Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
[linux-3.10.git] / arch / arm / kernel / kprobes.c
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 #include "patch.h"
33
34 #define MIN_STACK_SIZE(addr)                            \
35         min((unsigned long)MAX_STACK_SIZE,              \
36             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
37
38 #define flush_insns(addr, size)                         \
39         flush_icache_range((unsigned long)(addr),       \
40                            (unsigned long)(addr) +      \
41                            (size))
42
43 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
44 #define JPROBE_MAGIC_ADDR               0xffffffff
45
46 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
47 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
48
49
50 int __kprobes arch_prepare_kprobe(struct kprobe *p)
51 {
52         kprobe_opcode_t insn;
53         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
54         unsigned long addr = (unsigned long)p->addr;
55         bool thumb;
56         kprobe_decode_insn_t *decode_insn;
57         int is;
58
59         if (in_exception_text(addr))
60                 return -EINVAL;
61
62 #ifdef CONFIG_THUMB2_KERNEL
63         thumb = true;
64         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
65         insn = ((u16 *)addr)[0];
66         if (is_wide_instruction(insn)) {
67                 insn <<= 16;
68                 insn |= ((u16 *)addr)[1];
69                 decode_insn = thumb32_kprobe_decode_insn;
70         } else
71                 decode_insn = thumb16_kprobe_decode_insn;
72 #else /* !CONFIG_THUMB2_KERNEL */
73         thumb = false;
74         if (addr & 0x3)
75                 return -EINVAL;
76         insn = *p->addr;
77         decode_insn = arm_kprobe_decode_insn;
78 #endif
79
80         p->opcode = insn;
81         p->ainsn.insn = tmp_insn;
82
83         switch ((*decode_insn)(insn, &p->ainsn)) {
84         case INSN_REJECTED:     /* not supported */
85                 return -EINVAL;
86
87         case INSN_GOOD:         /* instruction uses slot */
88                 p->ainsn.insn = get_insn_slot();
89                 if (!p->ainsn.insn)
90                         return -ENOMEM;
91                 for (is = 0; is < MAX_INSN_SIZE; ++is)
92                         p->ainsn.insn[is] = tmp_insn[is];
93                 flush_insns(p->ainsn.insn,
94                                 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
95                 p->ainsn.insn_fn = (kprobe_insn_fn_t *)
96                                         ((uintptr_t)p->ainsn.insn | thumb);
97                 break;
98
99         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
100                 p->ainsn.insn = NULL;
101                 break;
102         }
103
104         return 0;
105 }
106
107 void __kprobes arch_arm_kprobe(struct kprobe *p)
108 {
109         unsigned int brkp;
110         void *addr;
111
112         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
113                 /* Remove any Thumb flag */
114                 addr = (void *)((uintptr_t)p->addr & ~1);
115
116                 if (is_wide_instruction(p->opcode))
117                         brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
118                 else
119                         brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
120         } else {
121                 kprobe_opcode_t insn = p->opcode;
122
123                 addr = p->addr;
124                 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
125
126                 if (insn >= 0xe0000000)
127                         brkp |= 0xe0000000;  /* Unconditional instruction */
128                 else
129                         brkp |= insn & 0xf0000000;  /* Copy condition from insn */
130         }
131
132         patch_text(addr, brkp);
133 }
134
135 /*
136  * The actual disarming is done here on each CPU and synchronized using
137  * stop_machine. This synchronization is necessary on SMP to avoid removing
138  * a probe between the moment the 'Undefined Instruction' exception is raised
139  * and the moment the exception handler reads the faulting instruction from
140  * memory. It is also needed to atomically set the two half-words of a 32-bit
141  * Thumb breakpoint.
142  */
143 int __kprobes __arch_disarm_kprobe(void *p)
144 {
145         struct kprobe *kp = p;
146         void *addr = (void *)((uintptr_t)kp->addr & ~1);
147
148         __patch_text(addr, kp->opcode);
149
150         return 0;
151 }
152
153 void __kprobes arch_disarm_kprobe(struct kprobe *p)
154 {
155         stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
156 }
157
158 void __kprobes arch_remove_kprobe(struct kprobe *p)
159 {
160         if (p->ainsn.insn) {
161                 free_insn_slot(p->ainsn.insn, 0);
162                 p->ainsn.insn = NULL;
163         }
164 }
165
166 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
167 {
168         kcb->prev_kprobe.kp = kprobe_running();
169         kcb->prev_kprobe.status = kcb->kprobe_status;
170 }
171
172 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
173 {
174         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
175         kcb->kprobe_status = kcb->prev_kprobe.status;
176 }
177
178 static void __kprobes set_current_kprobe(struct kprobe *p)
179 {
180         __get_cpu_var(current_kprobe) = p;
181 }
182
183 static void __kprobes
184 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
185 {
186 #ifdef CONFIG_THUMB2_KERNEL
187         regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
188         if (is_wide_instruction(p->opcode))
189                 regs->ARM_pc += 4;
190         else
191                 regs->ARM_pc += 2;
192 #else
193         regs->ARM_pc += 4;
194 #endif
195 }
196
197 static inline void __kprobes
198 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
199 {
200         p->ainsn.insn_singlestep(p, regs);
201 }
202
203 /*
204  * Called with IRQs disabled. IRQs must remain disabled from that point
205  * all the way until processing this kprobe is complete.  The current
206  * kprobes implementation cannot process more than one nested level of
207  * kprobe, and that level is reserved for user kprobe handlers, so we can't
208  * risk encountering a new kprobe in an interrupt handler.
