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, info->dabrx);
  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, 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         info->dabrx = DABRX_ALL;
 174         if (bp->attr.exclude_user)
 175                 info->dabrx &= ~DABRX_USER;
 176         if (bp->attr.exclude_kernel)
 177                 info->dabrx &= ~DABRX_KERNEL;
 178         if (bp->attr.exclude_hv)
 179                 info->dabrx &= ~DABRX_HYP;
 180
 181         /*
 182          * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
 183          * and breakpoint addresses are aligned to nearest double-word
 184          * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
 185          * 'symbolsize' should satisfy the check below.
 186          */
 187         if (info->len >
 188             (HW_BREAKPOINT_LEN - (info->address & HW_BREAKPOINT_ALIGN)))
 189                 return -EINVAL;
 190         return 0;
 191 }
 192
 193 /*
 194  * Restores the breakpoint on the debug registers.
 195  * Invoke this function if it is known that the execution context is
 196  * about to change to cause loss of MSR_SE settings.
 197  */
 198 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 199 {
 200         struct arch_hw_breakpoint *info;
 201
 202         if (likely(!tsk->thread.last_hit_ubp))
 203                 return;
 204
 205         info = counter_arch_bp(tsk->thread.last_hit_ubp);
 206         regs->msr &= ~MSR_SE;
 207         set_dabr(info->address | info->type | DABR_TRANSLATION, info->dabrx);
 208         tsk->thread.last_hit_ubp = NULL;
 209 }
 210
 211 /*
 212  * Handle debug exception notifications.
 213  */
 214 int __kprobes hw_breakpoint_handler(struct die_args *args)
 215 {
 216         int rc = NOTIFY_STOP;
 217         struct perf_event *bp;
 218         struct pt_regs *regs = args->regs;
 219         int stepped = 1;
 220         struct arch_hw_breakpoint *info;
 221         unsigned int instr;
 222         unsigned long dar = regs->dar;
 223
 224         /* Disable breakpoints during exception handling */
 225         set_dabr(0, 0);
 226
 227         /*
 228          * The counter may be concurrently released but that can only
 229          * occur from a call_rcu() path. We can then safely fetch
 230          * the breakpoint, use its callback, touch its counter
 231          * while we are in an rcu_read_lock() path.
 232          */
 233         rcu_read_lock();
 234
 235         bp = __get_cpu_var(bp_per_reg);
 236         if (!bp)
 237                 goto out;
 238         info = counter_arch_bp(bp);
 239
 240         /*
 241          * Return early after invoking user-callback function without restoring
 242          * DABR if the breakpoint is from ptrace which always operates in
 243          * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
 244          * generated in do_dabr().
 245          */
 246         if (bp->overflow_handler == ptrace_triggered) {
 247                 perf_bp_event(bp, regs);
 248                 rc = NOTIFY_DONE;
 249                 goto out;
 250         }
 251
 252         /*
 253          * Verify if dar lies within the address range occupied by the symbol
 254          * being watched to filter extraneous exceptions.  If it doesn't,
 255          * we still need to single-step the instruction, but we don't
 256          * generate an event.
 257          */
 258         info->extraneous_interrupt = !((bp->attr.bp_addr <= dar) &&
 259                         (dar - bp->attr.bp_addr < bp->attr.bp_len));
 260
 261         /* Do not emulate user-space instructions, instead single-step them */
 262         if (user_mode(regs)) {
 263                 current->thread.last_hit_ubp = bp;
 264                 regs->msr |= MSR_SE;
 265                 goto out;
 266         }
 267
 268         stepped = 0;
 269         instr = 0;
 270         if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
 271                 stepped = emulate_step(regs, instr);
 272
 273         /*
 274          * emulate_step() could not execute it. We've failed in reliably
 275          * handling the hw-breakpoint. Unregister it and throw a warning
 276          * message to let the user know about it.
 277          */
 278         if (!stepped) {
 279                 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
 280                         "0x%lx will be disabled.", info->address);
 281                 perf_event_disable(bp);
 282                 goto out;
 283         }
 284         /*
 285          * As a policy, the callback is invoked in a 'trigger-after-execute'
 286          * fashion
 287          */
 288         if (!info->extraneous_interrupt)
 289                 perf_bp_event(bp, regs);
 290
 291         set_dabr(info->address | info->type | DABR_TRANSLATION, info->dabrx);
 292 out:
 293         rcu_read_unlock();
 294         return rc;
 295 }
 296
 297 /*
 298  * Handle single-step exceptions following a DABR hit.
 299  */
 300 int __kprobes single_step_dabr_instruction(struct die_args *args)
 301 {
 302         struct pt_regs *regs = args->regs;
 303         struct perf_event *bp = NULL;
 304         struct arch_hw_breakpoint *info;
 305
 306         bp = current->thread.last_hit_ubp;
 307         /*
 308          * Check if we are single-stepping as a result of a
 309          * previous HW Breakpoint exception
 310          */
 311         if (!bp)
 312                 return NOTIFY_DONE;
 313
 314         info = counter_arch_bp(bp);
 315
 316         /*
 317          * We shall invoke the user-defined callback function in the single
 318          * stepping handler to confirm to 'trigger-after-execute' semantics
 319          */
 320         if (!info->extraneous_interrupt)
 321                 perf_bp_event(bp, regs);
 322
 323         set_dabr(info->address | info->type | DABR_TRANSLATION, info->dabrx);
 324         current->thread.last_hit_ubp = NULL;
 325
 326         /*
 327          * If the process was being single-stepped by ptrace, let the
 328          * other single-step actions occur (e.g. generate SIGTRAP).
 329          */
 330         if (test_thread_flag(TIF_SINGLESTEP))
 331                 return NOTIFY_DONE;
 332
 333         return NOTIFY_STOP;
 334 }
 335
 336 /*
 337  * Handle debug exception notifications.
 338  */
 339 int __kprobes hw_breakpoint_exceptions_notify(
 340                 struct notifier_block *unused, unsigned long val, void *data)
 341 {
 342         int ret = NOTIFY_DONE;
 343
 344         switch (val) {
 345         case DIE_DABR_MATCH:
 346                 ret = hw_breakpoint_handler(data);
 347                 break;
 348         case DIE_SSTEP:
 349                 ret = single_step_dabr_instruction(data);
 350                 break;
 351         }
 352
 353         return ret;
 354 }
 355
 356 /*
 357  * Release the user breakpoints used by ptrace
 358  */
 359 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 360 {
 361         struct thread_struct *t = &tsk->thread;
 362
 363         unregister_hw_breakpoint(t->ptrace_bps[0]);
 364         t->ptrace_bps[0] = NULL;
 365 }
 366
 367 void hw_breakpoint_pmu_read(struct perf_event *bp)
 368 {
 369         /* TODO */
 370 }