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;
22 static volatile size_t cache_size = 1024;
23 static struct kmem_cache *whitelist_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
118 /*
119 * This checks for whole-object size validation with hardened usercopy,
120 * with or without usercopy whitelisting.
121 */
do_usercopy_heap_size(bool to_user)122 static void do_usercopy_heap_size(bool to_user)
123 {
124 unsigned long user_addr;
125 unsigned char *one, *two;
126 void __user *test_user_addr;
127 void *test_kern_addr;
128 size_t size = unconst + 1024;
129
130 one = kmalloc(size, GFP_KERNEL);
131 two = kmalloc(size, GFP_KERNEL);
132 if (!one || !two) {
133 pr_warn("Failed to allocate kernel memory\n");
134 goto free_kernel;
135 }
136
137 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
138 PROT_READ | PROT_WRITE | PROT_EXEC,
139 MAP_ANONYMOUS | MAP_PRIVATE, 0);
140 if (user_addr >= TASK_SIZE) {
141 pr_warn("Failed to allocate user memory\n");
142 goto free_kernel;
143 }
144
145 memset(one, 'A', size);
146 memset(two, 'B', size);
147
148 test_user_addr = (void __user *)(user_addr + 16);
149 test_kern_addr = one + 16;
150
151 if (to_user) {
152 pr_info("attempting good copy_to_user of correct size\n");
153 if (copy_to_user(test_user_addr, test_kern_addr, size / 2)) {
154 pr_warn("copy_to_user failed unexpectedly?!\n");
155 goto free_user;
156 }
157
158 pr_info("attempting bad copy_to_user of too large size\n");
159 if (copy_to_user(test_user_addr, test_kern_addr, size)) {
160 pr_warn("copy_to_user failed, but lacked Oops\n");
161 goto free_user;
162 }
163 } else {
164 pr_info("attempting good copy_from_user of correct size\n");
165 if (copy_from_user(test_kern_addr, test_user_addr, size / 2)) {
166 pr_warn("copy_from_user failed unexpectedly?!\n");
167 goto free_user;
168 }
169
170 pr_info("attempting bad copy_from_user of too large size\n");
171 if (copy_from_user(test_kern_addr, test_user_addr, size)) {
172 pr_warn("copy_from_user failed, but lacked Oops\n");
173 goto free_user;
174 }
175 }
176
177 free_user:
178 vm_munmap(user_addr, PAGE_SIZE);
179 free_kernel:
180 kfree(one);
181 kfree(two);
182 }
183
184 /*
185 * This checks for the specific whitelist window within an object. If this
186 * test passes, then do_usercopy_heap_size() tests will pass too.
187 */
do_usercopy_heap_whitelist(bool to_user)188 static void do_usercopy_heap_whitelist(bool to_user)
189 {
190 unsigned long user_alloc;
191 unsigned char *buf = NULL;
192 unsigned char __user *user_addr;
193 size_t offset, size;
194
195 /* Make sure cache was prepared. */
196 if (!whitelist_cache) {
197 pr_warn("Failed to allocate kernel cache\n");
198 return;
199 }
200
201 /*
202 * Allocate a buffer with a whitelisted window in the buffer.
