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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/cacheflush.h>
30
31#include "kprobes.h"
32
33#define MIN_STACK_SIZE(addr) \
34 min((unsigned long)MAX_STACK_SIZE, \
35 (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
36
37#define flush_insns(addr, size) \
38 flush_icache_range((unsigned long)(addr), \
39 (unsigned long)(addr) + \
40 (size))
41
42/* Used as a marker in ARM_pc to note when we're in a jprobe. */
43#define JPROBE_MAGIC_ADDR 0xffffffff
44
45DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
46DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
47
48
49int __kprobes arch_prepare_kprobe(struct kprobe *p)
50{
51 kprobe_opcode_t insn;
52 kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
53 unsigned long addr = (unsigned long)p->addr;
54 bool thumb;
55 kprobe_decode_insn_t *decode_insn;
56 int is;
57
58 if (in_exception_text(addr))
59 return -EINVAL;
60
61#ifdef CONFIG_THUMB2_KERNEL
62 thumb = true;
63 addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
64 insn = ((u16 *)addr)[0];
65 if (is_wide_instruction(insn)) {
66 insn <<= 16;
67 insn |= ((u16 *)addr)[1];
68 decode_insn = thumb32_kprobe_decode_insn;
69 } else
70 decode_insn = thumb16_kprobe_decode_insn;
71#else /* !CONFIG_THUMB2_KERNEL */
72 thumb = false;
73 if (addr & 0x3)
74 return -EINVAL;
75 insn = *p->addr;
76 decode_insn = arm_kprobe_decode_insn;
77#endif
78
79 p->opcode = insn;
80 p->ainsn.insn = tmp_insn;
81
82 switch ((*decode_insn)(insn, &p->ainsn)) {
83 case INSN_REJECTED: /* not supported */
84 return -EINVAL;
85
86 case INSN_GOOD: /* instruction uses slot */
87 p->ainsn.insn = get_insn_slot();
88 if (!p->ainsn.insn)
89 return -ENOMEM;
90 for (is = 0; is < MAX_INSN_SIZE; ++is)
91 p->ainsn.insn[is] = tmp_insn[is];
92 flush_insns(p->ainsn.insn,
93 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
94 p->ainsn.insn_fn = (kprobe_insn_fn_t *)
95 ((uintptr_t)p->ainsn.insn | thumb);
96 break;
97
98 case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
99 p->ainsn.insn = NULL;
100 break;
101 }
102
103 return 0;
104}
105
106#ifdef CONFIG_THUMB2_KERNEL
107
108/*
109 * For a 32-bit Thumb breakpoint spanning two memory words we need to take
110 * special precautions to insert the breakpoint atomically, especially on SMP
111 * systems. This is achieved by calling this arming function using stop_machine.
112 */
113static int __kprobes set_t32_breakpoint(void *addr)
114{
115 ((u16 *)addr)[0] = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION >> 16;
116 ((u16 *)addr)[1] = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION & 0xffff;
117 flush_insns(addr, 2*sizeof(u16));
118 return 0;
119}
120
121void __kprobes arch_arm_kprobe(struct kprobe *p)
122{
123 uintptr_t addr = (uintptr_t)p->addr & ~1; /* Remove any Thumb flag */
124
125 if (!is_wide_instruction(p->opcode)) {
126 *(u16 *)addr = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
127 flush_insns(addr, sizeof(u16));
128 } else if (addr & 2) {
129 /* A 32-bit instruction spanning two words needs special care */
130 stop_machine(set_t32_breakpoint, (void *)addr, &cpu_online_map);
131 } else {
132 /* Word aligned 32-bit instruction can be written atomically */
133 u32 bkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
134#ifndef __ARMEB__ /* Swap halfwords for little-endian */
135 bkp = (bkp >> 16) | (bkp << 16);
136#endif
137 *(u32 *)addr = bkp;
138 flush_insns(addr, sizeof(u32));
139 }
140}
141
142#else /* !CONFIG_THUMB2_KERNEL */
143
144void __kprobes arch_arm_kprobe(struct kprobe *p)
145{
146 kprobe_opcode_t insn = p->opcode;
147 kprobe_opcode_t brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
148 if (insn >= 0xe0000000)
149 brkp |= 0xe0000000; /* Unconditional instruction */
150 else
151 brkp |= insn & 0xf0000000; /* Copy condition from insn */
152 *p->addr = brkp;
153 flush_insns(p->addr, sizeof(p->addr[0]));
154}
155
156#endif /* !CONFIG_THUMB2_KERNEL */
157
158/*
159 * The actual disarming is done here on each CPU and synchronized using
160 * stop_machine. This synchronization is necessary on SMP to avoid removing
161 * a probe between the moment the 'Undefined Instruction' exception is raised
162 * and the moment the exception handler reads the faulting instruction from
163 * memory. It is also needed to atomically set the two half-words of a 32-bit
164 * Thumb breakpoint.
