1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Kernel Probes (KProbes)
4 * arch/mips/kernel/kprobes.c
5 *
6 * Copyright 2006 Sony Corp.
7 * Copyright 2010 Cavium Networks
8 *
9 * Some portions copied from the powerpc version.
10 *
11 * Copyright (C) IBM Corporation, 2002, 2004
12 */
13
14 #define pr_fmt(fmt) "kprobes: " fmt
15
16 #include <linux/kprobes.h>
17 #include <linux/preempt.h>
18 #include <linux/uaccess.h>
19 #include <linux/kdebug.h>
20 #include <linux/slab.h>
21
22 #include <asm/ptrace.h>
23 #include <asm/branch.h>
24 #include <asm/break.h>
25
26 #include "probes-common.h"
27
28 static const union mips_instruction breakpoint_insn = {
29 .b_format = {
30 .opcode = spec_op,
31 .code = BRK_KPROBE_BP,
32 .func = break_op
33 }
34 };
35
36 static const union mips_instruction breakpoint2_insn = {
37 .b_format = {
38 .opcode = spec_op,
39 .code = BRK_KPROBE_SSTEPBP,
40 .func = break_op
41 }
42 };
43
44 DEFINE_PER_CPU(struct kprobe *, current_kprobe);
45 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
46
47 static int insn_has_delayslot(union mips_instruction insn)
48 {
49 return __insn_has_delay_slot(insn);
50 }
51 NOKPROBE_SYMBOL(insn_has_delayslot);
52
53 /*
54 * insn_has_ll_or_sc function checks whether instruction is ll or sc
55 * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
56 * so we need to prevent it and refuse kprobes insertion for such
57 * instructions; cannot do much about breakpoint in the middle of
58 * ll/sc pair; it is up to user to avoid those places
59 */
60 static int insn_has_ll_or_sc(union mips_instruction insn)
61 {
62 int ret = 0;
63
64 switch (insn.i_format.opcode) {
65 case ll_op:
66 case lld_op:
67 case sc_op:
68 case scd_op:
69 ret = 1;
70 break;
71 default:
72 break;
73 }
74 return ret;
75 }
76 NOKPROBE_SYMBOL(insn_has_ll_or_sc);
77
78 int arch_prepare_kprobe(struct kprobe *p)
79 {
80 union mips_instruction insn;
81 union mips_instruction prev_insn;
82 int ret = 0;
83
84 insn = p->addr[0];
85
86 if (insn_has_ll_or_sc(insn)) {
87 pr_notice("Kprobes for ll and sc instructions are not supported\n");
88 ret = -EINVAL;
89 goto out;
90 }
91
92 if (copy_from_kernel_nofault(&prev_insn, p->addr - 1,
93 sizeof(mips_instruction)) == 0 &&
94 insn_has_delayslot(prev_insn)) {
95 pr_notice("Kprobes for branch delayslot are not supported\n");
96 ret = -EINVAL;
97 goto out;
98 }
99
100 if (__insn_is_compact_branch(insn)) {
101 pr_notice("Kprobes for compact branches are not supported\n");
102 ret = -EINVAL;
103 goto out;
104 }
105
106 /* insn: must be on special executable page on mips. */
107 p->ainsn.insn = get_insn_slot();
108 if (!p->ainsn.insn) {
109 ret = -ENOMEM;
110 goto out;
111 }
112
113 /*
114 * In the kprobe->ainsn.insn[] array we store the original
115 * instruction at index zero and a break trap instruction at
116 * index one.
117 *
118 * On MIPS arch if the instruction at probed address is a
119 * branch instruction, we need to execute the instruction at
120 * Branch Delayslot (BD) at the time of probe hit. As MIPS also
121 * doesn't have single stepping support, the BD instruction can
122 * not be executed in-line and it would be executed on SSOL slot
123 * using a normal breakpoint instruction in the next slot.
124 * So, read the instruction and save it for later execution.
