arch/riscv/kernel/probes/kprobes.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2
   3 #include <linux/kprobes.h>
   4 #include <linux/extable.h>
   5 #include <linux/slab.h>
   6 #include <linux/stop_machine.h>
   7 #include <asm/ptrace.h>
   8 #include <linux/uaccess.h>
   9 #include <asm/sections.h>
  10 #include <asm/cacheflush.h>
  11 #include <asm/bug.h>
  12 #include <asm/patch.h>
  13
  14 #include "decode-insn.h"
  15
  16 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  17 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  18
  19 static void __kprobes
  20 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  21
  22 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  23 {
  24         unsigned long offset = GET_INSN_LENGTH(p->opcode);
  25
  26         p->ainsn.api.restore = (unsigned long)p->addr + offset;
  27
  28         patch_text(p->ainsn.api.insn, p->opcode);
  29         patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
  30                    __BUG_INSN_32);
  31 }
  32
  33 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  34 {
  35         p->ainsn.api.restore = 0;
  36 }
  37
  38 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  39 {
  40         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  41
  42         if (p->ainsn.api.handler)
  43                 p->ainsn.api.handler((u32)p->opcode,
  44                                         (unsigned long)p->addr, regs);
  45
  46         post_kprobe_handler(kcb, regs);
  47 }
  48
  49 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  50 {
  51         unsigned long probe_addr = (unsigned long)p->addr;
  52
  53         if (probe_addr & 0x1) {
  54                 pr_warn("Address not aligned.\n");
  55
  56                 return -EINVAL;
  57         }
  58
  59         /* copy instruction */
  60         p->opcode = *p->addr;
  61
  62         /* decode instruction */
  63         switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
  64         case INSN_REJECTED:     /* insn not supported */
  65                 return -EINVAL;
  66
  67         case INSN_GOOD_NO_SLOT: /* insn need simulation */
  68                 p->ainsn.api.insn = NULL;
  69                 break;
  70
  71         case INSN_GOOD: /* instruction uses slot */
  72                 p->ainsn.api.insn = get_insn_slot();
  73                 if (!p->ainsn.api.insn)
  74                         return -ENOMEM;
  75                 break;
  76         }
  77
  78         /* prepare the instruction */
  79         if (p->ainsn.api.insn)
  80                 arch_prepare_ss_slot(p);
  81         else
  82                 arch_prepare_simulate(p);
  83
  84         return 0;
  85 }
  86
  87 /* install breakpoint in text */
  88 void __kprobes arch_arm_kprobe(struct kprobe *p)
  89 {
  90         if ((p->opcode & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
  91                 patch_text(p->addr, __BUG_INSN_32);
  92         else
  93                 patch_text(p->addr, __BUG_INSN_16);
  94 }
  95
  96 /* remove breakpoint from text */
  97 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  98 {
  99         patch_text(p->addr, p->opcode);
 100 }
 101
 102 void __kprobes arch_remove_kprobe(struct kprobe *p)
 103 {
 104 }
 105
 106 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 107 {
 108         kcb->prev_kprobe.kp = kprobe_running();
 109         kcb->prev_kprobe.status = kcb->kprobe_status;
 110 }
 111
 112 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 113 {
 114         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 115         kcb->kprobe_status = kcb->prev_kprobe.status;
 116 }
 117
 118 static void __kprobes set_current_kprobe(struct kprobe *p)
 119 {
 120         __this_cpu_write(current_kprobe, p);
 121 }
 122
 123 /*
 124  * Interrupts need to be disabled before single-step mode is set, and not
 125  * reenabled until after single-step mode ends.
 126  * Without disabling interrupt on local CPU, there is a chance of
 127  * interrupt occurrence in the period of exception return and  start of
 128  * out-of-line single-step, that result in wrongly single stepping
 129  * into the interrupt handler.
