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Linux/arch/arm64/kernel/probes/kprobes.c

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  1 /*
  2  * arch/arm64/kernel/probes/kprobes.c
  3  *
  4  * Kprobes support for ARM64
  5  *
  6  * Copyright (C) 2013 Linaro Limited.
  7  * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
  8  *
  9  * This program is free software; you can redistribute it and/or modify
 10  * it under the terms of the GNU General Public License version 2 as
 11  * published by the Free Software Foundation.
 12  *
 13  * This program is distributed in the hope that it will be useful,
 14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 16  * General Public License for more details.
 17  *
 18  */
 19 #include <linux/kasan.h>
 20 #include <linux/kernel.h>
 21 #include <linux/kprobes.h>
 22 #include <linux/extable.h>
 23 #include <linux/slab.h>
 24 #include <linux/stop_machine.h>
 25 #include <linux/sched/debug.h>
 26 #include <linux/stringify.h>
 27 #include <asm/traps.h>
 28 #include <asm/ptrace.h>
 29 #include <asm/cacheflush.h>
 30 #include <asm/debug-monitors.h>
 31 #include <asm/system_misc.h>
 32 #include <asm/insn.h>
 33 #include <linux/uaccess.h>
 34 #include <asm/irq.h>
 35 #include <asm/sections.h>
 36 
 37 #include "decode-insn.h"
 38 
 39 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 40 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 41 
 42 static void __kprobes
 43 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
 44 
 45 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 46 {
 47         /* prepare insn slot */
 48         p->ainsn.api.insn[0] = cpu_to_le32(p->opcode);
 49 
 50         flush_icache_range((uintptr_t) (p->ainsn.api.insn),
 51                            (uintptr_t) (p->ainsn.api.insn) +
 52                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 53 
 54         /*
 55          * Needs restoring of return address after stepping xol.
 56          */
 57         p->ainsn.api.restore = (unsigned long) p->addr +
 58           sizeof(kprobe_opcode_t);
 59 }
 60 
 61 static void __kprobes arch_prepare_simulate(struct kprobe *p)
 62 {
 63         /* This instructions is not executed xol. No need to adjust the PC */
 64         p->ainsn.api.restore = 0;
 65 }
 66 
 67 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 68 {
 69         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 70 
 71         if (p->ainsn.api.handler)
 72                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
 73 
 74         /* single step simulated, now go for post processing */
 75         post_kprobe_handler(kcb, regs);
 76 }
 77 
 78 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 79 {
 80         unsigned long probe_addr = (unsigned long)p->addr;
 81         extern char __start_rodata[];
 82         extern char __end_rodata[];
 83 
 84         if (probe_addr & 0x3)
 85                 return -EINVAL;
 86 
 87         /* copy instruction */
 88         p->opcode = le32_to_cpu(*p->addr);
 89 
 90         if (in_exception_text(probe_addr))
 91                 return -EINVAL;
 92         if (probe_addr >= (unsigned long) __start_rodata &&
 93             probe_addr <= (unsigned long) __end_rodata)
 94                 return -EINVAL;
 95 
 96         /* decode instruction */
 97         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
 98         case INSN_REJECTED:     /* insn not supported */
 99                 return -EINVAL;
100 
101         case INSN_GOOD_NO_SLOT: /* insn need simulation */
102                 p->ainsn.api.insn = NULL;
103                 break;
104 
105         case INSN_GOOD: /* instruction uses slot */
106                 p->ainsn.api.insn = get_insn_slot();
107                 if (!p->ainsn.api.insn)
108                         return -ENOMEM;
109                 break;
110         };
111 
112         /* prepare the instruction */
113         if (p->ainsn.api.insn)
114                 arch_prepare_ss_slot(p);
115         else
116                 arch_prepare_simulate(p);
117 
118         return 0;
119 }
120 
121 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
122 {
123         void *addrs[1];
124         u32 insns[1];
125 
126         addrs[0] = (void *)addr;
127         insns[0] = (u32)opcode;
128 
129         return aarch64_insn_patch_text(addrs, insns, 1);
130 }
131 
132 /* arm kprobe: install breakpoint in text */
133 void __kprobes arch_arm_kprobe(struct kprobe *p)
134 {
135         patch_text(p->addr, BRK64_OPCODE_KPROBES);
136 }
137 
138 /* disarm kprobe: remove breakpoint from text */
139 void __kprobes arch_disarm_kprobe(struct kprobe *p)
140 {
141         patch_text(p->addr, p->opcode);
142 }
143 
144 void __kprobes arch_remove_kprobe(struct kprobe *p)
145 {
146         if (p->ainsn.api.insn) {
147                 free_insn_slot(p->ainsn.api.insn, 0);
148                 p->ainsn.api.insn = NULL;
149         }
150 }
151 
152 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
153 {
154         kcb->prev_kprobe.kp = kprobe_running();
155         kcb->prev_kprobe.status = kcb->kprobe_status;
156 }
157 
158 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
159 {
160         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
161         kcb->kprobe_status = kcb->prev_kprobe.status;
162 }
163 
164 static void __kprobes set_current_kprobe(struct kprobe *p)
165 {
166         __this_cpu_write(current_kprobe, p);
167 }
168 
169 /*
170  * When PSTATE.D is set (masked), then software step exceptions can not be
171  * generated.
