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
8 static int called_count;
9
10 /* Function taking one argument, without a return value. */
lkdtm_increment_void(int * counter)11 static noinline void lkdtm_increment_void(int *counter)
12 {
13 (*counter)++;
14 }
15
16 /* Function taking one argument, returning int. */
lkdtm_increment_int(int * counter)17 static 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. */
lkdtm_indirect_call(void (* func)(int *))25 static 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 */
lkdtm_CFI_FORWARD_PROTO(void)33 static 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 # define __no_pac "branch-protection=none"
58 # endif
59 # define __no_ret_protection __noscs __attribute__((__target__(__no_pac)))
60 #else
61 # define __no_ret_protection __noscs
62 #endif
63
64 #define no_pac_addr(addr) \
65 ((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET))
66
67 /* The ultimate ROP gadget. */
68 static noinline __no_ret_protection
set_return_addr_unchecked(unsigned long * expected,unsigned long * addr)69 void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
70 {
71 /* Use of volatile is to make sure final write isn't seen as a dead store. */
72 unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
73
74 /* Make sure we've found the right place on the stack before writing it. */
75 if (no_pac_addr(*ret_addr) == expected)
76 *ret_addr = (addr);
77 else
78 /* Check architecture, stack layout, or compiler behavior... */
79 pr_warn("Eek: return address mismatch! %px != %px\n",
80 *ret_addr, addr);
81 }
82
83 static noinline
set_return_addr(unsigned long * expected,unsigned long * addr)84 void set_return_addr(unsigned long *expected, unsigned long *addr)
85 {
86 /* Use of volatile is to make sure final write isn't seen as a dead store. */
87 unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
88
89 /* Make sure we've found the right place on the stack before writing it. */
90 if (no_pac_addr(*ret_addr) == expected)
91 *ret_addr = (addr);
92 else
93 /* Check architecture, stack layout, or compiler behavior... */
94 pr_warn("Eek: return address mismatch! %px != %px\n",
95 *ret_addr, addr);
96 }
97
98 static volatile int force_check;
99
lkdtm_CFI_BACKWARD(void)100 static void lkdtm_CFI_BACKWARD(void)
101 {
102 /* Use calculated gotos to keep labels addressable. */
103 void *labels[] = { NULL, &&normal, &&redirected, &&check_normal, &&check_redirected };
104
105 pr_info("Attempting unchecked stack return address redirection ...\n");
106
107 /* Always false */
108 if (force_check) {
109 /*
110 * Prepare to call with NULLs to avoid parameters being treated as
111 * constants in -02.
112 */
113 set_return_addr_unchecked(NULL, NULL);
114 set_return_addr(NULL, NULL);
115 if (force_check)
116 goto *labels[1];
117 if (force_check)
118 goto *labels[2];
119 if (force_check)
120 goto *labels[3];
121 if (force_check)
122 goto *labels[4];
123 return;
124 }
125
126 /*
127 * Use fallthrough switch case to keep basic block ordering between
128 * set_return_addr*() and the label after it.
129 */
130 switch (force_check) {
131 case 0:
132 set_return_addr_unchecked(&&normal, &&redirected);
133 fallthrough;
134 case 1:
135 normal:
136 /* Always true */
137 if (!force_check) {
138 pr_err("FAIL: stack return address manipulation failed!\n");
139 /* If we can't redirect "normally", we can't test mitigations. */
140 return;
141 }
142 break;
143 default:
144 redirected:
145 pr_info("ok: redirected stack return address.\n");
146 break;
147 }
148
149 pr_info("Attempting checked stack return address redirection ...\n");
150
151 switch (force_check) {
152 case 0:
153 set_return_addr(&&check_normal, &&check_redirected);
154 fallthrough;
155 case 1:
156 check_normal:
157 /* Always true */
158 if (!force_check) {
159 pr_info("ok: control flow unchanged.\n");
160 return;
161 }
162
163 check_redirected:
164 pr_err("FAIL: stack return address was redirected!\n");
165 break;
166 }
167
168 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
169 pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL);
170 return;
171 }
172 if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
173 pr_expected_config(CONFIG_SHADOW_CALL_STACK);
174 return;
175 }
176 pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n",
177 lkdtm_kernel_info,
178 "CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK");
179 }
180
181 static struct crashtype crashtypes[] = {
182 CRASHTYPE(CFI_FORWARD_PROTO),
183 CRASHTYPE(CFI_BACKWARD),
184 };
185
186 struct crashtype_category cfi_crashtypes = {
187 .crashtypes = crashtypes,
188 .len = ARRAY_SIZE(crashtypes),
189 };
190