xref: /linux/arch/powerpc/kernel/kprobes.c (revision 26b0d14106954ae46d2f4f7eec3481828a210f7d)
1 /*
2  *  Kernel Probes (KProbes)
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright (C) IBM Corporation, 2002, 2004
19  *
20  * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
21  *		Probes initial implementation ( includes contributions from
22  *		Rusty Russell).
23  * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
24  *		interface to access function arguments.
25  * 2004-Nov	Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
26  *		for PPC64
27  */
28 
29 #include <linux/kprobes.h>
30 #include <linux/ptrace.h>
31 #include <linux/preempt.h>
32 #include <linux/module.h>
33 #include <linux/kdebug.h>
34 #include <linux/slab.h>
35 #include <asm/cacheflush.h>
36 #include <asm/sstep.h>
37 #include <asm/uaccess.h>
38 
39 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
40 #define MSR_SINGLESTEP	(MSR_DE)
41 #else
42 #define MSR_SINGLESTEP	(MSR_SE)
43 #endif
44 
45 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
46 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
47 
48 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
49 
50 int __kprobes arch_prepare_kprobe(struct kprobe *p)
51 {
52 	int ret = 0;
53 	kprobe_opcode_t insn = *p->addr;
54 
55 	if ((unsigned long)p->addr & 0x03) {
56 		printk("Attempt to register kprobe at an unaligned address\n");
57 		ret = -EINVAL;
58 	} else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
59 		printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
60 		ret = -EINVAL;
61 	}
62 
63 	/* insn must be on a special executable page on ppc64.  This is
64 	 * not explicitly required on ppc32 (right now), but it doesn't hurt */
65 	if (!ret) {
66 		p->ainsn.insn = get_insn_slot();
67 		if (!p->ainsn.insn)
68 			ret = -ENOMEM;
69 	}
70 
71 	if (!ret) {
72 		memcpy(p->ainsn.insn, p->addr,
73 				MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
74 		p->opcode = *p->addr;
75 		flush_icache_range((unsigned long)p->ainsn.insn,
76 			(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
77 	}
78 
79 	p->ainsn.boostable = 0;
80 	return ret;
81 }
82 
83 void __kprobes arch_arm_kprobe(struct kprobe *p)
84 {
85 	*p->addr = BREAKPOINT_INSTRUCTION;
86 	flush_icache_range((unsigned long) p->addr,
87 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
88 }
89 
90 void __kprobes arch_disarm_kprobe(struct kprobe *p)
91 {
92 	*p->addr = p->opcode;
93 	flush_icache_range((unsigned long) p->addr,
94 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
95 }
96 
97 void __kprobes arch_remove_kprobe(struct kprobe *p)
98 {
99 	if (p->ainsn.insn) {
100 		free_insn_slot(p->ainsn.insn, 0);
101 		p->ainsn.insn = NULL;
102 	}
103 }
104 
105 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
106 {
107 	/* We turn off async exceptions to ensure that the single step will
108 	 * be for the instruction we have the kprobe on, if we dont its
109 	 * possible we'd get the single step reported for an exception handler
110 	 * like Decrementer or External Interrupt */
111 	regs->msr &= ~MSR_EE;
112 	regs->msr |= MSR_SINGLESTEP;
113 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
114 	regs->msr &= ~MSR_CE;
115 	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
116 #ifdef CONFIG_PPC_47x
117 	isync();
118 #endif
119 #endif
120 
121 	/*
122 	 * On powerpc we should single step on the original
123 	 * instruction even if the probed insn is a trap
124 	 * variant as values in regs could play a part in
125 	 * if the trap is taken or not
126 	 */
127 	regs->nip = (unsigned long)p->ainsn.insn;
128 }
129 
130 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
131 {
132 	kcb->prev_kprobe.kp = kprobe_running();
133 	kcb->prev_kprobe.status = kcb->kprobe_status;
134 	kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
135 }
136 
137 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
138 {
139 	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
140 	kcb->kprobe_status = kcb->prev_kprobe.status;
141 	kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
142 }
143 
144 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
145 				struct kprobe_ctlblk *kcb)
146 {
147 	__get_cpu_var(current_kprobe) = p;
148 	kcb->kprobe_saved_msr = regs->msr;
149 }
150 
151 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
152 				      struct pt_regs *regs)
153 {
154 	ri->ret_addr = (kprobe_opcode_t *)regs->link;
155 
156 	/* Replace the return addr with trampoline addr */
157 	regs->link = (unsigned long)kretprobe_trampoline;
158 }
159 
160 static int __kprobes kprobe_handler(struct pt_regs *regs)
161 {
162 	struct kprobe *p;
163 	int ret = 0;
164 	unsigned int *addr = (unsigned int *)regs->nip;
165 	struct kprobe_ctlblk *kcb;
166 
167 	/*
168 	 * We don't want to be preempted for the entire
169 	 * duration of kprobe processing
170 	 */
171 	preempt_disable();
172 	kcb = get_kprobe_ctlblk();
173 
174 	/* Check we're not actually recursing */
175 	if (kprobe_running()) {
176 		p = get_kprobe(addr);
177 		if (p) {
178 			kprobe_opcode_t insn = *p->ainsn.insn;
179 			if (kcb->kprobe_status == KPROBE_HIT_SS &&
180 					is_trap(insn)) {
181 				/* Turn off 'trace' bits */
182 				regs->msr &= ~MSR_SINGLESTEP;
183 				regs->msr |= kcb->kprobe_saved_msr;
184 				goto no_kprobe;
185 			}
186 			/* We have reentered the kprobe_handler(), since
187 			 * another probe was hit while within the handler.
