arch/sparc/kernel/kprobes.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* arch/sparc64/kernel/kprobes.c
   3  *
   4  * Copyright (C) 2004 David S. Miller <davem@davemloft.net>
   5  */
   6
   7 #include <linux/kernel.h>
   8 #include <linux/kprobes.h>
   9 #include <linux/extable.h>
  10 #include <linux/kdebug.h>
  11 #include <linux/slab.h>
  12 #include <linux/context_tracking.h>
  13 #include <asm/signal.h>
  14 #include <asm/cacheflush.h>
  15 #include <linux/uaccess.h>
  16
  17 /* We do not have hardware single-stepping on sparc64.
  18  * So we implement software single-stepping with breakpoint
  19  * traps.  The top-level scheme is similar to that used
  20  * in the x86 kprobes implementation.
  21  *
  22  * In the kprobe->ainsn.insn[] array we store the original
  23  * instruction at index zero and a break instruction at
  24  * index one.
  25  *
  26  * When we hit a kprobe we:
  27  * - Run the pre-handler
  28  * - Remember "regs->tnpc" and interrupt level stored in
  29  *   "regs->tstate" so we can restore them later
  30  * - Disable PIL interrupts
  31  * - Set regs->tpc to point to kprobe->ainsn.insn[0]
  32  * - Set regs->tnpc to point to kprobe->ainsn.insn[1]
  33  * - Mark that we are actively in a kprobe
  34  *
  35  * At this point we wait for the second breakpoint at
  36  * kprobe->ainsn.insn[1] to hit.  When it does we:
  37  * - Run the post-handler
  38  * - Set regs->tpc to "remembered" regs->tnpc stored above,
  39  *   restore the PIL interrupt level in "regs->tstate" as well
  40  * - Make any adjustments necessary to regs->tnpc in order
  41  *   to handle relative branches correctly.  See below.
  42  * - Mark that we are no longer actively in a kprobe.
  43  */
  44
  45 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  46 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  47
  48 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  49
  50 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  51 {
  52         if ((unsigned long) p->addr & 0x3UL)
  53                 return -EILSEQ;
  54
  55         p->ainsn.insn[0] = *p->addr;
  56         flushi(&p->ainsn.insn[0]);
  57
  58         p->ainsn.insn[1] = BREAKPOINT_INSTRUCTION_2;
  59         flushi(&p->ainsn.insn[1]);
  60
  61         p->opcode = *p->addr;
  62         return 0;
  63 }
  64
  65 void __kprobes arch_arm_kprobe(struct kprobe *p)
  66 {
  67         *p->addr = BREAKPOINT_INSTRUCTION;
  68         flushi(p->addr);
  69 }
  70
  71 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  72 {
  73         *p->addr = p->opcode;
  74         flushi(p->addr);
  75 }
  76
  77 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
  78 {
  79         kcb->prev_kprobe.kp = kprobe_running();
  80         kcb->prev_kprobe.status = kcb->kprobe_status;
  81         kcb->prev_kprobe.orig_tnpc = kcb->kprobe_orig_tnpc;
  82         kcb->prev_kprobe.orig_tstate_pil = kcb->kprobe_orig_tstate_pil;
  83 }
  84
  85 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
  86 {
  87         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
  88         kcb->kprobe_status = kcb->prev_kprobe.status;
  89         kcb->kprobe_orig_tnpc = kcb->prev_kprobe.orig_tnpc;
  90         kcb->kprobe_orig_tstate_pil = kcb->prev_kprobe.orig_tstate_pil;
  91 }
  92
  93 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
  94                                 struct kprobe_ctlblk *kcb)
  95 {
  96         __this_cpu_write(current_kprobe, p);
  97         kcb->kprobe_orig_tnpc = regs->tnpc;
  98         kcb->kprobe_orig_tstate_pil = (regs->tstate & TSTATE_PIL);
  99 }
 100
 101 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
 102                         struct kprobe_ctlblk *kcb)
 103 {
 104         regs->tstate |= TSTATE_PIL;
 105
 106         /*single step inline, if it a breakpoint instruction*/
 107         if (p->opcode == BREAKPOINT_INSTRUCTION) {
 108                 regs->tpc = (unsigned long) p->addr;
 109                 regs->tnpc = kcb->kprobe_orig_tnpc;
 110         } else {
 111                 regs->tpc = (unsigned long) &p->ainsn.insn[0];
 112                 regs->tnpc = (unsigned long) &p->ainsn.insn[1];
 113         }
 114 }
 115
 116 static int __kprobes kprobe_handler(struct pt_regs *regs)
 117 {
 118         struct kprobe *p;
 119         void *addr = (void *) regs->tpc;
 120         int ret = 0;
 121         struct kprobe_ctlblk *kcb;
 122
 123         /*
 124          * We don't want to be preempted for the entire
 125          * duration of kprobe processing
 126          */
 127         preempt_disable();
 128         kcb = get_kprobe_ctlblk();
 129
 130         if (kprobe_running()) {
 131                 p = get_kprobe(addr);
 132                 if (p) {
 133                         if (kcb->kprobe_status == KPROBE_HIT_SS) {
 134                                 regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
 135                                         kcb->kprobe_orig_tstate_pil);
 136                                 goto no_kprobe;
 137                         }
 138                         /* We have reentered the kprobe_handler(), since
 139                          * another probe was hit while within the handler.
