arch/arm64/kernel/probes/kprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm64/kernel/probes/kprobes.c
   4  *
   5  * Kprobes support for ARM64
   6  *
   7  * Copyright (C) 2013 Linaro Limited.
   8  * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
   9  */
  10
  11 #define pr_fmt(fmt) "kprobes: " fmt
  12
  13 #include <linux/extable.h>
  14 #include <linux/kasan.h>
  15 #include <linux/kernel.h>
  16 #include <linux/kprobes.h>
  17 #include <linux/sched/debug.h>
  18 #include <linux/set_memory.h>
  19 #include <linux/slab.h>
  20 #include <linux/stop_machine.h>
  21 #include <linux/stringify.h>
  22 #include <linux/uaccess.h>
  23 #include <linux/vmalloc.h>
  24
  25 #include <asm/cacheflush.h>
  26 #include <asm/daifflags.h>
  27 #include <asm/debug-monitors.h>
  28 #include <asm/insn.h>
  29 #include <asm/irq.h>
  30 #include <asm/patching.h>
  31 #include <asm/ptrace.h>
  32 #include <asm/sections.h>
  33 #include <asm/system_misc.h>
  34 #include <asm/traps.h>
  35
  36 #include "decode-insn.h"
  37
  38 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  39 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  40
  41 static void __kprobes
  42 post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
  43
  44 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  45 {
  46         kprobe_opcode_t *addr = p->ainsn.api.insn;
  47
  48         /*
  49          * Prepare insn slot, Mark Rutland points out it depends on a coupe of
  50          * subtleties:
  51          *
  52          * - That the I-cache maintenance for these instructions is complete
  53          *   *before* the kprobe BRK is written (and aarch64_insn_patch_text_nosync()
  54          *   ensures this, but just omits causing a Context-Synchronization-Event
  55          *   on all CPUS).
  56          *
  57          * - That the kprobe BRK results in an exception (and consequently a
  58          *   Context-Synchronoization-Event), which ensures that the CPU will
  59          *   fetch thesingle-step slot instructions *after* this, ensuring that
  60          *   the new instructions are used
  61          *
  62          * It supposes to place ISB after patching to guarantee I-cache maintenance
  63          * is observed on all CPUS, however, single-step slot is installed in
  64          * the BRK exception handler, so it is unnecessary to generate
  65          * Contex-Synchronization-Event via ISB again.
  66          */
  67         aarch64_insn_patch_text_nosync(addr, p->opcode);
  68         aarch64_insn_patch_text_nosync(addr + 1, BRK64_OPCODE_KPROBES_SS);
  69
  70         /*
  71          * Needs restoring of return address after stepping xol.
  72          */
  73         p->ainsn.api.restore = (unsigned long) p->addr +
  74           sizeof(kprobe_opcode_t);
  75 }
  76
  77 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  78 {
  79         /* This instructions is not executed xol. No need to adjust the PC */
  80         p->ainsn.api.restore = 0;
  81 }
  82
  83 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  84 {
  85         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  86
  87         if (p->ainsn.api.handler)
  88                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  89
  90         /* single step simulated, now go for post processing */
  91         post_kprobe_handler(p, kcb, regs);
  92 }
  93
  94 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  95 {
  96         unsigned long probe_addr = (unsigned long)p->addr;
  97
  98         if (probe_addr & 0x3)
  99                 return -EINVAL;
 100
 101         /* copy instruction */
 102         p->opcode = le32_to_cpu(*p->addr);
 103
 104         if (search_exception_tables(probe_addr))
 105                 return -EINVAL;
 106
 107         /* decode instruction */
 108         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
 109         case INSN_REJECTED:     /* insn not supported */
 110                 return -EINVAL;
 111
 112         case INSN_GOOD_NO_SLOT: /* insn need simulation */
 113                 p->ainsn.api.insn = NULL;
 114                 break;
 115
 116         case INSN_GOOD: /* instruction uses slot */
 117                 p->ainsn.api.insn = get_insn_slot();
 118                 if (!p->ainsn.api.insn)
 119                         return -ENOMEM;
 120                 break;
 121         }
 122
 123         /* prepare the instruction */
 124         if (p->ainsn.api.insn)
 125                 arch_prepare_ss_slot(p);
 126         else
 127                 arch_prepare_simulate(p);
 128
 129         return 0;
 130 }
 131
 132 void *alloc_insn_page(void)
 133 {
 134         return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
 135                         GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
 136                         NUMA_NO_NODE, __builtin_return_address(0));
 137 }
 138
 139 /* arm kprobe: install breakpoint in text */
 140 void __kprobes arch_arm_kprobe(struct kprobe *p)
 141 {
 142         void *addr = p->addr;
