xref: /linux/arch/powerpc/kernel/kprobes.c (revision 14b42963f64b98ab61fa9723c03d71aa5ef4f862)
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 <asm/cacheflush.h>
34 #include <asm/kdebug.h>
35 #include <asm/sstep.h>
36 #include <asm/uaccess.h>
37 
38 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
39 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
40 
41 int __kprobes arch_prepare_kprobe(struct kprobe *p)
42 {
43 	int ret = 0;
44 	kprobe_opcode_t insn = *p->addr;
45 
46 	if ((unsigned long)p->addr & 0x03) {
47 		printk("Attempt to register kprobe at an unaligned address\n");
48 		ret = -EINVAL;
49 	} else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
50 		printk("Cannot register a kprobe on rfid or mtmsrd\n");
51 		ret = -EINVAL;
52 	}
53 
54 	/* insn must be on a special executable page on ppc64 */
55 	if (!ret) {
56 		p->ainsn.insn = get_insn_slot();
57 		if (!p->ainsn.insn)
58 			ret = -ENOMEM;
59 	}
60 
61 	if (!ret) {
62 		memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
63 		p->opcode = *p->addr;
64 	}
65 
66 	return ret;
67 }
68 
69 void __kprobes arch_arm_kprobe(struct kprobe *p)
70 {
71 	*p->addr = BREAKPOINT_INSTRUCTION;
72 	flush_icache_range((unsigned long) p->addr,
73 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
74 }
75 
76 void __kprobes arch_disarm_kprobe(struct kprobe *p)
77 {
78 	*p->addr = p->opcode;
79 	flush_icache_range((unsigned long) p->addr,
80 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
81 }
82 
83 void __kprobes arch_remove_kprobe(struct kprobe *p)
84 {
85 	mutex_lock(&kprobe_mutex);
86 	free_insn_slot(p->ainsn.insn);
87 	mutex_unlock(&kprobe_mutex);
88 }
89 
90 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
91 {
92 	regs->msr |= MSR_SE;
93 
94 	/*
95 	 * On powerpc we should single step on the original
96 	 * instruction even if the probed insn is a trap
97 	 * variant as values in regs could play a part in
98 	 * if the trap is taken or not
99 	 */
100 	regs->nip = (unsigned long)p->ainsn.insn;
101 }
102 
103 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
104 {
105 	kcb->prev_kprobe.kp = kprobe_running();
106 	kcb->prev_kprobe.status = kcb->kprobe_status;
107 	kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
108 }
109 
110 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
111 {
112 	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
113 	kcb->kprobe_status = kcb->prev_kprobe.status;
114 	kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
115 }
116 
117 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
118 				struct kprobe_ctlblk *kcb)
119 {
120 	__get_cpu_var(current_kprobe) = p;
121 	kcb->kprobe_saved_msr = regs->msr;
122 }
123 
124 /* Called with kretprobe_lock held */
125 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
126 				      struct pt_regs *regs)
127 {
128 	struct kretprobe_instance *ri;
129 
130 	if ((ri = get_free_rp_inst(rp)) != NULL) {
131 		ri->rp = rp;
132 		ri->task = current;
133 		ri->ret_addr = (kprobe_opcode_t *)regs->link;
134 
135 		/* Replace the return addr with trampoline addr */
136 		regs->link = (unsigned long)kretprobe_trampoline;
137 		add_rp_inst(ri);
138 	} else {
139 		rp->nmissed++;
140 	}
141 }
142 
143 static 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 				regs->msr &= ~MSR_SE;
165 				regs->msr |= kcb->kprobe_saved_msr;
166 				goto no_kprobe;
167 			}
168 			/* We have reentered the kprobe_handler(), since
169 			 * another probe was hit while within the handler.
170 			 * We here save the original kprobes variables and
171 			 * just single step on the instruction of the new probe
172 			 * without calling any user handlers.
173 			 */
174 			save_previous_kprobe(kcb);
175 			set_current_kprobe(p, regs, kcb);
176 			kcb->kprobe_saved_msr = regs->msr;
177 			kprobes_inc_nmissed_count(p);
178 			prepare_singlestep(p, regs);
179 			kcb->kprobe_status = KPROBE_REENTER;
180 			return 1;
181 		} else {
182 			if (*addr != BREAKPOINT_INSTRUCTION) {
183 				/* If trap variant, then it belongs not to us */
184 				kprobe_opcode_t cur_insn = *addr;
185 				if (is_trap(cur_insn))
186 		       			goto no_kprobe;
187 				/* The breakpoint instruction was removed by
188 				 * another cpu right after we hit, no further
189 				 * handling of this interrupt is appropriate
190 				 */
191 				ret = 1;
192 				goto no_kprobe;
193 			}
194 			p = __get_cpu_var(current_kprobe);
195 			if (p->break_handler && p->break_handler(p, regs)) {
196 				goto ss_probe;
197 			}
198 		}
199 		goto no_kprobe;
200 	}
201 
202 	p = get_kprobe(addr);
203 	if (!p) {
204 		if (*addr != BREAKPOINT_INSTRUCTION) {
205 			/*
206 			 * PowerPC has multiple variants of the "trap"
207 			 * instruction. If the current instruction is a
208 			 * trap variant, it could belong to someone else
209 			 */
210 			kprobe_opcode_t cur_insn = *addr;
211 			if (is_trap(cur_insn))
212 		       		goto no_kprobe;
213 			/*
214 			 * The breakpoint instruction was removed right
215 			 * after we hit it.  Another cpu has removed
216 			 * either a probepoint or a debugger breakpoint
217 			 * at this address.  In either case, no further
218 			 * handling of this interrupt is appropriate.
