1// SPDX-License-Identifier: GPL-2.0+
2/*
3 *  Kernel Probes (KProbes)
4 *
5 * Copyright IBM Corp. 2002, 2006
6 *
7 * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
8 */
9
10#define pr_fmt(fmt) "kprobes: " fmt
11
12#include <linux/moduleloader.h>
13#include <linux/kprobes.h>
14#include <linux/ptrace.h>
15#include <linux/preempt.h>
16#include <linux/stop_machine.h>
17#include <linux/kdebug.h>
18#include <linux/uaccess.h>
19#include <linux/extable.h>
20#include <linux/module.h>
21#include <linux/slab.h>
22#include <linux/hardirq.h>
23#include <linux/ftrace.h>
24#include <asm/set_memory.h>
25#include <asm/sections.h>
26#include <asm/dis.h>
27#include "kprobes.h"
28#include "entry.h"
29
30DEFINE_PER_CPU(struct kprobe *, current_kprobe);
31DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
32
33struct kretprobe_blackpoint kretprobe_blacklist[] = { };
34
35static int insn_page_in_use;
36
37void *alloc_insn_page(void)
38{
39	void *page;
40
41	page = module_alloc(PAGE_SIZE);
42	if (!page)
43		return NULL;
44	set_memory_rox((unsigned long)page, 1);
45	return page;
46}
47
48static void *alloc_s390_insn_page(void)
49{
50	if (xchg(&insn_page_in_use, 1) == 1)
51		return NULL;
52	return &kprobes_insn_page;
53}
54
55static void free_s390_insn_page(void *page)
56{
57	xchg(&insn_page_in_use, 0);
58}
59
60struct kprobe_insn_cache kprobe_s390_insn_slots = {
61	.mutex = __MUTEX_INITIALIZER(kprobe_s390_insn_slots.mutex),
62	.alloc = alloc_s390_insn_page,
63	.free = free_s390_insn_page,
64	.pages = LIST_HEAD_INIT(kprobe_s390_insn_slots.pages),
65	.insn_size = MAX_INSN_SIZE,
66};
67
68static void copy_instruction(struct kprobe *p)
69{
70	kprobe_opcode_t insn[MAX_INSN_SIZE];
71	s64 disp, new_disp;
72	u64 addr, new_addr;
73	unsigned int len;
74
75	len = insn_length(*p->addr >> 8);
76	memcpy(&insn, p->addr, len);
77	p->opcode = insn[0];
78	if (probe_is_insn_relative_long(&insn[0])) {
79		/*
80		 * For pc-relative instructions in RIL-b or RIL-c format patch
81		 * the RI2 displacement field. We have already made sure that
82		 * the insn slot for the patched instruction is within the same
83		 * 2GB area as the original instruction (either kernel image or
84		 * module area). Therefore the new displacement will always fit.
85		 */
86		disp = *(s32 *)&insn[1];
87		addr = (u64)(unsigned long)p->addr;
88		new_addr = (u64)(unsigned long)p->ainsn.insn;
89		new_disp = ((addr + (disp * 2)) - new_addr) / 2;
90		*(s32 *)&insn[1] = new_disp;
91	}
92	s390_kernel_write(p->ainsn.insn, &insn, len);
93}
94NOKPROBE_SYMBOL(copy_instruction);
95
96static int s390_get_insn_slot(struct kprobe *p)
97{
98	/*
99	 * Get an insn slot that is within the same 2GB area like the original
100	 * instruction. That way instructions with a 32bit signed displacement
101	 * field can be patched and executed within the insn slot.
102	 */
103	p->ainsn.insn = NULL;
104	if (is_kernel((unsigned long)p->addr))
105		p->ainsn.insn = get_s390_insn_slot();
106	else if (is_module_addr(p->addr))
107		p->ainsn.insn = get_insn_slot();
108	return p->ainsn.insn ? 0 : -ENOMEM;
109}
110NOKPROBE_SYMBOL(s390_get_insn_slot);
111
112static void s390_free_insn_slot(struct kprobe *p)
113{
114	if (!p->ainsn.insn)
115		return;
116	if (is_kernel((unsigned long)p->addr))
117		free_s390_insn_slot(p->ainsn.insn, 0);
118	else
119		free_insn_slot(p->ainsn.insn, 0);
120	p->ainsn.insn = NULL;
121}
122NOKPROBE_SYMBOL(s390_free_insn_slot);
123
124/* Check if paddr is at an instruction boundary */
125static bool can_probe(unsigned long paddr)
126{
127	unsigned long addr, offset = 0;
128	kprobe_opcode_t insn;
129	struct kprobe *kp;
130
131	if (paddr & 0x01)
132		return false;
133
134	if (!kallsyms_lookup_size_offset(paddr, NULL, &offset))
135		return false;
136
137	/* Decode instructions */
138	addr = paddr - offset;
139	while (addr < paddr) {
140		if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(insn)))
141			return false;
142
143		if (insn >> 8 == 0) {
144			if (insn != BREAKPOINT_INSTRUCTION) {
145				/*
146				 * Note that QEMU inserts opcode 0x0000 to implement
147				 * software breakpoints for guests. Since the size of
148				 * the original instruction is unknown, stop following
149				 * instructions and prevent setting a kprobe.
