/arch/x86_64/kernel/kprobes.c

  1/*
  2 *  Kernel Probes (KProbes)
  3 *  arch/x86_64/kernel/kprobes.c
  4 *
  5 * This program is free software; you can redistribute it and/or modify
  6 * it under the terms of the GNU General Public License as published by
  7 * the Free Software Foundation; either version 2 of the License, or
  8 * (at your option) any later version.
  9 *
 10 * This program is distributed in the hope that it will be useful,
 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 13 * GNU General Public License for more details.
 14 *
 15 * You should have received a copy of the GNU General Public License
 16 * along with this program; if not, write to the Free Software
 17 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 18 *
 19 * Copyright (C) IBM Corporation, 2002, 2004
 20 *
 21 * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 22 *		Probes initial implementation ( includes contributions from
 23 *		Rusty Russell).
 24 * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 25 *		interface to access function arguments.
 26 * 2004-Oct	Jim Keniston <kenistoj@us.ibm.com> and Prasanna S Panchamukhi
 27 *		<prasanna@in.ibm.com> adapted for x86_64
 28 * 2005-Mar	Roland McGrath <roland@redhat.com>
 29 *		Fixed to handle %rip-relative addressing mode correctly.
 30 */
 31
 32#include <linux/config.h>
 33#include <linux/kprobes.h>
 34#include <linux/ptrace.h>
 35#include <linux/spinlock.h>
 36#include <linux/string.h>
 37#include <linux/slab.h>
 38#include <linux/preempt.h>
 39#include <linux/moduleloader.h>
 40
 41#include <asm/pgtable.h>
 42#include <asm/kdebug.h>
 43
 44static DECLARE_MUTEX(kprobe_mutex);
 45
 46/* kprobe_status settings */
 47#define KPROBE_HIT_ACTIVE	0x00000001
 48#define KPROBE_HIT_SS		0x00000002
 49
 50static struct kprobe *current_kprobe;
 51static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
 52static struct pt_regs jprobe_saved_regs;
 53static long *jprobe_saved_rsp;
 54static kprobe_opcode_t *get_insn_slot(void);
 55static void free_insn_slot(kprobe_opcode_t *slot);
 56void jprobe_return_end(void);
 57
 58/* copy of the kernel stack at the probe fire time */
 59static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
 60
 61/*
 62 * returns non-zero if opcode modifies the interrupt flag.
 63 */
 64static inline int is_IF_modifier(kprobe_opcode_t *insn)
 65{
 66	switch (*insn) {
 67	case 0xfa:		/* cli */
 68	case 0xfb:		/* sti */
 69	case 0xcf:		/* iret/iretd */
 70	case 0x9d:		/* popf/popfd */
 71		return 1;
 72	}
 73
 74	if (*insn  >= 0x40 && *insn <= 0x4f && *++insn == 0xcf)
 75		return 1;
 76	return 0;
 77}
 78
 79int arch_prepare_kprobe(struct kprobe *p)
 80{
 81	/* insn: must be on special executable page on x86_64. */
 82	up(&kprobe_mutex);
 83	p->ainsn.insn = get_insn_slot();
 84	down(&kprobe_mutex);
 85	if (!p->ainsn.insn) {
 86		return -ENOMEM;
 87	}
 88	return 0;
 89}
 90
 91/*
 92 * Determine if the instruction uses the %rip-relative addressing mode.
 93 * If it does, return the address of the 32-bit displacement word.
 94 * If not, return null.