219 			 */
220 			ret = 1;
221 		}
222 		/* Not one of ours: let kernel handle it */
223 		goto no_kprobe;
224 	}
225 
226 	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
227 	set_current_kprobe(p, regs, kcb);
228 	if (p->pre_handler && p->pre_handler(p, regs))
229 		/* handler has already set things up, so skip ss setup */
230 		return 1;
231 
232 ss_probe:
233 	prepare_singlestep(p, regs);
234 	kcb->kprobe_status = KPROBE_HIT_SS;
235 	return 1;
236 
237 no_kprobe:
238 	preempt_enable_no_resched();
239 	return ret;
240 }
241 
242 /*
243  * Function return probe trampoline:
244  * 	- init_kprobes() establishes a probepoint here
245  * 	- When the probed function returns, this probe
246  * 		causes the handlers to fire
247  */
248 void kretprobe_trampoline_holder(void)
249 {
250 	asm volatile(".global kretprobe_trampoline\n"
251 			"kretprobe_trampoline:\n"
252 			"nop\n");
253 }
254 
255 /*
256  * Called when the probe at kretprobe trampoline is hit
257  */
258 int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
259 {
260         struct kretprobe_instance *ri = NULL;
261         struct hlist_head *head;
262         struct hlist_node *node, *tmp;
263 	unsigned long flags, orig_ret_address = 0;
264 	unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
265 
266 	spin_lock_irqsave(&kretprobe_lock, flags);
267         head = kretprobe_inst_table_head(current);
268 
269 	/*
270 	 * It is possible to have multiple instances associated with a given
271 	 * task either because an multiple functions in the call path
272 	 * have a return probe installed on them, and/or more then one return
273 	 * return probe was registered for a target function.
274 	 *
275 	 * We can handle this because:
276 	 *     - instances are always inserted at the head of the list
277 	 *     - when multiple return probes are registered for the same
278          *       function, the first instance's ret_addr will point to the
279 	 *       real return address, and all the rest will point to
280 	 *       kretprobe_trampoline
281 	 */
282 	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
283                 if (ri->task != current)
284 			/* another task is sharing our hash bucket */
285                         continue;
286 
287 		if (ri->rp && ri->rp->handler)
288 			ri->rp->handler(ri, regs);
289 
290 		orig_ret_address = (unsigned long)ri->ret_addr;
291 		recycle_rp_inst(ri);
292 
293 		if (orig_ret_address != trampoline_address)
294 			/*
295 			 * This is the real return address. Any other
296 			 * instances associated with this task are for
297 			 * other calls deeper on the call stack
298 			 */
299 			break;
300 	}
301 
302 	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
303 	regs->nip = orig_ret_address;
304 
305 	reset_current_kprobe();
306 	spin_unlock_irqrestore(&kretprobe_lock, flags);
307 	preempt_enable_no_resched();
308 
309         /*
310          * By returning a non-zero value, we are telling
311          * kprobe_handler() that we don't want the post_handler
312          * to run (and have re-enabled preemption)
313          */
314         return 1;
315 }
316 
317 /*
318  * Called after single-stepping.  p->addr is the address of the
319  * instruction whose first byte has been replaced by the "breakpoint"
320  * instruction.  To avoid the SMP problems that can occur when we
321  * temporarily put back the original opcode to single-step, we
322  * single-stepped a copy of the instruction.  The address of this
323  * copy is p->ainsn.insn.
324  */
325 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
326 {
327 	int ret;
328 	unsigned int insn = *p->ainsn.insn;
329 
330 	regs->nip = (unsigned long)p->addr;
331 	ret = emulate_step(regs, insn);
332 	if (ret == 0)
333 		regs->nip = (unsigned long)p->addr + 4;
334 }
335 
336 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
337 {
338 	struct kprobe *cur = kprobe_running();
339 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
340 
341 	if (!cur)
342 		return 0;
343 
344 	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
345 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
346 		cur->post_handler(cur, regs, 0);
347 	}
348 
349 	resume_execution(cur, regs);
350 	regs->msr |= kcb->kprobe_saved_msr;
351 
352 	/*Restore back the original saved kprobes variables and continue. */
353 	if (kcb->kprobe_status == KPROBE_REENTER) {
354 		restore_previous_kprobe(kcb);
355 		goto out;
356 	}
357 	reset_current_kprobe();
358 out:
359 	preempt_enable_no_resched();
360 
361 	/*
362 	 * if somebody else is singlestepping across a probe point, msr
363 	 * will have SE set, in which case, continue the remaining processing
364 	 * of do_debug, as if this is not a probe hit.
