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 # 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. */
79 static noinline __no_ret_protection
set_return_addr_unchecked(unsigned long * expected,unsigned long * addr)80 void 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
95 static noinline
set_return_addr(unsigned long * expected,unsigned long * addr)96 void 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
111 static volatile int force_check;
112
lkdtm_CFI_BACKWARD(void)113 static 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:
148 normal:
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:
157 redirected:
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:
169 check_normal:
170 /* Always true */
171 if (!force_check) {
172 pr_info("ok: control flow unchanged.\n");
173 return;
174 }
175
176 check_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
194 static struct crashtype crashtypes[] = {
195 CRASHTYPE(CFI_FORWARD_PROTO),
196 CRASHTYPE(CFI_BACKWARD),
197 };
198
199 struct crashtype_category cfi_crashtypes = {
200 .crashtypes = crashtypes,
201 .len = ARRAY_SIZE(crashtypes),
202 };
203