1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This is for all the tests related to copy_to_user() and copy_from_user()
4 * hardening.
5 */
6 #include "lkdtm.h"
7 #include <linux/slab.h>
8 #include <linux/vmalloc.h>
9 #include <linux/sched/task_stack.h>
10 #include <linux/mman.h>
11 #include <linux/uaccess.h>
12 #include <asm/cacheflush.h>
13
14 /*
15 * Many of the tests here end up using const sizes, but those would
16 * normally be ignored by hardened usercopy, so force the compiler
17 * into choosing the non-const path to make sure we trigger the
18 * hardened usercopy checks by added "unconst" to all the const copies,
19 * and making sure "cache_size" isn't optimized into a const.
20 */
21 static volatile size_t unconst = 0;
22 static volatile size_t cache_size = 1024;
23 static struct kmem_cache *bad_cache;
24
25 static const unsigned char test_text[] = "This is a test.\n";
26
27 /*
28 * Instead of adding -Wno-return-local-addr, just pass the stack address
29 * through a function to obfuscate it from the compiler.
30 */
trick_compiler(unsigned char * stack)31 static noinline unsigned char *trick_compiler(unsigned char *stack)
32 {
33 return stack + 0;
34 }
35
do_usercopy_stack_callee(int value)36 static noinline unsigned char *do_usercopy_stack_callee(int value)
37 {
38 unsigned char buf[32];
39 int i;
40
41 /* Exercise stack to avoid everything living in registers. */
42 for (i = 0; i < sizeof(buf); i++) {
43 buf[i] = value & 0xff;
44 }
45
46 return trick_compiler(buf);
47 }
48
do_usercopy_stack(bool to_user,bool bad_frame)49 static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
50 {
51 unsigned long user_addr;
52 unsigned char good_stack[32];
53 unsigned char *bad_stack;
54 int i;
55
56 /* Exercise stack to avoid everything living in registers. */
57 for (i = 0; i < sizeof(good_stack); i++)
58 good_stack[i] = test_text[i % sizeof(test_text)];
59
60 /* This is a pointer to outside our current stack frame. */
61 if (bad_frame) {
62 bad_stack = do_usercopy_stack_callee((uintptr_t)&bad_stack);
63 } else {
64 /* Put start address just inside stack. */
65 bad_stack = task_stack_page(current) + THREAD_SIZE;
66 bad_stack -= sizeof(unsigned long);
67 }
68
69 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
70 PROT_READ | PROT_WRITE | PROT_EXEC,
71 MAP_ANONYMOUS | MAP_PRIVATE, 0);
72 if (user_addr >= TASK_SIZE) {
73 pr_warn("Failed to allocate user memory\n");
74 return;
75 }
76
77 if (to_user) {
78 pr_info("attempting good copy_to_user of local stack\n");
79 if (copy_to_user((void __user *)user_addr, good_stack,
80 unconst + sizeof(good_stack))) {
81 pr_warn("copy_to_user failed unexpectedly?!\n");
82 goto free_user;
83 }
84
85 pr_info("attempting bad copy_to_user of distant stack\n");
86 if (copy_to_user((void __user *)user_addr, bad_stack,
87 unconst + sizeof(good_stack))) {
88 pr_warn("copy_to_user failed, but lacked Oops\n");
89 goto free_user;
90 }
91 } else {
92 /*
93 * There isn't a safe way to not be protected by usercopy
94 * if we're going to write to another thread's stack.