172  * SPSR's D bit shows the value of PSTATE.D immediately before the
173  * exception was taken. PSTATE.D is set while entering into any exception
174  * mode, however software clears it for any normal (none-debug-exception)
175  * mode in the exception entry. Therefore, when we are entering into kprobe
176  * breakpoint handler from any normal mode then SPSR.D bit is already
177  * cleared, however it is set when we are entering from any debug exception
178  * mode.
179  * Since we always need to generate single step exception after a kprobe
180  * breakpoint exception therefore we need to clear it unconditionally, when
181  * we become sure that the current breakpoint exception is for kprobe.
182  */
183 static void __kprobes
184 spsr_set_debug_flag(struct pt_regs *regs, int mask)
185 {
186         unsigned long spsr = regs->pstate;
187 
188         if (mask)
189                 spsr |= PSR_D_BIT;
190         else
191                 spsr &= ~PSR_D_BIT;
192 
193         regs->pstate = spsr;
194 }
195 
196 /*
197  * Interrupts need to be disabled before single-step mode is set, and not
198  * reenabled until after single-step mode ends.
199  * Without disabling interrupt on local CPU, there is a chance of
200  * interrupt occurrence in the period of exception return and  start of
201  * out-of-line single-step, that result in wrongly single stepping
202  * into the interrupt handler.
203  */
204 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
205                                                 struct pt_regs *regs)
206 {
207         kcb->saved_irqflag = regs->pstate;
208         regs->pstate |= PSR_I_BIT;
209 }
210 
211 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
212                                                 struct pt_regs *regs)
213 {
214         if (kcb->saved_irqflag & PSR_I_BIT)
215                 regs->pstate |= PSR_I_BIT;
216         else
217                 regs->pstate &= ~PSR_I_BIT;
218 }
219 
220 static void __kprobes
221 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
222 {
223         kcb->ss_ctx.ss_pending = true;
224         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
225 }
226 
227 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
228 {
229         kcb->ss_ctx.ss_pending = false;
230         kcb->ss_ctx.match_addr = 0;
231 }
232 
233 static void __kprobes setup_singlestep(struct kprobe *p,
234                                        struct pt_regs *regs,
235                                        struct kprobe_ctlblk *kcb, int reenter)
236 {
237         unsigned long slot;
238 
239         if (reenter) {
240                 save_previous_kprobe(kcb);
241                 set_current_kprobe(p);
242                 kcb->kprobe_status = KPROBE_REENTER;
243         } else {
244                 kcb->kprobe_status = KPROBE_HIT_SS;
245         }
246 
247 
248         if (p->ainsn.api.insn) {
249                 /* prepare for single stepping */
250                 slot = (unsigned long)p->ainsn.api.insn;
251 
252                 set_ss_context(kcb, slot);      /* mark pending ss */
253 
254                 spsr_set_debug_flag(regs, 0);
255 
256                 /* IRQs and single stepping do not mix well. */
257                 kprobes_save_local_irqflag(kcb, regs);
258                 kernel_enable_single_step(regs);
259                 instruction_pointer_set(regs, slot);
260         } else {
261                 /* insn simulation */
262                 arch_simulate_insn(p, regs);
263         }
264 }
265 
266 static int __kprobes reenter_kprobe(struct kprobe *p,
267                                     struct pt_regs *regs,
268                                     struct kprobe_ctlblk *kcb)
269 {
270         switch (kcb->kprobe_status) {
271         case KPROBE_HIT_SSDONE:
272         case KPROBE_HIT_ACTIVE:
273                 kprobes_inc_nmissed_count(p);
274                 setup_singlestep(p, regs, kcb, 1);
275                 break;
276         case KPROBE_HIT_SS:
277         case KPROBE_REENTER:
278                 pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
279                 dump_kprobe(p);
280                 BUG();
281                 break;
282         default:
283                 WARN_ON(1);
284                 return 0;
285         }
286 
287         return 1;
288 }
289 
290 static void __kprobes
291 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
