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/kdebug.h>
  36 #include <asm/sstep.h>
  37
  38 /* kprobe_status settings */
  39 #define KPROBE_HIT_ACTIVE       0x00000001
  40 #define KPROBE_HIT_SS           0x00000002
  41
  42 static struct kprobe *current_kprobe;
  43 static unsigned long kprobe_status, kprobe_saved_msr;
  44 static struct pt_regs jprobe_saved_regs;
  45
  46 int arch_prepare_kprobe(struct kprobe *p)
  47 {
  48         int ret = 0;
  49         kprobe_opcode_t insn = *p->addr;
  50
  51         if ((unsigned long)p->addr & 0x03) {
  52                 printk("Attempt to register kprobe at an unaligned address\n");
  53                 ret = -EINVAL;
  54         } else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
  55                 printk("Cannot register a kprobe on rfid or mtmsrd\n");
  56                 ret = -EINVAL;
  57         }
  58         return ret;
  59 }
  60
  61 void arch_copy_kprobe(struct kprobe *p)
  62 {
  63         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  64 }
  65
  66 void arch_remove_kprobe(struct kprobe *p)
  67 {
  68 }
  69
  70 static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
  71 {
  72         *p->addr = p->opcode;
  73         regs->nip = (unsigned long)p->addr;
  74 }
  75
  76 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  77 {
  78         regs->msr |= MSR_SE;
  79         /*single step inline if it a breakpoint instruction*/
  80         if (p->opcode == BREAKPOINT_INSTRUCTION)
  81                 regs->nip = (unsigned long)p->addr;
  82         else
  83                 regs->nip = (unsigned long)&p->ainsn.insn;
  84 }
  85
  86 static inline int kprobe_handler(struct pt_regs *regs)
  87 {
  88         struct kprobe *p;
  89         int ret = 0;
  90         unsigned int *addr = (unsigned int *)regs->nip;
  91
  92         /* Check we're not actually recursing */
  93         if (kprobe_running()) {
  94                 /* We *are* holding lock here, so this is safe.
  95                    Disarm the probe we just hit, and ignore it. */
  96                 p = get_kprobe(addr);
  97                 if (p) {
  98                         if (kprobe_status == KPROBE_HIT_SS) {
  99                                 regs->msr &= ~MSR_SE;
 100                                 regs->msr |= kprobe_saved_msr;
 101                                 unlock_kprobes();
 102                                 goto no_kprobe;
 103                         }
 104                         disarm_kprobe(p, regs);
 105                         ret = 1;
 106                 } else {
 107                         p = current_kprobe;
 108                         if (p->break_handler && p->break_handler(p, regs)) {
 109                                 goto ss_probe;
 110                         }
 111                 }
 112                 /* If it's not ours, can't be delete race, (we hold lock). */
 113                 goto no_kprobe;
 114         }
 115
 116         lock_kprobes();
 117         p = get_kprobe(addr);
 118         if (!p) {
 119                 unlock_kprobes();
 120                 if (*addr != BREAKPOINT_INSTRUCTION) {
 121                         /*
 122                          * PowerPC has multiple variants of the "trap"
 123                          * instruction. If the current instruction is a
 124                          * trap variant, it could belong to someone else
 125                          */
 126                         kprobe_opcode_t cur_insn = *addr;
 127                         if (IS_TW(cur_insn) || IS_TD(cur_insn) ||
 128                                         IS_TWI(cur_insn) || IS_TDI(cur_insn))
 129                                 goto no_kprobe;
 130                         /*
 131                          * The breakpoint instruction was removed right
 132                          * after we hit it.  Another cpu has removed
 133                          * either a probepoint or a debugger breakpoint
 134                          * at this address.  In either case, no further
 135                          * handling of this interrupt is appropriate.
 136                          */
 137                         ret = 1;
 138                 }
 139                 /* Not one of ours: let kernel handle it */
 140                 goto no_kprobe;
 141         }
 142
 143         kprobe_status = KPROBE_HIT_ACTIVE;
 144         current_kprobe = p;
 145         kprobe_saved_msr = regs->msr;
 146         if (p->pre_handler && p->pre_handler(p, regs))
 147                 /* handler has already set things up, so skip ss setup */
 148                 return 1;
 149
 150 ss_probe:
 151         prepare_singlestep(p, regs);
 152         kprobe_status = KPROBE_HIT_SS;
 153         /*
 154          * This preempt_disable() matches the preempt_enable_no_resched()
 155          * in post_kprobe_handler().