209  */
210 void __kprobes kprobe_handler(struct pt_regs *regs)
211 {
212         struct kprobe *p, *cur;
213         struct kprobe_ctlblk *kcb;
214
215         kcb = get_kprobe_ctlblk();
216         cur = kprobe_running();
217
218 #ifdef CONFIG_THUMB2_KERNEL
219         /*
220          * First look for a probe which was registered using an address with
221          * bit 0 set, this is the usual situation for pointers to Thumb code.
222          * If not found, fallback to looking for one with bit 0 clear.
223          */
224         p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
225         if (!p)
226                 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
227
228 #else /* ! CONFIG_THUMB2_KERNEL */
229         p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
230 #endif
231
232         if (p) {
233                 if (cur) {
234                         /* Kprobe is pending, so we're recursing. */
235                         switch (kcb->kprobe_status) {
236                         case KPROBE_HIT_ACTIVE:
237                         case KPROBE_HIT_SSDONE:
238                                 /* A pre- or post-handler probe got us here. */
239                                 kprobes_inc_nmissed_count(p);
240                                 save_previous_kprobe(kcb);
241                                 set_current_kprobe(p);
242                                 kcb->kprobe_status = KPROBE_REENTER;
243                                 singlestep(p, regs, kcb);
244                                 restore_previous_kprobe(kcb);
245                                 break;
246                         default:
247                                 /* impossible cases */
248                                 BUG();
249                         }
250                 } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
251                         /* Probe hit and conditional execution check ok. */
252                         set_current_kprobe(p);
253                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
254
255                         /*
256                          * If we have no pre-handler or it returned 0, we
257                          * continue with normal processing.  If we have a
258                          * pre-handler and it returned non-zero, it prepped
259                          * for calling the break_handler below on re-entry,
260                          * so get out doing nothing more here.
261                          */
262                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
263                                 kcb->kprobe_status = KPROBE_HIT_SS;
264                                 singlestep(p, regs, kcb);
265                                 if (p->post_handler) {
266                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
267                                         p->post_handler(p, regs, 0);
268                                 }
269                                 reset_current_kprobe();
270                         }
271                 } else {
272                         /*
273                          * Probe hit but conditional execution check failed,
274                          * so just skip the instruction and continue as if
275                          * nothing had happened.
276                          */
277                         singlestep_skip(p, regs);
278                 }
279         } else if (cur) {
280                 /* We probably hit a jprobe.  Call its break handler. */
281                 if (cur->break_handler && cur->break_handler(cur, regs)) {
282                         kcb->kprobe_status = KPROBE_HIT_SS;
283                         singlestep(cur, regs, kcb);
284                         if (cur->post_handler) {
285                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
286                                 cur->post_handler(cur, regs, 0);
287                         }
288                 }
289                 reset_current_kprobe();
290         } else {
291                 /*
292                  * The probe was removed and a race is in progress.
293                  * There is nothing we can do about it.  Let's restart
294                  * the instruction.  By the time we can restart, the
295                  * real instruction will be there.
296                  */
297         }
298 }
299
300 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
301 {
302         unsigned long flags;
303         local_irq_save(flags);
304         kprobe_handler(regs);
305         local_irq_restore(flags);
306         return 0;
307 }
308
309 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
310 {
311         struct kprobe *cur = kprobe_running();
312         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
313
314         switch (kcb->kprobe_status) {
315         case KPROBE_HIT_SS:
316         case KPROBE_REENTER:
317                 /*
318                  * We are here because the instruction being single
319                  * stepped caused a page fault. We reset the current
320                  * kprobe and the PC to point back to the probe address
321                  * and allow the page fault handler to continue as a
322                  * normal page fault.
323                  */
324                 regs->ARM_pc = (long)cur->addr;
325                 if (kcb->kprobe_status == KPROBE_REENTER) {
326                         restore_previous_kprobe(kcb);
327                 } else {
328                         reset_current_kprobe();
329                 }
330                 break;
331
332         case KPROBE_HIT_ACTIVE:
333         case KPROBE_HIT_SSDONE:
334                 /*
335                  * We increment the nmissed count for accounting,
336                  * we can also use npre/npostfault count for accounting
337                  * these specific fault cases.
