arch/powerpc/kernel/hw_breakpoint.c

   1 /*
   2  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
   3  * using the CPU's debug registers. Derived from
   4  * "arch/x86/kernel/hw_breakpoint.c"
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  19  *
  20  * Copyright 2010 IBM Corporation
  21  * Author: K.Prasad <prasad@linux.vnet.ibm.com>
  22  *
  23  */
  24
  25 #include <linux/hw_breakpoint.h>
  26 #include <linux/notifier.h>
  27 #include <linux/kprobes.h>
  28 #include <linux/percpu.h>
  29 #include <linux/kernel.h>
  30 #include <linux/module.h>
  31 #include <linux/sched.h>
  32 #include <linux/init.h>
  33 #include <linux/smp.h>
  34
  35 #include <asm/hw_breakpoint.h>
  36 #include <asm/processor.h>
  37 #include <asm/sstep.h>
  38 #include <asm/uaccess.h>
  39
  40 /*
  41  * Stores the breakpoints currently in use on each breakpoint address
  42  * register for every cpu
  43  */
  44 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
  45
  46 /*
  47  * Returns total number of data or instruction breakpoints available.
  48  */
  49 int hw_breakpoint_slots(int type)
  50 {
  51         if (type == TYPE_DATA)
  52                 return HBP_NUM;
  53         return 0;               /* no instruction breakpoints available */
  54 }
  55
  56 /*
  57  * Install a perf counter breakpoint.
  58  *
  59  * We seek a free debug address register and use it for this
  60  * breakpoint.
  61  *
  62  * Atomic: we hold the counter->ctx->lock and we only handle variables
  63  * and registers local to this cpu.
  64  */
  65 int arch_install_hw_breakpoint(struct perf_event *bp)
  66 {
  67         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
  68         struct perf_event **slot = &__get_cpu_var(bp_per_reg);
  69
  70         *slot = bp;
  71
  72         /*
  73          * Do not install DABR values if the instruction must be single-stepped.
  74          * If so, DABR will be populated in single_step_dabr_instruction().
  75          */
  76         if (current->thread.last_hit_ubp != bp)
  77                 set_dabr(info->address | info->type | DABR_TRANSLATION);
  78
  79         return 0;
  80 }
  81
  82 /*
  83  * Uninstall the breakpoint contained in the given counter.
  84  *
  85  * First we search the debug address register it uses and then we disable
  86  * it.
  87  *
  88  * Atomic: we hold the counter->ctx->lock and we only handle variables
  89  * and registers local to this cpu.
  90  */
  91 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
  92 {
  93         struct perf_event **slot = &__get_cpu_var(bp_per_reg);
  94
  95         if (*slot != bp) {
  96                 WARN_ONCE(1, "Can't find the breakpoint");
  97                 return;
  98         }
  99
 100         *slot = NULL;
 101         set_dabr(0);
 102 }
 103
 104 /*
 105  * Perform cleanup of arch-specific counters during unregistration
 106  * of the perf-event
 107  */
 108 void arch_unregister_hw_breakpoint(struct perf_event *bp)
 109 {
 110         /*
 111          * If the breakpoint is unregistered between a hw_breakpoint_handler()
 112          * and the single_step_dabr_instruction(), then cleanup the breakpoint
 113          * restoration variables to prevent dangling pointers.
 114          */
 115         if (bp->ctx->task)
 116                 bp->ctx->task->thread.last_hit_ubp = NULL;
 117 }
 118
 119 /*
 120  * Check for virtual address in kernel space.
 121  */
 122 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 123 {
 124         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 125
 126         return is_kernel_addr(info->address);
 127 }
 128
 129 int arch_bp_generic_fields(int type, int *gen_bp_type)
 130 {
 131         switch (type) {
 132         case DABR_DATA_READ:
 133                 *gen_bp_type = HW_BREAKPOINT_R;
 134                 break;
 135         case DABR_DATA_WRITE:
 136                 *gen_bp_type = HW_BREAKPOINT_W;
 137                 break;
 138         case (DABR_DATA_WRITE | DABR_DATA_READ):
 139                 *gen_bp_type = (HW_BREAKPOINT_W | HW_BREAKPOINT_R);
 140                 break;
 141         default:
 142                 return -EINVAL;
 143         }
 144         return 0;
 145 }
 146
 147 /*
 148  * Validate the arch-specific HW Breakpoint register settings
 149  */
 150 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 151 {
 152         int ret = -EINVAL;
 153         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 154
 155         if (!bp)
 156                 return ret;
 157
 158         switch (bp->attr.bp_type) {
 159         case HW_BREAKPOINT_R:
 160                 info->type = DABR_DATA_READ;
 161                 break;
 162         case HW_BREAKPOINT_W:
 163                 info->type = DABR_DATA_WRITE;
 164                 break;
 165         case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
 166                 info->type = (DABR_DATA_READ | DABR_DATA_WRITE);
 167                 break;
 168         default:
 169                 return ret;
 170         }
 171
 172         info->address = bp->attr.bp_addr;
 173         info->len = bp->attr.bp_len;
 174
 175         /*
 176          * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
 177          * and breakpoint addresses are aligned to nearest double-word
 178          * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
 179          * 'symbolsize' should satisfy the check below.
 180          */
 181         if (info->len >
 182             (HW_BREAKPOINT_LEN - (info->address & HW_BREAKPOINT_ALIGN)))
 183                 return -EINVAL;
 184         return 0;
 185 }
 186
 187 /*
 188  * Restores the breakpoint on the debug registers.
 189  * Invoke this function if it is known that the execution context is
 190  * about to change to cause loss of MSR_SE settings.