292 {
293         struct kprobe *cur = kprobe_running();
294 
295         if (!cur)
296                 return;
297 
298         /* return addr restore if non-branching insn */
299         if (cur->ainsn.api.restore != 0)
300                 instruction_pointer_set(regs, cur->ainsn.api.restore);
301 
302         /* restore back original saved kprobe variables and continue */
303         if (kcb->kprobe_status == KPROBE_REENTER) {
304                 restore_previous_kprobe(kcb);
305                 return;
306         }
307         /* call post handler */
308         kcb->kprobe_status = KPROBE_HIT_SSDONE;
309         if (cur->post_handler)  {
310                 /* post_handler can hit breakpoint and single step
311                  * again, so we enable D-flag for recursive exception.
312                  */
313                 cur->post_handler(cur, regs, 0);
314         }
315 
316         reset_current_kprobe();
317 }
318 
319 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
320 {
321         struct kprobe *cur = kprobe_running();
322         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
323 
324         switch (kcb->kprobe_status) {
325         case KPROBE_HIT_SS:
326         case KPROBE_REENTER:
327                 /*
328                  * We are here because the instruction being single
329                  * stepped caused a page fault. We reset the current
330                  * kprobe and the ip points back to the probe address
331                  * and allow the page fault handler to continue as a
332                  * normal page fault.
333                  */
334                 instruction_pointer_set(regs, (unsigned long) cur->addr);
335                 if (!instruction_pointer(regs))
336                         BUG();
337 
338                 kernel_disable_single_step();
339 
340                 if (kcb->kprobe_status == KPROBE_REENTER)
341                         restore_previous_kprobe(kcb);
342                 else
343                         reset_current_kprobe();
344 
345                 break;
346         case KPROBE_HIT_ACTIVE:
347         case KPROBE_HIT_SSDONE:
348                 /*
349                  * We increment the nmissed count for accounting,
350                  * we can also use npre/npostfault count for accounting
351                  * these specific fault cases.
352                  */
353                 kprobes_inc_nmissed_count(cur);
354 
355                 /*
356                  * We come here because instructions in the pre/post
357                  * handler caused the page_fault, this could happen
358                  * if handler tries to access user space by
359                  * copy_from_user(), get_user() etc. Let the
360                  * user-specified handler try to fix it first.
361                  */
362                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
363                         return 1;
364 
365                 /*
366                  * In case the user-specified fault handler returned
367                  * zero, try to fix up.
368                  */
369                 if (fixup_exception(regs))
370                         return 1;
371         }
372         return 0;
373 }
374 
375 static void __kprobes kprobe_handler(struct pt_regs *regs)
376 {
377         struct kprobe *p, *cur_kprobe;
378         struct kprobe_ctlblk *kcb;
379         unsigned long addr = instruction_pointer(regs);
380 
381         kcb = get_kprobe_ctlblk();
382         cur_kprobe = kprobe_running();
383 
384         p = get_kprobe((kprobe_opcode_t *) addr);
385 
386         if (p) {
387                 if (cur_kprobe) {
388                         if (reenter_kprobe(p, regs, kcb))
389                                 return;
390                 } else {
391                         /* Probe hit */
392                         set_current_kprobe(p);
393                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
394 
395                         /*
396                          * If we have no pre-handler or it returned 0, we
397                          * continue with normal processing.  If we have a
398                          * pre-handler and it returned non-zero, it prepped
399                          * for calling the break_handler below on re-entry,
400                          * so get out doing nothing more here.