 95 */
 96static inline s32 *is_riprel(u8 *insn)
 97{
 98#define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)		      \
 99	(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
100	  (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
101	  (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
102	  (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
103	 << (row % 64))
104	static const u64 onebyte_has_modrm[256 / 64] = {
105		/*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
106		/*      -------------------------------         */
107		W(0x00, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 00 */
108		W(0x10, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 10 */
109		W(0x20, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 20 */
110		W(0x30, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0), /* 30 */
111		W(0x40, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 40 */
112		W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 50 */
113		W(0x60, 0,0,1,1,0,0,0,0,0,1,0,1,0,0,0,0)| /* 60 */
114		W(0x70, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 70 */
115		W(0x80, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 80 */
116		W(0x90, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 90 */
117		W(0xa0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* a0 */
118		W(0xb0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* b0 */
119		W(0xc0, 1,1,0,0,1,1,1,1,0,0,0,0,0,0,0,0)| /* c0 */
120		W(0xd0, 1,1,1,1,0,0,0,0,1,1,1,1,1,1,1,1)| /* d0 */
121		W(0xe0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* e0 */
122		W(0xf0, 0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1)  /* f0 */
123		/*      -------------------------------         */
124		/*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
125	};
126	static const u64 twobyte_has_modrm[256 / 64] = {
127		/*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
128		/*      -------------------------------         */
129		W(0x00, 1,1,1,1,0,0,0,0,0,0,0,0,0,1,0,1)| /* 0f */
130		W(0x10, 1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0)| /* 1f */
131		W(0x20, 1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1)| /* 2f */
132		W(0x30, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 3f */
133		W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 4f */
134		W(0x50, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 5f */
135		W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 6f */
136		W(0x70, 1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1), /* 7f */
137		W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 8f */
138		W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 9f */
139		W(0xa0, 0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,1)| /* af */
140		W(0xb0, 1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1), /* bf */
141		W(0xc0, 1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0)| /* cf */
142		W(0xd0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* df */
143		W(0xe0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* ef */
144		W(0xf0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0)  /* ff */
145		/*      -------------------------------         */
146		/*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
147	};
148#undef	W
149	int need_modrm;
150
151	/* Skip legacy instruction prefixes.  */
152	while (1) {
153		switch (*insn) {
154		case 0x66:
155		case 0x67:
156		case 0x2e:
157		case 0x3e:
158		case 0x26:
159		case 0x64:
160		case 0x65:
161		case 0x36:
162		case 0xf0:
163		case 0xf3:
164		case 0xf2:
165			++insn;
166			continue;
167		}
168		break;
169	}
170
171	/* Skip REX instruction prefix.  */
172	if ((*insn & 0xf0) == 0x40)
173		++insn;
174
175	if (*insn == 0x0f) {	/* Two-byte opcode.  */
176		++insn;
177		need_modrm = test_bit(*insn, twobyte_has_modrm);
178	} else {		/* One-byte opcode.  */
179		need_modrm = test_bit(*insn, onebyte_has_modrm);
180	}
181
182	if (need_modrm) {
183		u8 modrm = *++insn;
184		if ((modrm & 0xc7) == 0x05) { /* %rip+disp32 addressing mode */
185			/* Displacement follows ModRM byte.  */
186			return (s32 *) ++insn;
187		}
188	}
189
190	/* No %rip-relative addressing mode here.  */
191	return NULL;
192}
193
194void arch_copy_kprobe(struct kprobe *p)
195{
196	s32 *ripdisp;
197	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE);
198	ripdisp = is_riprel(p->ainsn.insn);
199	if (ripdisp) {
200		/*
201		 * The copied instruction uses the %rip-relative
202		 * addressing mode.  Adjust the displacement for the
203		 * difference between the original location of this
204		 * instruction and the location of the copy that will
205		 * actually be run.  The tricky bit here is making sure
206		 * that the sign extension happens correctly in this
207		 * calculation, since we need a signed 32-bit result to
208		 * be sign-extended to 64 bits when it's added to the
209		 * %rip value and yield the same 64-bit result that the
210		 * sign-extension of the original signed 32-bit
211		 * displacement would have given.
212		 */
213		s64 disp = (u8 *) p->addr + *ripdisp - (u8 *) p->ainsn.insn;
214		BUG_ON((s64) (s32) disp != disp); /* Sanity check.  */
215		*ripdisp = disp;
216	}
217}
218
219void arch_remove_kprobe(struct kprobe *p)
220{
221	up(&kprobe_mutex);
222	free_insn_slot(p->ainsn.insn);
223	down(&kprobe_mutex);
224}
225
226static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
227{
228	*p->addr = p->opcode;
229	regs->rip = (unsigned long)p->addr;
230}
231
232static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
233{
234	regs->eflags |= TF_MASK;
235	regs->eflags &= ~IF_MASK;
236	/*single step inline if the instruction is an int3*/
237	if (p->opcode == BREAKPOINT_INSTRUCTION)
238		regs->rip = (unsigned long)p->addr;
239	else
240		regs->rip = (unsigned long)p->ainsn.insn;
241}
242
243/*
244 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
245 * remain disabled thorough out this function.
246 */
247int kprobe_handler(struct pt_regs *regs)
248{
249	struct kprobe *p;
250	int ret = 0;
251	kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
252
253	/* We're in an interrupt, but this is clear and BUG()-safe. */
254	preempt_disable();
255
256	/* Check we're not actually recursing */
257	if (kprobe_running()) {
258		/* We *are* holding lock here, so this is safe.
