1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This is for all the tests related to logic bugs (e.g. bad dereferences,
4 * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
5 * lockups) along with other things that don't fit well into existing LKDTM
6 * test source files.
7 */
8 #include "lkdtm.h"
9 #include <linux/list.h>
10 #include <linux/sched.h>
11 #include <linux/sched/signal.h>
12 #include <linux/sched/task_stack.h>
13 #include <linux/uaccess.h>
14 #include <linux/slab.h>
15
16 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
17 #include <asm/desc.h>
18 #endif
19
20 struct lkdtm_list {
21 struct list_head node;
22 };
23
24 /*
25 * Make sure our attempts to over run the kernel stack doesn't trigger
26 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
27 * recurse past the end of THREAD_SIZE by default.
28 */
29 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
30 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
31 #else
32 #define REC_STACK_SIZE (THREAD_SIZE / 8)
33 #endif
34 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)
35
36 static int recur_count = REC_NUM_DEFAULT;
37
38 static DEFINE_SPINLOCK(lock_me_up);
39
40 /*
41 * Make sure compiler does not optimize this function or stack frame away:
42 * - function marked noinline
43 * - stack variables are marked volatile
44 * - stack variables are written (memset()) and read (pr_info())
45 * - function has external effects (pr_info())
46 * */
recursive_loop(int remaining)47 static int noinline recursive_loop(int remaining)
48 {
49 volatile char buf[REC_STACK_SIZE];
50
51 memset((void *)buf, remaining & 0xFF, sizeof(buf));
52 pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
53 recur_count);
54 if (!remaining)
55 return 0;
56 else
57 return recursive_loop(remaining - 1);
58 }
59
60 /* If the depth is negative, use the default, otherwise keep parameter. */
lkdtm_bugs_init(int * recur_param)61 void __init lkdtm_bugs_init(int *recur_param)
62 {
63 if (*recur_param < 0)
64 *recur_param = recur_count;
65 else
66 recur_count = *recur_param;
67 }
68
lkdtm_PANIC(void)69 void lkdtm_PANIC(void)
70 {
71 panic("dumptest");
72 }
73
lkdtm_BUG(void)74 void lkdtm_BUG(void)
75 {
76 BUG();
77 }
78
79 static int warn_counter;
80
lkdtm_WARNING(void)81 void lkdtm_WARNING(void)
82 {
83 WARN_ON(++warn_counter);
84 }
85
lkdtm_WARNING_MESSAGE(void)86 void lkdtm_WARNING_MESSAGE(void)
87 {
88 WARN(1, "Warning message trigger count: %d\n", ++warn_counter);
89 }
90
lkdtm_EXCEPTION(void)91 void lkdtm_EXCEPTION(void)
92 {
93 *((volatile int *) 0) = 0;
94 }
95
lkdtm_LOOP(void)96 void lkdtm_LOOP(void)
97 {
98 for (;;)
99 ;
100 }
101
lkdtm_EXHAUST_STACK(void)102 void lkdtm_EXHAUST_STACK(void)
103 {
104 pr_info("Calling function with %lu frame size to depth %d ...\n",
105 REC_STACK_SIZE, recur_count);
106 recursive_loop(recur_count);
107 pr_info("FAIL: survived without exhausting stack?!\n");
108 }
109
__lkdtm_CORRUPT_STACK(void * stack)110 static noinline void __lkdtm_CORRUPT_STACK(void *stack)
111 {
112 memset(stack, '\xff', 64);
113 }
114
115 /* This should trip the stack canary, not corrupt the return address. */
lkdtm_CORRUPT_STACK(void)116 noinline void lkdtm_CORRUPT_STACK(void)
117 {
118 /* Use default char array length that triggers stack protection. */
119 char data[8] __aligned(sizeof(void *));
120
121 pr_info("Corrupting stack containing char array ...\n");
122 __lkdtm_CORRUPT_STACK((void *)&data);
123 }
124
