arch/mips/kernel/kprobes.c

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