arch/arm/probes/kprobes/core.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm/kernel/kprobes.c
   4  *
   5  * Kprobes on ARM
   6  *
   7  * Abhishek Sagar <sagar.abhishek@gmail.com>
   8  * Copyright (C) 2006, 2007 Motorola Inc.
   9  *
  10  * Nicolas Pitre <nico@marvell.com>
  11  * Copyright (C) 2007 Marvell Ltd.
  12  */
  13
  14 #define pr_fmt(fmt) "kprobes: " fmt
  15
  16 #include <linux/kernel.h>
  17 #include <linux/kprobes.h>
  18 #include <linux/module.h>
  19 #include <linux/slab.h>
  20 #include <linux/stop_machine.h>
  21 #include <linux/sched/debug.h>
  22 #include <linux/stringify.h>
  23 #include <asm/traps.h>
  24 #include <asm/opcodes.h>
  25 #include <asm/cacheflush.h>
  26 #include <linux/percpu.h>
  27 #include <linux/bug.h>
  28 #include <asm/patch.h>
  29 #include <asm/sections.h>
  30
  31 #include "../decode-arm.h"
  32 #include "../decode-thumb.h"
  33 #include "core.h"
  34
  35 #define MIN_STACK_SIZE(addr)                            \
  36         min((unsigned long)MAX_STACK_SIZE,              \
  37             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  38
  39 #define flush_insns(addr, size)                         \
  40         flush_icache_range((unsigned long)(addr),       \
  41                            (unsigned long)(addr) +      \
  42                            (size))
  43
  44 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  45 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  46
  47
  48 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  49 {
  50         kprobe_opcode_t insn;
  51         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  52         unsigned long addr = (unsigned long)p->addr;
  53         bool thumb;
  54         kprobe_decode_insn_t *decode_insn;
  55         const union decode_action *actions;
  56         int is;
  57         const struct decode_checker **checkers;
  58
  59 #ifdef CONFIG_THUMB2_KERNEL
  60         thumb = true;
  61         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
  62         insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
  63         if (is_wide_instruction(insn)) {
  64                 u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
  65                 insn = __opcode_thumb32_compose(insn, inst2);
  66                 decode_insn = thumb32_probes_decode_insn;
  67                 actions = kprobes_t32_actions;
  68                 checkers = kprobes_t32_checkers;
  69         } else {
  70                 decode_insn = thumb16_probes_decode_insn;
  71                 actions = kprobes_t16_actions;
  72                 checkers = kprobes_t16_checkers;
  73         }
  74 #else /* !CONFIG_THUMB2_KERNEL */
  75         thumb = false;
  76         if (addr & 0x3)
  77                 return -EINVAL;
  78         insn = __mem_to_opcode_arm(*p->addr);
  79         decode_insn = arm_probes_decode_insn;
  80         actions = kprobes_arm_actions;
  81         checkers = kprobes_arm_checkers;
  82 #endif
  83
  84         p->opcode = insn;
  85         p->ainsn.insn = tmp_insn;
  86
  87         switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
  88         case INSN_REJECTED:     /* not supported */
  89                 return -EINVAL;
  90
  91         case INSN_GOOD:         /* instruction uses slot */
  92                 p->ainsn.insn = get_insn_slot();
  93                 if (!p->ainsn.insn)
  94                         return -ENOMEM;
  95                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  96                         p->ainsn.insn[is] = tmp_insn[is];
  97                 flush_insns(p->ainsn.insn,
  98                                 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
  99                 p->ainsn.insn_fn = (probes_insn_fn_t *)
 100                                         ((uintptr_t)p->ainsn.insn | thumb);
 101                 break;
 102
 103         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
 104                 p->ainsn.insn = NULL;
 105                 break;
 106         }
 107
 108         /*
 109          * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
 110          * 'str r0, [sp, #-68]' should also be prohibited.
 111          * See __und_svc.