 140                          * We here save the original kprobes variables and
 141                          * just single step on the instruction of the new probe
 142                          * without calling any user handlers.
 143                          */
 144                         save_previous_kprobe(kcb);
 145                         set_current_kprobe(p, regs, kcb);
 146                         kprobes_inc_nmissed_count(p);
 147                         kcb->kprobe_status = KPROBE_REENTER;
 148                         prepare_singlestep(p, regs, kcb);
 149                         return 1;
 150                 } else if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
 151                         /* The breakpoint instruction was removed by
 152                          * another cpu right after we hit, no further
 153                          * handling of this interrupt is appropriate
 154                          */
 155                         ret = 1;
 156                 }
 157                 goto no_kprobe;
 158         }
 159
 160         p = get_kprobe(addr);
 161         if (!p) {
 162                 if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
 163                         /*
 164                          * The breakpoint instruction was removed right
 165                          * after we hit it.  Another cpu has removed
 166                          * either a probepoint or a debugger breakpoint
 167                          * at this address.  In either case, no further
 168                          * handling of this interrupt is appropriate.
 169                          */
 170                         ret = 1;
 171                 }
 172                 /* Not one of ours: let kernel handle it */
 173                 goto no_kprobe;
 174         }
 175
 176         set_current_kprobe(p, regs, kcb);
 177         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 178         if (p->pre_handler && p->pre_handler(p, regs)) {
 179                 reset_current_kprobe();
 180                 preempt_enable_no_resched();
 181                 return 1;
 182         }
 183
 184         prepare_singlestep(p, regs, kcb);
 185         kcb->kprobe_status = KPROBE_HIT_SS;
 186         return 1;
 187
 188 no_kprobe:
 189         preempt_enable_no_resched();
 190         return ret;
 191 }
 192
 193 /* If INSN is a relative control transfer instruction,
 194  * return the corrected branch destination value.
 195  *
 196  * regs->tpc and regs->tnpc still hold the values of the
 197  * program counters at the time of trap due to the execution
 198  * of the BREAKPOINT_INSTRUCTION_2 at p->ainsn.insn[1]
 199  *
 200  */
 201 static unsigned long __kprobes relbranch_fixup(u32 insn, struct kprobe *p,
 202                                                struct pt_regs *regs)
 203 {
 204         unsigned long real_pc = (unsigned long) p->addr;
 205
 206         /* Branch not taken, no mods necessary.  */
 207         if (regs->tnpc == regs->tpc + 0x4UL)
 208                 return real_pc + 0x8UL;
 209
 210         /* The three cases are call, branch w/prediction,
 211          * and traditional branch.
 212          */
 213         if ((insn & 0xc0000000) == 0x40000000 ||
 214             (insn & 0xc1c00000) == 0x00400000 ||
 215             (insn & 0xc1c00000) == 0x00800000) {
 216                 unsigned long ainsn_addr;
 217
 218                 ainsn_addr = (unsigned long) &p->ainsn.insn[0];
 219
 220                 /* The instruction did all the work for us
 221                  * already, just apply the offset to the correct
 222                  * instruction location.
 223                  */
 224                 return (real_pc + (regs->tnpc - ainsn_addr));
 225         }
 226
 227         /* It is jmpl or some other absolute PC modification instruction,
 228          * leave NPC as-is.
 229          */
 230         return regs->tnpc;
 231 }
 232
 233 /* If INSN is an instruction which writes it's PC location
 234  * into a destination register, fix that up.