95 */
96 if (!bad_frame)
97 goto free_user;
98
99 pr_info("attempting good copy_from_user of local stack\n");
100 if (copy_from_user(good_stack, (void __user *)user_addr,
101 unconst + sizeof(good_stack))) {
102 pr_warn("copy_from_user failed unexpectedly?!\n");
103 goto free_user;
104 }
105
106 pr_info("attempting bad copy_from_user of distant stack\n");
107 if (copy_from_user(bad_stack, (void __user *)user_addr,
108 unconst + sizeof(good_stack))) {
109 pr_warn("copy_from_user failed, but lacked Oops\n");
110 goto free_user;
111 }
112 }
113
114 free_user:
115 vm_munmap(user_addr, PAGE_SIZE);
116 }
117
do_usercopy_heap_size(bool to_user)118 static void do_usercopy_heap_size(bool to_user)
119 {
120 unsigned long user_addr;
121 unsigned char *one, *two;
122 size_t size = unconst + 1024;
123
124 one = kmalloc(size, GFP_KERNEL);
125 two = kmalloc(size, GFP_KERNEL);
126 if (!one || !two) {
127 pr_warn("Failed to allocate kernel memory\n");
128 goto free_kernel;
129 }
130
131 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
132 PROT_READ | PROT_WRITE | PROT_EXEC,
133 MAP_ANONYMOUS | MAP_PRIVATE, 0);
134 if (user_addr >= TASK_SIZE) {
135 pr_warn("Failed to allocate user memory\n");
136 goto free_kernel;
137 }
138
139 memset(one, 'A', size);
140 memset(two, 'B', size);
141
142 if (to_user) {
143 pr_info("attempting good copy_to_user of correct size\n");
144 if (copy_to_user((void __user *)user_addr, one, size)) {
145 pr_warn("copy_to_user failed unexpectedly?!\n");
146 goto free_user;
147 }
148
149 pr_info("attempting bad copy_to_user of too large size\n");
150 if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
151 pr_warn("copy_to_user failed, but lacked Oops\n");
152 goto free_user;
153 }
154 } else {
155 pr_info("attempting good copy_from_user of correct size\n");
156 if (copy_from_user(one, (void __user *)user_addr, size)) {
157 pr_warn("copy_from_user failed unexpectedly?!\n");
158 goto free_user;
159 }
160
161 pr_info("attempting bad copy_from_user of too large size\n");
162 if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
163 pr_warn("copy_from_user failed, but lacked Oops\n");
164 goto free_user;
165 }
166 }
167
168 free_user:
169 vm_munmap(user_addr, PAGE_SIZE);
170 free_kernel:
171 kfree(one);
172 kfree(two);
173 }
174
do_usercopy_heap_flag(bool to_user)175 static void do_usercopy_heap_flag(bool to_user)
176 {
177 unsigned long user_addr;
178 unsigned char *good_buf = NULL;
179 unsigned char *bad_buf = NULL;
180
181 /* Make sure cache was prepared. */
182 if (!bad_cache) {
183 pr_warn("Failed to allocate kernel cache\n");
184 return;
185 }
186
187 /*
188 * Allocate one buffer from each cache (kmalloc will have the
189 * SLAB_USERCOPY flag already, but "bad_cache" won't).
190 */
191 good_buf = kmalloc(cache_size, GFP_KERNEL);
192 bad_buf = kmem_cache_alloc(bad_cache, GFP_KERNEL);
193 if (!good_buf || !bad_buf) {
194 pr_warn("Failed to allocate buffers from caches\n");
195 goto free_alloc;
196 }
197
198 /* Allocate user memory we'll poke at. */
199 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
200 PROT_READ | PROT_WRITE | PROT_EXEC,
201 MAP_ANONYMOUS | MAP_PRIVATE, 0);
202 if (user_addr >= TASK_SIZE) {
203 pr_warn("Failed to allocate user memory\n");
204 goto free_alloc;
205 }
206
207 memset(good_buf, 'A', cache_size);
