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1/*
2 * arch/arm/kernel/kprobes.c
3 *
4 * Kprobes on ARM
5 *
6 * Abhishek Sagar <sagar.abhishek@gmail.com>
7 * Copyright (C) 2006, 2007 Motorola Inc.
8 *
9 * Nicolas Pitre <nico@marvell.com>
10 * Copyright (C) 2007 Marvell Ltd.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2 as
14 * published by the Free Software Foundation.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * General Public License for more details.
20 */
21
22#include <linux/kernel.h>
23#include <linux/kprobes.h>
24#include <linux/module.h>
25#include <linux/slab.h>
26#include <linux/stop_machine.h>
27#include <linux/stringify.h>
28#include <asm/traps.h>
29#include <asm/opcodes.h>
30#include <asm/cacheflush.h>
31#include <linux/percpu.h>
32#include <linux/bug.h>
33
34#include "kprobes.h"
35#include "probes-arm.h"
36#include "probes-thumb.h"
37#include "patch.h"
38
39#define MIN_STACK_SIZE(addr) \
40 min((unsigned long)MAX_STACK_SIZE, \
41 (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
42
43#define flush_insns(addr, size) \
44 flush_icache_range((unsigned long)(addr), \
45 (unsigned long)(addr) + \
46 (size))
47
48/* Used as a marker in ARM_pc to note when we're in a jprobe. */
49#define JPROBE_MAGIC_ADDR 0xffffffff
50
51DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
52DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
53
54
55int __kprobes arch_prepare_kprobe(struct kprobe *p)
56{
57 kprobe_opcode_t insn;
58 kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
59 unsigned long addr = (unsigned long)p->addr;
60 bool thumb;
61 kprobe_decode_insn_t *decode_insn;
62 const union decode_action *actions;
63 int is;
64
65 if (in_exception_text(addr))
66 return -EINVAL;
67
68#ifdef CONFIG_THUMB2_KERNEL
69 thumb = true;
70 addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
71 insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
72 if (is_wide_instruction(insn)) {
73 u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
74 insn = __opcode_thumb32_compose(insn, inst2);
75 decode_insn = thumb32_probes_decode_insn;
76 actions = kprobes_t32_actions;
77 } else {
78 decode_insn = thumb16_probes_decode_insn;
79 actions = kprobes_t16_actions;
80 }
81#else /* !CONFIG_THUMB2_KERNEL */
82 thumb = false;
83 if (addr & 0x3)
84 return -EINVAL;
85 insn = __mem_to_opcode_arm(*p->addr);
86 decode_insn = arm_probes_decode_insn;
87 actions = kprobes_arm_actions;
88#endif
89
90 p->opcode = insn;
91 p->ainsn.insn = tmp_insn;
92
93 switch ((*decode_insn)(insn, &p->ainsn, true, actions)) {
94 case INSN_REJECTED: /* not supported */
95 return -EINVAL;
96
97 case INSN_GOOD: /* instruction uses slot */
98 p->ainsn.insn = get_insn_slot();
99 if (!p->ainsn.insn)
100 return -ENOMEM;
101 for (is = 0; is < MAX_INSN_SIZE; ++is)
102 p->ainsn.insn[is] = tmp_insn[is];
103 flush_insns(p->ainsn.insn,
104 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
105 p->ainsn.insn_fn = (probes_insn_fn_t *)
106 ((uintptr_t)p->ainsn.insn | thumb);
107 break;
108
109 case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
110 p->ainsn.insn = NULL;
111 break;
112 }
113
114 return 0;
115}
116
117void __kprobes arch_arm_kprobe(struct kprobe *p)
118{
119 unsigned int brkp;
120 void *addr;
121
122 if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
123 /* Remove any Thumb flag */
124 addr = (void *)((uintptr_t)p->addr & ~1);
125
126 if (is_wide_instruction(p->opcode))
127 brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
128 else
129 brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
130 } else {
131 kprobe_opcode_t insn = p->opcode;
132
133 addr = p->addr;
134 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
135
136 if (insn >= 0xe0000000)
137 brkp |= 0xe0000000; /* Unconditional instruction */
138 else
139 brkp |= insn & 0xf0000000; /* Copy condition from insn */
140 }
141
142 patch_text(addr, brkp);
143}
144
145/*
146 * The actual disarming is done here on each CPU and synchronized using
147 * stop_machine. This synchronization is necessary on SMP to avoid removing
148 * a probe between the moment the 'Undefined Instruction' exception is raised
149 * and the moment the exception handler reads the faulting instruction from
150 * memory. It is also needed to atomically set the two half-words of a 32-bit
151 * Thumb breakpoint.