188 			 * We here save the original kprobes variables and
189 			 * just single step on the instruction of the new probe
190 			 * without calling any user handlers.
191 			 */
192 			save_previous_kprobe(kcb);
193 			set_current_kprobe(p, regs, kcb);
194 			kcb->kprobe_saved_msr = regs->msr;
195 			kprobes_inc_nmissed_count(p);
196 			prepare_singlestep(p, regs);
197 			kcb->kprobe_status = KPROBE_REENTER;
198 			return 1;
199 		} else {
200 			if (*addr != BREAKPOINT_INSTRUCTION) {
201 				/* If trap variant, then it belongs not to us */
202 				kprobe_opcode_t cur_insn = *addr;
203 				if (is_trap(cur_insn))
204 		       			goto no_kprobe;
205 				/* The breakpoint instruction was removed by
206 				 * another cpu right after we hit, no further
207 				 * handling of this interrupt is appropriate
208 				 */
209 				ret = 1;
210 				goto no_kprobe;
211 			}
212 			p = __get_cpu_var(current_kprobe);
213 			if (p->break_handler && p->break_handler(p, regs)) {
214 				goto ss_probe;
215 			}
216 		}
217 		goto no_kprobe;
218 	}
219 
220 	p = get_kprobe(addr);
221 	if (!p) {
222 		if (*addr != BREAKPOINT_INSTRUCTION) {
223 			/*
224 			 * PowerPC has multiple variants of the "trap"
225 			 * instruction. If the current instruction is a
226 			 * trap variant, it could belong to someone else
227 			 */
228 			kprobe_opcode_t cur_insn = *addr;
229 			if (is_trap(cur_insn))
230 		       		goto no_kprobe;
231 			/*
232 			 * The breakpoint instruction was removed right
233 			 * after we hit it.  Another cpu has removed
234 			 * either a probepoint or a debugger breakpoint
235 			 * at this address.  In either case, no further
236 			 * handling of this interrupt is appropriate.
237 			 */
238 			ret = 1;
239 		}
240 		/* Not one of ours: let kernel handle it */
241 		goto no_kprobe;
242 	}
243 
244 	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
245 	set_current_kprobe(p, regs, kcb);
246 	if (p->pre_handler && p->pre_handler(p, regs))
247 		/* handler has already set things up, so skip ss setup */
248 		return 1;
249 
250 ss_probe:
251 	if (p->ainsn.boostable >= 0) {
252 		unsigned int insn = *p->ainsn.insn;
253 
254 		/* regs->nip is also adjusted if emulate_step returns 1 */
255 		ret = emulate_step(regs, insn);
256 		if (ret > 0) {
257 			/*
258 			 * Once this instruction has been boosted
259 			 * successfully, set the boostable flag
260 			 */
261 			if (unlikely(p->ainsn.boostable == 0))
262 				p->ainsn.boostable = 1;
263 
264 			if (p->post_handler)
265 				p->post_handler(p, regs, 0);
266 
267 			kcb->kprobe_status = KPROBE_HIT_SSDONE;
268 			reset_current_kprobe();
269 			preempt_enable_no_resched();
270 			return 1;
271 		} else if (ret < 0) {
272 			/*
273 			 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
274 			 * So, we should never get here... but, its still
275 			 * good to catch them, just in case...
