arch/ppc64/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *  arch/ppc64/kernel/kprobes.c
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18  *
  19  * Copyright (C) IBM Corporation, 2002, 2004
  20  *
  21  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  22  *              Probes initial implementation ( includes contributions from
  23  *              Rusty Russell).
  24  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  25  *              interface to access function arguments.
  26  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  27  *              for PPC64
  28  */
  29
  30 #include <linux/config.h>
  31 #include <linux/kprobes.h>
  32 #include <linux/ptrace.h>
  33 #include <linux/spinlock.h>
  34 #include <linux/preempt.h>
  35 #include <asm/cacheflush.h>
  36 #include <asm/kdebug.h>
  37 #include <asm/sstep.h>
  38
  39 static struct kprobe *current_kprobe;
  40 static unsigned long kprobe_status, kprobe_saved_msr;
  41 static struct kprobe *kprobe_prev;
  42 static unsigned long kprobe_status_prev, kprobe_saved_msr_prev;
  43 static struct pt_regs jprobe_saved_regs;
  44
  45 int arch_prepare_kprobe(struct kprobe *p)
  46 {
  47         int ret = 0;
  48         kprobe_opcode_t insn = *p->addr;
  49
  50         if ((unsigned long)p->addr & 0x03) {
  51                 printk("Attempt to register kprobe at an unaligned address\n");
  52                 ret = -EINVAL;
  53         } else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
  54                 printk("Cannot register a kprobe on rfid or mtmsrd\n");
  55                 ret = -EINVAL;
  56         }
  57         return ret;
  58 }
  59
  60 void arch_copy_kprobe(struct kprobe *p)
  61 {
  62         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  63         p->opcode = *p->addr;
  64 }
  65
  66 void arch_arm_kprobe(struct kprobe *p)
  67 {
  68         *p->addr = BREAKPOINT_INSTRUCTION;
  69         flush_icache_range((unsigned long) p->addr,
  70                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  71 }
  72
  73 void arch_disarm_kprobe(struct kprobe *p)
  74 {
  75         *p->addr = p->opcode;
  76         flush_icache_range((unsigned long) p->addr,
  77                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  78 }
  79
  80 void arch_remove_kprobe(struct kprobe *p)
  81 {
  82 }
  83
  84 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  85 {
  86         regs->msr |= MSR_SE;
  87         /*single step inline if it a breakpoint instruction*/
  88         if (p->opcode == BREAKPOINT_INSTRUCTION)
  89                 regs->nip = (unsigned long)p->addr;
  90         else
  91                 regs->nip = (unsigned long)&p->ainsn.insn;
  92 }
  93
  94 static inline void save_previous_kprobe(void)
  95 {
  96         kprobe_prev = current_kprobe;
  97         kprobe_status_prev = kprobe_status;
  98         kprobe_saved_msr_prev = kprobe_saved_msr;
  99 }
 100
 101 static inline void restore_previous_kprobe(void)
 102 {
 103         current_kprobe = kprobe_prev;
 104         kprobe_status = kprobe_status_prev;
 105         kprobe_saved_msr = kprobe_saved_msr_prev;
 106 }
 107
 108 static inline int kprobe_handler(struct pt_regs *regs)
 109 {
 110         struct kprobe *p;
 111         int ret = 0;
 112         unsigned int *addr = (unsigned int *)regs->nip;
 113
 114         /* Check we're not actually recursing */
 115         if (kprobe_running()) {
 116                 /* We *are* holding lock here, so this is safe.
 117                    Disarm the probe we just hit, and ignore it. */
 118                 p = get_kprobe(addr);
 119                 if (p) {
 120                         if (kprobe_status == KPROBE_HIT_SS) {
 121                                 regs->msr &= ~MSR_SE;
 122                                 regs->msr |= kprobe_saved_msr;
 123                                 unlock_kprobes();
 124                                 goto no_kprobe;
 125                         }
 126                         /* We have reentered the kprobe_handler(), since
 127                          * another probe was hit while within the handler.
 128                          * We here save the original kprobes variables and
 129                          * just single step on the instruction of the new probe
 130                          * without calling any user handlers.
 131                          */
 132                         save_previous_kprobe();
 133                         current_kprobe = p;
 134                         kprobe_saved_msr = regs->msr;
 135                         p->nmissed++;
 136                         prepare_singlestep(p, regs);
 137                         kprobe_status = KPROBE_REENTER;
 138                         return 1;
 139                 } else {
 140                         p = current_kprobe;
 141                         if (p->break_handler && p->break_handler(p, regs)) {
 142                                 goto ss_probe;
 143                         }
 144                 }
 145                 /* If it's not ours, can't be delete race, (we hold lock). */
 146                 goto no_kprobe;
 147         }
 148
 149         lock_kprobes();
 150         p = get_kprobe(addr);
 151         if (!p) {
 152                 unlock_kprobes();
 153                 if (*addr != BREAKPOINT_INSTRUCTION) {
 154                         /*
 155                          * PowerPC has multiple variants of the "trap"
 156                          * instruction. If the current instruction is a
 157                          * trap variant, it could belong to someone else
 158                          */
 159                         kprobe_opcode_t cur_insn = *addr;
 160                         if (IS_TW(cur_insn) || IS_TD(cur_insn) ||
 161                                         IS_TWI(cur_insn) || IS_TDI(cur_insn))
 162                                 goto no_kprobe;
 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         kprobe_status = KPROBE_HIT_ACTIVE;
 177         current_kprobe = p;
 178         kprobe_saved_msr = regs->msr;
 179         if (p->pre_handler && p->pre_handler(p, regs))
 180                 /* handler has already set things up, so skip ss setup */
 181                 return 1;
 182
 183 ss_probe:
 184         prepare_singlestep(p, regs);
 185         kprobe_status = KPROBE_HIT_SS;
 186         /*
 187          * This preempt_disable() matches the preempt_enable_no_resched()
 188          * in post_kprobe_handler().
