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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 */
21static volatile size_t unconst;
22static volatile size_t cache_size = 1024;
23static struct kmem_cache *whitelist_cache;
24
25static 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 */
31static noinline unsigned char *trick_compiler(unsigned char *stack)
32{
33 return stack + 0;
34}
35
36static 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
49static 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
114free_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 */
122static 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 pr_err("FAIL: bad usercopy not detected!\n");
177 pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
178
179free_user:
180 vm_munmap(user_addr, PAGE_SIZE);
181free_kernel:
182 kfree(one);
183 kfree(two);
184}
185
186/*
187 * This checks for the specific whitelist window within an object. If this
188 * test passes, then do_usercopy_heap_size() tests will pass too.
189 */
190static void do_usercopy_heap_whitelist(bool to_user)
191{
192 unsigned long user_alloc;
193 unsigned char *buf = NULL;
194 unsigned char __user *user_addr;
195 size_t offset, size;
196
197 /* Make sure cache was prepared. */
198 if (!whitelist_cache) {
199 pr_warn("Failed to allocate kernel cache\n");
200 return;
201 }
202
203 /*
204 * Allocate a buffer with a whitelisted window in the buffer.
205 */
206 buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
207 if (!buf) {
208 pr_warn("Failed to allocate buffer from whitelist cache\n");
209 goto free_alloc;
210 }
211
212 /* Allocate user memory we'll poke at. */
213 user_alloc = vm_mmap(NULL, 0, PAGE_SIZE,
214 PROT_READ | PROT_WRITE | PROT_EXEC,
215 MAP_ANONYMOUS | MAP_PRIVATE, 0);
216 if (user_alloc >= TASK_SIZE) {
217 pr_warn("Failed to allocate user memory\n");
218 goto free_alloc;
219 }
220 user_addr = (void __user *)user_alloc;
221
222 memset(buf, 'B', cache_size);
223
224 /* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
225 offset = (cache_size / 4) + unconst;
226 size = (cache_size / 16) + unconst;
227
228 if (to_user) {
229 pr_info("attempting good copy_to_user inside whitelist\n");
230 if (copy_to_user(user_addr, buf + offset, size)) {
231 pr_warn("copy_to_user failed unexpectedly?!\n");
232 goto free_user;
233 }
234
235 pr_info("attempting bad copy_to_user outside whitelist\n");
236 if (copy_to_user(user_addr, buf + offset - 1, size)) {
237 pr_warn("copy_to_user failed, but lacked Oops\n");
238 goto free_user;
239 }
240 } else {
241 pr_info("attempting good copy_from_user inside whitelist\n");
242 if (copy_from_user(buf + offset, user_addr, size)) {
243 pr_warn("copy_from_user failed unexpectedly?!\n");
244 goto free_user;
245 }
246
247 pr_info("attempting bad copy_from_user outside whitelist\n");
248 if (copy_from_user(buf + offset - 1, user_addr, size)) {
249 pr_warn("copy_from_user failed, but lacked Oops\n");
250 goto free_user;
251 }
252 }
253 pr_err("FAIL: bad usercopy not detected!\n");
254 pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
255
256free_user:
257 vm_munmap(user_alloc, PAGE_SIZE);
258free_alloc:
259 if (buf)
260 kmem_cache_free(whitelist_cache, buf);
261}
262
263/* Callable tests. */
264void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
265{
266 do_usercopy_heap_size(true);
267}
268
269void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
270{
271 do_usercopy_heap_size(false);
272}
273
274void lkdtm_USERCOPY_HEAP_WHITELIST_TO(void)
275{
276 do_usercopy_heap_whitelist(true);
277}
278
279void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
280{
281 do_usercopy_heap_whitelist(false);
282}
283
284void lkdtm_USERCOPY_STACK_FRAME_TO(void)
285{
286 do_usercopy_stack(true, true);
287}
288
289void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
290{
291 do_usercopy_stack(false, true);
292}
293
294void lkdtm_USERCOPY_STACK_BEYOND(void)
295{
296 do_usercopy_stack(true, false);
297}
298
299void lkdtm_USERCOPY_KERNEL(void)
300{
301 unsigned long user_addr;
302
303 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
304 PROT_READ | PROT_WRITE | PROT_EXEC,
305 MAP_ANONYMOUS | MAP_PRIVATE, 0);
306 if (user_addr >= TASK_SIZE) {
307 pr_warn("Failed to allocate user memory\n");
308 return;
309 }
310
311 pr_info("attempting good copy_to_user from kernel rodata: %px\n",
312 test_text);
313 if (copy_to_user((void __user *)user_addr, test_text,
314 unconst + sizeof(test_text))) {
315 pr_warn("copy_to_user failed unexpectedly?!\n");
316 goto free_user;
317 }
318
319 pr_info("attempting bad copy_to_user from kernel text: %px\n",
320 vm_mmap);
321 if (copy_to_user((void __user *)user_addr, function_nocfi(vm_mmap),
322 unconst + PAGE_SIZE)) {
323 pr_warn("copy_to_user failed, but lacked Oops\n");
324 goto free_user;
325 }
326 pr_err("FAIL: bad copy_to_user() not detected!\n");
327 pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
328
329free_user:
330 vm_munmap(user_addr, PAGE_SIZE);
331}
332
333void __init lkdtm_usercopy_init(void)
334{
335 /* Prepare cache that lacks SLAB_USERCOPY flag. */
336 whitelist_cache =
337 kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
338 0, 0,
339 cache_size / 4,
340 cache_size / 16,
341 NULL);
342}
343
344void __exit lkdtm_usercopy_exit(void)
345{
346 kmem_cache_destroy(whitelist_cache);
347}