125 */
126 if (insn_has_delayslot(insn))
127 memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
128 else
129 memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
130
131 p->ainsn.insn[1] = breakpoint2_insn;
132 p->opcode = *p->addr;
133
134 out:
135 return ret;
136 }
137 NOKPROBE_SYMBOL(arch_prepare_kprobe);
138
139 void arch_arm_kprobe(struct kprobe *p)
140 {
141 *p->addr = breakpoint_insn;
142 flush_insn_slot(p);
143 }
144 NOKPROBE_SYMBOL(arch_arm_kprobe);
145
146 void arch_disarm_kprobe(struct kprobe *p)
147 {
148 *p->addr = p->opcode;
149 flush_insn_slot(p);
150 }
151 NOKPROBE_SYMBOL(arch_disarm_kprobe);
152
153 void arch_remove_kprobe(struct kprobe *p)
154 {
155 if (p->ainsn.insn) {
156 free_insn_slot(p->ainsn.insn, 0);
157 p->ainsn.insn = NULL;
158 }
159 }
160 NOKPROBE_SYMBOL(arch_remove_kprobe);
161
162 static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
163 {
164 kcb->prev_kprobe.kp = kprobe_running();
165 kcb->prev_kprobe.status = kcb->kprobe_status;
166 kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
167 kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
168 kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
169 }
170
171 static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
172 {
173 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
174 kcb->kprobe_status = kcb->prev_kprobe.status;
175 kcb->kprobe_old_SR = kcb->prev_kprobe.old_SR;
176 kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
177 kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
178 }
179
180 static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
181 struct kprobe_ctlblk *kcb)
182 {
183 __this_cpu_write(current_kprobe, p);
184 kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
185 kcb->kprobe_saved_epc = regs->cp0_epc;
186 }
187
188 /**
189 * evaluate_branch_instrucion -
190 *
191 * Evaluate the branch instruction at probed address during probe hit. The
192 * result of evaluation would be the updated epc. The insturction in delayslot
193 * would actually be single stepped using a normal breakpoint) on SSOL slot.
194 *
195 * The result is also saved in the kprobe control block for later use,
196 * in case we need to execute the delayslot instruction. The latter will be
197 * false for NOP instruction in dealyslot and the branch-likely instructions
198 * when the branch is taken. And for those cases we set a flag as
199 * SKIP_DELAYSLOT in the kprobe control block
200 */
201 static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
202 struct kprobe_ctlblk *kcb)
203 {
204 union mips_instruction insn = p->opcode;
205 long epc;
206 int ret = 0;
207
208 epc = regs->cp0_epc;
209 if (epc & 3)
210 goto unaligned;
211
212 if (p->ainsn.insn->word == 0)
213 kcb->flags |= SKIP_DELAYSLOT;
214 else
215 kcb->flags &= ~SKIP_DELAYSLOT;
216
217 ret = __compute_return_epc_for_insn(regs, insn);
218 if (ret < 0)
219 return ret;
220
221 if (ret == BRANCH_LIKELY_TAKEN)
222 kcb->flags |= SKIP_DELAYSLOT;
223
224 kcb->target_epc = regs->cp0_epc;
225
226 return 0;
227
228 unaligned:
229 pr_notice("Failed to emulate branch instruction because of unaligned epc - sending SIGBUS to %s.\n", current->comm);
230 force_sig(SIGBUS);
231 return -EFAULT;
232
233 }
234
235 static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
236 struct kprobe_ctlblk *kcb)
237 {
238 int ret = 0;
239
240 regs->cp0_status &= ~ST0_IE;
241
242 /* single step inline if the instruction is a break */
243 if (p->opcode.word == breakpoint_insn.word ||
244 p->opcode.word == breakpoint2_insn.word)
245 regs->cp0_epc = (unsigned long)p->addr;
246 else if (insn_has_delayslot(p->opcode)) {
247 ret = evaluate_branch_instruction(p, regs, kcb);
248 if (ret < 0)
249 return;
250 }
251 regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
252 }
253
254 /*
255 * Called after single-stepping. p->addr is the address of the
256 * instruction whose first byte has been replaced by the "break 0"
257 * instruction. To avoid the SMP problems that can occur when we
258 * temporarily put back the original opcode to single-step, we
259 * single-stepped a copy of the instruction. The address of this
260 * copy is p->ainsn.insn.