152 */
153int __kprobes __arch_disarm_kprobe(void *p)
154{
155 struct kprobe *kp = p;
156 void *addr = (void *)((uintptr_t)kp->addr & ~1);
157
158 __patch_text(addr, kp->opcode);
159
160 return 0;
161}
162
163void __kprobes arch_disarm_kprobe(struct kprobe *p)
164{
165 stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
166}
167
168void __kprobes arch_remove_kprobe(struct kprobe *p)
169{
170 if (p->ainsn.insn) {
171 free_insn_slot(p->ainsn.insn, 0);
172 p->ainsn.insn = NULL;
173 }
174}
175
176static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
177{
178 kcb->prev_kprobe.kp = kprobe_running();
179 kcb->prev_kprobe.status = kcb->kprobe_status;
180}
181
182static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
183{
184 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
185 kcb->kprobe_status = kcb->prev_kprobe.status;
186}
187
188static void __kprobes set_current_kprobe(struct kprobe *p)
189{
190 __this_cpu_write(current_kprobe, p);
191}
192
193static void __kprobes
194singlestep_skip(struct kprobe *p, struct pt_regs *regs)
195{
196#ifdef CONFIG_THUMB2_KERNEL
197 regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
198 if (is_wide_instruction(p->opcode))
199 regs->ARM_pc += 4;
200 else
201 regs->ARM_pc += 2;
202#else
203 regs->ARM_pc += 4;
204#endif
205}
206
207static inline void __kprobes
208singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
209{
210 p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
211}
212
213/*
214 * Called with IRQs disabled. IRQs must remain disabled from that point
215 * all the way until processing this kprobe is complete. The current
216 * kprobes implementation cannot process more than one nested level of
217 * kprobe, and that level is reserved for user kprobe handlers, so we can't
218 * risk encountering a new kprobe in an interrupt handler.
219 */
220void __kprobes kprobe_handler(struct pt_regs *regs)
221{
222 struct kprobe *p, *cur;
223 struct kprobe_ctlblk *kcb;
224
225 kcb = get_kprobe_ctlblk();
226 cur = kprobe_running();
227
228#ifdef CONFIG_THUMB2_KERNEL
229 /*
230 * First look for a probe which was registered using an address with
231 * bit 0 set, this is the usual situation for pointers to Thumb code.
232 * If not found, fallback to looking for one with bit 0 clear.
233 */
234 p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
235 if (!p)
236 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
237
238#else /* ! CONFIG_THUMB2_KERNEL */
239 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
240#endif
241
242 if (p) {
243 if (cur) {
244 /* Kprobe is pending, so we're recursing. */
245 switch (kcb->kprobe_status) {
246 case KPROBE_HIT_ACTIVE:
247 case KPROBE_HIT_SSDONE:
248 /* A pre- or post-handler probe got us here. */
249 kprobes_inc_nmissed_count(p);
250 save_previous_kprobe(kcb);
251 set_current_kprobe(p);
252 kcb->kprobe_status = KPROBE_REENTER;
253 singlestep(p, regs, kcb);
254 restore_previous_kprobe(kcb);
255 break;
256 default:
257 /* impossible cases */
258 BUG();
259 }
260 } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
261 /* Probe hit and conditional execution check ok. */
262 set_current_kprobe(p);
263 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
264
265 /*
266 * If we have no pre-handler or it returned 0, we
267 * continue with normal processing. If we have a
268 * pre-handler and it returned non-zero, it prepped
269 * for calling the break_handler below on re-entry,
270 * so get out doing nothing more here.