 235  */
 236 static void __kprobes retpc_fixup(struct pt_regs *regs, u32 insn,
 237                                   unsigned long real_pc)
 238 {
 239         unsigned long *slot = NULL;
 240
 241         /* Simplest case is 'call', which always uses %o7 */
 242         if ((insn & 0xc0000000) == 0x40000000) {
 243                 slot = &regs->u_regs[UREG_I7];
 244         }
 245
 246         /* 'jmpl' encodes the register inside of the opcode */
 247         if ((insn & 0xc1f80000) == 0x81c00000) {
 248                 unsigned long rd = ((insn >> 25) & 0x1f);
 249
 250                 if (rd <= 15) {
 251                         slot = &regs->u_regs[rd];
 252                 } else {
 253                         /* Hard case, it goes onto the stack. */
 254                         flushw_all();
 255
 256                         rd -= 16;
 257                         slot = (unsigned long *)
 258                                 (regs->u_regs[UREG_FP] + STACK_BIAS);
 259                         slot += rd;
 260                 }
 261         }
 262         if (slot != NULL)
 263                 *slot = real_pc;
 264 }
 265
 266 /*
 267  * Called after single-stepping.  p->addr is the address of the
 268  * instruction which has been replaced by the breakpoint
 269  * instruction.  To avoid the SMP problems that can occur when we
 270  * temporarily put back the original opcode to single-step, we
 271  * single-stepped a copy of the instruction.  The address of this
 272  * copy is &p->ainsn.insn[0].
 273  *
 274  * This function prepares to return from the post-single-step
 275  * breakpoint trap.
 276  */
 277 static void __kprobes resume_execution(struct kprobe *p,
 278                 struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 279 {
 280         u32 insn = p->ainsn.insn[0];
 281
 282         regs->tnpc = relbranch_fixup(insn, p, regs);
 283
 284         /* This assignment must occur after relbranch_fixup() */
 285         regs->tpc = kcb->kprobe_orig_tnpc;
 286
 287         retpc_fixup(regs, insn, (unsigned long) p->addr);
 288
 289         regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
 290                         kcb->kprobe_orig_tstate_pil);
 291 }
 292
 293 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 294 {
 295         struct kprobe *cur = kprobe_running();
 296         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 297
 298         if (!cur)
 299                 return 0;
 300
 301         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 302                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 303                 cur->post_handler(cur, regs, 0);
 304         }
 305
 306         resume_execution(cur, regs, kcb);
 307
 308         /*Restore back the original saved kprobes variables and continue. */
 309         if (kcb->kprobe_status == KPROBE_REENTER) {
 310                 restore_previous_kprobe(kcb);
 311                 goto out;
 312         }
 313         reset_current_kprobe();
 314 out:
 315         preempt_enable_no_resched();
 316
 317         return 1;
 318 }
 319
 320 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 321 {
 322         struct kprobe *cur = kprobe_running();
 323         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 324         const struct exception_table_entry *entry;
 325
 326         switch(kcb->kprobe_status) {
 327         case KPROBE_HIT_SS:
 328         case KPROBE_REENTER:
 329                 /*
 330                  * We are here because the instruction being single
 331                  * stepped caused a page fault. We reset the current
 332                  * kprobe and the tpc points back to the probe address
 333                  * and allow the page fault handler to continue as a
 334                  * normal page fault.
 335                  */
 336                 regs->tpc = (unsigned long)cur->addr;
 337                 regs->tnpc = kcb->kprobe_orig_tnpc;
 338                 regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
 339                                 kcb->kprobe_orig_tstate_pil);
 340                 if (kcb->kprobe_status == KPROBE_REENTER)
 341                         restore_previous_kprobe(kcb);
 342                 else
 343                         reset_current_kprobe();
 344                 preempt_enable_no_resched();
 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, trapnr))
 363                         return 1;
 364
 365                 /*
 366                  * In case the user-specified fault handler returned
 367                  * zero, try to fix up.
 368                  */
 369
 370                 entry = search_exception_tables(regs->tpc);
 371                 if (entry) {
 372                         regs->tpc = entry->fixup;
 373                         regs->tnpc = regs->tpc + 4;
 374                         return 1;
 375                 }
 376
 377                 /*
 378                  * fixup_exception() could not handle it,
 379                  * Let do_page_fault() fix it.
 380                  */
 381                 break;
 382         default:
 383                 break;
 384         }
 385
 386         return 0;
 387 }
 388
 389 /*
 390  * Wrapper routine to for handling exceptions.