165 */
166int __kprobes __arch_disarm_kprobe(void *p)
167{
168 struct kprobe *kp = p;
169#ifdef CONFIG_THUMB2_KERNEL
170 u16 *addr = (u16 *)((uintptr_t)kp->addr & ~1);
171 kprobe_opcode_t insn = kp->opcode;
172 unsigned int len;
173
174 if (is_wide_instruction(insn)) {
175 ((u16 *)addr)[0] = insn>>16;
176 ((u16 *)addr)[1] = insn;
177 len = 2*sizeof(u16);
178 } else {
179 ((u16 *)addr)[0] = insn;
180 len = sizeof(u16);
181 }
182 flush_insns(addr, len);
183
184#else /* !CONFIG_THUMB2_KERNEL */
185 *kp->addr = kp->opcode;
186 flush_insns(kp->addr, sizeof(kp->addr[0]));
187#endif
188 return 0;
189}
190
191void __kprobes arch_disarm_kprobe(struct kprobe *p)
192{
193 stop_machine(__arch_disarm_kprobe, p, &cpu_online_map);
194}
195
196void __kprobes arch_remove_kprobe(struct kprobe *p)
197{
198 if (p->ainsn.insn) {
199 free_insn_slot(p->ainsn.insn, 0);
200 p->ainsn.insn = NULL;
201 }
202}
203
204static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
205{
206 kcb->prev_kprobe.kp = kprobe_running();
207 kcb->prev_kprobe.status = kcb->kprobe_status;
208}
209
210static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
211{
212 __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
213 kcb->kprobe_status = kcb->prev_kprobe.status;
214}
215
216static void __kprobes set_current_kprobe(struct kprobe *p)
217{
218 __get_cpu_var(current_kprobe) = p;
219}
220
221static void __kprobes
222singlestep_skip(struct kprobe *p, struct pt_regs *regs)
223{
224#ifdef CONFIG_THUMB2_KERNEL
225 regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
226 if (is_wide_instruction(p->opcode))
227 regs->ARM_pc += 4;
228 else
229 regs->ARM_pc += 2;
230#else
231 regs->ARM_pc += 4;
232#endif
233}
234
235static inline void __kprobes
236singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
237{
238 p->ainsn.insn_singlestep(p, regs);
239}
240
241/*
242 * Called with IRQs disabled. IRQs must remain disabled from that point
243 * all the way until processing this kprobe is complete. The current
244 * kprobes implementation cannot process more than one nested level of
245 * kprobe, and that level is reserved for user kprobe handlers, so we can't
246 * risk encountering a new kprobe in an interrupt handler.
247 */
248void __kprobes kprobe_handler(struct pt_regs *regs)
249{
250 struct kprobe *p, *cur;
251 struct kprobe_ctlblk *kcb;
252
253 kcb = get_kprobe_ctlblk();
254 cur = kprobe_running();
255
256#ifdef CONFIG_THUMB2_KERNEL
257 /*
258 * First look for a probe which was registered using an address with
259 * bit 0 set, this is the usual situation for pointers to Thumb code.
260 * If not found, fallback to looking for one with bit 0 clear.