 112          */
 113         if ((p->ainsn.stack_space < 0) ||
 114                         (p->ainsn.stack_space > MAX_STACK_SIZE))
 115                 return -EINVAL;
 116
 117         return 0;
 118 }
 119
 120 void __kprobes arch_arm_kprobe(struct kprobe *p)
 121 {
 122         unsigned int brkp;
 123         void *addr;
 124
 125         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 126                 /* Remove any Thumb flag */
 127                 addr = (void *)((uintptr_t)p->addr & ~1);
 128
 129                 if (is_wide_instruction(p->opcode))
 130                         brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
 131                 else
 132                         brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
 133         } else {
 134                 kprobe_opcode_t insn = p->opcode;
 135
 136                 addr = p->addr;
 137                 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
 138
 139                 if (insn >= 0xe0000000)
 140                         brkp |= 0xe0000000;  /* Unconditional instruction */
 141                 else
 142                         brkp |= insn & 0xf0000000;  /* Copy condition from insn */
 143         }
 144
 145         patch_text(addr, brkp);
 146 }
 147
 148 /*
 149  * The actual disarming is done here on each CPU and synchronized using
 150  * stop_machine. This synchronization is necessary on SMP to avoid removing
 151  * a probe between the moment the 'Undefined Instruction' exception is raised
 152  * and the moment the exception handler reads the faulting instruction from
 153  * memory. It is also needed to atomically set the two half-words of a 32-bit
 154  * Thumb breakpoint.
 155  */
 156 struct patch {
 157         void *addr;
 158         unsigned int insn;
 159 };
 160
 161 static int __kprobes_remove_breakpoint(void *data)
 162 {
 163         struct patch *p = data;
 164         __patch_text(p->addr, p->insn);
 165         return 0;
 166 }
 167
 168 void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
 169 {
 170         struct patch p = {
 171                 .addr = addr,
 172                 .insn = insn,
 173         };
 174         stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
 175                                 cpu_online_mask);
 176 }
 177
 178 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 179 {
 180         kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
 181                         p->opcode);
 182 }
 183
 184 void __kprobes arch_remove_kprobe(struct kprobe *p)
 185 {
 186         if (p->ainsn.insn) {
 187                 free_insn_slot(p->ainsn.insn, 0);
 188                 p->ainsn.insn = NULL;
 189         }
 190 }
 191
 192 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 193 {
 194         kcb->prev_kprobe.kp = kprobe_running();
 195         kcb->prev_kprobe.status = kcb->kprobe_status;
 196 }
 197
 198 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 199 {
 200         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 201         kcb->kprobe_status = kcb->prev_kprobe.status;
 202 }
 203
 204 static void __kprobes set_current_kprobe(struct kprobe *p)
 205 {
 206         __this_cpu_write(current_kprobe, p);
 207 }
 208
 209 static void __kprobes
 210 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
 211 {
 212 #ifdef CONFIG_THUMB2_KERNEL
 213         regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
 214         if (is_wide_instruction(p->opcode))
 215                 regs->ARM_pc += 4;
 216         else
 217                 regs->ARM_pc += 2;
 218 #else
 219         regs->ARM_pc += 4;
 220 #endif
 221 }
 222
 223 static inline void __kprobes
 224 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 225 {
 226         p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
 227 }
 228
 229 /*
 230  * Called with IRQs disabled. IRQs must remain disabled from that point
 231  * all the way until processing this kprobe is complete.  The current
 232  * kprobes implementation cannot process more than one nested level of
 233  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 234  * risk encountering a new kprobe in an interrupt handler.
 235  */
 236 static void __kprobes kprobe_handler(struct pt_regs *regs)
 237 {
 238         struct kprobe *p, *cur;
 239         struct kprobe_ctlblk *kcb;
 240
 241         kcb = get_kprobe_ctlblk();
 242         cur = kprobe_running();
 243
 244 #ifdef CONFIG_THUMB2_KERNEL
 245         /*
 246          * First look for a probe which was registered using an address with
 247          * bit 0 set, this is the usual situation for pointers to Thumb code.
 248          * If not found, fallback to looking for one with bit 0 clear.
 249          */
 250         p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
 251         if (!p)
 252                 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 253
 254 #else /* ! CONFIG_THUMB2_KERNEL */
 255         p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 256 #endif
 257
 258         if (p) {
 259                 if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
 260                         /*
 261                          * Probe hit but conditional execution check failed,
 262                          * so just skip the instruction and continue as if
 263                          * nothing had happened.
 264                          * In this case, we can skip recursing check too.