 391  */
 392 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 393                                        unsigned long val, void *data)
 394 {
 395         struct die_args *args = (struct die_args *)data;
 396         int ret = NOTIFY_DONE;
 397
 398         if (args->regs && user_mode(args->regs))
 399                 return ret;
 400
 401         switch (val) {
 402         case DIE_DEBUG:
 403                 if (kprobe_handler(args->regs))
 404                         ret = NOTIFY_STOP;
 405                 break;
 406         case DIE_DEBUG_2:
 407                 if (post_kprobe_handler(args->regs))
 408                         ret = NOTIFY_STOP;
 409                 break;
 410         default:
 411                 break;
 412         }
 413         return ret;
 414 }
 415
 416 asmlinkage void __kprobes kprobe_trap(unsigned long trap_level,
 417                                       struct pt_regs *regs)
 418 {
 419         enum ctx_state prev_state = exception_enter();
 420
 421         BUG_ON(trap_level != 0x170 && trap_level != 0x171);
 422
 423         if (user_mode(regs)) {
 424                 local_irq_enable();
 425                 bad_trap(regs, trap_level);
 426                 goto out;
 427         }
 428
 429         /* trap_level == 0x170 --> ta 0x70
 430          * trap_level == 0x171 --> ta 0x71
 431          */
 432         if (notify_die((trap_level == 0x170) ? DIE_DEBUG : DIE_DEBUG_2,
 433                        (trap_level == 0x170) ? "debug" : "debug_2",
 434                        regs, 0, trap_level, SIGTRAP) != NOTIFY_STOP)
 435                 bad_trap(regs, trap_level);
 436 out:
 437         exception_exit(prev_state);
 438 }
 439
 440 /* The value stored in the return address register is actually 2
 441  * instructions before where the callee will return to.
 442  * Sequences usually look something like this
 443  *
 444  *              call    some_function   <--- return register points here
 445  *               nop                    <--- call delay slot
 446  *              whatever                <--- where callee returns to
 447  *
 448  * To keep trampoline_probe_handler logic simpler, we normalize the
 449  * value kept in ri->ret_addr so we don't need to keep adjusting it
 450  * back and forth.
 451  */
 452 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 453                                       struct pt_regs *regs)
 454 {
 455         ri->ret_addr = (kprobe_opcode_t *)(regs->u_regs[UREG_RETPC] + 8);
 456
 457         /* Replace the return addr with trampoline addr */
 458         regs->u_regs[UREG_RETPC] =
 459                 ((unsigned long)kretprobe_trampoline) - 8;
 460 }
 461
 462 /*
 463  * Called when the probe at kretprobe trampoline is hit
 464  */
 465 static int __kprobes trampoline_probe_handler(struct kprobe *p,
 466                                               struct pt_regs *regs)
 467 {
 468         struct kretprobe_instance *ri = NULL;
 469         struct hlist_head *head, empty_rp;
 470         struct hlist_node *tmp;
 471         unsigned long flags, orig_ret_address = 0;
 472         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 473
 474         INIT_HLIST_HEAD(&empty_rp);
 475         kretprobe_hash_lock(current, &head, &flags);
 476
 477         /*
 478          * It is possible to have multiple instances associated with a given
 479          * task either because an multiple functions in the call path
 480          * have a return probe installed on them, and/or more than one return
 481          * return probe was registered for a target function.
 482          *
 483          * We can handle this because:
 484          *     - instances are always inserted at the head of the list
 485          *     - when multiple return probes are registered for the same
 486          *       function, the first instance's ret_addr will point to the
 487          *       real return address, and all the rest will point to
 488          *       kretprobe_trampoline
 489          */
 490         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 491                 if (ri->task != current)
 492                         /* another task is sharing our hash bucket */
 493                         continue;
 494
 495                 if (ri->rp && ri->rp->handler)
 496                         ri->rp->handler(ri, regs);
 497
 498                 orig_ret_address = (unsigned long)ri->ret_addr;
 499                 recycle_rp_inst(ri, &empty_rp);
 500
 501                 if (orig_ret_address != trampoline_address)
 502                         /*
 503                          * This is the real return address. Any other
 504                          * instances associated with this task are for
 505                          * other calls deeper on the call stack
 506                          */
 507                         break;
 508         }
 509
 510         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 511         regs->tpc = orig_ret_address;
 512         regs->tnpc = orig_ret_address + 4;
 513
 514         kretprobe_hash_unlock(current, &flags);
 515
 516         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 517                 hlist_del(&ri->hlist);
 518                 kfree(ri);
 519         }
 520         /*
 521          * By returning a non-zero value, we are telling
 522          * kprobe_handler() that we don't want the post_handler
 523          * to run (and have re-enabled preemption)
 524          */
 525         return 1;
 526 }
 527
 528 static void __used kretprobe_trampoline_holder(void)
 529 {
 530         asm volatile(".global kretprobe_trampoline\n"
 531                      "kretprobe_trampoline:\n"
 532                      "\tnop\n"
 533                      "\tnop\n");
 534 }
 535 static struct kprobe trampoline_p = {
 536         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 537         .pre_handler = trampoline_probe_handler
 538 };
 539
 540 int __init arch_init_kprobes(void)
 541 {
 542         return register_kprobe(&trampoline_p);
 543 }
 544
 545 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 546 {
 547         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 548                 return 1;
 549
 550         return 0;
 551 }