276 			 */
277 			printk("Can't step on instruction %x\n", insn);
278 			BUG();
279 		} else if (ret == 0)
280 			/* This instruction can't be boosted */
281 			p->ainsn.boostable = -1;
282 	}
283 	prepare_singlestep(p, regs);
284 	kcb->kprobe_status = KPROBE_HIT_SS;
285 	return 1;
286 
287 no_kprobe:
288 	preempt_enable_no_resched();
289 	return ret;
290 }
291 
292 /*
293  * Function return probe trampoline:
294  * 	- init_kprobes() establishes a probepoint here
295  * 	- When the probed function returns, this probe
296  * 		causes the handlers to fire
297  */
298 static void __used kretprobe_trampoline_holder(void)
299 {
300 	asm volatile(".global kretprobe_trampoline\n"
301 			"kretprobe_trampoline:\n"
302 			"nop\n");
303 }
304 
305 /*
306  * Called when the probe at kretprobe trampoline is hit
307  */
308 static int __kprobes trampoline_probe_handler(struct kprobe *p,
309 						struct pt_regs *regs)
310 {
311 	struct kretprobe_instance *ri = NULL;
312 	struct hlist_head *head, empty_rp;
313 	struct hlist_node *node, *tmp;
314 	unsigned long flags, orig_ret_address = 0;
315 	unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
316 
317 	INIT_HLIST_HEAD(&empty_rp);
318 	kretprobe_hash_lock(current, &head, &flags);
319 
320 	/*
321 	 * It is possible to have multiple instances associated with a given
322 	 * task either because an multiple functions in the call path
323 	 * have a return probe installed on them, and/or more than one return
324 	 * return probe was registered for a target function.
325 	 *
326 	 * We can handle this because:
327 	 *     - instances are always inserted at the head of the list
328 	 *     - when multiple return probes are registered for the same
329 	 *       function, the first instance's ret_addr will point to the
330 	 *       real return address, and all the rest will point to
331 	 *       kretprobe_trampoline
332 	 */
333 	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
334 		if (ri->task != current)
335 			/* another task is sharing our hash bucket */
336 			continue;
337 
338 		if (ri->rp && ri->rp->handler)
339 			ri->rp->handler(ri, regs);
340 
341 		orig_ret_address = (unsigned long)ri->ret_addr;
342 		recycle_rp_inst(ri, &empty_rp);
343 
344 		if (orig_ret_address != trampoline_address)
345 			/*
346 			 * This is the real return address. Any other
347 			 * instances associated with this task are for
348 			 * other calls deeper on the call stack
349 			 */
350 			break;
351 	}
352 
353 	kretprobe_assert(ri, orig_ret_address, trampoline_address);
354 	regs->nip = orig_ret_address;
355 
356 	reset_current_kprobe();
357 	kretprobe_hash_unlock(current, &flags);
358 	preempt_enable_no_resched();
359 
360 	hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
361 		hlist_del(&ri->hlist);
362 		kfree(ri);
363 	}
364 	/*
365 	 * By returning a non-zero value, we are telling
366 	 * kprobe_handler() that we don't want the post_handler
367 	 * to run (and have re-enabled preemption)
368 	 */
369 	return 1;
370 }
371 
372 /*
373  * Called after single-stepping.  p->addr is the address of the
374  * instruction whose first byte has been replaced by the "breakpoint"
375  * instruction.  To avoid the SMP problems that can occur when we
376  * temporarily put back the original opcode to single-step, we
377  * single-stepped a copy of the instruction.  The address of this
378  * copy is p->ainsn.insn.
379  */
380 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
381 {
382 	struct kprobe *cur = kprobe_running();
383 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
384 
385 	if (!cur)
386 		return 0;
387 
388 	/* make sure we got here for instruction we have a kprobe on */
389 	if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
390 		return 0;
391 
392 	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
393 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
394 		cur->post_handler(cur, regs, 0);
395 	}
396 
397 	/* Adjust nip to after the single-stepped instruction */
398 	regs->nip = (unsigned long)cur->addr + 4;
399 	regs->msr |= kcb->kprobe_saved_msr;
400 
401 	/*Restore back the original saved kprobes variables and continue. */
402 	if (kcb->kprobe_status == KPROBE_REENTER) {
403 		restore_previous_kprobe(kcb);
404 		goto out;
405 	}
406 	reset_current_kprobe();
407 out:
408 	preempt_enable_no_resched();
409 
410 	/*
411 	 * if somebody else is singlestepping across a probe point, msr
412 	 * will have DE/SE set, in which case, continue the remaining processing
413 	 * of do_debug, as if this is not a probe hit.