271 */
272 if (!p->pre_handler || !p->pre_handler(p, regs)) {
273 kcb->kprobe_status = KPROBE_HIT_SS;
274 singlestep(p, regs, kcb);
275 if (p->post_handler) {
276 kcb->kprobe_status = KPROBE_HIT_SSDONE;
277 p->post_handler(p, regs, 0);
278 }
279 reset_current_kprobe();
280 }
281 } else {
282 /*
283 * Probe hit but conditional execution check failed,
284 * so just skip the instruction and continue as if
285 * nothing had happened.
286 */
287 singlestep_skip(p, regs);
288 }
289 } else if (cur) {
290 /* We probably hit a jprobe. Call its break handler. */
291 if (cur->break_handler && cur->break_handler(cur, regs)) {
292 kcb->kprobe_status = KPROBE_HIT_SS;
293 singlestep(cur, regs, kcb);
294 if (cur->post_handler) {
295 kcb->kprobe_status = KPROBE_HIT_SSDONE;
296 cur->post_handler(cur, regs, 0);
297 }
298 }
299 reset_current_kprobe();
300 } else {
301 /*
302 * The probe was removed and a race is in progress.
303 * There is nothing we can do about it. Let's restart
304 * the instruction. By the time we can restart, the
305 * real instruction will be there.
306 */
307 }
308}
309
310static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
311{
312 unsigned long flags;
313 local_irq_save(flags);
314 kprobe_handler(regs);
315 local_irq_restore(flags);
316 return 0;
317}
318
319int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
320{
321 struct kprobe *cur = kprobe_running();
322 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
323
324 switch (kcb->kprobe_status) {
325 case KPROBE_HIT_SS:
326 case KPROBE_REENTER:
327 /*
328 * We are here because the instruction being single
329 * stepped caused a page fault. We reset the current
330 * kprobe and the PC to point back to the probe address
331 * and allow the page fault handler to continue as a
332 * normal page fault.
333 */
334 regs->ARM_pc = (long)cur->addr;
335 if (kcb->kprobe_status == KPROBE_REENTER) {
336 restore_previous_kprobe(kcb);
337 } else {
338 reset_current_kprobe();
339 }
340 break;
341
342 case KPROBE_HIT_ACTIVE:
343 case KPROBE_HIT_SSDONE:
344 /*
345 * We increment the nmissed count for accounting,
346 * we can also use npre/npostfault count for accounting
347 * these specific fault cases.
348 */
349 kprobes_inc_nmissed_count(cur);
350
351 /*
352 * We come here because instructions in the pre/post
353 * handler caused the page_fault, this could happen
354 * if handler tries to access user space by
355 * copy_from_user(), get_user() etc. Let the
356 * user-specified handler try to fix it.
357 */
358 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
359 return 1;
360 break;
361
362 default:
363 break;
364 }
365
366 return 0;
367}
368
369int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
370 unsigned long val, void *data)
371{
372 /*
373 * notify_die() is currently never called on ARM,
374 * so this callback is currently empty.
375 */
376 return NOTIFY_DONE;
377}
378
379/*
380 * When a retprobed function returns, trampoline_handler() is called,
381 * calling the kretprobe's handler. We construct a struct pt_regs to
382 * give a view of registers r0-r11 to the user return-handler. This is
383 * not a complete pt_regs structure, but that should be plenty sufficient
384 * for kretprobe handlers which should normally be interested in r0 only
385 * anyway.