 143         u32 insn = BRK64_OPCODE_KPROBES;
 144
 145         aarch64_insn_patch_text(&addr, &insn, 1);
 146 }
 147
 148 /* disarm kprobe: remove breakpoint from text */
 149 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 150 {
 151         void *addr = p->addr;
 152
 153         aarch64_insn_patch_text(&addr, &p->opcode, 1);
 154 }
 155
 156 void __kprobes arch_remove_kprobe(struct kprobe *p)
 157 {
 158         if (p->ainsn.api.insn) {
 159                 free_insn_slot(p->ainsn.api.insn, 0);
 160                 p->ainsn.api.insn = NULL;
 161         }
 162 }
 163
 164 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 165 {
 166         kcb->prev_kprobe.kp = kprobe_running();
 167         kcb->prev_kprobe.status = kcb->kprobe_status;
 168 }
 169
 170 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 171 {
 172         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 173         kcb->kprobe_status = kcb->prev_kprobe.status;
 174 }
 175
 176 static void __kprobes set_current_kprobe(struct kprobe *p)
 177 {
 178         __this_cpu_write(current_kprobe, p);
 179 }
 180
 181 /*
 182  * Mask all of DAIF while executing the instruction out-of-line, to keep things
 183  * simple and avoid nesting exceptions. Interrupts do have to be disabled since
 184  * the kprobe state is per-CPU and doesn't get migrated.
 185  */
 186 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 187                                                 struct pt_regs *regs)
 188 {
 189         kcb->saved_irqflag = regs->pstate & DAIF_MASK;
 190         regs->pstate |= DAIF_MASK;
 191 }
 192
 193 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 194                                                 struct pt_regs *regs)
 195 {
 196         regs->pstate &= ~DAIF_MASK;
 197         regs->pstate |= kcb->saved_irqflag;
 198 }
 199
 200 static void __kprobes setup_singlestep(struct kprobe *p,
 201                                        struct pt_regs *regs,
 202                                        struct kprobe_ctlblk *kcb, int reenter)
 203 {
 204         unsigned long slot;
 205
 206         if (reenter) {
 207                 save_previous_kprobe(kcb);
 208                 set_current_kprobe(p);
 209                 kcb->kprobe_status = KPROBE_REENTER;
 210         } else {
 211                 kcb->kprobe_status = KPROBE_HIT_SS;
 212         }
 213
 214
 215         if (p->ainsn.api.insn) {
 216                 /* prepare for single stepping */
 217                 slot = (unsigned long)p->ainsn.api.insn;
 218
 219                 kprobes_save_local_irqflag(kcb, regs);
 220                 instruction_pointer_set(regs, slot);
 221         } else {
 222                 /* insn simulation */
 223                 arch_simulate_insn(p, regs);
 224         }
 225 }
 226
 227 static int __kprobes reenter_kprobe(struct kprobe *p,
 228                                     struct pt_regs *regs,
 229                                     struct kprobe_ctlblk *kcb)
 230 {
 231         switch (kcb->kprobe_status) {
 232         case KPROBE_HIT_SSDONE:
 233         case KPROBE_HIT_ACTIVE:
 234                 kprobes_inc_nmissed_count(p);
 235                 setup_singlestep(p, regs, kcb, 1);
 236                 break;
 237         case KPROBE_HIT_SS:
 238         case KPROBE_REENTER:
 239                 pr_warn("Failed to recover from reentered kprobes.\n");
 240                 dump_kprobe(p);
 241                 BUG();
 242                 break;
 243         default:
 244                 WARN_ON(1);
 245                 return 0;
 246         }
 247
 248         return 1;
 249 }
 250
 251 static void __kprobes
 252 post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 253 {
 254         /* return addr restore if non-branching insn */
 255         if (cur->ainsn.api.restore != 0)
 256                 instruction_pointer_set(regs, cur->ainsn.api.restore);
 257
 258         /* restore back original saved kprobe variables and continue */
 259         if (kcb->kprobe_status == KPROBE_REENTER) {
 260                 restore_previous_kprobe(kcb);
 261                 return;
 262         }
 263         /* call post handler */
 264         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 265         if (cur->post_handler)
 266                 cur->post_handler(cur, regs, 0);
 267
 268         reset_current_kprobe();
 269 }
 270
 271 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 272 {
 273         struct kprobe *cur = kprobe_running();
 274         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 275
 276         switch (kcb->kprobe_status) {
 277         case KPROBE_HIT_SS:
 278         case KPROBE_REENTER:
 279                 /*
 280                  * We are here because the instruction being single
 281                  * stepped caused a page fault. We reset the current
 282                  * kprobe and the ip points back to the probe address
 283                  * and allow the page fault handler to continue as a
 284                  * normal page fault.