401                          *
402                          * pre_handler can hit a breakpoint and can step thru
403                          * before return, keep PSTATE D-flag enabled until
404                          * pre_handler return back.
405                          */
406                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
407                                 setup_singlestep(p, regs, kcb, 0);
408                                 return;
409                         }
410                 }
411         } else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
412             BRK64_OPCODE_KPROBES) && cur_kprobe) {
413                 /* We probably hit a jprobe.  Call its break handler. */
414                 if (cur_kprobe->break_handler  &&
415                      cur_kprobe->break_handler(cur_kprobe, regs)) {
416                         setup_singlestep(cur_kprobe, regs, kcb, 0);
417                         return;
418                 }
419         }
420         /*
421          * The breakpoint instruction was removed right
422          * after we hit it.  Another cpu has removed
423          * either a probepoint or a debugger breakpoint
424          * at this address.  In either case, no further
425          * handling of this interrupt is appropriate.
426          * Return back to original instruction, and continue.
427          */
428 }
429 
430 static int __kprobes
431 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
432 {
433         if ((kcb->ss_ctx.ss_pending)
434             && (kcb->ss_ctx.match_addr == addr)) {
435                 clear_ss_context(kcb);  /* clear pending ss */
436                 return DBG_HOOK_HANDLED;
437         }
438         /* not ours, kprobes should ignore it */
439         return DBG_HOOK_ERROR;
440 }
441 
442 int __kprobes
443 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
444 {
445         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
446         int retval;
447 
448         /* return error if this is not our step */
449         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
450 
451         if (retval == DBG_HOOK_HANDLED) {
452                 kprobes_restore_local_irqflag(kcb, regs);
453                 kernel_disable_single_step();
454 
455                 post_kprobe_handler(kcb, regs);
456         }
457 
458         return retval;
459 }
460 
461 int __kprobes
462 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
463 {
464         kprobe_handler(regs);
465         return DBG_HOOK_HANDLED;
466 }
467 
468 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
469 {
470         struct jprobe *jp = container_of(p, struct jprobe, kp);
471         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
472 
473         kcb->jprobe_saved_regs = *regs;
474         /*
475          * Since we can't be sure where in the stack frame "stacked"
476          * pass-by-value arguments are stored we just don't try to
477          * duplicate any of the stack. Do not use jprobes on functions that
478          * use more than 64 bytes (after padding each to an 8 byte boundary)
479          * of arguments, or pass individual arguments larger than 16 bytes.
480          */
481 
482         instruction_pointer_set(regs, (unsigned long) jp->entry);
483         preempt_disable();
484         pause_graph_tracing();
485         return 1;
486 }
487 
488 void __kprobes jprobe_return(void)
489 {
490         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
491 
492         /*
493          * Jprobe handler return by entering break exception,
494          * encoded same as kprobe, but with following conditions
495          * -a special PC to identify it from the other kprobes.