 156          */
 157         preempt_disable();
 158         return 1;
 159
 160 no_kprobe:
 161         return ret;
 162 }
 163
 164 /*
 165  * Called after single-stepping.  p->addr is the address of the
 166  * instruction whose first byte has been replaced by the "breakpoint"
 167  * instruction.  To avoid the SMP problems that can occur when we
 168  * temporarily put back the original opcode to single-step, we
 169  * single-stepped a copy of the instruction.  The address of this
 170  * copy is p->ainsn.insn.
 171  */
 172 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 173 {
 174         int ret;
 175
 176         regs->nip = (unsigned long)p->addr;
 177         ret = emulate_step(regs, p->ainsn.insn[0]);
 178         if (ret == 0)
 179                 regs->nip = (unsigned long)p->addr + 4;
 180 }
 181
 182 static inline int post_kprobe_handler(struct pt_regs *regs)
 183 {
 184         if (!kprobe_running())
 185                 return 0;
 186
 187         if (current_kprobe->post_handler)
 188                 current_kprobe->post_handler(current_kprobe, regs, 0);
 189
 190         resume_execution(current_kprobe, regs);
 191         regs->msr |= kprobe_saved_msr;
 192
 193         unlock_kprobes();
 194         preempt_enable_no_resched();
 195
 196         /*
 197          * if somebody else is singlestepping across a probe point, msr
 198          * will have SE set, in which case, continue the remaining processing
 199          * of do_debug, as if this is not a probe hit.
 200          */
 201         if (regs->msr & MSR_SE)
 202                 return 0;
 203
 204         return 1;
 205 }
 206
 207 /* Interrupts disabled, kprobe_lock held. */
 208 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 209 {
 210         if (current_kprobe->fault_handler
 211             && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
 212                 return 1;
 213
 214         if (kprobe_status & KPROBE_HIT_SS) {
 215                 resume_execution(current_kprobe, regs);
 216                 regs->msr &= ~MSR_SE;
 217                 regs->msr |= kprobe_saved_msr;
 218
 219                 unlock_kprobes();
 220                 preempt_enable_no_resched();
 221         }
 222         return 0;
 223 }
 224
 225 /*
 226  * Wrapper routine to for handling exceptions.
 227  */
 228 int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
 229                              void *data)
 230 {
 231         struct die_args *args = (struct die_args *)data;
 232         int ret = NOTIFY_DONE;
 233
 234         /*
 235          * Interrupts are not disabled here.  We need to disable
 236          * preemption, because kprobe_running() uses smp_processor_id().
 237          */
 238         preempt_disable();
 239         switch (val) {
 240         case DIE_BPT:
 241                 if (kprobe_handler(args->regs))
 242                         ret = NOTIFY_STOP;
 243                 break;
 244         case DIE_SSTEP:
 245                 if (post_kprobe_handler(args->regs))
 246                         ret = NOTIFY_STOP;
 247                 break;
 248         case DIE_GPF:
 249         case DIE_PAGE_FAULT:
 250                 if (kprobe_running() &&
 251                     kprobe_fault_handler(args->regs, args->trapnr))
 252                         ret = NOTIFY_STOP;
 253                 break;
 254         default:
 255                 break;
 256         }
 257         preempt_enable();
 258         return ret;
 259 }
 260
 261 int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 262 {
 263         struct jprobe *jp = container_of(p, struct jprobe, kp);
 264
 265         memcpy(&jprobe_saved_regs, regs, sizeof(struct pt_regs));
 266
 267         /* setup return addr to the jprobe handler routine */
 268         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
 269         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 270
 271         return 1;
 272 }
 273
 274 void jprobe_return(void)
 275 {
 276         asm volatile("trap" ::: "memory");
 277 }
 278
 279 void jprobe_return_end(void)
 280 {
 281 };
 282
 283 int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 284 {
 285         /*
 286          * FIXME - we should ideally be validating that we got here 'cos
 287          * of the "trap" in jprobe_return() above, before restoring the
 288          * saved regs...
 289          */
 290         memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs));
 291         return 1;
 292 }