 189          */
 190         preempt_disable();
 191         return 1;
 192
 193 no_kprobe:
 194         return ret;
 195 }
 196
 197 /*
 198  * Called after single-stepping.  p->addr is the address of the
 199  * instruction whose first byte has been replaced by the "breakpoint"
 200  * instruction.  To avoid the SMP problems that can occur when we
 201  * temporarily put back the original opcode to single-step, we
 202  * single-stepped a copy of the instruction.  The address of this
 203  * copy is p->ainsn.insn.
 204  */
 205 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 206 {
 207         int ret;
 208
 209         regs->nip = (unsigned long)p->addr;
 210         ret = emulate_step(regs, p->ainsn.insn[0]);
 211         if (ret == 0)
 212                 regs->nip = (unsigned long)p->addr + 4;
 213 }
 214
 215 static inline int post_kprobe_handler(struct pt_regs *regs)
 216 {
 217         if (!kprobe_running())
 218                 return 0;
 219
 220         if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
 221                 kprobe_status = KPROBE_HIT_SSDONE;
 222                 current_kprobe->post_handler(current_kprobe, regs, 0);
 223         }
 224
 225         resume_execution(current_kprobe, regs);
 226         regs->msr |= kprobe_saved_msr;
 227
 228         /*Restore back the original saved kprobes variables and continue. */
 229         if (kprobe_status == KPROBE_REENTER) {
 230                 restore_previous_kprobe();
 231                 goto out;
 232         }
 233         unlock_kprobes();
 234 out:
 235         preempt_enable_no_resched();
 236
 237         /*
 238          * if somebody else is singlestepping across a probe point, msr
 239          * will have SE set, in which case, continue the remaining processing
 240          * of do_debug, as if this is not a probe hit.
 241          */
 242         if (regs->msr & MSR_SE)
 243                 return 0;
 244
 245         return 1;
 246 }
 247
 248 /* Interrupts disabled, kprobe_lock held. */
 249 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 250 {
 251         if (current_kprobe->fault_handler
 252             && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
 253                 return 1;
 254
 255         if (kprobe_status & KPROBE_HIT_SS) {
 256                 resume_execution(current_kprobe, regs);
 257                 regs->msr &= ~MSR_SE;
 258                 regs->msr |= kprobe_saved_msr;
 259
 260                 unlock_kprobes();
 261                 preempt_enable_no_resched();
 262         }
 263         return 0;
 264 }
 265
 266 /*
 267  * Wrapper routine to for handling exceptions.
 268  */
 269 int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
 270                              void *data)
 271 {
 272         struct die_args *args = (struct die_args *)data;
 273         int ret = NOTIFY_DONE;
 274
 275         /*
 276          * Interrupts are not disabled here.  We need to disable
 277          * preemption, because kprobe_running() uses smp_processor_id().
 278          */
 279         preempt_disable();
 280         switch (val) {
 281         case DIE_BPT:
 282                 if (kprobe_handler(args->regs))
 283                         ret = NOTIFY_STOP;
 284                 break;
 285         case DIE_SSTEP:
 286                 if (post_kprobe_handler(args->regs))
 287                         ret = NOTIFY_STOP;
 288                 break;
 289         case DIE_GPF:
 290         case DIE_PAGE_FAULT:
 291                 if (kprobe_running() &&
 292                     kprobe_fault_handler(args->regs, args->trapnr))
 293                         ret = NOTIFY_STOP;
 294                 break;
 295         default:
 296                 break;
 297         }
 298         preempt_enable();
 299         return ret;
 300 }
 301
 302 int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 303 {
 304         struct jprobe *jp = container_of(p, struct jprobe, kp);
 305
 306         memcpy(&jprobe_saved_regs, regs, sizeof(struct pt_regs));
 307
 308         /* setup return addr to the jprobe handler routine */
 309         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
 310         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 311
 312         return 1;
 313 }
 314
 315 void jprobe_return(void)
 316 {
 317         asm volatile("trap" ::: "memory");
 318 }
 319
 320 void jprobe_return_end(void)
 321 {
 322 };
 323
 324 int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 325 {
 326         /*
 327          * FIXME - we should ideally be validating that we got here 'cos
 328          * of the "trap" in jprobe_return() above, before restoring the
 329          * saved regs...
 330          */
 331         memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs));
 332         return 1;
 333 }