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/smp.h>
  32
  33 #include <asm/hw_breakpoint.h>
  34 #include <asm/processor.h>
  35 #include <asm/sstep.h>
  36 #include <asm/uaccess.h>
  37
  38 /*
  39  * Stores the breakpoints currently in use on each breakpoint address
  40  * register for every cpu
  41  */
  42 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
  43
  44 /*
  45  * Returns total number of data or instruction breakpoints available.
  46  */
  47 int hw_breakpoint_slots(int type)
  48 {
  49         if (type == TYPE_DATA)
  50                 return HBP_NUM;
  51         return 0;               /* no instruction breakpoints available */
  52 }
  53
  54 /*
  55  * Install a perf counter breakpoint.
  56  *
  57  * We seek a free debug address register and use it for this
  58  * breakpoint.
  59  *
  60  * Atomic: we hold the counter->ctx->lock and we only handle variables
  61  * and registers local to this cpu.
  62  */
  63 int arch_install_hw_breakpoint(struct perf_event *bp)
  64 {
  65         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
  66         struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
  67
  68         *slot = bp;
  69
  70         /*
  71          * Do not install DABR values if the instruction must be single-stepped.
  72          * If so, DABR will be populated in single_step_dabr_instruction().
  73          */
  74         if (current->thread.last_hit_ubp != bp)
  75                 __set_breakpoint(info);
  76
  77         return 0;
  78 }
  79
  80 /*
  81  * Uninstall the breakpoint contained in the given counter.
  82  *
  83  * First we search the debug address register it uses and then we disable
  84  * it.
  85  *
  86  * Atomic: we hold the counter->ctx->lock and we only handle variables
  87  * and registers local to this cpu.
  88  */
  89 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
  90 {
  91         struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
  92
  93         if (*slot != bp) {
  94                 WARN_ONCE(1, "Can't find the breakpoint");
  95                 return;
  96         }
  97
  98         *slot = NULL;
  99         hw_breakpoint_disable();
 100 }
 101
 102 /*
 103  * Perform cleanup of arch-specific counters during unregistration
 104  * of the perf-event
 105  */
 106 void arch_unregister_hw_breakpoint(struct perf_event *bp)
 107 {
 108         /*
 109          * If the breakpoint is unregistered between a hw_breakpoint_handler()
 110          * and the single_step_dabr_instruction(), then cleanup the breakpoint
 111          * restoration variables to prevent dangling pointers.
 112          */
 113         if (bp->ctx && bp->ctx->task)
 114                 bp->ctx->task->thread.last_hit_ubp = NULL;
 115 }
 116
 117 /*
 118  * Check for virtual address in kernel space.
 119  */
 120 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 121 {
 122         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 123
 124         return is_kernel_addr(info->address);
 125 }
 126
 127 int arch_bp_generic_fields(int type, int *gen_bp_type)
 128 {
 129         *gen_bp_type = 0;
 130         if (type & HW_BRK_TYPE_READ)
 131                 *gen_bp_type |= HW_BREAKPOINT_R;
 132         if (type & HW_BRK_TYPE_WRITE)
 133                 *gen_bp_type |= HW_BREAKPOINT_W;
 134         if (*gen_bp_type == 0)
 135                 return -EINVAL;
 136         return 0;
 137 }
 138
 139 /*
 140  * Validate the arch-specific HW Breakpoint register settings
 141  */
 142 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 143 {
 144         int ret = -EINVAL, length_max;
 145         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 146
 147         if (!bp)
 148                 return ret;
 149
 150         info->type = HW_BRK_TYPE_TRANSLATE;
 151         if (bp->attr.bp_type & HW_BREAKPOINT_R)
 152                 info->type |= HW_BRK_TYPE_READ;
 153         if (bp->attr.bp_type & HW_BREAKPOINT_W)
 154                 info->type |= HW_BRK_TYPE_WRITE;
 155         if (info->type == HW_BRK_TYPE_TRANSLATE)
 156                 /* must set alteast read or write */
 157                 return ret;
 158         if (!(bp->attr.exclude_user))
 159                 info->type |= HW_BRK_TYPE_USER;
 160         if (!(bp->attr.exclude_kernel))
 161                 info->type |= HW_BRK_TYPE_KERNEL;
 162         if (!(bp->attr.exclude_hv))
 163                 info->type |= HW_BRK_TYPE_HYP;
 164         info->address = bp->attr.bp_addr;
 165         info->len = bp->attr.bp_len;
 166
 167         /*
 168          * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
 169          * and breakpoint addresses are aligned to nearest double-word
 170          * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
 171          * 'symbolsize' should satisfy the check below.