261 */
262 p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
263 if (!p)
264 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
265
266#else /* ! CONFIG_THUMB2_KERNEL */
267 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
268#endif
269
270 if (p) {
271 if (cur) {
272 /* Kprobe is pending, so we're recursing. */
273 switch (kcb->kprobe_status) {
274 case KPROBE_HIT_ACTIVE:
275 case KPROBE_HIT_SSDONE:
276 /* A pre- or post-handler probe got us here. */
277 kprobes_inc_nmissed_count(p);
278 save_previous_kprobe(kcb);
279 set_current_kprobe(p);
280 kcb->kprobe_status = KPROBE_REENTER;
281 singlestep(p, regs, kcb);
282 restore_previous_kprobe(kcb);
283 break;
284 default:
285 /* impossible cases */
286 BUG();
287 }
288 } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
289 /* Probe hit and conditional execution check ok. */
290 set_current_kprobe(p);
291 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
292
293 /*
294 * If we have no pre-handler or it returned 0, we
295 * continue with normal processing. If we have a
296 * pre-handler and it returned non-zero, it prepped
297 * for calling the break_handler below on re-entry,
298 * so get out doing nothing more here.
299 */
300 if (!p->pre_handler || !p->pre_handler(p, regs)) {
301 kcb->kprobe_status = KPROBE_HIT_SS;
302 singlestep(p, regs, kcb);
303 if (p->post_handler) {
304 kcb->kprobe_status = KPROBE_HIT_SSDONE;
305 p->post_handler(p, regs, 0);
306 }
307 reset_current_kprobe();
308 }
309 } else {
310 /*
311 * Probe hit but conditional execution check failed,
312 * so just skip the instruction and continue as if
313 * nothing had happened.
314 */
315 singlestep_skip(p, regs);
316 }
317 } else if (cur) {
318 /* We probably hit a jprobe. Call its break handler. */
319 if (cur->break_handler && cur->break_handler(cur, regs)) {
320 kcb->kprobe_status = KPROBE_HIT_SS;
321 singlestep(cur, regs, kcb);
322 if (cur->post_handler) {
323 kcb->kprobe_status = KPROBE_HIT_SSDONE;
324 cur->post_handler(cur, regs, 0);
325 }
326 }
327 reset_current_kprobe();
328 } else {
329 /*
330 * The probe was removed and a race is in progress.
331 * There is nothing we can do about it. Let's restart
332 * the instruction. By the time we can restart, the
333 * real instruction will be there.
334 */
335 }
336}
337
338static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
339{
340 unsigned long flags;
341 local_irq_save(flags);
342 kprobe_handler(regs);
343 local_irq_restore(flags);
344 return 0;
345}
346
347int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
348{
349 struct kprobe *cur = kprobe_running();
350 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
351
352 switch (kcb->kprobe_status) {
353 case KPROBE_HIT_SS:
354 case KPROBE_REENTER:
355 /*
356 * We are here because the instruction being single
357 * stepped caused a page fault. We reset the current
358 * kprobe and the PC to point back to the probe address
359 * and allow the page fault handler to continue as a
360 * normal page fault.
361 */
362 regs->ARM_pc = (long)cur->addr;
363 if (kcb->kprobe_status == KPROBE_REENTER) {
364 restore_previous_kprobe(kcb);
365 } else {
366 reset_current_kprobe();
367 }
368 break;
369
370 case KPROBE_HIT_ACTIVE:
371 case KPROBE_HIT_SSDONE:
372 /*
373 * We increment the nmissed count for accounting,
374 * we can also use npre/npostfault count for accounting
375 * these specific fault cases.
376 */
377 kprobes_inc_nmissed_count(cur);
378
379 /*
380 * We come here because instructions in the pre/post
381 * handler caused the page_fault, this could happen
382 * if handler tries to access user space by
383 * copy_from_user(), get_user() etc. Let the
384 * user-specified handler try to fix it.
385 */
386 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
387 return 1;
388 break;
389
390 default:
391 break;
392 }
393
394 return 0;
395}
396
397int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
398 unsigned long val, void *data)
399{
400 /*
401 * notify_die() is currently never called on ARM,
402 * so this callback is currently empty.
403 */
404 return NOTIFY_DONE;
405}
406
407/*
408 * When a retprobed function returns, trampoline_handler() is called,
409 * calling the kretprobe's handler. We construct a struct pt_regs to
410 * give a view of registers r0-r11 to the user return-handler. This is
411 * not a complete pt_regs structure, but that should be plenty sufficient
412 * for kretprobe handlers which should normally be interested in r0 only
413 * anyway.