208 memset(bad_buf, 'B', cache_size);
209
210 if (to_user) {
211 pr_info("attempting good copy_to_user with SLAB_USERCOPY\n");
212 if (copy_to_user((void __user *)user_addr, good_buf,
213 cache_size)) {
214 pr_warn("copy_to_user failed unexpectedly?!\n");
215 goto free_user;
216 }
217
218 pr_info("attempting bad copy_to_user w/o SLAB_USERCOPY\n");
219 if (copy_to_user((void __user *)user_addr, bad_buf,
220 cache_size)) {
221 pr_warn("copy_to_user failed, but lacked Oops\n");
222 goto free_user;
223 }
224 } else {
225 pr_info("attempting good copy_from_user with SLAB_USERCOPY\n");
226 if (copy_from_user(good_buf, (void __user *)user_addr,
227 cache_size)) {
228 pr_warn("copy_from_user failed unexpectedly?!\n");
229 goto free_user;
230 }
231
232 pr_info("attempting bad copy_from_user w/o SLAB_USERCOPY\n");
233 if (copy_from_user(bad_buf, (void __user *)user_addr,
234 cache_size)) {
235 pr_warn("copy_from_user failed, but lacked Oops\n");
236 goto free_user;
237 }
238 }
239
240 free_user:
241 vm_munmap(user_addr, PAGE_SIZE);
242 free_alloc:
243 if (bad_buf)
244 kmem_cache_free(bad_cache, bad_buf);
245 kfree(good_buf);
246 }
247
248 /* Callable tests. */
lkdtm_USERCOPY_HEAP_SIZE_TO(void)249 void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
250 {
251 do_usercopy_heap_size(true);
252 }
253
lkdtm_USERCOPY_HEAP_SIZE_FROM(void)254 void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
255 {
256 do_usercopy_heap_size(false);
257 }
258
lkdtm_USERCOPY_HEAP_FLAG_TO(void)259 void lkdtm_USERCOPY_HEAP_FLAG_TO(void)
260 {
261 do_usercopy_heap_flag(true);
262 }
263
lkdtm_USERCOPY_HEAP_FLAG_FROM(void)264 void lkdtm_USERCOPY_HEAP_FLAG_FROM(void)
265 {
266 do_usercopy_heap_flag(false);
267 }
268
lkdtm_USERCOPY_STACK_FRAME_TO(void)269 void lkdtm_USERCOPY_STACK_FRAME_TO(void)
270 {
271 do_usercopy_stack(true, true);
272 }
273
lkdtm_USERCOPY_STACK_FRAME_FROM(void)274 void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
275 {
276 do_usercopy_stack(false, true);
277 }
278
lkdtm_USERCOPY_STACK_BEYOND(void)279 void lkdtm_USERCOPY_STACK_BEYOND(void)
280 {
281 do_usercopy_stack(true, false);
282 }
283
lkdtm_USERCOPY_KERNEL(void)284 void lkdtm_USERCOPY_KERNEL(void)
285 {
286 unsigned long user_addr;
287
288 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
289 PROT_READ | PROT_WRITE | PROT_EXEC,
290 MAP_ANONYMOUS | MAP_PRIVATE, 0);
291 if (user_addr >= TASK_SIZE) {
292 pr_warn("Failed to allocate user memory\n");
293 return;
294 }
295
296 pr_info("attempting good copy_to_user from kernel rodata\n");
297 if (copy_to_user((void __user *)user_addr, test_text,
298 unconst + sizeof(test_text))) {
299 pr_warn("copy_to_user failed unexpectedly?!\n");
300 goto free_user;
301 }
302
303 pr_info("attempting bad copy_to_user from kernel text\n");
304 if (copy_to_user((void __user *)user_addr, vm_mmap,
305 unconst + PAGE_SIZE)) {
306 pr_warn("copy_to_user failed, but lacked Oops\n");
307 goto free_user;
308 }
309
310 free_user:
311 vm_munmap(user_addr, PAGE_SIZE);
312 }
313
lkdtm_usercopy_init(void)314 void __init lkdtm_usercopy_init(void)
315 {
316 /* Prepare cache that lacks SLAB_USERCOPY flag. */
317 bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,
318 0, NULL);
319 }
320
lkdtm_usercopy_exit(void)321 void __exit lkdtm_usercopy_exit(void)
322 {
323 kmem_cache_destroy(bad_cache);
324 }
325