386 */
387void __naked __kprobes kretprobe_trampoline(void)
388{
389 __asm__ __volatile__ (
390 "stmdb sp!, {r0 - r11} \n\t"
391 "mov r0, sp \n\t"
392 "bl trampoline_handler \n\t"
393 "mov lr, r0 \n\t"
394 "ldmia sp!, {r0 - r11} \n\t"
395#ifdef CONFIG_THUMB2_KERNEL
396 "bx lr \n\t"
397#else
398 "mov pc, lr \n\t"
399#endif
400 : : : "memory");
401}
402
403/* Called from kretprobe_trampoline */
404static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
405{
406 struct kretprobe_instance *ri = NULL;
407 struct hlist_head *head, empty_rp;
408 struct hlist_node *tmp;
409 unsigned long flags, orig_ret_address = 0;
410 unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
411
412 INIT_HLIST_HEAD(&empty_rp);
413 kretprobe_hash_lock(current, &head, &flags);
414
415 /*
416 * It is possible to have multiple instances associated with a given
417 * task either because multiple functions in the call path have
418 * a return probe installed on them, and/or more than one return
419 * probe was registered for a target function.
420 *
421 * We can handle this because:
422 * - instances are always inserted at the head of the list
423 * - when multiple return probes are registered for the same
424 * function, the first instance's ret_addr will point to the
425 * real return address, and all the rest will point to
426 * kretprobe_trampoline
427 */
428 hlist_for_each_entry_safe(ri, tmp, head, hlist) {
429 if (ri->task != current)
430 /* another task is sharing our hash bucket */
431 continue;
432
433 if (ri->rp && ri->rp->handler) {
434 __this_cpu_write(current_kprobe, &ri->rp->kp);
435 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
436 ri->rp->handler(ri, regs);
437 __this_cpu_write(current_kprobe, NULL);
438 }
439
440 orig_ret_address = (unsigned long)ri->ret_addr;
441 recycle_rp_inst(ri, &empty_rp);
442
443 if (orig_ret_address != trampoline_address)
444 /*
445 * This is the real return address. Any other
446 * instances associated with this task are for
447 * other calls deeper on the call stack
448 */
449 break;
450 }
451
452 kretprobe_assert(ri, orig_ret_address, trampoline_address);
453 kretprobe_hash_unlock(current, &flags);
454
455 hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
456 hlist_del(&ri->hlist);
457 kfree(ri);
458 }
459
460 return (void *)orig_ret_address;
461}
462
463void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
464 struct pt_regs *regs)
465{
466 ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
467
468 /* Replace the return addr with trampoline addr. */
469 regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
470}
471
472int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
473{
474 struct jprobe *jp = container_of(p, struct jprobe, kp);
475 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
476 long sp_addr = regs->ARM_sp;
477 long cpsr;
478
479 kcb->jprobe_saved_regs = *regs;
480 memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
481 regs->ARM_pc = (long)jp->entry;
482
483 cpsr = regs->ARM_cpsr | PSR_I_BIT;
484#ifdef CONFIG_THUMB2_KERNEL
485 /* Set correct Thumb state in cpsr */
486 if (regs->ARM_pc & 1)
487 cpsr |= PSR_T_BIT;
488 else
489 cpsr &= ~PSR_T_BIT;
490#endif
491 regs->ARM_cpsr = cpsr;
492
493 preempt_disable();
494 return 1;
495}
496
497void __kprobes jprobe_return(void)
498{
499 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
500
501 __asm__ __volatile__ (
502 /*
503 * Setup an empty pt_regs. Fill SP and PC fields as
504 * they're needed by longjmp_break_handler.
505 *
506 * We allocate some slack between the original SP and start of
507 * our fabricated regs. To be precise we want to have worst case
508 * covered which is STMFD with all 16 regs so we allocate 2 *
509 * sizeof(struct_pt_regs)).
510 *
511 * This is to prevent any simulated instruction from writing
512 * over the regs when they are accessing the stack.
513 */
514#ifdef CONFIG_THUMB2_KERNEL
515 "sub r0, %0, %1 \n\t"
516 "mov sp, r0 \n\t"
517#else
518 "sub sp, %0, %1 \n\t"
519#endif
520 "ldr r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
521 "str %0, [sp, %2] \n\t"
522 "str r0, [sp, %3] \n\t"
523 "mov r0, sp \n\t"
524 "bl kprobe_handler \n\t"
525
526 /*
527 * Return to the context saved by setjmp_pre_handler
528 * and restored by longjmp_break_handler.