150				 */
151				return false;
152			}
153			/*
154			 * Check if the instruction has been modified by another
155			 * kprobe, in which case the original instruction is
156			 * decoded.
157			 */
158			kp = get_kprobe((void *)addr);
159			if (!kp) {
160				/* not a kprobe */
161				return false;
162			}
163			insn = kp->opcode;
164		}
165		addr += insn_length(insn >> 8);
166	}
167	return addr == paddr;
168}
169
170int arch_prepare_kprobe(struct kprobe *p)
171{
172	if (!can_probe((unsigned long)p->addr))
173		return -EINVAL;
174	/* Make sure the probe isn't going on a difficult instruction */
175	if (probe_is_prohibited_opcode(p->addr))
176		return -EINVAL;
177	if (s390_get_insn_slot(p))
178		return -ENOMEM;
179	copy_instruction(p);
180	return 0;
181}
182NOKPROBE_SYMBOL(arch_prepare_kprobe);
183
184struct swap_insn_args {
185	struct kprobe *p;
186	unsigned int arm_kprobe : 1;
187};
188
189static int swap_instruction(void *data)
190{
191	struct swap_insn_args *args = data;
192	struct kprobe *p = args->p;
193	u16 opc;
194
195	opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
196	s390_kernel_write(p->addr, &opc, sizeof(opc));
197	return 0;
198}
199NOKPROBE_SYMBOL(swap_instruction);
200
201void arch_arm_kprobe(struct kprobe *p)
202{
203	struct swap_insn_args args = {.p = p, .arm_kprobe = 1};
204
205	stop_machine_cpuslocked(swap_instruction, &args, NULL);
206}
207NOKPROBE_SYMBOL(arch_arm_kprobe);
208
209void arch_disarm_kprobe(struct kprobe *p)
210{
211	struct swap_insn_args args = {.p = p, .arm_kprobe = 0};
212
213	stop_machine_cpuslocked(swap_instruction, &args, NULL);
214}
215NOKPROBE_SYMBOL(arch_disarm_kprobe);
216
217void arch_remove_kprobe(struct kprobe *p)
218{
219	s390_free_insn_slot(p);
220}
221NOKPROBE_SYMBOL(arch_remove_kprobe);
222
223static void enable_singlestep(struct kprobe_ctlblk *kcb,
224			      struct pt_regs *regs,
225			      unsigned long ip)
226{
227	union {
228		struct ctlreg regs[3];
229		struct {
230			struct ctlreg control;
231			struct ctlreg start;
232			struct ctlreg end;
233		};
234	} per_kprobe;
235
236	/* Set up the PER control registers %cr9-%cr11 */
237	per_kprobe.control.val = PER_EVENT_IFETCH;
238	per_kprobe.start.val = ip;
239	per_kprobe.end.val = ip;
240
241	/* Save control regs and psw mask */
242	__local_ctl_store(9, 11, kcb->kprobe_saved_ctl);
243	kcb->kprobe_saved_imask = regs->psw.mask &
244		(PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT);
245
246	/* Set PER control regs, turns on single step for the given address */
247	__local_ctl_load(9, 11, per_kprobe.regs);
248	regs->psw.mask |= PSW_MASK_PER;
249	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT);
250	regs->psw.addr = ip;
251}
252NOKPROBE_SYMBOL(enable_singlestep);
253
254static void disable_singlestep(struct kprobe_ctlblk *kcb,
255			       struct pt_regs *regs,
256			       unsigned long ip)
257{
258	/* Restore control regs and psw mask, set new psw address */
259	__local_ctl_load(9, 11, kcb->kprobe_saved_ctl);
260	regs->psw.mask &= ~PSW_MASK_PER;
261	regs->psw.mask |= kcb->kprobe_saved_imask;
262	regs->psw.addr = ip;
263}
264NOKPROBE_SYMBOL(disable_singlestep);
265
266/*
267 * Activate a kprobe by storing its pointer to current_kprobe. The
268 * previous kprobe is stored in kcb->prev_kprobe. A stack of up to
269 * two kprobes can be active, see KPROBE_REENTER.
