1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This is for all the tests related to validating kernel memory
4 * permissions: non-executable regions, non-writable regions, and
5 * even non-readable regions.
6 */
7 #include "lkdtm.h"
8 #include <linux/slab.h>
9 #include <linux/vmalloc.h>
10 #include <linux/mman.h>
11 #include <linux/uaccess.h>
12 #include <asm/cacheflush.h>
13 #include <asm/sections.h>
14
15 /* Whether or not to fill the target memory area with do_nothing(). */
16 #define CODE_WRITE true
17 #define CODE_AS_IS false
18
19 /* How many bytes to copy to be sure we've copied enough of do_nothing(). */
20 #define EXEC_SIZE 64
21
22 /* This is non-const, so it will end up in the .data section. */
23 static u8 data_area[EXEC_SIZE];
24
25 /* This is const, so it will end up in the .rodata section. */
26 static const unsigned long rodata = 0xAA55AA55;
27
28 /* This is marked __ro_after_init, so it should ultimately be .rodata. */
29 static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
30
31 /*
32 * This just returns to the caller. It is designed to be copied into
33 * non-executable memory regions.
34 */
do_nothing(void)35 static noinline void do_nothing(void)
36 {
37 return;
38 }
39
40 /* Must immediately follow do_nothing for size calculuations to work out. */
do_overwritten(void)41 static noinline void do_overwritten(void)
42 {
43 pr_info("do_overwritten wasn't overwritten!\n");
44 return;
45 }
46
do_almost_nothing(void)47 static noinline void do_almost_nothing(void)
48 {
49 pr_info("do_nothing was hijacked!\n");
50 }
51
setup_function_descriptor(func_desc_t * fdesc,void * dst)52 static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
53 {
54 if (!have_function_descriptors())
55 return dst;
56
57 memcpy(fdesc, do_nothing, sizeof(*fdesc));
58 fdesc->addr = (unsigned long)dst;
59 barrier();
60
61 return fdesc;
62 }
63
execute_location(void * dst,bool write)64 static noinline __nocfi void execute_location(void *dst, bool write)
65 {
66 void (*func)(void);
67 func_desc_t fdesc;
68 void *do_nothing_text = dereference_function_descriptor(do_nothing);
69
70 pr_info("attempting ok execution at %px\n", do_nothing_text);
71 do_nothing();
72
73 if (write == CODE_WRITE) {
74 memcpy(dst, do_nothing_text, EXEC_SIZE);
75 flush_icache_range((unsigned long)dst,
76 (unsigned long)dst + EXEC_SIZE);
77 }
78 pr_info("attempting bad execution at %px\n", dst);
79 func = setup_function_descriptor(&fdesc, dst);
80 func();
81 pr_err("FAIL: func returned\n");
82 }
83
execute_user_location(void * dst)84 static void execute_user_location(void *dst)
85 {
86 int copied;
87
88 /* Intentionally crossing kernel/user memory boundary. */
89 void (*func)(void);
90 func_desc_t fdesc;
91 void *do_nothing_text = dereference_function_descriptor(do_nothing);
92
93 pr_info("attempting ok execution at %px\n", do_nothing_text);
94 do_nothing();
95
96 copied = access_process_vm(current, (unsigned long)dst, do_nothing_text,
97 EXEC_SIZE, FOLL_WRITE);
98 if (copied < EXEC_SIZE)
99 return;
100 pr_info("attempting bad execution at %px\n", dst);
101 func = setup_function_descriptor(&fdesc, dst);
102 func();
103 pr_err("FAIL: func returned\n");
104 }
105
lkdtm_WRITE_RO(void)106 static void lkdtm_WRITE_RO(void)
107 {
108 /* Explicitly cast away "const" for the test and make volatile. */
109 volatile unsigned long *ptr = (unsigned long *)&rodata;
110
111 pr_info("attempting bad rodata write at %px\n", ptr);
112 *ptr ^= 0xabcd1234;
113 pr_err("FAIL: survived bad write\n");
114 }
115
lkdtm_WRITE_RO_AFTER_INIT(void)116 static void lkdtm_WRITE_RO_AFTER_INIT(void)
117 {
118 volatile unsigned long *ptr = &ro_after_init;
119
120 /*
121 * Verify we were written to during init. Since an Oops
122 * is considered a "success", a failure is to just skip the
123 * real test.