496          * -restore stack addr to original saved pt_regs
497          */
498         asm volatile("                          mov sp, %0      \n"
499                      "jprobe_return_break:      brk %1          \n"
500                      :
501                      : "r" (kcb->jprobe_saved_regs.sp),
502                        "I" (BRK64_ESR_KPROBES)
503                      : "memory");
504 
505         unreachable();
506 }
507 
508 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
509 {
510         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
511         long stack_addr = kcb->jprobe_saved_regs.sp;
512         long orig_sp = kernel_stack_pointer(regs);
513         struct jprobe *jp = container_of(p, struct jprobe, kp);
514         extern const char jprobe_return_break[];
515 
516         if (instruction_pointer(regs) != (u64) jprobe_return_break)
517                 return 0;
518 
519         if (orig_sp != stack_addr) {
520                 struct pt_regs *saved_regs =
521                     (struct pt_regs *)kcb->jprobe_saved_regs.sp;
522                 pr_err("current sp %lx does not match saved sp %lx\n",
523                        orig_sp, stack_addr);
524                 pr_err("Saved registers for jprobe %p\n", jp);
525                 __show_regs(saved_regs);
526                 pr_err("Current registers\n");
527                 __show_regs(regs);
528                 BUG();
529         }
530         unpause_graph_tracing();
531         *regs = kcb->jprobe_saved_regs;
532         preempt_enable_no_resched();
533         return 1;
534 }
535 
536 bool arch_within_kprobe_blacklist(unsigned long addr)
537 {
538         if ((addr >= (unsigned long)__kprobes_text_start &&
539             addr < (unsigned long)__kprobes_text_end) ||
540             (addr >= (unsigned long)__entry_text_start &&
541             addr < (unsigned long)__entry_text_end) ||
542             (addr >= (unsigned long)__idmap_text_start &&
543             addr < (unsigned long)__idmap_text_end) ||
544             !!search_exception_tables(addr))
545                 return true;
546 
547         if (!is_kernel_in_hyp_mode()) {
548                 if ((addr >= (unsigned long)__hyp_text_start &&
549                     addr < (unsigned long)__hyp_text_end) ||
550                     (addr >= (unsigned long)__hyp_idmap_text_start &&
551                     addr < (unsigned long)__hyp_idmap_text_end))
552                         return true;
553         }
554 
555         return false;
556 }
557 
558 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
559 {
560         struct kretprobe_instance *ri = NULL;
561         struct hlist_head *head, empty_rp;
562         struct hlist_node *tmp;
563         unsigned long flags, orig_ret_address = 0;
564         unsigned long trampoline_address =
565                 (unsigned long)&kretprobe_trampoline;
566         kprobe_opcode_t *correct_ret_addr = NULL;
567 
568         INIT_HLIST_HEAD(&empty_rp);
569         kretprobe_hash_lock(current, &head, &flags);
570 
571         /*
572          * It is possible to have multiple instances associated with a given
573          * task either because multiple functions in the call path have
574          * return probes installed on them, and/or more than one
575          * return probe was registered for a target function.
576          *
577          * We can handle this because:
578          *     - instances are always pushed into the head of the list
579          *     - when multiple return probes are registered for the same
580          *       function, the (chronologically) first instance's ret_addr
581          *       will be the real return address, and all the rest will
582          *       point to kretprobe_trampoline.
583          */
584         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
585                 if (ri->task != current)
586                         /* another task is sharing our hash bucket */
587                         continue;
588 
589                 orig_ret_address = (unsigned long)ri->ret_addr;
590 
591                 if (orig_ret_address != trampoline_address)
592                         /*
593                          * This is the real return address. Any other
594                          * instances associated with this task are for
595                          * other calls deeper on the call stack
596                          */
597                         break;
598         }
599 
600         kretprobe_assert(ri, orig_ret_address, trampoline_address);
601 
602         correct_ret_addr = ri->ret_addr;
603         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
604                 if (ri->task != current)
605                         /* another task is sharing our hash bucket */
606                         continue;
607 
608                 orig_ret_address = (unsigned long)ri->ret_addr;
609                 if (ri->rp && ri->rp->handler) {
610                         __this_cpu_write(current_kprobe, &ri->rp->kp);
611                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
612                         ri->ret_addr = correct_ret_addr;
613                         ri->rp->handler(ri, regs);
614                         __this_cpu_write(current_kprobe, NULL);
615                 }
616 
617                 recycle_rp_inst(ri, &empty_rp);
618 
619                 if (orig_ret_address != trampoline_address)
620                         /*
621                          * This is the real return address. Any other
622                          * instances associated with this task are for
623                          * other calls deeper on the call stack
624                          */
625                         break;
626         }
627 
628         kretprobe_hash_unlock(current, &flags);
629 
630         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
631                 hlist_del(&ri->hlist);
632                 kfree(ri);
633         }
634         return (void *)orig_ret_address;
635 }
636 
637 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
638                                       struct pt_regs *regs)
639 {
640         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
641 
642         /* replace return addr (x30) with trampoline */
643         regs->regs[30] = (long)&kretprobe_trampoline;
644 }
645 
646 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
647 {
648         return 0;
649 }
650 
651 int __init arch_init_kprobes(void)
652 {
653         return 0;
654 }
655 

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