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 / 8UL)
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 (buf[..] passed as arg)
45 * - function may have external effects (memzero_explicit())
46 * - no tail recursion possible
47 */
recursive_loop(int remaining)48 static int noinline recursive_loop(int remaining)
49 {
50 volatile char buf[REC_STACK_SIZE];
51 volatile int ret;
52
53 memset((void *)buf, remaining & 0xFF, sizeof(buf));
54 if (!remaining)
55 ret = 0;
56 else
57 ret = recursive_loop((int)buf[remaining % sizeof(buf)] - 1);
58 memzero_explicit((void *)buf, sizeof(buf));
59 return ret;
60 }
61
62 /* If the depth is negative, use the default, otherwise keep parameter. */
lkdtm_bugs_init(int * recur_param)63 void __init lkdtm_bugs_init(int *recur_param)
64 {
65 if (*recur_param < 0)
66 *recur_param = recur_count;
67 else
68 recur_count = *recur_param;
69 }
70
lkdtm_PANIC(void)71 static void lkdtm_PANIC(void)
72 {
73 panic("dumptest");
74 }
75
lkdtm_BUG(void)76 static void lkdtm_BUG(void)
77 {
78 BUG();
79 }
80
81 static int warn_counter;
82
lkdtm_WARNING(void)83 static void lkdtm_WARNING(void)
84 {
85 WARN_ON(++warn_counter);
86 }
87
lkdtm_WARNING_MESSAGE(void)88 static void lkdtm_WARNING_MESSAGE(void)
89 {
90 WARN(1, "Warning message trigger count: %d\n", ++warn_counter);
91 }
92
lkdtm_EXCEPTION(void)93 static void lkdtm_EXCEPTION(void)
94 {
95 *((volatile int *) 0) = 0;
96 }
97
lkdtm_LOOP(void)98 static void lkdtm_LOOP(void)
99 {
100 for (;;)
101 ;
102 }
103
lkdtm_EXHAUST_STACK(void)104 static void lkdtm_EXHAUST_STACK(void)
105 {
106 pr_info("Calling function with %lu frame size to depth %d ...\n",
107 REC_STACK_SIZE, recur_count);
108 recursive_loop(recur_count);
109 pr_info("FAIL: survived without exhausting stack?!\n");
110 }
111
__lkdtm_CORRUPT_STACK(void * stack)112 static noinline void __lkdtm_CORRUPT_STACK(void *stack)
113 {
114 memset(stack, '\xff', 64);
115 }
116
117 /* This should trip the stack canary, not corrupt the return address. */
lkdtm_CORRUPT_STACK(void)118 static noinline void lkdtm_CORRUPT_STACK(void)
119 {
120 /* Use default char array length that triggers stack protection. */
121 char data[8] __aligned(sizeof(void *));
122
123 pr_info("Corrupting stack containing char array ...\n");
124 __lkdtm_CORRUPT_STACK((void *)&data);
125 }
126
127 /* Same as above but will only get a canary with -fstack-protector-strong */
lkdtm_CORRUPT_STACK_STRONG(void)128 static noinline void lkdtm_CORRUPT_STACK_STRONG(void)
129 {
130 union {
131 unsigned short shorts[4];
132 unsigned long *ptr;
133 } data __aligned(sizeof(void *));
134
135 pr_info("Corrupting stack containing union ...\n");
136 __lkdtm_CORRUPT_STACK((void *)&data);
137 }
138
139 static pid_t stack_pid;
140 static unsigned long stack_addr;
141
lkdtm_REPORT_STACK(void)142 static void lkdtm_REPORT_STACK(void)
143 {
144 volatile uintptr_t magic;
145 pid_t pid = task_pid_nr(current);
146
147 if (pid != stack_pid) {
148 pr_info("Starting stack offset tracking for pid %d\n", pid);
149 stack_pid = pid;
150 stack_addr = (uintptr_t)&magic;
151 }
152
153 pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic));
154 }
155
156 static pid_t stack_canary_pid;
157 static unsigned long stack_canary;
158 static unsigned long stack_canary_offset;
159
__lkdtm_REPORT_STACK_CANARY(void * stack)160 static noinline void __lkdtm_REPORT_STACK_CANARY(void *stack)
161 {
162 int i = 0;
163 pid_t pid = task_pid_nr(current);
164 unsigned long *canary = (unsigned long *)stack;
165 unsigned long current_offset = 0, init_offset = 0;
166
167 /* Do our best to find the canary in a 16 word window ... */
168 for (i = 1; i < 16; i++) {
169 canary = (unsigned long *)stack + i;
170 #ifdef CONFIG_STACKPROTECTOR
171 if (*canary == current->stack_canary)
172 current_offset = i;
173 if (*canary == init_task.stack_canary)
174 init_offset = i;
175 #endif
176 }
177
178 if (current_offset == 0) {
179 /*
180 * If the canary doesn't match what's in the task_struct,
181 * we're either using a global canary or the stack frame
182 * layout changed.