124 */
125 if ((*ptr & 0xAA) != 0xAA) {
126 pr_info("%p was NOT written during init!?\n", ptr);
127 return;
128 }
129
130 pr_info("attempting bad ro_after_init write at %px\n", ptr);
131 *ptr ^= 0xabcd1234;
132 pr_err("FAIL: survived bad write\n");
133 }
134
lkdtm_WRITE_KERN(void)135 static void lkdtm_WRITE_KERN(void)
136 {
137 size_t size;
138 volatile unsigned char *ptr;
139
140 size = (unsigned long)dereference_function_descriptor(do_overwritten) -
141 (unsigned long)dereference_function_descriptor(do_nothing);
142 ptr = dereference_function_descriptor(do_overwritten);
143
144 pr_info("attempting bad %zu byte write at %px\n", size, ptr);
145 memcpy((void *)ptr, (unsigned char *)do_nothing, size);
146 flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
147 pr_err("FAIL: survived bad write\n");
148
149 do_overwritten();
150 }
151
lkdtm_WRITE_OPD(void)152 static void lkdtm_WRITE_OPD(void)
153 {
154 size_t size = sizeof(func_desc_t);
155 void (*func)(void) = do_nothing;
156
157 if (!have_function_descriptors()) {
158 pr_info("XFAIL: Platform doesn't use function descriptors.\n");
159 return;
160 }
161 pr_info("attempting bad %zu bytes write at %px\n", size, do_nothing);
162 memcpy(do_nothing, do_almost_nothing, size);
163 pr_err("FAIL: survived bad write\n");
164
165 asm("" : "=m"(func));
166 func();
167 }
168
lkdtm_EXEC_DATA(void)169 static void lkdtm_EXEC_DATA(void)
170 {
171 execute_location(data_area, CODE_WRITE);
172 }
173
lkdtm_EXEC_STACK(void)174 static void lkdtm_EXEC_STACK(void)
175 {
176 u8 stack_area[EXEC_SIZE];
177 execute_location(stack_area, CODE_WRITE);
178 }
179
lkdtm_EXEC_KMALLOC(void)180 static void lkdtm_EXEC_KMALLOC(void)
181 {
182 u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
183 execute_location(kmalloc_area, CODE_WRITE);
184 kfree(kmalloc_area);
185 }
186
lkdtm_EXEC_VMALLOC(void)187 static void lkdtm_EXEC_VMALLOC(void)
188 {
189 u32 *vmalloc_area = vmalloc(EXEC_SIZE);
190 execute_location(vmalloc_area, CODE_WRITE);
191 vfree(vmalloc_area);
192 }
193
lkdtm_EXEC_RODATA(void)194 static void lkdtm_EXEC_RODATA(void)
195 {
196 execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing),
197 CODE_AS_IS);
198 }
199
lkdtm_EXEC_USERSPACE(void)200 static void lkdtm_EXEC_USERSPACE(void)
201 {
202 unsigned long user_addr;
203
204 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
205 PROT_READ | PROT_WRITE | PROT_EXEC,
206 MAP_ANONYMOUS | MAP_PRIVATE, 0);
207 if (user_addr >= TASK_SIZE) {
208 pr_warn("Failed to allocate user memory\n");
209 return;
210 }
211 execute_user_location((void *)user_addr);
212 vm_munmap(user_addr, PAGE_SIZE);
213 }
214
lkdtm_EXEC_NULL(void)215 static void lkdtm_EXEC_NULL(void)
216 {
217 execute_location(NULL, CODE_AS_IS);
218 }
219
lkdtm_ACCESS_USERSPACE(void)220 static void lkdtm_ACCESS_USERSPACE(void)
221 {
222 unsigned long user_addr, tmp = 0;
223 unsigned long *ptr;
224
225 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
226 PROT_READ | PROT_WRITE | PROT_EXEC,
227 MAP_ANONYMOUS | MAP_PRIVATE, 0);
228 if (user_addr >= TASK_SIZE) {
229 pr_warn("Failed to allocate user memory\n");
230 return;
231 }
232
233 if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
234 pr_warn("copy_to_user failed\n");
235 vm_munmap(user_addr, PAGE_SIZE);
236 return;
237 }
238
239 ptr = (unsigned long *)user_addr;
240
241 pr_info("attempting bad read at %px\n", ptr);
242 tmp = *ptr;
243 tmp += 0xc0dec0de;
244 pr_err("FAIL: survived bad read\n");
245
246 pr_info("attempting bad write at %px\n", ptr);
247 *ptr = tmp;
248 pr_err("FAIL: survived bad write\n");
249
250 vm_munmap(user_addr, PAGE_SIZE);
251 }
252
lkdtm_ACCESS_NULL(void)253 static void lkdtm_ACCESS_NULL(void)
254 {
255 unsigned long tmp;
256 volatile unsigned long *ptr = (unsigned long *)NULL;
257
258 pr_info("attempting bad read at %px\n", ptr);
259 tmp = *ptr;
260 tmp += 0xc0dec0de;
261 pr_err("FAIL: survived bad read\n");
262
263 pr_info("attempting bad write at %px\n", ptr);
264 *ptr = tmp;
265 pr_err("FAIL: survived bad write\n");
266 }
267
lkdtm_perms_init(void)268 void __init lkdtm_perms_init(void)
269 {
270 /* Make sure we can write to __ro_after_init values during __init */
271 ro_after_init |= 0xAA;
272 }
273
274 static struct crashtype crashtypes[] = {
275 CRASHTYPE(WRITE_RO),
276 CRASHTYPE(WRITE_RO_AFTER_INIT),
277 CRASHTYPE(WRITE_KERN),
278 CRASHTYPE(WRITE_OPD),
279 CRASHTYPE(EXEC_DATA),
280 CRASHTYPE(EXEC_STACK),
281 CRASHTYPE(EXEC_KMALLOC),
282 CRASHTYPE(EXEC_VMALLOC),
283 CRASHTYPE(EXEC_RODATA),
284 CRASHTYPE(EXEC_USERSPACE),
285 CRASHTYPE(EXEC_NULL),
286 CRASHTYPE(ACCESS_USERSPACE),
287 CRASHTYPE(ACCESS_NULL),
288 };
289
290 struct crashtype_category perms_crashtypes = {
291 .crashtypes = crashtypes,
292 .len = ARRAY_SIZE(crashtypes),
293 };
294