338                  */
339                 kprobes_inc_nmissed_count(cur);
340
341                 /*
342                  * We come here because instructions in the pre/post
343                  * handler caused the page_fault, this could happen
344                  * if handler tries to access user space by
345                  * copy_from_user(), get_user() etc. Let the
346                  * user-specified handler try to fix it.
347                  */
348                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
349                         return 1;
350                 break;
351
352         default:
353                 break;
354         }
355
356         return 0;
357 }
358
359 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
360                                        unsigned long val, void *data)
361 {
362         /*
363          * notify_die() is currently never called on ARM,
364          * so this callback is currently empty.
365          */
366         return NOTIFY_DONE;
367 }
368
369 /*
370  * When a retprobed function returns, trampoline_handler() is called,
371  * calling the kretprobe's handler. We construct a struct pt_regs to
372  * give a view of registers r0-r11 to the user return-handler.  This is
373  * not a complete pt_regs structure, but that should be plenty sufficient
374  * for kretprobe handlers which should normally be interested in r0 only
375  * anyway.
376  */
377 void __naked __kprobes kretprobe_trampoline(void)
378 {
379         __asm__ __volatile__ (
380                 "stmdb  sp!, {r0 - r11}         \n\t"
381                 "mov    r0, sp                  \n\t"
382                 "bl     trampoline_handler      \n\t"
383                 "mov    lr, r0                  \n\t"
384                 "ldmia  sp!, {r0 - r11}         \n\t"
385 #ifdef CONFIG_THUMB2_KERNEL
386                 "bx     lr                      \n\t"
387 #else
388                 "mov    pc, lr                  \n\t"
389 #endif
390                 : : : "memory");
391 }
392
393 /* Called from kretprobe_trampoline */
394 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
395 {
396         struct kretprobe_instance *ri = NULL;
397         struct hlist_head *head, empty_rp;
398         struct hlist_node *tmp;
399         unsigned long flags, orig_ret_address = 0;
400         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
401
402         INIT_HLIST_HEAD(&empty_rp);
403         kretprobe_hash_lock(current, &head, &flags);
404
405         /*
406          * It is possible to have multiple instances associated with a given
407          * task either because multiple functions in the call path have
408          * a return probe installed on them, and/or more than one return
409          * probe was registered for a target function.
410          *
411          * We can handle this because:
412          *     - instances are always inserted at the head of the list
413          *     - when multiple return probes are registered for the same
414          *       function, the first instance's ret_addr will point to the
415          *       real return address, and all the rest will point to
416          *       kretprobe_trampoline
417          */
418         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
419                 if (ri->task != current)
420                         /* another task is sharing our hash bucket */
421                         continue;
422
423                 if (ri->rp && ri->rp->handler) {
424                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
425                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
426                         ri->rp->handler(ri, regs);
427                         __get_cpu_var(current_kprobe) = NULL;
428                 }
429
430                 orig_ret_address = (unsigned long)ri->ret_addr;
431                 recycle_rp_inst(ri, &empty_rp);
432
433                 if (orig_ret_address != trampoline_address)
434                         /*
435                          * This is the real return address. Any other
436                          * instances associated with this task are for
437                          * other calls deeper on the call stack
438                          */
439                         break;
440         }
441
442         kretprobe_assert(ri, orig_ret_address, trampoline_address);
443         kretprobe_hash_unlock(current, &flags);
444
445         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
446                 hlist_del(&ri->hlist);
447                 kfree(ri);
448         }
449
450         return (void *)orig_ret_address;
451 }
452
453 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
454                                       struct pt_regs *regs)
455 {
456         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
457
458         /* Replace the return addr with trampoline addr. */
459         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
460 }
461
462 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
463 {
464         struct jprobe *jp = container_of(p, struct jprobe, kp);
465         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
466         long sp_addr = regs->ARM_sp;
467         long cpsr;
468
469         kcb->jprobe_saved_regs = *regs;
470         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
471         regs->ARM_pc = (long)jp->entry;
472
473         cpsr = regs->ARM_cpsr | PSR_I_BIT;
474 #ifdef CONFIG_THUMB2_KERNEL
475         /* Set correct Thumb state in cpsr */
476         if (regs->ARM_pc & 1)
477                 cpsr |= PSR_T_BIT;
478         else
479                 cpsr &= ~PSR_T_BIT;
480 #endif
481         regs->ARM_cpsr = cpsr;
482
483         preempt_disable();
484         return 1;
485 }
486
487 void __kprobes jprobe_return(void)
488 {
489         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
490
491         __asm__ __volatile__ (
492                 /*
493                  * Setup an empty pt_regs. Fill SP and PC fields as
494                  * they're needed by longjmp_break_handler.