183 */
184 if (init_offset != 0) {
185 pr_err("FAIL: global stack canary found at offset %ld (canary for pid %d matches init_task's)!\n",
186 init_offset, pid);
187 } else {
188 pr_warn("FAIL: did not correctly locate stack canary :(\n");
189 pr_expected_config(CONFIG_STACKPROTECTOR);
190 }
191
192 return;
193 } else if (init_offset != 0) {
194 pr_warn("WARNING: found both current and init_task canaries nearby?!\n");
195 }
196
197 canary = (unsigned long *)stack + current_offset;
198 if (stack_canary_pid == 0) {
199 stack_canary = *canary;
200 stack_canary_pid = pid;
201 stack_canary_offset = current_offset;
202 pr_info("Recorded stack canary for pid %d at offset %ld\n",
203 stack_canary_pid, stack_canary_offset);
204 } else if (pid == stack_canary_pid) {
205 pr_warn("ERROR: saw pid %d again -- please use a new pid\n", pid);
206 } else {
207 if (current_offset != stack_canary_offset) {
208 pr_warn("ERROR: canary offset changed from %ld to %ld!?\n",
209 stack_canary_offset, current_offset);
210 return;
211 }
212
213 if (*canary == stack_canary) {
214 pr_warn("FAIL: canary identical for pid %d and pid %d at offset %ld!\n",
215 stack_canary_pid, pid, current_offset);
216 } else {
217 pr_info("ok: stack canaries differ between pid %d and pid %d at offset %ld.\n",
218 stack_canary_pid, pid, current_offset);
219 /* Reset the test. */
220 stack_canary_pid = 0;
221 }
222 }
223 }
224
lkdtm_REPORT_STACK_CANARY(void)225 static void lkdtm_REPORT_STACK_CANARY(void)
226 {
227 /* Use default char array length that triggers stack protection. */
228 char data[8] __aligned(sizeof(void *)) = { };
229
230 __lkdtm_REPORT_STACK_CANARY((void *)&data);
231 }
232
lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)233 static void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
234 {
235 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
236 u32 *p;
237 u32 val = 0x12345678;
238
239 p = (u32 *)(data + 1);
240 if (*p == 0)
241 val = 0x87654321;
242 *p = val;
243
244 if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
245 pr_err("XFAIL: arch has CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS\n");
246 }
247
lkdtm_SOFTLOCKUP(void)248 static void lkdtm_SOFTLOCKUP(void)
249 {
250 preempt_disable();
251 for (;;)
252 cpu_relax();
253 }
254
lkdtm_HARDLOCKUP(void)255 static void lkdtm_HARDLOCKUP(void)
256 {
257 local_irq_disable();
258 for (;;)
259 cpu_relax();
260 }
261
lkdtm_SPINLOCKUP(void)262 static void lkdtm_SPINLOCKUP(void)
263 {
264 /* Must be called twice to trigger. */
265 spin_lock(&lock_me_up);
266 /* Let sparse know we intended to exit holding the lock. */
267 __release(&lock_me_up);
268 }
269
lkdtm_HUNG_TASK(void)270 static void lkdtm_HUNG_TASK(void)
271 {
272 set_current_state(TASK_UNINTERRUPTIBLE);
273 schedule();
274 }
275
276 volatile unsigned int huge = INT_MAX - 2;
277 volatile unsigned int ignored;
278
