ARM: kprobes: Fix probing of conditionally executed instructions
[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 #define MIN_STACK_SIZE(addr)                            \
32         min((unsigned long)MAX_STACK_SIZE,              \
33             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
34
35 #define flush_insns(addr, cnt)                          \
36         flush_icache_range((unsigned long)(addr),       \
37                            (unsigned long)(addr) +      \
38                            sizeof(kprobe_opcode_t) * (cnt))
39
40 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
41 #define JPROBE_MAGIC_ADDR               0xffffffff
42
43 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
44 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
45
46
47 int __kprobes arch_prepare_kprobe(struct kprobe *p)
48 {
49         kprobe_opcode_t insn;
50         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
51         unsigned long addr = (unsigned long)p->addr;
52         int is;
53
54         if (addr & 0x3 || in_exception_text(addr))
55                 return -EINVAL;
56
57         insn = *p->addr;
58         p->opcode = insn;
59         p->ainsn.insn = tmp_insn;
60
61         switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
62         case INSN_REJECTED:     /* not supported */
63                 return -EINVAL;
64
65         case INSN_GOOD:         /* instruction uses slot */
66                 p->ainsn.insn = get_insn_slot();
67                 if (!p->ainsn.insn)
68                         return -ENOMEM;
69                 for (is = 0; is < MAX_INSN_SIZE; ++is)
70                         p->ainsn.insn[is] = tmp_insn[is];
71                 flush_insns(p->ainsn.insn, MAX_INSN_SIZE);
72                 break;
73
74         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
75                 p->ainsn.insn = NULL;
76                 break;
77         }
78
79         return 0;
80 }
81
82 void __kprobes arch_arm_kprobe(struct kprobe *p)
83 {
84         *p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
85         flush_insns(p->addr, 1);
86 }
87
88 /*
89  * The actual disarming is done here on each CPU and synchronized using
90  * stop_machine. This synchronization is necessary on SMP to avoid removing
91  * a probe between the moment the 'Undefined Instruction' exception is raised
92  * and the moment the exception handler reads the faulting instruction from
93  * memory.
94  */
95 int __kprobes __arch_disarm_kprobe(void *p)
96 {
97         struct kprobe *kp = p;
98         *kp->addr = kp->opcode;
99         flush_insns(kp->addr, 1);
100         return 0;
101 }
102
103 void __kprobes arch_disarm_kprobe(struct kprobe *p)
104 {
105         stop_machine(__arch_disarm_kprobe, p, &cpu_online_map);
106 }
107
108 void __kprobes arch_remove_kprobe(struct kprobe *p)
109 {
110         if (p->ainsn.insn) {
111                 free_insn_slot(p->ainsn.insn, 0);
112                 p->ainsn.insn = NULL;
113         }
114 }
115
116 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
117 {
118         kcb->prev_kprobe.kp = kprobe_running();
119         kcb->prev_kprobe.status = kcb->kprobe_status;
120 }
121
122 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
123 {
124         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
125         kcb->kprobe_status = kcb->prev_kprobe.status;
126 }
127
128 static void __kprobes set_current_kprobe(struct kprobe *p)
129 {
130         __get_cpu_var(current_kprobe) = p;
131 }
132
133 static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
134                                  struct kprobe_ctlblk *kcb)
135 {
136         regs->ARM_pc += 4;
137         if (p->ainsn.insn_check_cc(regs->ARM_cpsr))
138                 p->ainsn.insn_handler(p, regs);
139 }
140
141 /*
142  * Called with IRQs disabled. IRQs must remain disabled from that point
143  * all the way until processing this kprobe is complete.  The current
144  * kprobes implementation cannot process more than one nested level of
145  * kprobe, and that level is reserved for user kprobe handlers, so we can't
146  * risk encountering a new kprobe in an interrupt handler.
147  */
148 void __kprobes kprobe_handler(struct pt_regs *regs)
149 {
150         struct kprobe *p, *cur;
151         struct kprobe_ctlblk *kcb;
152         kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc;
153
154         kcb = get_kprobe_ctlblk();
155         cur = kprobe_running();
156         p = get_kprobe(addr);
157
158         if (p) {
159                 if (cur) {
160                         /* Kprobe is pending, so we're recursing. */
161                         switch (kcb->kprobe_status) {
162                         case KPROBE_HIT_ACTIVE:
163                         case KPROBE_HIT_SSDONE:
164                                 /* A pre- or post-handler probe got us here. */
165                                 kprobes_inc_nmissed_count(p);
166                                 save_previous_kprobe(kcb);
167                                 set_current_kprobe(p);
168                                 kcb->kprobe_status = KPROBE_REENTER;
169                                 singlestep(p, regs, kcb);
170                                 restore_previous_kprobe(kcb);
171                                 break;
172                         default:
173                                 /* impossible cases */
174                                 BUG();
175                         }
176                 } else {
177                         set_current_kprobe(p);
178                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
179
180                         /*
181                          * If we have no pre-handler or it returned 0, we
182                          * continue with normal processing.  If we have a
183                          * pre-handler and it returned non-zero, it prepped
184                          * for calling the break_handler below on re-entry,
185                          * so get out doing nothing more here.