495                  *
496                  * We allocate some slack between the original SP and start of
497                  * our fabricated regs. To be precise we want to have worst case
498                  * covered which is STMFD with all 16 regs so we allocate 2 *
499                  * sizeof(struct_pt_regs)).
500                  *
501                  * This is to prevent any simulated instruction from writing
502                  * over the regs when they are accessing the stack.
503                  */
504 #ifdef CONFIG_THUMB2_KERNEL
505                 "sub    r0, %0, %1              \n\t"
506                 "mov    sp, r0                  \n\t"
507 #else
508                 "sub    sp, %0, %1              \n\t"
509 #endif
510                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
511                 "str    %0, [sp, %2]            \n\t"
512                 "str    r0, [sp, %3]            \n\t"
513                 "mov    r0, sp                  \n\t"
514                 "bl     kprobe_handler          \n\t"
515
516                 /*
517                  * Return to the context saved by setjmp_pre_handler
518                  * and restored by longjmp_break_handler.
519                  */
520 #ifdef CONFIG_THUMB2_KERNEL
521                 "ldr    lr, [sp, %2]            \n\t" /* lr = saved sp */
522                 "ldrd   r0, r1, [sp, %5]        \n\t" /* r0,r1 = saved lr,pc */
523                 "ldr    r2, [sp, %4]            \n\t" /* r2 = saved psr */
524                 "stmdb  lr!, {r0, r1, r2}       \n\t" /* push saved lr and */
525                                                       /* rfe context */
526                 "ldmia  sp, {r0 - r12}          \n\t"
527                 "mov    sp, lr                  \n\t"
528                 "ldr    lr, [sp], #4            \n\t"
529                 "rfeia  sp!                     \n\t"
530 #else
531                 "ldr    r0, [sp, %4]            \n\t"
532                 "msr    cpsr_cxsf, r0           \n\t"
533                 "ldmia  sp, {r0 - pc}           \n\t"
534 #endif
535                 :
536                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
537                   "I" (sizeof(struct pt_regs) * 2),
538                   "J" (offsetof(struct pt_regs, ARM_sp)),
539                   "J" (offsetof(struct pt_regs, ARM_pc)),
540                   "J" (offsetof(struct pt_regs, ARM_cpsr)),
541                   "J" (offsetof(struct pt_regs, ARM_lr))
542                 : "memory", "cc");
543 }
544
545 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
546 {
547         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
548         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
549         long orig_sp = regs->ARM_sp;
550         struct jprobe *jp = container_of(p, struct jprobe, kp);
551
552         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
553                 if (orig_sp != stack_addr) {
554                         struct pt_regs *saved_regs =
555                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
556                         printk("current sp %lx does not match saved sp %lx\n",
557                                orig_sp, stack_addr);
558                         printk("Saved registers for jprobe %p\n", jp);
559                         show_regs(saved_regs);
560                         printk("Current registers\n");
561                         show_regs(regs);
562                         BUG();
563                 }
564                 *regs = kcb->jprobe_saved_regs;
565                 memcpy((void *)stack_addr, kcb->jprobes_stack,
566                        MIN_STACK_SIZE(stack_addr));
567                 preempt_enable_no_resched();
568                 return 1;
569         }
570         return 0;
571 }
572
573 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
574 {
575         return 0;
576 }
577
578 #ifdef CONFIG_THUMB2_KERNEL
579
580 static struct undef_hook kprobes_thumb16_break_hook = {
581         .instr_mask     = 0xffff,
582         .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
583         .cpsr_mask      = MODE_MASK,
584         .cpsr_val       = SVC_MODE,
585         .fn             = kprobe_trap_handler,
586 };
587
588 static struct undef_hook kprobes_thumb32_break_hook = {
589         .instr_mask     = 0xffffffff,
590         .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
591         .cpsr_mask      = MODE_MASK,
592         .cpsr_val       = SVC_MODE,
593         .fn             = kprobe_trap_handler,
594 };
595
596 #else  /* !CONFIG_THUMB2_KERNEL */
597
598 static struct undef_hook kprobes_arm_break_hook = {
599         .instr_mask     = 0x0fffffff,
600         .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
601         .cpsr_mask      = MODE_MASK,
602         .cpsr_val       = SVC_MODE,
603         .fn             = kprobe_trap_handler,
604 };
605
606 #endif /* !CONFIG_THUMB2_KERNEL */
607
608 int __init arch_init_kprobes()
609 {
610         arm_kprobe_decode_init();
611 #ifdef CONFIG_THUMB2_KERNEL
612         register_undef_hook(&kprobes_thumb16_break_hook);
613         register_undef_hook(&kprobes_thumb32_break_hook);
614 #else
615         register_undef_hook(&kprobes_arm_break_hook);
616 #endif
617         return 0;
618 }