125 /* Same as above but will only get a canary with -fstack-protector-strong */
lkdtm_CORRUPT_STACK_STRONG(void)126 noinline void lkdtm_CORRUPT_STACK_STRONG(void)
127 {
128 union {
129 unsigned short shorts[4];
130 unsigned long *ptr;
131 } data __aligned(sizeof(void *));
132
133 pr_info("Corrupting stack containing union ...\n");
134 __lkdtm_CORRUPT_STACK((void *)&data);
135 }
136
137 static pid_t stack_pid;
138 static unsigned long stack_addr;
139
lkdtm_REPORT_STACK(void)140 void lkdtm_REPORT_STACK(void)
141 {
142 volatile uintptr_t magic;
143 pid_t pid = task_pid_nr(current);
144
145 if (pid != stack_pid) {
146 pr_info("Starting stack offset tracking for pid %d\n", pid);
147 stack_pid = pid;
148 stack_addr = (uintptr_t)&magic;
149 }
150
151 pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic));
152 }
153
lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)154 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
155 {
156 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
157 u32 *p;
158 u32 val = 0x12345678;
159
160 p = (u32 *)(data + 1);
161 if (*p == 0)
162 val = 0x87654321;
163 *p = val;
164
165 if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
166 pr_err("XFAIL: arch has CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS\n");
167 }
168
lkdtm_SOFTLOCKUP(void)169 void lkdtm_SOFTLOCKUP(void)
170 {
171 preempt_disable();
172 for (;;)
173 cpu_relax();
174 }
175
lkdtm_HARDLOCKUP(void)176 void lkdtm_HARDLOCKUP(void)
177 {
178 local_irq_disable();
179 for (;;)
180 cpu_relax();
181 }
182
lkdtm_SPINLOCKUP(void)183 void lkdtm_SPINLOCKUP(void)
184 {
185 /* Must be called twice to trigger. */
186 spin_lock(&lock_me_up);
187 /* Let sparse know we intended to exit holding the lock. */
188 __release(&lock_me_up);
189 }
190
lkdtm_HUNG_TASK(void)191 void lkdtm_HUNG_TASK(void)
192 {
193 set_current_state(TASK_UNINTERRUPTIBLE);
194 schedule();
195 }
196
197 volatile unsigned int huge = INT_MAX - 2;
198 volatile unsigned int ignored;
199
lkdtm_OVERFLOW_SIGNED(void)200 void lkdtm_OVERFLOW_SIGNED(void)
201 {
202 int value;
203
204 value = huge;
205 pr_info("Normal signed addition ...\n");
206 value += 1;
207 ignored = value;
208
209 pr_info("Overflowing signed addition ...\n");
210 value += 4;
211 ignored = value;
212 }
213
214
lkdtm_OVERFLOW_UNSIGNED(void)215 void lkdtm_OVERFLOW_UNSIGNED(void)
216 {
217 unsigned int value;
218
219 value = huge;
220 pr_info("Normal unsigned addition ...\n");
221 value += 1;
222 ignored = value;
223
224 pr_info("Overflowing unsigned addition ...\n");
225 value += 4;
226 ignored = value;
227 }
228
229 /* Intentionally using old-style flex array definition of 1 byte. */
230 struct array_bounds_flex_array {
231 int one;
232 int two;
233 char data[1];
234 };
235
236 struct array_bounds {
237 int one;
238 int two;
239 char data[8];
240 int three;
241 };
242
lkdtm_ARRAY_BOUNDS(void)243 void lkdtm_ARRAY_BOUNDS(void)
244 {
245 struct array_bounds_flex_array *not_checked;
246 struct array_bounds *checked;
247 volatile int i;
248
249 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
250 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
251
252 pr_info("Array access within bounds ...\n");
253 /* For both, touch all bytes in the actual member size. */
254 for (i = 0; i < sizeof(checked->data); i++)
255 checked->data[i] = 'A';
256 /*
257 * For the uninstrumented flex array member, also touch 1 byte
258 * beyond to verify it is correctly uninstrumented.