261 *
262 * This function prepares to return from the post-single-step
263 * breakpoint trap. In case of branch instructions, the target
264 * epc to be restored.
265 */
266 static void resume_execution(struct kprobe *p,
267 struct pt_regs *regs,
268 struct kprobe_ctlblk *kcb)
269 {
270 if (insn_has_delayslot(p->opcode))
271 regs->cp0_epc = kcb->target_epc;
272 else {
273 unsigned long orig_epc = kcb->kprobe_saved_epc;
274 regs->cp0_epc = orig_epc + 4;
275 }
276 }
277 NOKPROBE_SYMBOL(resume_execution);
278
279 static int kprobe_handler(struct pt_regs *regs)
280 {
281 struct kprobe *p;
282 int ret = 0;
283 kprobe_opcode_t *addr;
284 struct kprobe_ctlblk *kcb;
285
286 addr = (kprobe_opcode_t *) regs->cp0_epc;
287
288 /*
289 * We don't want to be preempted for the entire
290 * duration of kprobe processing
291 */
292 preempt_disable();
293 kcb = get_kprobe_ctlblk();
294
295 /* Check we're not actually recursing */
296 if (kprobe_running()) {
297 p = get_kprobe(addr);
298 if (p) {
299 if (kcb->kprobe_status == KPROBE_HIT_SS &&
300 p->ainsn.insn->word == breakpoint_insn.word) {
301 regs->cp0_status &= ~ST0_IE;
302 regs->cp0_status |= kcb->kprobe_saved_SR;
303 goto no_kprobe;
304 }
305 /*
306 * We have reentered the kprobe_handler(), since
307 * another probe was hit while within the handler.
308 * We here save the original kprobes variables and
309 * just single step on the instruction of the new probe
310 * without calling any user handlers.
311 */
312 save_previous_kprobe(kcb);
313 set_current_kprobe(p, regs, kcb);
314 kprobes_inc_nmissed_count(p);
315 prepare_singlestep(p, regs, kcb);
316 kcb->kprobe_status = KPROBE_REENTER;
317 if (kcb->flags & SKIP_DELAYSLOT) {
318 resume_execution(p, regs, kcb);
319 restore_previous_kprobe(kcb);
320 preempt_enable_no_resched();
321 }
322 return 1;
323 } else if (addr->word != breakpoint_insn.word) {
324 /*
325 * The breakpoint instruction was removed by
326 * another cpu right after we hit, no further
327 * handling of this interrupt is appropriate
328 */
329 ret = 1;
330 }
331 goto no_kprobe;
332 }
333
334 p = get_kprobe(addr);
335 if (!p) {
336 if (addr->word != breakpoint_insn.word) {
337 /*
338 * The breakpoint instruction was removed right
339 * after we hit it. Another cpu has removed
340 * either a probepoint or a debugger breakpoint
341 * at this address. In either case, no further
342 * handling of this interrupt is appropriate.
343 */
344 ret = 1;
345 }
346 /* Not one of ours: let kernel handle it */
347 goto no_kprobe;
348 }
349
350 set_current_kprobe(p, regs, kcb);
351 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
352
353 if (p->pre_handler && p->pre_handler(p, regs)) {
354 /* handler has already set things up, so skip ss setup */
355 reset_current_kprobe();
356 preempt_enable_no_resched();
357 return 1;
358 }
359
360 prepare_singlestep(p, regs, kcb);
361 if (kcb->flags & SKIP_DELAYSLOT) {
362 kcb->kprobe_status = KPROBE_HIT_SSDONE;
363 if (p->post_handler)
364 p->post_handler(p, regs, 0);
365 resume_execution(p, regs, kcb);
366 preempt_enable_no_resched();
367 } else
368 kcb->kprobe_status = KPROBE_HIT_SS;
369
370 return 1;
371
372 no_kprobe:
373 preempt_enable_no_resched();
374 return ret;
375
376 }
377 NOKPROBE_SYMBOL(kprobe_handler);
378
379 static inline int post_kprobe_handler(struct pt_regs *regs)
380 {
381 struct kprobe *cur = kprobe_running();
382 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
383
384 if (!cur)
385 return 0;
386
387 if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
388 kcb->kprobe_status = KPROBE_HIT_SSDONE;
389 cur->post_handler(cur, regs, 0);
390 }
391
392 resume_execution(cur, regs, kcb);
393
394 regs->cp0_status |= kcb->kprobe_saved_SR;
395
396 /* Restore back the original saved kprobes variables and continue. */
397 if (kcb->kprobe_status == KPROBE_REENTER) {
398 restore_previous_kprobe(kcb);
399 goto out;
400 }
401 reset_current_kprobe();
402 out:
403 preempt_enable_no_resched();
404
405 return 1;
406 }
407
408 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
409 {
410 struct kprobe *cur = kprobe_running();
411 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
412
413 if (kcb->kprobe_status & KPROBE_HIT_SS) {
414 resume_execution(cur, regs, kcb);
415 regs->cp0_status |= kcb->kprobe_old_SR;
416
417 reset_current_kprobe();
418 preempt_enable_no_resched();
419 }
420 return 0;
421 }
422
423 /*
424 * Wrapper routine for handling exceptions.