186                          */
187                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
188                                 kcb->kprobe_status = KPROBE_HIT_SS;
189                                 singlestep(p, regs, kcb);
190                                 if (p->post_handler) {
191                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
192                                         p->post_handler(p, regs, 0);
193                                 }
194                                 reset_current_kprobe();
195                         }
196                 }
197         } else if (cur) {
198                 /* We probably hit a jprobe.  Call its break handler. */
199                 if (cur->break_handler && cur->break_handler(cur, regs)) {
200                         kcb->kprobe_status = KPROBE_HIT_SS;
201                         singlestep(cur, regs, kcb);
202                         if (cur->post_handler) {
203                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
204                                 cur->post_handler(cur, regs, 0);
205                         }
206                 }
207                 reset_current_kprobe();
208         } else {
209                 /*
210                  * The probe was removed and a race is in progress.
211                  * There is nothing we can do about it.  Let's restart
212                  * the instruction.  By the time we can restart, the
213                  * real instruction will be there.
214                  */
215         }
216 }
217
218 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
219 {
220         unsigned long flags;
221         local_irq_save(flags);
222         kprobe_handler(regs);
223         local_irq_restore(flags);
224         return 0;
225 }
226
227 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
228 {
229         struct kprobe *cur = kprobe_running();
230         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
231
232         switch (kcb->kprobe_status) {
233         case KPROBE_HIT_SS:
234         case KPROBE_REENTER:
235                 /*
236                  * We are here because the instruction being single
237                  * stepped caused a page fault. We reset the current
238                  * kprobe and the PC to point back to the probe address
239                  * and allow the page fault handler to continue as a
240                  * normal page fault.
241                  */
242                 regs->ARM_pc = (long)cur->addr;
243                 if (kcb->kprobe_status == KPROBE_REENTER) {
244                         restore_previous_kprobe(kcb);
245                 } else {
246                         reset_current_kprobe();
247                 }
248                 break;
249
250         case KPROBE_HIT_ACTIVE:
251         case KPROBE_HIT_SSDONE:
252                 /*
253                  * We increment the nmissed count for accounting,
254                  * we can also use npre/npostfault count for accounting
255                  * these specific fault cases.
256                  */
257                 kprobes_inc_nmissed_count(cur);
258
259                 /*
260                  * We come here because instructions in the pre/post
261                  * handler caused the page_fault, this could happen
262                  * if handler tries to access user space by
263                  * copy_from_user(), get_user() etc. Let the
264                  * user-specified handler try to fix it.
265                  */
266                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
267                         return 1;
268                 break;
269
270         default:
271                 break;
272         }
273
274         return 0;
275 }
276
277 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
278                                        unsigned long val, void *data)
279 {
280         /*
281          * notify_die() is currently never called on ARM,
282          * so this callback is currently empty.
283          */
284         return NOTIFY_DONE;
285 }
286
287 /*
288  * When a retprobed function returns, trampoline_handler() is called,
289  * calling the kretprobe's handler. We construct a struct pt_regs to
290  * give a view of registers r0-r11 to the user return-handler.  This is
291  * not a complete pt_regs structure, but that should be plenty sufficient
292  * for kretprobe handlers which should normally be interested in r0 only
293  * anyway.
294  */
295 void __naked __kprobes kretprobe_trampoline(void)
296 {
297         __asm__ __volatile__ (
298                 "stmdb  sp!, {r0 - r11}         \n\t"
299                 "mov    r0, sp                  \n\t"
300                 "bl     trampoline_handler      \n\t"
301                 "mov    lr, r0                  \n\t"
302                 "ldmia  sp!, {r0 - r11}         \n\t"
303                 "mov    pc, lr                  \n\t"
304                 : : : "memory");
305 }
306
307 /* Called from kretprobe_trampoline */
308 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
309 {
310         struct kretprobe_instance *ri = NULL;
311         struct hlist_head *head, empty_rp;
312         struct hlist_node *node, *tmp;
313         unsigned long flags, orig_ret_address = 0;
314         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
315
316         INIT_HLIST_HEAD(&empty_rp);
317         kretprobe_hash_lock(current, &head, &flags);
318
319         /*
320          * It is possible to have multiple instances associated with a given
321          * task either because multiple functions in the call path have
322          * a return probe installed on them, and/or more than one return
323          * probe was registered for a target function.