414 */
415void __naked __kprobes kretprobe_trampoline(void)
416{
417 __asm__ __volatile__ (
418 "stmdb sp!, {r0 - r11} \n\t"
419 "mov r0, sp \n\t"
420 "bl trampoline_handler \n\t"
421 "mov lr, r0 \n\t"
422 "ldmia sp!, {r0 - r11} \n\t"
423#ifdef CONFIG_THUMB2_KERNEL
424 "bx lr \n\t"
425#else
426 "mov pc, lr \n\t"
427#endif
428 : : : "memory");
429}
430
431/* Called from kretprobe_trampoline */
432static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
433{
434 struct kretprobe_instance *ri = NULL;
435 struct hlist_head *head, empty_rp;
436 struct hlist_node *node, *tmp;
437 unsigned long flags, orig_ret_address = 0;
438 unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
439
440 INIT_HLIST_HEAD(&empty_rp);
441 kretprobe_hash_lock(current, &head, &flags);
442
443 /*
444 * It is possible to have multiple instances associated with a given
445 * task either because multiple functions in the call path have
446 * a return probe installed on them, and/or more than one return
447 * probe was registered for a target function.
448 *
449 * We can handle this because:
450 * - instances are always inserted at the head of the list
451 * - when multiple return probes are registered for the same
452 * function, the first instance's ret_addr will point to the
453 * real return address, and all the rest will point to
454 * kretprobe_trampoline
455 */
456 hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
457 if (ri->task != current)
458 /* another task is sharing our hash bucket */
459 continue;
460
461 if (ri->rp && ri->rp->handler) {
462 __get_cpu_var(current_kprobe) = &ri->rp->kp;
463 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
464 ri->rp->handler(ri, regs);
465 __get_cpu_var(current_kprobe) = NULL;
466 }
467
468 orig_ret_address = (unsigned long)ri->ret_addr;
469 recycle_rp_inst(ri, &empty_rp);
470
471 if (orig_ret_address != trampoline_address)
472 /*
473 * This is the real return address. Any other
474 * instances associated with this task are for
475 * other calls deeper on the call stack
476 */
477 break;
478 }
479
480 kretprobe_assert(ri, orig_ret_address, trampoline_address);
481 kretprobe_hash_unlock(current, &flags);
482
483 hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
484 hlist_del(&ri->hlist);
485 kfree(ri);
486 }
487
488 return (void *)orig_ret_address;
489}
490
491void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
492 struct pt_regs *regs)
493{
494 ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
495
496 /* Replace the return addr with trampoline addr. */
497 regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
498}
499
500int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
501{
502 struct jprobe *jp = container_of(p, struct jprobe, kp);
503 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
504 long sp_addr = regs->ARM_sp;
505 long cpsr;
506
507 kcb->jprobe_saved_regs = *regs;
508 memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
509 regs->ARM_pc = (long)jp->entry;
510
511 cpsr = regs->ARM_cpsr | PSR_I_BIT;
512#ifdef CONFIG_THUMB2_KERNEL
513 /* Set correct Thumb state in cpsr */
514 if (regs->ARM_pc & 1)
515 cpsr |= PSR_T_BIT;
516 else
517 cpsr &= ~PSR_T_BIT;
518#endif
519 regs->ARM_cpsr = cpsr;
520
521 preempt_disable();
522 return 1;
523}
524
525void __kprobes jprobe_return(void)
526{
527 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
528
529 __asm__ __volatile__ (
530 /*
531 * Setup an empty pt_regs. Fill SP and PC fields as
532 * they're needed by longjmp_break_handler.
533 *
534 * We allocate some slack between the original SP and start of
535 * our fabricated regs. To be precise we want to have worst case
536 * covered which is STMFD with all 16 regs so we allocate 2 *
537 * sizeof(struct_pt_regs)).
538 *
539 * This is to prevent any simulated instruction from writing
540 * over the regs when they are accessing the stack.