270 */
271static void push_kprobe(struct kprobe_ctlblk *kcb, struct kprobe *p)
272{
273	kcb->prev_kprobe.kp = __this_cpu_read(current_kprobe);
274	kcb->prev_kprobe.status = kcb->kprobe_status;
275	__this_cpu_write(current_kprobe, p);
276}
277NOKPROBE_SYMBOL(push_kprobe);
278
279/*
280 * Deactivate a kprobe by backing up to the previous state. If the
281 * current state is KPROBE_REENTER prev_kprobe.kp will be non-NULL,
282 * for any other state prev_kprobe.kp will be NULL.
283 */
284static void pop_kprobe(struct kprobe_ctlblk *kcb)
285{
286	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
287	kcb->kprobe_status = kcb->prev_kprobe.status;
288	kcb->prev_kprobe.kp = NULL;
289}
290NOKPROBE_SYMBOL(pop_kprobe);
291
292static void kprobe_reenter_check(struct kprobe_ctlblk *kcb, struct kprobe *p)
293{
294	switch (kcb->kprobe_status) {
295	case KPROBE_HIT_SSDONE:
296	case KPROBE_HIT_ACTIVE:
297		kprobes_inc_nmissed_count(p);
298		break;
299	case KPROBE_HIT_SS:
300	case KPROBE_REENTER:
301	default:
302		/*
303		 * A kprobe on the code path to single step an instruction
304		 * is a BUG. The code path resides in the .kprobes.text
305		 * section and is executed with interrupts disabled.
306		 */
307		pr_err("Failed to recover from reentered kprobes.\n");
308		dump_kprobe(p);
309		BUG();
310	}
311}
312NOKPROBE_SYMBOL(kprobe_reenter_check);
313
314static int kprobe_handler(struct pt_regs *regs)
315{
316	struct kprobe_ctlblk *kcb;
317	struct kprobe *p;
318
319	/*
320	 * We want to disable preemption for the entire duration of kprobe
321	 * processing. That includes the calls to the pre/post handlers
322	 * and single stepping the kprobe instruction.
323	 */
324	preempt_disable();
325	kcb = get_kprobe_ctlblk();
326	p = get_kprobe((void *)(regs->psw.addr - 2));
327
328	if (p) {
329		if (kprobe_running()) {
330			/*
331			 * We have hit a kprobe while another is still
332			 * active. This can happen in the pre and post
333			 * handler. Single step the instruction of the
334			 * new probe but do not call any handler function
335			 * of this secondary kprobe.
336			 * push_kprobe and pop_kprobe saves and restores
337			 * the currently active kprobe.
338			 */
339			kprobe_reenter_check(kcb, p);
340			push_kprobe(kcb, p);
341			kcb->kprobe_status = KPROBE_REENTER;
342		} else {
343			/*
344			 * If we have no pre-handler or it returned 0, we
345			 * continue with single stepping. If we have a
346			 * pre-handler and it returned non-zero, it prepped
347			 * for changing execution path, so get out doing
348			 * nothing more here.
349			 */
350			push_kprobe(kcb, p);
351			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
352			if (p->pre_handler && p->pre_handler(p, regs)) {
353				pop_kprobe(kcb);
354				preempt_enable_no_resched();
355				return 1;
356			}
357			kcb->kprobe_status = KPROBE_HIT_SS;
358		}
359		enable_singlestep(kcb, regs, (unsigned long) p->ainsn.insn);
360		return 1;
361	} /* else:
362	   * No kprobe at this address and no active kprobe. The trap has
363	   * not been caused by a kprobe breakpoint. The race of breakpoint
364	   * vs. kprobe remove does not exist because on s390 as we use
365	   * stop_machine to arm/disarm the breakpoints.