 191  */
 192 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 193 {
 194         struct arch_hw_breakpoint *info;
 195
 196         if (likely(!tsk->thread.last_hit_ubp))
 197                 return;
 198
 199         info = counter_arch_bp(tsk->thread.last_hit_ubp);
 200         regs->msr &= ~MSR_SE;
 201         set_dabr(info->address | info->type | DABR_TRANSLATION);
 202         tsk->thread.last_hit_ubp = NULL;
 203 }
 204
 205 /*
 206  * Handle debug exception notifications.
 207  */
 208 int __kprobes hw_breakpoint_handler(struct die_args *args)
 209 {
 210         int rc = NOTIFY_STOP;
 211         struct perf_event *bp;
 212         struct pt_regs *regs = args->regs;
 213         int stepped = 1;
 214         struct arch_hw_breakpoint *info;
 215         unsigned int instr;
 216         unsigned long dar = regs->dar;
 217
 218         /* Disable breakpoints during exception handling */
 219         set_dabr(0);
 220
 221         /*
 222          * The counter may be concurrently released but that can only
 223          * occur from a call_rcu() path. We can then safely fetch
 224          * the breakpoint, use its callback, touch its counter
 225          * while we are in an rcu_read_lock() path.
 226          */
 227         rcu_read_lock();
 228
 229         bp = __get_cpu_var(bp_per_reg);
 230         if (!bp)
 231                 goto out;
 232         info = counter_arch_bp(bp);
 233
 234         /*
 235          * Return early after invoking user-callback function without restoring
 236          * DABR if the breakpoint is from ptrace which always operates in
 237          * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
 238          * generated in do_dabr().
 239          */
 240         if (bp->overflow_handler == ptrace_triggered) {
 241                 perf_bp_event(bp, regs);
 242                 rc = NOTIFY_DONE;
 243                 goto out;
 244         }
 245
 246         /*
 247          * Verify if dar lies within the address range occupied by the symbol
 248          * being watched to filter extraneous exceptions.  If it doesn't,
 249          * we still need to single-step the instruction, but we don't
 250          * generate an event.
 251          */
 252         info->extraneous_interrupt = !((bp->attr.bp_addr <= dar) &&
 253                         (dar - bp->attr.bp_addr < bp->attr.bp_len));
 254
 255         /* Do not emulate user-space instructions, instead single-step them */
 256         if (user_mode(regs)) {
 257                 bp->ctx->task->thread.last_hit_ubp = bp;
 258                 regs->msr |= MSR_SE;
 259                 goto out;
 260         }
 261
 262         stepped = 0;
 263         instr = 0;
 264         if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
 265                 stepped = emulate_step(regs, instr);
 266
 267         /*
 268          * emulate_step() could not execute it. We've failed in reliably
 269          * handling the hw-breakpoint. Unregister it and throw a warning
 270          * message to let the user know about it.
 271          */
 272         if (!stepped) {
 273                 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
 274                         "0x%lx will be disabled.", info->address);
 275                 perf_event_disable(bp);
 276                 goto out;
 277         }
 278         /*
 279          * As a policy, the callback is invoked in a 'trigger-after-execute'
 280          * fashion
 281          */
 282         if (!info->extraneous_interrupt)
 283                 perf_bp_event(bp, regs);
 284
 285         set_dabr(info->address | info->type | DABR_TRANSLATION);
 286 out:
 287         rcu_read_unlock();
 288         return rc;
 289 }
 290
 291 /*
 292  * Handle single-step exceptions following a DABR hit.
 293  */
 294 int __kprobes single_step_dabr_instruction(struct die_args *args)
 295 {
 296         struct pt_regs *regs = args->regs;
 297         struct perf_event *bp = NULL;
 298         struct arch_hw_breakpoint *bp_info;
 299
 300         bp = current->thread.last_hit_ubp;
 301         /*
 302          * Check if we are single-stepping as a result of a
 303          * previous HW Breakpoint exception
 304          */
 305         if (!bp)
 306                 return NOTIFY_DONE;
 307
 308         bp_info = counter_arch_bp(bp);
 309
 310         /*
 311          * We shall invoke the user-defined callback function in the single
 312          * stepping handler to confirm to 'trigger-after-execute' semantics
 313          */
 314         if (!bp_info->extraneous_interrupt)
 315                 perf_bp_event(bp, regs);
 316
 317         set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
 318         current->thread.last_hit_ubp = NULL;
 319
 320         /*
 321          * If the process was being single-stepped by ptrace, let the
 322          * other single-step actions occur (e.g. generate SIGTRAP).
 323          */
 324         if (test_thread_flag(TIF_SINGLESTEP))
 325                 return NOTIFY_DONE;
 326
 327         return NOTIFY_STOP;
 328 }
 329
 330 /*
 331  * Handle debug exception notifications.
 332  */
 333 int __kprobes hw_breakpoint_exceptions_notify(
 334                 struct notifier_block *unused, unsigned long val, void *data)
 335 {
 336         int ret = NOTIFY_DONE;
 337
 338         switch (val) {
 339         case DIE_DABR_MATCH:
 340                 ret = hw_breakpoint_handler(data);
 341                 break;
 342         case DIE_SSTEP:
 343                 ret = single_step_dabr_instruction(data);
 344                 break;
 345         }
 346
 347         return ret;
 348 }
 349
 350 /*
 351  * Release the user breakpoints used by ptrace
 352  */
 353 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 354 {
 355         struct thread_struct *t = &tsk->thread;
 356
 357         unregister_hw_breakpoint(t->ptrace_bps[0]);
 358         t->ptrace_bps[0] = NULL;
 359 }
 360
 361 void hw_breakpoint_pmu_read(struct perf_event *bp)
 362 {
 363         /* TODO */
 364 }