259		   Disarm the probe we just hit, and ignore it. */
260		p = get_kprobe(addr);
261		if (p) {
262			if (kprobe_status == KPROBE_HIT_SS) {
263				regs->eflags &= ~TF_MASK;
264				regs->eflags |= kprobe_saved_rflags;
265				unlock_kprobes();
266				goto no_kprobe;
267			}
268			disarm_kprobe(p, regs);
269			ret = 1;
270		} else {
271			p = current_kprobe;
272			if (p->break_handler && p->break_handler(p, regs)) {
273				goto ss_probe;
274			}
275		}
276		/* If it's not ours, can't be delete race, (we hold lock). */
277		goto no_kprobe;
278	}
279
280	lock_kprobes();
281	p = get_kprobe(addr);
282	if (!p) {
283		unlock_kprobes();
284		if (*addr != BREAKPOINT_INSTRUCTION) {
285			/*
286			 * The breakpoint instruction was removed right
287			 * after we hit it.  Another cpu has removed
288			 * either a probepoint or a debugger breakpoint
289			 * at this address.  In either case, no further
290			 * handling of this interrupt is appropriate.
291			 */
292			ret = 1;
293		}
294		/* Not one of ours: let kernel handle it */
295		goto no_kprobe;
296	}
297
298	kprobe_status = KPROBE_HIT_ACTIVE;
299	current_kprobe = p;
300	kprobe_saved_rflags = kprobe_old_rflags
301	    = (regs->eflags & (TF_MASK | IF_MASK));
302	if (is_IF_modifier(p->ainsn.insn))
303		kprobe_saved_rflags &= ~IF_MASK;
304
305	if (p->pre_handler && p->pre_handler(p, regs))
306		/* handler has already set things up, so skip ss setup */
307		return 1;
308
309ss_probe:
310	prepare_singlestep(p, regs);
311	kprobe_status = KPROBE_HIT_SS;
312	return 1;
313
314no_kprobe:
315	preempt_enable_no_resched();
316	return ret;
317}
318
319/*
320 * Called after single-stepping.  p->addr is the address of the
321 * instruction whose first byte has been replaced by the "int 3"
322 * instruction.  To avoid the SMP problems that can occur when we
323 * temporarily put back the original opcode to single-step, we
324 * single-stepped a copy of the instruction.  The address of this
325 * copy is p->ainsn.insn.
326 *
327 * This function prepares to return from the post-single-step
328 * interrupt.  We have to fix up the stack as follows:
329 *
330 * 0) Except in the case of absolute or indirect jump or call instructions,
331 * the new rip is relative to the copied instruction.  We need to make
332 * it relative to the original instruction.
333 *
334 * 1) If the single-stepped instruction was pushfl, then the TF and IF
335 * flags are set in the just-pushed eflags, and may need to be cleared.
336 *
337 * 2) If the single-stepped instruction was a call, the return address
338 * that is atop the stack is the address following the copied instruction.
339 * We need to make it the address following the original instruction.
340 */
341static void resume_execution(struct kprobe *p, struct pt_regs *regs)
342{
343	unsigned long *tos = (unsigned long *)regs->rsp;
344	unsigned long next_rip = 0;
345	unsigned long copy_rip = (unsigned long)p->ainsn.insn;
346	unsigned long orig_rip = (unsigned long)p->addr;
347	kprobe_opcode_t *insn = p->ainsn.insn;
348
349	/*skip the REX prefix*/
350	if (*insn >= 0x40 && *insn <= 0x4f)
351		insn++;
352
353	switch (*insn) {
354	case 0x9c:		/* pushfl */
355		*tos &= ~(TF_MASK | IF_MASK);
356		*tos |= kprobe_old_rflags;
357		break;
358	case 0xe8:		/* call relative - Fix return addr */
359		*tos = orig_rip + (*tos - copy_rip);
360		break;
361	case 0xff:
362		if ((*insn & 0x30) == 0x10) {
363			/* call absolute, indirect */
364			/* Fix return addr; rip is correct. */
365			next_rip = regs->rip;
366			*tos = orig_rip + (*tos - copy_rip);
367		} else if (((*insn & 0x31) == 0x20) ||	/* jmp near, absolute indirect */
368			   ((*insn & 0x31) == 0x21)) {	/* jmp far, absolute indirect */
369			/* rip is correct. */
370			next_rip = regs->rip;
371		}
372		break;
373	case 0xea:		/* jmp absolute -- rip is correct */
374		next_rip = regs->rip;
375		break;
376	default:
377		break;
378	}
379
380	regs->eflags &= ~TF_MASK;
381	if (next_rip) {
382		regs->rip = next_rip;
383	} else {
384		regs->rip = orig_rip + (regs->rip - copy_rip);
385	}
386}
387
388/*
389 * Interrupts are disabled on entry as trap1 is an interrupt gate and they
390 * remain disabled thoroughout this function.  And we hold kprobe lock.