 130  */
 131 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 132                                                 struct pt_regs *regs)
 133 {
 134         kcb->saved_status = regs->status;
 135         regs->status &= ~SR_SPIE;
 136 }
 137
 138 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 139                                                 struct pt_regs *regs)
 140 {
 141         regs->status = kcb->saved_status;
 142 }
 143
 144 static void __kprobes
 145 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr, struct kprobe *p)
 146 {
 147         unsigned long offset = GET_INSN_LENGTH(p->opcode);
 148
 149         kcb->ss_ctx.ss_pending = true;
 150         kcb->ss_ctx.match_addr = addr + offset;
 151 }
 152
 153 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 154 {
 155         kcb->ss_ctx.ss_pending = false;
 156         kcb->ss_ctx.match_addr = 0;
 157 }
 158
 159 static void __kprobes setup_singlestep(struct kprobe *p,
 160                                        struct pt_regs *regs,
 161                                        struct kprobe_ctlblk *kcb, int reenter)
 162 {
 163         unsigned long slot;
 164
 165         if (reenter) {
 166                 save_previous_kprobe(kcb);
 167                 set_current_kprobe(p);
 168                 kcb->kprobe_status = KPROBE_REENTER;
 169         } else {
 170                 kcb->kprobe_status = KPROBE_HIT_SS;
 171         }
 172
 173         if (p->ainsn.api.insn) {
 174                 /* prepare for single stepping */
 175                 slot = (unsigned long)p->ainsn.api.insn;
 176
 177                 set_ss_context(kcb, slot, p);   /* mark pending ss */
 178
 179                 /* IRQs and single stepping do not mix well. */
 180                 kprobes_save_local_irqflag(kcb, regs);
 181
 182                 instruction_pointer_set(regs, slot);
 183         } else {
 184                 /* insn simulation */
 185                 arch_simulate_insn(p, regs);
 186         }
 187 }
 188
 189 static int __kprobes reenter_kprobe(struct kprobe *p,
 190                                     struct pt_regs *regs,
 191                                     struct kprobe_ctlblk *kcb)
 192 {
 193         switch (kcb->kprobe_status) {
 194         case KPROBE_HIT_SSDONE:
 195         case KPROBE_HIT_ACTIVE:
 196                 kprobes_inc_nmissed_count(p);
 197                 setup_singlestep(p, regs, kcb, 1);
 198                 break;
 199         case KPROBE_HIT_SS:
 200         case KPROBE_REENTER:
 201                 pr_warn("Unrecoverable kprobe detected.\n");
 202                 dump_kprobe(p);
 203                 BUG();
 204                 break;
 205         default:
 206                 WARN_ON(1);
 207                 return 0;
 208         }
 209
 210         return 1;
 211 }
 212
 213 static void __kprobes
 214 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 215 {
 216         struct kprobe *cur = kprobe_running();
 217
 218         if (!cur)
 219                 return;
 220
 221         /* return addr restore if non-branching insn */
 222         if (cur->ainsn.api.restore != 0)
 223                 regs->epc = cur->ainsn.api.restore;
 224
 225         /* restore back original saved kprobe variables and continue */
 226         if (kcb->kprobe_status == KPROBE_REENTER) {
 227                 restore_previous_kprobe(kcb);
 228                 return;
 229         }
 230
 231         /* call post handler */
 232         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 233         if (cur->post_handler)  {
 234                 /* post_handler can hit breakpoint and single step
 235                  * again, so we enable D-flag for recursive exception.
 236                  */
 237                 cur->post_handler(cur, regs, 0);
 238         }
 239
 240         reset_current_kprobe();
 241 }
 242
 243 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr)
 244 {
 245         struct kprobe *cur = kprobe_running();
 246         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 247
 248         switch (kcb->kprobe_status) {
 249         case KPROBE_HIT_SS:
 250         case KPROBE_REENTER:
 251                 /*
 252                  * We are here because the instruction being single
 253                  * stepped caused a page fault. We reset the current
 254                  * kprobe and the ip points back to the probe address
 255                  * and allow the page fault handler to continue as a
 256                  * normal page fault.