 265                          */
 266                         singlestep_skip(p, regs);
 267                 } else if (cur) {
 268                         /* Kprobe is pending, so we're recursing. */
 269                         switch (kcb->kprobe_status) {
 270                         case KPROBE_HIT_ACTIVE:
 271                         case KPROBE_HIT_SSDONE:
 272                         case KPROBE_HIT_SS:
 273                                 /* A pre- or post-handler probe got us here. */
 274                                 kprobes_inc_nmissed_count(p);
 275                                 save_previous_kprobe(kcb);
 276                                 set_current_kprobe(p);
 277                                 kcb->kprobe_status = KPROBE_REENTER;
 278                                 singlestep(p, regs, kcb);
 279                                 restore_previous_kprobe(kcb);
 280                                 break;
 281                         case KPROBE_REENTER:
 282                                 /* A nested probe was hit in FIQ, it is a BUG */
 283                                 pr_warn("Failed to recover from reentered kprobes.\n");
 284                                 dump_kprobe(p);
 285                                 fallthrough;
 286                         default:
 287                                 /* impossible cases */
 288                                 BUG();
 289                         }
 290                 } else {
 291                         /* Probe hit and conditional execution check ok. */
 292                         set_current_kprobe(p);
 293                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 294
 295                         /*
 296                          * If we have no pre-handler or it returned 0, we
 297                          * continue with normal processing. If we have a
 298                          * pre-handler and it returned non-zero, it will
 299                          * modify the execution path and no need to single
 300                          * stepping. Let's just reset current kprobe and exit.
 301                          */
 302                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 303                                 kcb->kprobe_status = KPROBE_HIT_SS;
 304                                 singlestep(p, regs, kcb);
 305                                 if (p->post_handler) {
 306                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 307                                         p->post_handler(p, regs, 0);
 308                                 }
 309                         }
 310                         reset_current_kprobe();
 311                 }
 312         } else {
 313                 /*
 314                  * The probe was removed and a race is in progress.
 315                  * There is nothing we can do about it.  Let's restart
 316                  * the instruction.  By the time we can restart, the
 317                  * real instruction will be there.
 318                  */
 319         }
 320 }
 321
 322 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 323 {
 324         unsigned long flags;
 325         local_irq_save(flags);
 326         kprobe_handler(regs);
 327         local_irq_restore(flags);
 328         return 0;
 329 }
 330
 331 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 332 {
 333         struct kprobe *cur = kprobe_running();
 334         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 335
 336         switch (kcb->kprobe_status) {
 337         case KPROBE_HIT_SS:
 338         case KPROBE_REENTER:
 339                 /*
 340                  * We are here because the instruction being single
 341                  * stepped caused a page fault. We reset the current
 342                  * kprobe and the PC to point back to the probe address
 343                  * and allow the page fault handler to continue as a
 344                  * normal page fault.
 345                  */
 346                 regs->ARM_pc = (long)cur->addr;
 347                 if (kcb->kprobe_status == KPROBE_REENTER) {
 348                         restore_previous_kprobe(kcb);
 349                 } else {
 350                         reset_current_kprobe();
 351                 }
 352                 break;
 353         }
 354
 355         return 0;
 356 }
 357
 358 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 359                                        unsigned long val, void *data)
 360 {
 361         /*
 362          * notify_die() is currently never called on ARM,
 363          * so this callback is currently empty.
 364          */
 365         return NOTIFY_DONE;
 366 }
 367
 368 /*
 369  * When a retprobed function returns, trampoline_handler() is called,
 370  * calling the kretprobe's handler. We construct a struct pt_regs to
 371  * give a view of registers r0-r11, sp, lr, and pc to the user
 372  * return-handler. This is not a complete pt_regs structure, but that
 373  * should be enough for stacktrace from the return handler with or
 374  * without pt_regs.