391 */
392int post_kprobe_handler(struct pt_regs *regs)
393{
394	if (!kprobe_running())
395		return 0;
396
397	if (current_kprobe->post_handler)
398		current_kprobe->post_handler(current_kprobe, regs, 0);
399
400	resume_execution(current_kprobe, regs);
401	regs->eflags |= kprobe_saved_rflags;
402
403	unlock_kprobes();
404	preempt_enable_no_resched();
405
406	/*
407	 * if somebody else is singlestepping across a probe point, eflags
408	 * will have TF set, in which case, continue the remaining processing
409	 * of do_debug, as if this is not a probe hit.
410	 */
411	if (regs->eflags & TF_MASK)
412		return 0;
413
414	return 1;
415}
416
417/* Interrupts disabled, kprobe_lock held. */
418int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
419{
420	if (current_kprobe->fault_handler
421	    && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
422		return 1;
423
424	if (kprobe_status & KPROBE_HIT_SS) {
425		resume_execution(current_kprobe, regs);
426		regs->eflags |= kprobe_old_rflags;
427
428		unlock_kprobes();
429		preempt_enable_no_resched();
430	}
431	return 0;
432}
433
434/*
435 * Wrapper routine for handling exceptions.
436 */
437int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
438			     void *data)
439{
440	struct die_args *args = (struct die_args *)data;
441	switch (val) {
442	case DIE_INT3:
443		if (kprobe_handler(args->regs))
444			return NOTIFY_STOP;
445		break;
446	case DIE_DEBUG:
447		if (post_kprobe_handler(args->regs))
448			return NOTIFY_STOP;
449		break;
450	case DIE_GPF:
451		if (kprobe_running() &&
452		    kprobe_fault_handler(args->regs, args->trapnr))
453			return NOTIFY_STOP;
454		break;
455	case DIE_PAGE_FAULT:
456		if (kprobe_running() &&
457		    kprobe_fault_handler(args->regs, args->trapnr))
458			return NOTIFY_STOP;
459		break;
460	default:
461		break;
462	}
463	return NOTIFY_DONE;
464}
465
466int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
467{
468	struct jprobe *jp = container_of(p, struct jprobe, kp);
469	unsigned long addr;
470
471	jprobe_saved_regs = *regs;
472	jprobe_saved_rsp = (long *) regs->rsp;
473	addr = (unsigned long)jprobe_saved_rsp;
474	/*
475	 * As Linus pointed out, gcc assumes that the callee
476	 * owns the argument space and could overwrite it, e.g.
477	 * tailcall optimization. So, to be absolutely safe
478	 * we also save and restore enough stack bytes to cover
479	 * the argument area.
480	 */
481	memcpy(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr));
482	regs->eflags &= ~IF_MASK;
483	regs->rip = (unsigned long)(jp->entry);
484	return 1;
485}
486
487void jprobe_return(void)
488{
489	preempt_enable_no_resched();
490	asm volatile ("       xchg   %%rbx,%%rsp     \n"
491		      "       int3			\n"
492		      "       .globl jprobe_return_end	\n"
493		      "       jprobe_return_end:	\n"
494		      "       nop			\n"::"b"
495		      (jprobe_saved_rsp):"memory");
496}
497
498int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
499{
500	u8 *addr = (u8 *) (regs->rip - 1);
501	unsigned long stack_addr = (unsigned long)jprobe_saved_rsp;
502	struct jprobe *jp = container_of(p, struct jprobe, kp);
503
504	if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
505		if ((long *)regs->rsp != jprobe_saved_rsp) {
506			struct pt_regs *saved_regs =
507			    container_of(jprobe_saved_rsp, struct pt_regs, rsp);
508			printk("current rsp %p does not match saved rsp %p\n",
509			       (long *)regs->rsp, jprobe_saved_rsp);
510			printk("Saved registers for jprobe %p\n", jp);
511			show_registers(saved_regs);
512			printk("Current registers\n");
513			show_registers(regs);
514			BUG();
515		}
516		*regs = jprobe_saved_regs;
517		memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack,
518		       MIN_STACK_SIZE(stack_addr));
519		return 1;
520	}
521	return 0;
522}
523
524/*
525 * kprobe->ainsn.insn points to the copy of the instruction to be single-stepped.