425 */
426 int kprobe_exceptions_notify(struct notifier_block *self,
427 unsigned long val, void *data)
428 {
429
430 struct die_args *args = (struct die_args *)data;
431 int ret = NOTIFY_DONE;
432
433 switch (val) {
434 case DIE_BREAK:
435 if (kprobe_handler(args->regs))
436 ret = NOTIFY_STOP;
437 break;
438 case DIE_SSTEPBP:
439 if (post_kprobe_handler(args->regs))
440 ret = NOTIFY_STOP;
441 break;
442
443 case DIE_PAGE_FAULT:
444 /* kprobe_running() needs smp_processor_id() */
445 preempt_disable();
446
447 if (kprobe_running()
448 && kprobe_fault_handler(args->regs, args->trapnr))
449 ret = NOTIFY_STOP;
450 preempt_enable();
451 break;
452 default:
453 break;
454 }
455 return ret;
456 }
457 NOKPROBE_SYMBOL(kprobe_exceptions_notify);
458
459 /*
460 * Function return probe trampoline:
461 * - init_kprobes() establishes a probepoint here
462 * - When the probed function returns, this probe causes the
463 * handlers to fire
464 */
465 static void __used kretprobe_trampoline_holder(void)
466 {
467 asm volatile(
468 ".set push\n\t"
469 /* Keep the assembler from reordering and placing JR here. */
470 ".set noreorder\n\t"
471 "nop\n\t"
472 ".global __kretprobe_trampoline\n"
473 "__kretprobe_trampoline:\n\t"
474 "nop\n\t"
475 ".set pop"
476 : : : "memory");
477 }
478
479 void __kretprobe_trampoline(void);
480
481 void arch_prepare_kretprobe(struct kretprobe_instance *ri,
482 struct pt_regs *regs)
483 {
484 ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];
485 ri->fp = NULL;
486
487 /* Replace the return addr with trampoline addr */
488 regs->regs[31] = (unsigned long)__kretprobe_trampoline;
489 }
490 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
491
492 /*
493 * Called when the probe at kretprobe trampoline is hit
494 */
495 static int trampoline_probe_handler(struct kprobe *p,
496 struct pt_regs *regs)
497 {
498 instruction_pointer(regs) = __kretprobe_trampoline_handler(regs, NULL);
499 /*
500 * By returning a non-zero value, we are telling
501 * kprobe_handler() that we don't want the post_handler
502 * to run (and have re-enabled preemption)
503 */
504 return 1;
505 }
506 NOKPROBE_SYMBOL(trampoline_probe_handler);
507
508 int arch_trampoline_kprobe(struct kprobe *p)
509 {
510 if (p->addr == (kprobe_opcode_t *)__kretprobe_trampoline)
511 return 1;
512
513 return 0;
514 }
515 NOKPROBE_SYMBOL(arch_trampoline_kprobe);
516
517 static struct kprobe trampoline_p = {
518 .addr = (kprobe_opcode_t *)__kretprobe_trampoline,
519 .pre_handler = trampoline_probe_handler
520 };
521
522 int __init arch_init_kprobes(void)
523 {
524 return register_kprobe(&trampoline_p);
525 }
526
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