259 */
260 for (i = 0; i < sizeof(not_checked->data) + 1; i++)
261 not_checked->data[i] = 'A';
262
263 pr_info("Array access beyond bounds ...\n");
264 for (i = 0; i < sizeof(checked->data) + 1; i++)
265 checked->data[i] = 'B';
266
267 kfree(not_checked);
268 kfree(checked);
269 pr_err("FAIL: survived array bounds overflow!\n");
270 pr_expected_config(CONFIG_UBSAN_BOUNDS);
271 }
272
lkdtm_CORRUPT_LIST_ADD(void)273 void lkdtm_CORRUPT_LIST_ADD(void)
274 {
275 /*
276 * Initially, an empty list via LIST_HEAD:
277 * test_head.next = &test_head
278 * test_head.prev = &test_head
279 */
280 LIST_HEAD(test_head);
281 struct lkdtm_list good, bad;
282 void *target[2] = { };
283 void *redirection = ⌖
284
285 pr_info("attempting good list addition\n");
286
287 /*
288 * Adding to the list performs these actions:
289 * test_head.next->prev = &good.node
290 * good.node.next = test_head.next
291 * good.node.prev = test_head
292 * test_head.next = good.node
293 */
294 list_add(&good.node, &test_head);
295
296 pr_info("attempting corrupted list addition\n");
297 /*
298 * In simulating this "write what where" primitive, the "what" is
299 * the address of &bad.node, and the "where" is the address held
300 * by "redirection".
301 */
302 test_head.next = redirection;
303 list_add(&bad.node, &test_head);
304
305 if (target[0] == NULL && target[1] == NULL)
306 pr_err("Overwrite did not happen, but no BUG?!\n");
307 else {
308 pr_err("list_add() corruption not detected!\n");
309 pr_expected_config(CONFIG_DEBUG_LIST);
310 }
311 }
312
lkdtm_CORRUPT_LIST_DEL(void)313 void lkdtm_CORRUPT_LIST_DEL(void)
314 {
315 LIST_HEAD(test_head);
316 struct lkdtm_list item;
317 void *target[2] = { };
318 void *redirection = ⌖
319
320 list_add(&item.node, &test_head);
321
322 pr_info("attempting good list removal\n");
323 list_del(&item.node);
324
325 pr_info("attempting corrupted list removal\n");
326 list_add(&item.node, &test_head);
327
328 /* As with the list_add() test above, this corrupts "next". */
329 item.node.next = redirection;
330 list_del(&item.node);
331
332 if (target[0] == NULL && target[1] == NULL)
333 pr_err("Overwrite did not happen, but no BUG?!\n");
334 else {
335 pr_err("list_del() corruption not detected!\n");
336 pr_expected_config(CONFIG_DEBUG_LIST);
337 }
338 }
339
340 /* Test that VMAP_STACK is actually allocating with a leading guard page */
lkdtm_STACK_GUARD_PAGE_LEADING(void)341 void lkdtm_STACK_GUARD_PAGE_LEADING(void)
342 {
343 const unsigned char *stack = task_stack_page(current);
344 const unsigned char *ptr = stack - 1;
345 volatile unsigned char byte;
346
347 pr_info("attempting bad read from page below current stack\n");
348
349 byte = *ptr;
350
351 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte);
352 }
353
354 /* Test that VMAP_STACK is actually allocating with a trailing guard page */
lkdtm_STACK_GUARD_PAGE_TRAILING(void)355 void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
356 {
357 const unsigned char *stack = task_stack_page(current);
358 const unsigned char *ptr = stack + THREAD_SIZE;
359 volatile unsigned char byte;
360
361 pr_info("attempting bad read from page above current stack\n");
362
363 byte = *ptr;
364
365 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte);
366 }
367
lkdtm_UNSET_SMEP(void)368 void lkdtm_UNSET_SMEP(void)
369 {
370 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML)
371 #define MOV_CR4_DEPTH 64
372 void (*direct_write_cr4)(unsigned long val);
373 unsigned char *insn;
374 unsigned long cr4;
375 int i;
376
377 cr4 = native_read_cr4();
378
379 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
380 pr_err("FAIL: SMEP not in use\n");
381 return;
382 }
383 cr4 &= ~(X86_CR4_SMEP);
384
385 pr_info("trying to clear SMEP normally\n");
386 native_write_cr4(cr4);
387 if (cr4 == native_read_cr4()) {
388 pr_err("FAIL: pinning SMEP failed!\n");
389 cr4 |= X86_CR4_SMEP;
390 pr_info("restoring SMEP\n");
391 native_write_cr4(cr4);
392 return;
393 }
394 pr_info("ok: SMEP did not get cleared\n");
395
396 /*
397 * To test the post-write pinning verification we need to call
398 * directly into the middle of native_write_cr4() where the
399 * cr4 write happens, skipping any pinning. This searches for
400 * the cr4 writing instruction.