529 */
530#ifdef CONFIG_THUMB2_KERNEL
531 "ldr lr, [sp, %2] \n\t" /* lr = saved sp */
532 "ldrd r0, r1, [sp, %5] \n\t" /* r0,r1 = saved lr,pc */
533 "ldr r2, [sp, %4] \n\t" /* r2 = saved psr */
534 "stmdb lr!, {r0, r1, r2} \n\t" /* push saved lr and */
535 /* rfe context */
536 "ldmia sp, {r0 - r12} \n\t"
537 "mov sp, lr \n\t"
538 "ldr lr, [sp], #4 \n\t"
539 "rfeia sp! \n\t"
540#else
541 "ldr r0, [sp, %4] \n\t"
542 "msr cpsr_cxsf, r0 \n\t"
543 "ldmia sp, {r0 - pc} \n\t"
544#endif
545 :
546 : "r" (kcb->jprobe_saved_regs.ARM_sp),
547 "I" (sizeof(struct pt_regs) * 2),
548 "J" (offsetof(struct pt_regs, ARM_sp)),
549 "J" (offsetof(struct pt_regs, ARM_pc)),
550 "J" (offsetof(struct pt_regs, ARM_cpsr)),
551 "J" (offsetof(struct pt_regs, ARM_lr))
552 : "memory", "cc");
553}
554
555int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
556{
557 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
558 long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
559 long orig_sp = regs->ARM_sp;
560 struct jprobe *jp = container_of(p, struct jprobe, kp);
561
562 if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
563 if (orig_sp != stack_addr) {
564 struct pt_regs *saved_regs =
565 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
566 printk("current sp %lx does not match saved sp %lx\n",
567 orig_sp, stack_addr);
568 printk("Saved registers for jprobe %p\n", jp);
569 show_regs(saved_regs);
570 printk("Current registers\n");
571 show_regs(regs);
572 BUG();
573 }
574 *regs = kcb->jprobe_saved_regs;
575 memcpy((void *)stack_addr, kcb->jprobes_stack,
576 MIN_STACK_SIZE(stack_addr));
577 preempt_enable_no_resched();
578 return 1;
579 }
580 return 0;
581}
582
583int __kprobes arch_trampoline_kprobe(struct kprobe *p)
584{
585 return 0;
586}
587
588#ifdef CONFIG_THUMB2_KERNEL
589
590static struct undef_hook kprobes_thumb16_break_hook = {
591 .instr_mask = 0xffff,
592 .instr_val = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
593 .cpsr_mask = MODE_MASK,
594 .cpsr_val = SVC_MODE,
595 .fn = kprobe_trap_handler,
596};
597
598static struct undef_hook kprobes_thumb32_break_hook = {
599 .instr_mask = 0xffffffff,
600 .instr_val = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
601 .cpsr_mask = MODE_MASK,
602 .cpsr_val = SVC_MODE,
603 .fn = kprobe_trap_handler,
604};
605
606#else /* !CONFIG_THUMB2_KERNEL */
607
608static struct undef_hook kprobes_arm_break_hook = {
609 .instr_mask = 0x0fffffff,
610 .instr_val = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
611 .cpsr_mask = MODE_MASK,
612 .cpsr_val = SVC_MODE,
613 .fn = kprobe_trap_handler,
614};
615
616#endif /* !CONFIG_THUMB2_KERNEL */
617
618int __init arch_init_kprobes()
619{
620 arm_probes_decode_init();
621#ifdef CONFIG_THUMB2_KERNEL
622 register_undef_hook(&kprobes_thumb16_break_hook);
623 register_undef_hook(&kprobes_thumb32_break_hook);
624#else
625 register_undef_hook(&kprobes_arm_break_hook);
626#endif
627 return 0;
628}