324          *
325          * We can handle this because:
326          *     - instances are always inserted at the head of the list
327          *     - when multiple return probes are registered for the same
328          *       function, the first instance's ret_addr will point to the
329          *       real return address, and all the rest will point to
330          *       kretprobe_trampoline
331          */
332         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
333                 if (ri->task != current)
334                         /* another task is sharing our hash bucket */
335                         continue;
336
337                 if (ri->rp && ri->rp->handler) {
338                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
339                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
340                         ri->rp->handler(ri, regs);
341                         __get_cpu_var(current_kprobe) = NULL;
342                 }
343
344                 orig_ret_address = (unsigned long)ri->ret_addr;
345                 recycle_rp_inst(ri, &empty_rp);
346
347                 if (orig_ret_address != trampoline_address)
348                         /*
349                          * This is the real return address. Any other
350                          * instances associated with this task are for
351                          * other calls deeper on the call stack
352                          */
353                         break;
354         }
355
356         kretprobe_assert(ri, orig_ret_address, trampoline_address);
357         kretprobe_hash_unlock(current, &flags);
358
359         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
360                 hlist_del(&ri->hlist);
361                 kfree(ri);
362         }
363
364         return (void *)orig_ret_address;
365 }
366
367 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
368                                       struct pt_regs *regs)
369 {
370         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
371
372         /* Replace the return addr with trampoline addr. */
373         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
374 }
375
376 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
377 {
378         struct jprobe *jp = container_of(p, struct jprobe, kp);
379         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
380         long sp_addr = regs->ARM_sp;
381
382         kcb->jprobe_saved_regs = *regs;
383         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
384         regs->ARM_pc = (long)jp->entry;
385         regs->ARM_cpsr |= PSR_I_BIT;
386         preempt_disable();
387         return 1;
388 }
389
390 void __kprobes jprobe_return(void)
391 {
392         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
393
394         __asm__ __volatile__ (
395                 /*
396                  * Setup an empty pt_regs. Fill SP and PC fields as
397                  * they're needed by longjmp_break_handler.
398                  *
399                  * We allocate some slack between the original SP and start of
400                  * our fabricated regs. To be precise we want to have worst case
401                  * covered which is STMFD with all 16 regs so we allocate 2 *
402                  * sizeof(struct_pt_regs)).
403                  *
404                  * This is to prevent any simulated instruction from writing
405                  * over the regs when they are accessing the stack.
406                  */
407                 "sub    sp, %0, %1              \n\t"
408                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
409                 "str    %0, [sp, %2]            \n\t"
410                 "str    r0, [sp, %3]            \n\t"
411                 "mov    r0, sp                  \n\t"
412                 "bl     kprobe_handler          \n\t"
413
414                 /*
415                  * Return to the context saved by setjmp_pre_handler
416                  * and restored by longjmp_break_handler.
417                  */
418                 "ldr    r0, [sp, %4]            \n\t"
419                 "msr    cpsr_cxsf, r0           \n\t"
420                 "ldmia  sp, {r0 - pc}           \n\t"
421                 :
422                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
423                   "I" (sizeof(struct pt_regs) * 2),
424                   "J" (offsetof(struct pt_regs, ARM_sp)),
425                   "J" (offsetof(struct pt_regs, ARM_pc)),
426                   "J" (offsetof(struct pt_regs, ARM_cpsr))
427                 : "memory", "cc");
428 }
429
430 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
431 {
432         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
433         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
434         long orig_sp = regs->ARM_sp;
435         struct jprobe *jp = container_of(p, struct jprobe, kp);
436
437         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
438                 if (orig_sp != stack_addr) {
439                         struct pt_regs *saved_regs =
440                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
441                         printk("current sp %lx does not match saved sp %lx\n",
442                                orig_sp, stack_addr);
443                         printk("Saved registers for jprobe %p\n", jp);
444                         show_regs(saved_regs);
445                         printk("Current registers\n");
446                         show_regs(regs);
447                         BUG();
448                 }
449                 *regs = kcb->jprobe_saved_regs;
450                 memcpy((void *)stack_addr, kcb->jprobes_stack,
451                        MIN_STACK_SIZE(stack_addr));
452                 preempt_enable_no_resched();
453                 return 1;
454         }
455         return 0;
456 }
457
458 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
459 {
460         return 0;
461 }
462
463 static struct undef_hook kprobes_break_hook = {
464         .instr_mask     = 0xffffffff,
465         .instr_val      = KPROBE_BREAKPOINT_INSTRUCTION,
466         .cpsr_mask      = MODE_MASK,
467         .cpsr_val       = SVC_MODE,
468         .fn             = kprobe_trap_handler,
469 };
470
471 int __init arch_init_kprobes()
472 {
473         arm_kprobe_decode_init();
474         register_undef_hook(&kprobes_break_hook);
475         return 0;
476 }