366	   */
367	preempt_enable_no_resched();
368	return 0;
369}
370NOKPROBE_SYMBOL(kprobe_handler);
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 */
380static void resume_execution(struct kprobe *p, struct pt_regs *regs)
381{
382	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
383	unsigned long ip = regs->psw.addr;
384	int fixup = probe_get_fixup_type(p->ainsn.insn);
385
386	if (fixup & FIXUP_PSW_NORMAL)
387		ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;
388
389	if (fixup & FIXUP_BRANCH_NOT_TAKEN) {
390		int ilen = insn_length(p->ainsn.insn[0] >> 8);
391		if (ip - (unsigned long) p->ainsn.insn == ilen)
392			ip = (unsigned long) p->addr + ilen;
393	}
394
395	if (fixup & FIXUP_RETURN_REGISTER) {
396		int reg = (p->ainsn.insn[0] & 0xf0) >> 4;
397		regs->gprs[reg] += (unsigned long) p->addr -
398				   (unsigned long) p->ainsn.insn;
399	}
400
401	disable_singlestep(kcb, regs, ip);
402}
403NOKPROBE_SYMBOL(resume_execution);
404
405static int post_kprobe_handler(struct pt_regs *regs)
406{
407	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
408	struct kprobe *p = kprobe_running();
409
410	if (!p)
411		return 0;
412
413	resume_execution(p, regs);
414	if (kcb->kprobe_status != KPROBE_REENTER && p->post_handler) {
415		kcb->kprobe_status = KPROBE_HIT_SSDONE;
416		p->post_handler(p, regs, 0);
417	}
418	pop_kprobe(kcb);
419	preempt_enable_no_resched();
420
421	/*
422	 * if somebody else is singlestepping across a probe point, psw mask
423	 * will have PER set, in which case, continue the remaining processing
424	 * of do_single_step, as if this is not a probe hit.
425	 */
426	if (regs->psw.mask & PSW_MASK_PER)
427		return 0;
428
429	return 1;
430}
431NOKPROBE_SYMBOL(post_kprobe_handler);
432
433static int kprobe_trap_handler(struct pt_regs *regs, int trapnr)
434{
435	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
436	struct kprobe *p = kprobe_running();
437
438	switch(kcb->kprobe_status) {
439	case KPROBE_HIT_SS:
440	case KPROBE_REENTER:
441		/*
442		 * We are here because the instruction being single
443		 * stepped caused a page fault. We reset the current
444		 * kprobe and the nip points back to the probe address
445		 * and allow the page fault handler to continue as a
446		 * normal page fault.
447		 */
448		disable_singlestep(kcb, regs, (unsigned long) p->addr);
449		pop_kprobe(kcb);
450		preempt_enable_no_resched();
451		break;
452	case KPROBE_HIT_ACTIVE:
453	case KPROBE_HIT_SSDONE:
454		/*
455		 * In case the user-specified fault handler returned
456		 * zero, try to fix up.
457		 */
458		if (fixup_exception(regs))
459			return 1;
460		/*
461		 * fixup_exception() could not handle it,
462		 * Let do_page_fault() fix it.
463		 */
464		break;
465	default:
466		break;
467	}
468	return 0;
469}
470NOKPROBE_SYMBOL(kprobe_trap_handler);
471
472int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
473{
474	int ret;
475
476	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
477		local_irq_disable();
478	ret = kprobe_trap_handler(regs, trapnr);
479	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
480		local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);
481	return ret;
482}
483NOKPROBE_SYMBOL(kprobe_fault_handler);
484
485/*
486 * Wrapper routine to for handling exceptions.
487 */
488int kprobe_exceptions_notify(struct notifier_block *self,
489			     unsigned long val, void *data)
490{
491	struct die_args *args = (struct die_args *) data;
492	struct pt_regs *regs = args->regs;
493	int ret = NOTIFY_DONE;
494
495	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
496		local_irq_disable();
497
498	switch (val) {
499	case DIE_BPT:
500		if (kprobe_handler(regs))
501			ret = NOTIFY_STOP;
502		break;
503	case DIE_SSTEP:
504		if (post_kprobe_handler(regs))
505			ret = NOTIFY_STOP;
506		break;
507	case DIE_TRAP:
508		if (!preemptible() && kprobe_running() &&
509		    kprobe_trap_handler(regs, args->trapnr))
510			ret = NOTIFY_STOP;
511		break;
512	default:
513		break;
514	}
515
516	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
517		local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);
518
519	return ret;
520}
521NOKPROBE_SYMBOL(kprobe_exceptions_notify);
522
523int __init arch_init_kprobes(void)
524{
525	return 0;
526}
527
528int arch_trampoline_kprobe(struct kprobe *p)
529{
530	return 0;
531}
532NOKPROBE_SYMBOL(arch_trampoline_kprobe);
533