365 	 */
366 	if (regs->msr & MSR_SE)
367 		return 0;
368 
369 	return 1;
370 }
371 
372 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
373 {
374 	struct kprobe *cur = kprobe_running();
375 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
376 	const struct exception_table_entry *entry;
377 
378 	switch(kcb->kprobe_status) {
379 	case KPROBE_HIT_SS:
380 	case KPROBE_REENTER:
381 		/*
382 		 * We are here because the instruction being single
383 		 * stepped caused a page fault. We reset the current
384 		 * kprobe and the nip points back to the probe address
385 		 * and allow the page fault handler to continue as a
386 		 * normal page fault.
387 		 */
388 		regs->nip = (unsigned long)cur->addr;
389 		regs->msr &= ~MSR_SE;
390 		regs->msr |= kcb->kprobe_saved_msr;
391 		if (kcb->kprobe_status == KPROBE_REENTER)
392 			restore_previous_kprobe(kcb);
393 		else
394 			reset_current_kprobe();
395 		preempt_enable_no_resched();
396 		break;
397 	case KPROBE_HIT_ACTIVE:
398 	case KPROBE_HIT_SSDONE:
399 		/*
400 		 * We increment the nmissed count for accounting,
401 		 * we can also use npre/npostfault count for accouting
402 		 * these specific fault cases.
403 		 */
404 		kprobes_inc_nmissed_count(cur);
405 
406 		/*
407 		 * We come here because instructions in the pre/post
408 		 * handler caused the page_fault, this could happen
409 		 * if handler tries to access user space by
410 		 * copy_from_user(), get_user() etc. Let the
411 		 * user-specified handler try to fix it first.
412 		 */
413 		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
414 			return 1;
415 
416 		/*
417 		 * In case the user-specified fault handler returned
418 		 * zero, try to fix up.
419 		 */
420 		if ((entry = search_exception_tables(regs->nip)) != NULL) {
421 			regs->nip = entry->fixup;
422 			return 1;
423 		}
424 
425 		/*
426 		 * fixup_exception() could not handle it,
427 		 * Let do_page_fault() fix it.
428 		 */
429 		break;
430 	default:
431 		break;
432 	}
433 	return 0;
434 }
435 
436 /*
437  * Wrapper routine to for handling exceptions.
438  */
439 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
440 				       unsigned long val, void *data)
441 {
442 	struct die_args *args = (struct die_args *)data;
443 	int ret = NOTIFY_DONE;
444 
445 	if (args->regs && user_mode(args->regs))
446 		return ret;
447 
448 	switch (val) {
449 	case DIE_BPT:
450 		if (kprobe_handler(args->regs))
451 			ret = NOTIFY_STOP;
452 		break;
453 	case DIE_SSTEP:
454 		if (post_kprobe_handler(args->regs))
455 			ret = NOTIFY_STOP;
456 		break;
457 	case DIE_PAGE_FAULT:
458 		/* kprobe_running() needs smp_processor_id() */
459 		preempt_disable();
460 		if (kprobe_running() &&
461 		    kprobe_fault_handler(args->regs, args->trapnr))
462 			ret = NOTIFY_STOP;
463 		preempt_enable();
464 		break;
465 	default:
466 		break;
467 	}
468 	return ret;
469 }
470 
471 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
472 {
473 	struct jprobe *jp = container_of(p, struct jprobe, kp);
474 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
475 
476 	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
477 
478 	/* setup return addr to the jprobe handler routine */
479 	regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
480 	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
481 
482 	return 1;
483 }
484 
485 void __kprobes jprobe_return(void)
486 {
487 	asm volatile("trap" ::: "memory");
488 }
489 
490 void __kprobes jprobe_return_end(void)
491 {
492 };
493 
494 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
495 {
496 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
497 
498 	/*
499 	 * FIXME - we should ideally be validating that we got here 'cos
500 	 * of the "trap" in jprobe_return() above, before restoring the
501 	 * saved regs...
502 	 */
503 	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
504 	preempt_enable_no_resched();
505 	return 1;
506 }
507 
508 static struct kprobe trampoline_p = {
509 	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
510 	.pre_handler = trampoline_probe_handler
511 };
512 
513 int __init arch_init_kprobes(void)
514 {
515 	return register_kprobe(&trampoline_p);
516 }
517