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