203 */
204 buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
205 if (!buf) {
206 pr_warn("Failed to allocate buffer from whitelist cache\n");
207 goto free_alloc;
208 }
209
210 /* Allocate user memory we'll poke at. */
211 user_alloc = vm_mmap(NULL, 0, PAGE_SIZE,
212 PROT_READ | PROT_WRITE | PROT_EXEC,
213 MAP_ANONYMOUS | MAP_PRIVATE, 0);
214 if (user_alloc >= TASK_SIZE) {
215 pr_warn("Failed to allocate user memory\n");
216 goto free_alloc;
217 }
218 user_addr = (void __user *)user_alloc;
219
220 memset(buf, 'B', cache_size);
221
222 /* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
223 offset = (cache_size / 4) + unconst;
224 size = (cache_size / 16) + unconst;
225
226 if (to_user) {
227 pr_info("attempting good copy_to_user inside whitelist\n");
228 if (copy_to_user(user_addr, buf + offset, size)) {
229 pr_warn("copy_to_user failed unexpectedly?!\n");
230 goto free_user;
231 }
232
233 pr_info("attempting bad copy_to_user outside whitelist\n");
234 if (copy_to_user(user_addr, buf + offset - 1, size)) {
235 pr_warn("copy_to_user failed, but lacked Oops\n");
236 goto free_user;
237 }
238 } else {
239 pr_info("attempting good copy_from_user inside whitelist\n");
240 if (copy_from_user(buf + offset, user_addr, size)) {
241 pr_warn("copy_from_user failed unexpectedly?!\n");
242 goto free_user;
243 }
244
245 pr_info("attempting bad copy_from_user outside whitelist\n");
246 if (copy_from_user(buf + offset - 1, user_addr, size)) {
247 pr_warn("copy_from_user failed, but lacked Oops\n");
248 goto free_user;
249 }
250 }
251
252 free_user:
253 vm_munmap(user_alloc, PAGE_SIZE);
254 free_alloc:
255 if (buf)
256 kmem_cache_free(whitelist_cache, buf);
257 }
258
259 /* Callable tests. */
lkdtm_USERCOPY_HEAP_SIZE_TO(void)260 void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
261 {
262 do_usercopy_heap_size(true);
263 }
264
lkdtm_USERCOPY_HEAP_SIZE_FROM(void)265 void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
266 {
267 do_usercopy_heap_size(false);
268 }
269
lkdtm_USERCOPY_HEAP_WHITELIST_TO(void)270 void lkdtm_USERCOPY_HEAP_WHITELIST_TO(void)
271 {
272 do_usercopy_heap_whitelist(true);
273 }
274
lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)275 void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
276 {
277 do_usercopy_heap_whitelist(false);
278 }
279
lkdtm_USERCOPY_STACK_FRAME_TO(void)280 void lkdtm_USERCOPY_STACK_FRAME_TO(void)
281 {
282 do_usercopy_stack(true, true);
283 }
284
lkdtm_USERCOPY_STACK_FRAME_FROM(void)285 void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
286 {
287 do_usercopy_stack(false, true);
288 }
289
lkdtm_USERCOPY_STACK_BEYOND(void)290 void lkdtm_USERCOPY_STACK_BEYOND(void)
291 {
292 do_usercopy_stack(true, false);
293 }
294
lkdtm_USERCOPY_KERNEL(void)295 void lkdtm_USERCOPY_KERNEL(void)
296 {
297 unsigned long user_addr;
298
299 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
300 PROT_READ | PROT_WRITE | PROT_EXEC,
301 MAP_ANONYMOUS | MAP_PRIVATE, 0);
302 if (user_addr >= TASK_SIZE) {
303 pr_warn("Failed to allocate user memory\n");
304 return;
305 }
306
307 pr_info("attempting good copy_to_user from kernel rodata: %px\n",
308 test_text);
309 if (copy_to_user((void __user *)user_addr, test_text,
310 unconst + sizeof(test_text))) {
311 pr_warn("copy_to_user failed unexpectedly?!\n");
312 goto free_user;
313 }
314
315 pr_info("attempting bad copy_to_user from kernel text: %px\n",
316 vm_mmap);
317 if (copy_to_user((void __user *)user_addr, vm_mmap,
318 unconst + PAGE_SIZE)) {
319 pr_warn("copy_to_user failed, but lacked Oops\n");
320 goto free_user;
321 }
322 pr_err("FAIL: survived bad copy_to_user()\n");
323
324 free_user:
325 vm_munmap(user_addr, PAGE_SIZE);
326 }
327
lkdtm_usercopy_init(void)328 void __init lkdtm_usercopy_init(void)
329 {
330 /* Prepare cache that lacks SLAB_USERCOPY flag. */
331 whitelist_cache =
332 kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
333 0, 0,
334 cache_size / 4,
335 cache_size / 16,
336 NULL);
337 }
338
lkdtm_usercopy_exit(void)339 void __exit lkdtm_usercopy_exit(void)
340 {
341 kmem_cache_destroy(whitelist_cache);
342 }
343
