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