414 	 */
415 	if (regs->msr & MSR_SINGLESTEP)
416 		return 0;
417 
418 	return 1;
419 }
420 
421 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
422 {
423 	struct kprobe *cur = kprobe_running();
424 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
425 	const struct exception_table_entry *entry;
426 
427 	switch(kcb->kprobe_status) {
428 	case KPROBE_HIT_SS:
429 	case KPROBE_REENTER:
430 		/*
431 		 * We are here because the instruction being single
432 		 * stepped caused a page fault. We reset the current
433 		 * kprobe and the nip points back to the probe address
434 		 * and allow the page fault handler to continue as a
435 		 * normal page fault.
436 		 */
437 		regs->nip = (unsigned long)cur->addr;
438 		regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
439 		regs->msr |= kcb->kprobe_saved_msr;
440 		if (kcb->kprobe_status == KPROBE_REENTER)
441 			restore_previous_kprobe(kcb);
442 		else
443 			reset_current_kprobe();
444 		preempt_enable_no_resched();
445 		break;
446 	case KPROBE_HIT_ACTIVE:
447 	case KPROBE_HIT_SSDONE:
448 		/*
449 		 * We increment the nmissed count for accounting,
450 		 * we can also use npre/npostfault count for accouting
451 		 * these specific fault cases.
452 		 */
453 		kprobes_inc_nmissed_count(cur);
454 
455 		/*
456 		 * We come here because instructions in the pre/post
457 		 * handler caused the page_fault, this could happen
458 		 * if handler tries to access user space by
459 		 * copy_from_user(), get_user() etc. Let the
460 		 * user-specified handler try to fix it first.
461 		 */
462 		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
463 			return 1;
464 
465 		/*
466 		 * In case the user-specified fault handler returned
467 		 * zero, try to fix up.
468 		 */
469 		if ((entry = search_exception_tables(regs->nip)) != NULL) {
470 			regs->nip = entry->fixup;
471 			return 1;
472 		}
473 
474 		/*
475 		 * fixup_exception() could not handle it,
476 		 * Let do_page_fault() fix it.
477 		 */
478 		break;
479 	default:
480 		break;
481 	}
482 	return 0;
483 }
484 
485 /*
486  * Wrapper routine to for handling exceptions.
487  */
488 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
489 				       unsigned long val, void *data)
490 {
491 	struct die_args *args = (struct die_args *)data;
492 	int ret = NOTIFY_DONE;
493 
494 	if (args->regs && user_mode(args->regs))
495 		return ret;
496 
497 	switch (val) {
498 	case DIE_BPT:
499 		if (kprobe_handler(args->regs))
500 			ret = NOTIFY_STOP;
501 		break;
502 	case DIE_SSTEP:
503 		if (post_kprobe_handler(args->regs))
504 			ret = NOTIFY_STOP;
505 		break;
506 	default:
507 		break;
508 	}
509 	return ret;
510 }
511 
512 #ifdef CONFIG_PPC64
513 unsigned long arch_deref_entry_point(void *entry)
514 {
515 	return ((func_descr_t *)entry)->entry;
516 }
517 #endif
518 
519 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
520 {
521 	struct jprobe *jp = container_of(p, struct jprobe, kp);
522 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
523 
524 	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
525 
526 	/* setup return addr to the jprobe handler routine */
527 	regs->nip = arch_deref_entry_point(jp->entry);
528 #ifdef CONFIG_PPC64
529 	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
530 #endif
531 
532 	return 1;
533 }
534 
535 void __used __kprobes jprobe_return(void)
536 {
537 	asm volatile("trap" ::: "memory");
538 }
539 
540 static void __used __kprobes jprobe_return_end(void)
541 {
542 };
543 
544 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
545 {
546 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
547 
548 	/*
549 	 * FIXME - we should ideally be validating that we got here 'cos
550 	 * of the "trap" in jprobe_return() above, before restoring the
551 	 * saved regs...
552 	 */
553 	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
554 	preempt_enable_no_resched();
555 	return 1;
556 }
557 
558 static struct kprobe trampoline_p = {
559 	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
560 	.pre_handler = trampoline_probe_handler
561 };
562 
563 int __init arch_init_kprobes(void)
564 {
565 	return register_kprobe(&trampoline_p);
566 }
567 
568 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
569 {
570 	if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
571 		return 1;
572 
573 	return 0;
574 }
575