lkdtm_OVERFLOW_SIGNED(void)279 static void lkdtm_OVERFLOW_SIGNED(void)
280 {
281 int value;
282
283 value = huge;
284 pr_info("Normal signed addition ...\n");
285 value += 1;
286 ignored = value;
287
288 pr_info("Overflowing signed addition ...\n");
289 value += 4;
290 ignored = value;
291 }
292
293
lkdtm_OVERFLOW_UNSIGNED(void)294 static void lkdtm_OVERFLOW_UNSIGNED(void)
295 {
296 unsigned int value;
297
298 value = huge;
299 pr_info("Normal unsigned addition ...\n");
300 value += 1;
301 ignored = value;
302
303 pr_info("Overflowing unsigned addition ...\n");
304 value += 4;
305 ignored = value;
306 }
307
308 /* Intentionally using old-style flex array definition of 1 byte. */
309 struct array_bounds_flex_array {
310 int one;
311 int two;
312 char data[1];
313 };
314
315 struct array_bounds {
316 int one;
317 int two;
318 char data[8];
319 int three;
320 };
321
lkdtm_ARRAY_BOUNDS(void)322 static void lkdtm_ARRAY_BOUNDS(void)
323 {
324 struct array_bounds_flex_array *not_checked;
325 struct array_bounds *checked;
326 volatile int i;
327
328 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
329 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
330 if (!not_checked || !checked) {
331 kfree(not_checked);
332 kfree(checked);
333 return;
334 }
335
336 pr_info("Array access within bounds ...\n");
337 /* For both, touch all bytes in the actual member size. */
338 for (i = 0; i < sizeof(checked->data); i++)
339 checked->data[i] = 'A';
340 /*
341 * For the uninstrumented flex array member, also touch 1 byte
342 * beyond to verify it is correctly uninstrumented.
343 */
344 for (i = 0; i < sizeof(not_checked->data) + 1; i++)
345 not_checked->data[i] = 'A';
346
347 pr_info("Array access beyond bounds ...\n");
348 for (i = 0; i < sizeof(checked->data) + 1; i++)
349 checked->data[i] = 'B';
350
351 kfree(not_checked);
352 kfree(checked);
353 pr_err("FAIL: survived array bounds overflow!\n");
354 if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))
355 pr_expected_config(CONFIG_UBSAN_TRAP);
356 else
357 pr_expected_config(CONFIG_UBSAN_BOUNDS);
358 }
359
lkdtm_CORRUPT_LIST_ADD(void)360 static void lkdtm_CORRUPT_LIST_ADD(void)
361 {
362 /*
363 * Initially, an empty list via LIST_HEAD:
364 * test_head.next = &test_head
365 * test_head.prev = &test_head
366 */
367 LIST_HEAD(test_head);
368 struct lkdtm_list good, bad;
369 void *target[2] = { };
370 void *redirection = ⌖
371
372 pr_info("attempting good list addition\n");
373
374 /*
375 * Adding to the list performs these actions:
376 * test_head.next->prev = &good.node
377 * good.node.next = test_head.next
378 * good.node.prev = test_head
379 * test_head.next = good.node
380 */
381 list_add(&good.node, &test_head);
382
383 pr_info("attempting corrupted list addition\n");
384 /*
385 * In simulating this "write what where" primitive, the "what" is
386 * the address of &bad.node, and the "where" is the address held
387 * by "redirection".
