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