526 * By default on x86_64, pages we get from kmalloc or vmalloc are not
527 * executable.  Single-stepping an instruction on such a page yields an
528 * oops.  So instead of storing the instruction copies in their respective
529 * kprobe objects, we allocate a page, map it executable, and store all the
530 * instruction copies there.  (We can allocate additional pages if somebody
531 * inserts a huge number of probes.)  Each page can hold up to INSNS_PER_PAGE
532 * instruction slots, each of which is MAX_INSN_SIZE*sizeof(kprobe_opcode_t)
533 * bytes.
534 */
535#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE*sizeof(kprobe_opcode_t)))
536struct kprobe_insn_page {
537	struct hlist_node hlist;
538	kprobe_opcode_t *insns;		/* page of instruction slots */
539	char slot_used[INSNS_PER_PAGE];
540	int nused;
541};
542
543static struct hlist_head kprobe_insn_pages;
544
545/**
546 * get_insn_slot() - Find a slot on an executable page for an instruction.
547 * We allocate an executable page if there's no room on existing ones.
548 */
549static kprobe_opcode_t *get_insn_slot(void)
550{
551	struct kprobe_insn_page *kip;
552	struct hlist_node *pos;
553
554	hlist_for_each(pos, &kprobe_insn_pages) {
555		kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
556		if (kip->nused < INSNS_PER_PAGE) {
557			int i;
558			for (i = 0; i < INSNS_PER_PAGE; i++) {
559				if (!kip->slot_used[i]) {
560					kip->slot_used[i] = 1;
561					kip->nused++;
562					return kip->insns + (i*MAX_INSN_SIZE);
563				}
564			}
565			/* Surprise!  No unused slots.  Fix kip->nused. */
566			kip->nused = INSNS_PER_PAGE;
567		}
568	}
569
570	/* All out of space.  Need to allocate a new page. Use slot 0.*/
571	kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
572	if (!kip) {
573		return NULL;
574	}
575
576	/*
577	 * For the %rip-relative displacement fixups to be doable, we
578	 * need our instruction copy to be within +/- 2GB of any data it
579	 * might access via %rip.  That is, within 2GB of where the
580	 * kernel image and loaded module images reside.  So we allocate
581	 * a page in the module loading area.
582	 */
583	kip->insns = module_alloc(PAGE_SIZE);
584	if (!kip->insns) {
585		kfree(kip);
586		return NULL;
587	}
588	INIT_HLIST_NODE(&kip->hlist);
589	hlist_add_head(&kip->hlist, &kprobe_insn_pages);
590	memset(kip->slot_used, 0, INSNS_PER_PAGE);
591	kip->slot_used[0] = 1;
592	kip->nused = 1;
593	return kip->insns;
594}
595
596/**
597 * free_insn_slot() - Free instruction slot obtained from get_insn_slot().
598 */
599static void free_insn_slot(kprobe_opcode_t *slot)
600{
601	struct kprobe_insn_page *kip;
602	struct hlist_node *pos;
603
604	hlist_for_each(pos, &kprobe_insn_pages) {
605		kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
606		if (kip->insns <= slot
607		    && slot < kip->insns+(INSNS_PER_PAGE*MAX_INSN_SIZE)) {
608			int i = (slot - kip->insns) / MAX_INSN_SIZE;
609			kip->slot_used[i] = 0;
610			kip->nused--;
611			if (kip->nused == 0) {
612				/*
613				 * Page is no longer in use.  Free it unless
614				 * it's the last one.  We keep the last one
615				 * so as not to have to set it up again the
616				 * next time somebody inserts a probe.
617				 */
618				hlist_del(&kip->hlist);
619				if (hlist_empty(&kprobe_insn_pages)) {
620					INIT_HLIST_NODE(&kip->hlist);
621					hlist_add_head(&kip->hlist,
622						&kprobe_insn_pages);
623				} else {
624					module_free(NULL, kip->insns);
625					kfree(kip);
626				}
627			}
628			return;
629		}
630	}
631}