41
42 pr_info("Calling mismatched prototype ...\n");
43 lkdtm_indirect_call((void *)lkdtm_increment_int);
44
45 pr_err("FAIL: survived mismatched prototype function call!\n");
46 pr_expected_config(CONFIG_CFI_CLANG);
47}
48
49/*
50 * This can stay local to LKDTM, as there should not be a production reason
51 * to disable PAC && SCS.
52 */
53#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
54# ifdef CONFIG_ARM64_BTI_KERNEL
55# define __no_pac "branch-protection=bti"
56# else
57# ifdef CONFIG_CC_HAS_BRANCH_PROT_PAC_RET
58# define __no_pac "branch-protection=none"
59# else
60# define __no_pac "sign-return-address=none"
61# endif
62# endif
63# define __no_ret_protection __noscs __attribute__((__target__(__no_pac)))
64#else
65# define __no_ret_protection __noscs
66#endif
67
68#define no_pac_addr(addr) \
69 ((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET))
70
71#ifdef CONFIG_RISCV
72/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#frame-pointer-convention */
73#define FRAME_RA_OFFSET (-1)
74#else
75#define FRAME_RA_OFFSET 1
76#endif
77
78/* The ultimate ROP gadget. */
79static noinline __no_ret_protection
80void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
81{
82 /* Use of volatile is to make sure final write isn't seen as a dead store. */
83 unsigned long * volatile *ret_addr =
84 (unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
85
86 /* Make sure we've found the right place on the stack before writing it. */
87 if (no_pac_addr(*ret_addr) == expected)
88 *ret_addr = (addr);
89 else
90 /* Check architecture, stack layout, or compiler behavior... */
91 pr_warn("Eek: return address mismatch! %px != %px\n",
92 *ret_addr, addr);
93}
94
95static noinline
96void set_return_addr(unsigned long *expected, unsigned long *addr)
97{
98 /* Use of volatile is to make sure final write isn't seen as a dead store. */
99 unsigned long * volatile *ret_addr =
100 (unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
101
102 /* Make sure we've found the right place on the stack before writing it. */
103 if (no_pac_addr(*ret_addr) == expected)
104 *ret_addr = (addr);
105 else
106 /* Check architecture, stack layout, or compiler behavior... */
107 pr_warn("Eek: return address mismatch! %px != %px\n",
108 *ret_addr, addr);
109}
110
111static volatile int force_check;
112
113static void lkdtm_CFI_BACKWARD(void)
114{
115 /* Use calculated gotos to keep labels addressable. */
116 void *labels[] = { NULL, &&normal, &&redirected, &&check_normal, &&check_redirected };
117
118 pr_info("Attempting unchecked stack return address redirection ...\n");
119
120 /* Always false */
121 if (force_check) {
122 /*
123 * Prepare to call with NULLs to avoid parameters being treated as
124 * constants in -02.
125 */
126 set_return_addr_unchecked(NULL, NULL);
127 set_return_addr(NULL, NULL);
128 if (force_check)
129 goto *labels[1];
130 if (force_check)
131 goto *labels[2];
132 if (force_check)
133 goto *labels[3];
134 if (force_check)
135 goto *labels[4];
136 return;
137 }
138
139 /*
140 * Use fallthrough switch case to keep basic block ordering between
141 * set_return_addr*() and the label after it.
142 */
143 switch (force_check) {
144 case 0:
145 set_return_addr_unchecked(&&normal, &&redirected);
146 fallthrough;
147 case 1:
148normal:
149 /* Always true */
150 if (!force_check) {
151 pr_err("FAIL: stack return address manipulation failed!\n");
152 /* If we can't redirect "normally", we can't test mitigations. */
153 return;
154 }
155 break;
156 default:
157redirected:
158 pr_info("ok: redirected stack return address.\n");
159 break;
160 }
161
162 pr_info("Attempting checked stack return address redirection ...\n");
163
164 switch (force_check) {
165 case 0:
166 set_return_addr(&&check_normal, &&check_redirected);
167 fallthrough;
168 case 1:
169check_normal:
170 /* Always true */
171 if (!force_check) {
172 pr_info("ok: control flow unchanged.\n");
173 return;
174 }
175
176check_redirected:
177 pr_err("FAIL: stack return address was redirected!\n");
178 break;
179 }
180
181 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
182 pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL);
183 return;
184 }
185 if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
186 pr_expected_config(CONFIG_SHADOW_CALL_STACK);
187 return;
188 }
189 pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n",
190 lkdtm_kernel_info,
191 "CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK");
192}
193
194static struct crashtype crashtypes[] = {
195 CRASHTYPE(CFI_FORWARD_PROTO),
196 CRASHTYPE(CFI_BACKWARD),
197};
198
199struct crashtype_category cfi_crashtypes = {
200 .crashtypes = crashtypes,
201 .len = ARRAY_SIZE(crashtypes),
202};
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This is for all the tests relating directly to Control Flow Integrity.
4 */
5#include "lkdtm.h"
6
7static int called_count;
8
9/* Function taking one argument, without a return value. */
10static noinline void lkdtm_increment_void(int *counter)
11{
12 (*counter)++;
13}
14
15/* Function taking one argument, returning int. */
16static noinline int lkdtm_increment_int(int *counter)
17{
18 (*counter)++;
19
20 return *counter;
21}
22/*
23 * This tries to call an indirect function with a mismatched prototype.
24 */
25void lkdtm_CFI_FORWARD_PROTO(void)
26{
27 /*
28 * Matches lkdtm_increment_void()'s prototype, but not
29 * lkdtm_increment_int()'s prototype.
30 */
31 void (*func)(int *);
32
33 pr_info("Calling matched prototype ...\n");
34 func = lkdtm_increment_void;
35 func(&called_count);
36
37 pr_info("Calling mismatched prototype ...\n");
38 func = (void *)lkdtm_increment_int;
39 func(&called_count);
40
41 pr_err("FAIL: survived mismatched prototype function call!\n");
42 pr_expected_config(CONFIG_CFI_CLANG);
43}