541 */
542#ifdef CONFIG_THUMB2_KERNEL
543 "sub r0, %0, %1 \n\t"
544 "mov sp, r0 \n\t"
545#else
546 "sub sp, %0, %1 \n\t"
547#endif
548 "ldr r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
549 "str %0, [sp, %2] \n\t"
550 "str r0, [sp, %3] \n\t"
551 "mov r0, sp \n\t"
552 "bl kprobe_handler \n\t"
553
554 /*
555 * Return to the context saved by setjmp_pre_handler
556 * and restored by longjmp_break_handler.
557 */
558#ifdef CONFIG_THUMB2_KERNEL
559 "ldr lr, [sp, %2] \n\t" /* lr = saved sp */
560 "ldrd r0, r1, [sp, %5] \n\t" /* r0,r1 = saved lr,pc */
561 "ldr r2, [sp, %4] \n\t" /* r2 = saved psr */
562 "stmdb lr!, {r0, r1, r2} \n\t" /* push saved lr and */
563 /* rfe context */
564 "ldmia sp, {r0 - r12} \n\t"
565 "mov sp, lr \n\t"
566 "ldr lr, [sp], #4 \n\t"
567 "rfeia sp! \n\t"
568#else
569 "ldr r0, [sp, %4] \n\t"
570 "msr cpsr_cxsf, r0 \n\t"
571 "ldmia sp, {r0 - pc} \n\t"
572#endif
573 :
574 : "r" (kcb->jprobe_saved_regs.ARM_sp),
575 "I" (sizeof(struct pt_regs) * 2),
576 "J" (offsetof(struct pt_regs, ARM_sp)),
577 "J" (offsetof(struct pt_regs, ARM_pc)),
578 "J" (offsetof(struct pt_regs, ARM_cpsr)),
579 "J" (offsetof(struct pt_regs, ARM_lr))
580 : "memory", "cc");
581}
582
583int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
584{
585 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
586 long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
587 long orig_sp = regs->ARM_sp;
588 struct jprobe *jp = container_of(p, struct jprobe, kp);
589
590 if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
591 if (orig_sp != stack_addr) {
592 struct pt_regs *saved_regs =
593 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
594 printk("current sp %lx does not match saved sp %lx\n",
595 orig_sp, stack_addr);
596 printk("Saved registers for jprobe %p\n", jp);
597 show_regs(saved_regs);
598 printk("Current registers\n");
599 show_regs(regs);
600 BUG();
601 }
602 *regs = kcb->jprobe_saved_regs;
603 memcpy((void *)stack_addr, kcb->jprobes_stack,
604 MIN_STACK_SIZE(stack_addr));
605 preempt_enable_no_resched();
606 return 1;
607 }
608 return 0;
609}
610
611int __kprobes arch_trampoline_kprobe(struct kprobe *p)
612{
613 return 0;
614}
615
616#ifdef CONFIG_THUMB2_KERNEL
617
618static struct undef_hook kprobes_thumb16_break_hook = {
619 .instr_mask = 0xffff,
620 .instr_val = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
621 .cpsr_mask = MODE_MASK,
622 .cpsr_val = SVC_MODE,
623 .fn = kprobe_trap_handler,
624};
625
626static struct undef_hook kprobes_thumb32_break_hook = {
627 .instr_mask = 0xffffffff,
628 .instr_val = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
629 .cpsr_mask = MODE_MASK,
630 .cpsr_val = SVC_MODE,
631 .fn = kprobe_trap_handler,
632};
633
634#else /* !CONFIG_THUMB2_KERNEL */
635
636static struct undef_hook kprobes_arm_break_hook = {
637 .instr_mask = 0x0fffffff,
638 .instr_val = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
639 .cpsr_mask = MODE_MASK,
640 .cpsr_val = SVC_MODE,
641 .fn = kprobe_trap_handler,
642};
643
644#endif /* !CONFIG_THUMB2_KERNEL */
645
646int __init arch_init_kprobes()
647{
648 arm_kprobe_decode_init();
649#ifdef CONFIG_THUMB2_KERNEL
650 register_undef_hook(&kprobes_thumb16_break_hook);
651 register_undef_hook(&kprobes_thumb32_break_hook);
652#else
653 register_undef_hook(&kprobes_arm_break_hook);
654#endif
655 return 0;
656}