 285                  */
 286                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 287                 BUG_ON(!instruction_pointer(regs));
 288
 289                 if (kcb->kprobe_status == KPROBE_REENTER) {
 290                         restore_previous_kprobe(kcb);
 291                 } else {
 292                         kprobes_restore_local_irqflag(kcb, regs);
 293                         reset_current_kprobe();
 294                 }
 295
 296                 break;
 297         }
 298         return 0;
 299 }
 300
 301 static int __kprobes
 302 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned long esr)
 303 {
 304         struct kprobe *p, *cur_kprobe;
 305         struct kprobe_ctlblk *kcb;
 306         unsigned long addr = instruction_pointer(regs);
 307
 308         kcb = get_kprobe_ctlblk();
 309         cur_kprobe = kprobe_running();
 310
 311         p = get_kprobe((kprobe_opcode_t *) addr);
 312         if (WARN_ON_ONCE(!p)) {
 313                 /*
 314                  * Something went wrong. This BRK used an immediate reserved
 315                  * for kprobes, but we couldn't find any corresponding probe.
 316                  */
 317                 return DBG_HOOK_ERROR;
 318         }
 319
 320         if (cur_kprobe) {
 321                 /* Hit a kprobe inside another kprobe */
 322                 if (!reenter_kprobe(p, regs, kcb))
 323                         return DBG_HOOK_ERROR;
 324         } else {
 325                 /* Probe hit */
 326                 set_current_kprobe(p);
 327                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 328
 329                 /*
 330                  * If we have no pre-handler or it returned 0, we
 331                  * continue with normal processing.  If we have a
 332                  * pre-handler and it returned non-zero, it will
 333                  * modify the execution path and not need to single-step
 334                  * Let's just reset current kprobe and exit.
 335                  */
 336                 if (!p->pre_handler || !p->pre_handler(p, regs))
 337                         setup_singlestep(p, regs, kcb, 0);
 338                 else
 339                         reset_current_kprobe();
 340         }
 341
 342         return DBG_HOOK_HANDLED;
 343 }
 344
 345 static struct break_hook kprobes_break_hook = {
 346         .imm = KPROBES_BRK_IMM,
 347         .fn = kprobe_breakpoint_handler,
 348 };
 349
 350 static int __kprobes
 351 kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned long esr)
 352 {
 353         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 354         unsigned long addr = instruction_pointer(regs);
 355         struct kprobe *cur = kprobe_running();
 356
 357         if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
 358             ((unsigned long)&cur->ainsn.api.insn[1] == addr)) {
 359                 kprobes_restore_local_irqflag(kcb, regs);
 360                 post_kprobe_handler(cur, kcb, regs);
 361
 362                 return DBG_HOOK_HANDLED;
 363         }
 364
 365         /* not ours, kprobes should ignore it */
 366         return DBG_HOOK_ERROR;
 367 }
 368
 369 static struct break_hook kprobes_break_ss_hook = {
 370         .imm = KPROBES_BRK_SS_IMM,
 371         .fn = kprobe_breakpoint_ss_handler,
 372 };
 373
 374 /*
 375  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
 376  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
 377  */
 378 int __init arch_populate_kprobe_blacklist(void)
 379 {
 380         int ret;
 381
 382         ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
 383                                         (unsigned long)__entry_text_end);
 384         if (ret)
 385                 return ret;
 386         ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
 387                                         (unsigned long)__irqentry_text_end);
 388         if (ret)
 389                 return ret;
 390         ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
 391                                         (unsigned long)__hyp_text_end);
 392         if (ret || is_kernel_in_hyp_mode())
 393                 return ret;
 394         ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
 395                                         (unsigned long)__hyp_idmap_text_end);
 396         return ret;
 397 }
 398
 399 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 400 {
 401         return (void *)kretprobe_trampoline_handler(regs, (void *)regs->regs[29]);
 402 }
 403
 404 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 405                                       struct pt_regs *regs)
 406 {
 407         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 408         ri->fp = (void *)regs->regs[29];
 409
 410         /* replace return addr (x30) with trampoline */
 411         regs->regs[30] = (long)&__kretprobe_trampoline;
 412 }
 413
 414 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 415 {
 416         return 0;
 417 }
 418
 419 int __init arch_init_kprobes(void)
 420 {
 421         register_kernel_break_hook(&kprobes_break_hook);
 422         register_kernel_break_hook(&kprobes_break_ss_hook);
 423
 424         return 0;
 425 }