 257                  */
 258                 regs->epc = (unsigned long) cur->addr;
 259                 BUG_ON(!instruction_pointer(regs));
 260
 261                 if (kcb->kprobe_status == KPROBE_REENTER)
 262                         restore_previous_kprobe(kcb);
 263                 else
 264                         reset_current_kprobe();
 265
 266                 break;
 267         case KPROBE_HIT_ACTIVE:
 268         case KPROBE_HIT_SSDONE:
 269                 /*
 270                  * We increment the nmissed count for accounting,
 271                  * we can also use npre/npostfault count for accounting
 272                  * these specific fault cases.
 273                  */
 274                 kprobes_inc_nmissed_count(cur);
 275
 276                 /*
 277                  * We come here because instructions in the pre/post
 278                  * handler caused the page_fault, this could happen
 279                  * if handler tries to access user space by
 280                  * copy_from_user(), get_user() etc. Let the
 281                  * user-specified handler try to fix it first.
 282                  */
 283                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 284                         return 1;
 285
 286                 /*
 287                  * In case the user-specified fault handler returned
 288                  * zero, try to fix up.
 289                  */
 290                 if (fixup_exception(regs))
 291                         return 1;
 292         }
 293         return 0;
 294 }
 295
 296 bool __kprobes
 297 kprobe_breakpoint_handler(struct pt_regs *regs)
 298 {
 299         struct kprobe *p, *cur_kprobe;
 300         struct kprobe_ctlblk *kcb;
 301         unsigned long addr = instruction_pointer(regs);
 302
 303         kcb = get_kprobe_ctlblk();
 304         cur_kprobe = kprobe_running();
 305
 306         p = get_kprobe((kprobe_opcode_t *) addr);
 307
 308         if (p) {
 309                 if (cur_kprobe) {
 310                         if (reenter_kprobe(p, regs, kcb))
 311                                 return true;
 312                 } else {
 313                         /* Probe hit */
 314                         set_current_kprobe(p);
 315                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 316
 317                         /*
 318                          * If we have no pre-handler or it returned 0, we
 319                          * continue with normal processing.  If we have a
 320                          * pre-handler and it returned non-zero, it will
 321                          * modify the execution path and no need to single
 322                          * stepping. Let's just reset current kprobe and exit.
 323                          *
 324                          * pre_handler can hit a breakpoint and can step thru
 325                          * before return.
 326                          */
 327                         if (!p->pre_handler || !p->pre_handler(p, regs))
 328                                 setup_singlestep(p, regs, kcb, 0);
 329                         else
 330                                 reset_current_kprobe();
 331                 }
 332                 return true;
 333         }
 334
 335         /*
 336          * The breakpoint instruction was removed right
 337          * after we hit it.  Another cpu has removed
 338          * either a probepoint or a debugger breakpoint
 339          * at this address.  In either case, no further
 340          * handling of this interrupt is appropriate.
 341          * Return back to original instruction, and continue.
 342          */
 343         return false;
 344 }
 345
 346 bool __kprobes
 347 kprobe_single_step_handler(struct pt_regs *regs)
 348 {
 349         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 350
 351         if ((kcb->ss_ctx.ss_pending)
 352             && (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
 353                 clear_ss_context(kcb);  /* clear pending ss */
 354
 355                 kprobes_restore_local_irqflag(kcb, regs);
 356
 357                 post_kprobe_handler(kcb, regs);
 358                 return true;
 359         }
 360         return false;
 361 }
 362
 363 /*
 364  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
 365  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
 366  */
 367 int __init arch_populate_kprobe_blacklist(void)
 368 {
 369         int ret;
 370
 371         ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
 372                                         (unsigned long)__irqentry_text_end);
 373         return ret;
 374 }
 375
 376 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 377 {
 378         return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline, NULL);
 379 }
 380
 381 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 382                                       struct pt_regs *regs)
 383 {
 384         ri->ret_addr = (kprobe_opcode_t *)regs->ra;
 385         ri->fp = NULL;
 386         regs->ra = (unsigned long) &kretprobe_trampoline;
 387 }
 388
 389 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 390 {
 391         return 0;
 392 }
 393
 394 int __init arch_init_kprobes(void)
 395 {
 396         return 0;
 397 }