401 */
402 insn = (unsigned char *)native_write_cr4;
403 for (i = 0; i < MOV_CR4_DEPTH; i++) {
404 /* mov %rdi, %cr4 */
405 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
406 break;
407 /* mov %rdi,%rax; mov %rax, %cr4 */
408 if (insn[i] == 0x48 && insn[i+1] == 0x89 &&
409 insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
410 insn[i+4] == 0x22 && insn[i+5] == 0xe0)
411 break;
412 }
413 if (i >= MOV_CR4_DEPTH) {
414 pr_info("ok: cannot locate cr4 writing call gadget\n");
415 return;
416 }
417 direct_write_cr4 = (void *)(insn + i);
418
419 pr_info("trying to clear SMEP with call gadget\n");
420 direct_write_cr4(cr4);
421 if (native_read_cr4() & X86_CR4_SMEP) {
422 pr_info("ok: SMEP removal was reverted\n");
423 } else {
424 pr_err("FAIL: cleared SMEP not detected!\n");
425 cr4 |= X86_CR4_SMEP;
426 pr_info("restoring SMEP\n");
427 native_write_cr4(cr4);
428 }
429 #else
430 pr_err("XFAIL: this test is x86_64-only\n");
431 #endif
432 }
433
lkdtm_DOUBLE_FAULT(void)434 void lkdtm_DOUBLE_FAULT(void)
435 {
436 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
437 /*
438 * Trigger #DF by setting the stack limit to zero. This clobbers
439 * a GDT TLS slot, which is okay because the current task will die
440 * anyway due to the double fault.
441 */
442 struct desc_struct d = {
443 .type = 3, /* expand-up, writable, accessed data */
444 .p = 1, /* present */
445 .d = 1, /* 32-bit */
446 .g = 0, /* limit in bytes */
447 .s = 1, /* not system */
448 };
449
450 local_irq_disable();
451 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()),
452 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S);
453
454 /*
455 * Put our zero-limit segment in SS and then trigger a fault. The
456 * 4-byte access to (%esp) will fault with #SS, and the attempt to
457 * deliver the fault will recursively cause #SS and result in #DF.
458 * This whole process happens while NMIs and MCEs are blocked by the
459 * MOV SS window. This is nice because an NMI with an invalid SS
460 * would also double-fault, resulting in the NMI or MCE being lost.
461 */
462 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" ::
463 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3)));
464
465 pr_err("FAIL: tried to double fault but didn't die\n");
466 #else
467 pr_err("XFAIL: this test is ia32-only\n");
468 #endif
469 }
470
471 #ifdef CONFIG_ARM64
change_pac_parameters(void)472 static noinline void change_pac_parameters(void)
473 {
474 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
475 /* Reset the keys of current task */
476 ptrauth_thread_init_kernel(current);
477 ptrauth_thread_switch_kernel(current);
478 }
479 }
480 #endif
481
lkdtm_CORRUPT_PAC(void)482 noinline void lkdtm_CORRUPT_PAC(void)
483 {
484 #ifdef CONFIG_ARM64
485 #define CORRUPT_PAC_ITERATE 10
486 int i;
487
488 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL))
489 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n");
490
491 if (!system_supports_address_auth()) {
492 pr_err("FAIL: CPU lacks pointer authentication feature\n");
493 return;
494 }
495
496 pr_info("changing PAC parameters to force function return failure...\n");
497 /*
498 * PAC is a hash value computed from input keys, return address and
499 * stack pointer. As pac has fewer bits so there is a chance of
500 * collision, so iterate few times to reduce the collision probability.
501 */
502 for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
503 change_pac_parameters();
504
505 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n");
506 #else
507 pr_err("XFAIL: this test is arm64-only\n");
508 #endif
509 }
510