 375  */
 376 void __naked __kprobes __kretprobe_trampoline(void)
 377 {
 378         __asm__ __volatile__ (
 379 #ifdef CONFIG_FRAME_POINTER
 380                 "ldr    lr, =__kretprobe_trampoline     \n\t"
 381         /* __kretprobe_trampoline makes a framepointer on pt_regs. */
 382 #ifdef CONFIG_CC_IS_CLANG
 383                 "stmdb  sp, {sp, lr, pc}        \n\t"
 384                 "sub    sp, sp, #12             \n\t"
 385                 /* In clang case, pt_regs->ip = lr. */
 386                 "stmdb  sp!, {r0 - r11, lr}     \n\t"
 387                 /* fp points regs->r11 (fp) */
 388                 "add    fp, sp, #44             \n\t"
 389 #else /* !CONFIG_CC_IS_CLANG */
 390                 /* In gcc case, pt_regs->ip = fp. */
 391                 "stmdb  sp, {fp, sp, lr, pc}    \n\t"
 392                 "sub    sp, sp, #16             \n\t"
 393                 "stmdb  sp!, {r0 - r11}         \n\t"
 394                 /* fp points regs->r15 (pc) */
 395                 "add    fp, sp, #60             \n\t"
 396 #endif /* CONFIG_CC_IS_CLANG */
 397 #else /* !CONFIG_FRAME_POINTER */
 398                 "sub    sp, sp, #16             \n\t"
 399                 "stmdb  sp!, {r0 - r11}         \n\t"
 400 #endif /* CONFIG_FRAME_POINTER */
 401                 "mov    r0, sp                  \n\t"
 402                 "bl     trampoline_handler      \n\t"
 403                 "mov    lr, r0                  \n\t"
 404                 "ldmia  sp!, {r0 - r11}         \n\t"
 405                 "add    sp, sp, #16             \n\t"
 406 #ifdef CONFIG_THUMB2_KERNEL
 407                 "bx     lr                      \n\t"
 408 #else
 409                 "mov    pc, lr                  \n\t"
 410 #endif
 411                 : : : "memory");
 412 }
 413
 414 /* Called from __kretprobe_trampoline */
 415 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 416 {
 417         return (void *)kretprobe_trampoline_handler(regs, (void *)regs->ARM_fp);
 418 }
 419
 420 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 421                                       struct pt_regs *regs)
 422 {
 423         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 424         ri->fp = (void *)regs->ARM_fp;
 425
 426         /* Replace the return addr with trampoline addr. */
 427         regs->ARM_lr = (unsigned long)&__kretprobe_trampoline;
 428 }
 429
 430 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 431 {
 432         return 0;
 433 }
 434
 435 #ifdef CONFIG_THUMB2_KERNEL
 436
 437 static struct undef_hook kprobes_thumb16_break_hook = {
 438         .instr_mask     = 0xffff,
 439         .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
 440         .cpsr_mask      = MODE_MASK,
 441         .cpsr_val       = SVC_MODE,
 442         .fn             = kprobe_trap_handler,
 443 };
 444
 445 static struct undef_hook kprobes_thumb32_break_hook = {
 446         .instr_mask     = 0xffffffff,
 447         .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
 448         .cpsr_mask      = MODE_MASK,
 449         .cpsr_val       = SVC_MODE,
 450         .fn             = kprobe_trap_handler,
 451 };
 452
 453 #else  /* !CONFIG_THUMB2_KERNEL */
 454
 455 static struct undef_hook kprobes_arm_break_hook = {
 456         .instr_mask     = 0x0fffffff,
 457         .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
 458         .cpsr_mask      = MODE_MASK,
 459         .cpsr_val       = SVC_MODE,
 460         .fn             = kprobe_trap_handler,
 461 };
 462
 463 #endif /* !CONFIG_THUMB2_KERNEL */
 464
 465 int __init arch_init_kprobes(void)
 466 {
 467         arm_probes_decode_init();
 468 #ifdef CONFIG_THUMB2_KERNEL
 469         register_undef_hook(&kprobes_thumb16_break_hook);
 470         register_undef_hook(&kprobes_thumb32_break_hook);
 471 #else
 472         register_undef_hook(&kprobes_arm_break_hook);
 473 #endif
 474         return 0;
 475 }
 476
 477 bool arch_within_kprobe_blacklist(unsigned long addr)
 478 {
 479         void *a = (void *)addr;
 480
 481         return __in_irqentry_text(addr) ||
 482                in_entry_text(addr) ||
 483                in_idmap_text(addr) ||
 484                memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
 485 }