388 */
389 test_head.next = redirection;
390 list_add(&bad.node, &test_head);
391
392 if (target[0] == NULL && target[1] == NULL)
393 pr_err("Overwrite did not happen, but no BUG?!\n");
394 else {
395 pr_err("list_add() corruption not detected!\n");
396 pr_expected_config(CONFIG_DEBUG_LIST);
397 }
398 }
399
lkdtm_CORRUPT_LIST_DEL(void)400 static void lkdtm_CORRUPT_LIST_DEL(void)
401 {
402 LIST_HEAD(test_head);
403 struct lkdtm_list item;
404 void *target[2] = { };
405 void *redirection = ⌖
406
407 list_add(&item.node, &test_head);
408
409 pr_info("attempting good list removal\n");
410 list_del(&item.node);
411
412 pr_info("attempting corrupted list removal\n");
413 list_add(&item.node, &test_head);
414
415 /* As with the list_add() test above, this corrupts "next". */
416 item.node.next = redirection;
417 list_del(&item.node);
418
419 if (target[0] == NULL && target[1] == NULL)
420 pr_err("Overwrite did not happen, but no BUG?!\n");
421 else {
422 pr_err("list_del() corruption not detected!\n");
423 pr_expected_config(CONFIG_DEBUG_LIST);
424 }
425 }
426
427 /* Test that VMAP_STACK is actually allocating with a leading guard page */
lkdtm_STACK_GUARD_PAGE_LEADING(void)428 static void lkdtm_STACK_GUARD_PAGE_LEADING(void)
429 {
430 const unsigned char *stack = task_stack_page(current);
431 const unsigned char *ptr = stack - 1;
432 volatile unsigned char byte;
433
434 pr_info("attempting bad read from page below current stack\n");
435
436 byte = *ptr;
437
438 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte);
439 }
440
441 /* Test that VMAP_STACK is actually allocating with a trailing guard page */
lkdtm_STACK_GUARD_PAGE_TRAILING(void)442 static void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
443 {
444 const unsigned char *stack = task_stack_page(current);
445 const unsigned char *ptr = stack + THREAD_SIZE;
446 volatile unsigned char byte;
447
448 pr_info("attempting bad read from page above current stack\n");
449
450 byte = *ptr;
451
452 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte);
453 }
454
lkdtm_UNSET_SMEP(void)455 static void lkdtm_UNSET_SMEP(void)
456 {
457 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML)
458 #define MOV_CR4_DEPTH 64
459 void (*direct_write_cr4)(unsigned long val);
460 unsigned char *insn;
461 unsigned long cr4;
462 int i;
463
464 cr4 = native_read_cr4();
465
466 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
467 pr_err("FAIL: SMEP not in use\n");
468 return;
469 }
470 cr4 &= ~(X86_CR4_SMEP);
471
472 pr_info("trying to clear SMEP normally\n");
473 native_write_cr4(cr4);
474 if (cr4 == native_read_cr4()) {
475 pr_err("FAIL: pinning SMEP failed!\n");
476 cr4 |= X86_CR4_SMEP;
477 pr_info("restoring SMEP\n");
478 native_write_cr4(cr4);
479 return;
480 }
481 pr_info("ok: SMEP did not get cleared\n");
482
483 /*
484 * To test the post-write pinning verification we need to call
485 * directly into the middle of native_write_cr4() where the
486 * cr4 write happens, skipping any pinning. This searches for
487 * the cr4 writing instruction.
488 */
489 insn = (unsigned char *)native_write_cr4;
490 for (i = 0; i < MOV_CR4_DEPTH; i++) {
491 /* mov %rdi, %cr4 */
492 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
493 break;
494 /* mov %rdi,%rax; mov %rax, %cr4 */
495 if (insn[i] == 0x48 && insn[i+1] == 0x89 &&
496 insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
497 insn[i+4] == 0x22 && insn[i+5] == 0xe0)
498 break;
499 }
500 if (i >= MOV_CR4_DEPTH) {
501 pr_info("ok: cannot locate cr4 writing call gadget\n");
502 return;
503 }
504 direct_write_cr4 = (void *)(insn + i);
505
506 pr_info("trying to clear SMEP with call gadget\n");
507 direct_write_cr4(cr4);
508 if (native_read_cr4() & X86_CR4_SMEP) {
509 pr_info("ok: SMEP removal was reverted\n");
510 } else {
511 pr_err("FAIL: cleared SMEP not detected!\n");
512 cr4 |= X86_CR4_SMEP;
513 pr_info("restoring SMEP\n");
514 native_write_cr4(cr4);
515 }
516 #else
517 pr_err("XFAIL: this test is x86_64-only\n");
518 #endif
519 }
520
lkdtm_DOUBLE_FAULT(void)521 static void lkdtm_DOUBLE_FAULT(void)
522 {
523 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
524 /*
525 * Trigger #DF by setting the stack limit to zero. This clobbers
526 * a GDT TLS slot, which is okay because the current task will die
527 * anyway due to the double fault.
528 */
529 struct desc_struct d = {
530 .type = 3, /* expand-up, writable, accessed data */
531 .p = 1, /* present */
532 .d = 1, /* 32-bit */
533 .g = 0, /* limit in bytes */
534 .s = 1, /* not system */
535 };
536
537 local_irq_disable();
538 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()),
539 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S);
540
541 /*
542 * Put our zero-limit segment in SS and then trigger a fault. The
543 * 4-byte access to (%esp) will fault with #SS, and the attempt to
544 * deliver the fault will recursively cause #SS and result in #DF.
545 * This whole process happens while NMIs and MCEs are blocked by the
546 * MOV SS window. This is nice because an NMI with an invalid SS
547 * would also double-fault, resulting in the NMI or MCE being lost.
548 */
549 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" ::
550 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3)));
551
552 pr_err("FAIL: tried to double fault but didn't die\n");
553 #else
554 pr_err("XFAIL: this test is ia32-only\n");
555 #endif
556 }
557
558 #ifdef CONFIG_ARM64
change_pac_parameters(void)559 static noinline void change_pac_parameters(void)
560 {
561 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
562 /* Reset the keys of current task */
563 ptrauth_thread_init_kernel(current);
564 ptrauth_thread_switch_kernel(current);
565 }
566 }
567 #endif
568
lkdtm_CORRUPT_PAC(void)569 static noinline void lkdtm_CORRUPT_PAC(void)
570 {
571 #ifdef CONFIG_ARM64
572 #define CORRUPT_PAC_ITERATE 10
573 int i;
574
575 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL))
576 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n");
577
578 if (!system_supports_address_auth()) {
579 pr_err("FAIL: CPU lacks pointer authentication feature\n");
580 return;
581 }
582
583 pr_info("changing PAC parameters to force function return failure...\n");
584 /*
585 * PAC is a hash value computed from input keys, return address and
586 * stack pointer. As pac has fewer bits so there is a chance of
587 * collision, so iterate few times to reduce the collision probability.
588 */
589 for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
590 change_pac_parameters();
591
592 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n");
593 #else
594 pr_err("XFAIL: this test is arm64-only\n");
595 #endif
596 }
597
598 static struct crashtype crashtypes[] = {
599 CRASHTYPE(PANIC),
600 CRASHTYPE(BUG),
601 CRASHTYPE(WARNING),
602 CRASHTYPE(WARNING_MESSAGE),
603 CRASHTYPE(EXCEPTION),
604 CRASHTYPE(LOOP),
605 CRASHTYPE(EXHAUST_STACK),
606 CRASHTYPE(CORRUPT_STACK),
607 CRASHTYPE(CORRUPT_STACK_STRONG),
608 CRASHTYPE(REPORT_STACK),
609 CRASHTYPE(REPORT_STACK_CANARY),
610 CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
611 CRASHTYPE(SOFTLOCKUP),
612 CRASHTYPE(HARDLOCKUP),
613 CRASHTYPE(SPINLOCKUP),
614 CRASHTYPE(HUNG_TASK),
615 CRASHTYPE(OVERFLOW_SIGNED),
616 CRASHTYPE(OVERFLOW_UNSIGNED),
617 CRASHTYPE(ARRAY_BOUNDS),
618 CRASHTYPE(CORRUPT_LIST_ADD),
619 CRASHTYPE(CORRUPT_LIST_DEL),
620 CRASHTYPE(STACK_GUARD_PAGE_LEADING),
621 CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
622 CRASHTYPE(UNSET_SMEP),
623 CRASHTYPE(DOUBLE_FAULT),
624 CRASHTYPE(CORRUPT_PAC),
625 };
626
627 struct crashtype_category bugs_crashtypes = {
628 .crashtypes = crashtypes,
629 .len = ARRAY_SIZE(crashtypes),
630 };
631