 172          */
 173         length_max = 8; /* DABR */
 174         if (cpu_has_feature(CPU_FTR_DAWR)) {
 175                 length_max = 512 ; /* 64 doublewords */
 176                 /* DAWR region can't cross 512 boundary */
 177                 if ((bp->attr.bp_addr >> 10) !=
 178                     ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
 179                         return -EINVAL;
 180         }
 181         if (info->len >
 182             (length_max - (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_breakpoint(info);
 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         hw_breakpoint_disable();
 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 = __this_cpu_read(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->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
 253         if (!((bp->attr.bp_addr <= dar) &&
 254               (dar - bp->attr.bp_addr < bp->attr.bp_len)))
 255                 info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
 256
 257         /* Do not emulate user-space instructions, instead single-step them */
 258         if (user_mode(regs)) {
 259                 current->thread.last_hit_ubp = bp;
 260                 regs->msr |= MSR_SE;
 261                 goto out;
 262         }
 263
 264         stepped = 0;
 265         instr = 0;
 266         if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
 267                 stepped = emulate_step(regs, instr);
 268
 269         /*
 270          * emulate_step() could not execute it. We've failed in reliably
 271          * handling the hw-breakpoint. Unregister it and throw a warning
 272          * message to let the user know about it.
 273          */
 274         if (!stepped) {
 275                 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
 276                         "0x%lx will be disabled.", info->address);
 277                 perf_event_disable(bp);
 278                 goto out;
 279         }
 280         /*
 281          * As a policy, the callback is invoked in a 'trigger-after-execute'
 282          * fashion
 283          */
 284         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
 285                 perf_bp_event(bp, regs);
 286
 287         __set_breakpoint(info);
 288 out:
 289         rcu_read_unlock();
 290         return rc;
 291 }
 292
 293 /*
 294  * Handle single-step exceptions following a DABR hit.
 295  */
 296 static int __kprobes single_step_dabr_instruction(struct die_args *args)
 297 {
 298         struct pt_regs *regs = args->regs;
 299         struct perf_event *bp = NULL;
 300         struct arch_hw_breakpoint *info;
 301
 302         bp = current->thread.last_hit_ubp;
 303         /*
 304          * Check if we are single-stepping as a result of a
 305          * previous HW Breakpoint exception
 306          */
 307         if (!bp)
 308                 return NOTIFY_DONE;
 309
 310         info = counter_arch_bp(bp);
 311
 312         /*
 313          * We shall invoke the user-defined callback function in the single
 314          * stepping handler to confirm to 'trigger-after-execute' semantics
 315          */
 316         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
 317                 perf_bp_event(bp, regs);
 318
 319         __set_breakpoint(info);
 320         current->thread.last_hit_ubp = NULL;
 321
 322         /*
 323          * If the process was being single-stepped by ptrace, let the
 324          * other single-step actions occur (e.g. generate SIGTRAP).
 325          */
 326         if (test_thread_flag(TIF_SINGLESTEP))
 327                 return NOTIFY_DONE;
 328
 329         return NOTIFY_STOP;
 330 }
 331
 332 /*
 333  * Handle debug exception notifications.
 334  */
 335 int __kprobes hw_breakpoint_exceptions_notify(
 336                 struct notifier_block *unused, unsigned long val, void *data)
 337 {
 338         int ret = NOTIFY_DONE;
 339
 340         switch (val) {
 341         case DIE_DABR_MATCH:
 342                 ret = hw_breakpoint_handler(data);
 343                 break;
 344         case DIE_SSTEP:
 345                 ret = single_step_dabr_instruction(data);
 346                 break;
 347         }
 348
 349         return ret;
 350 }
 351
 352 /*
 353  * Release the user breakpoints used by ptrace
 354  */
 355 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 356 {
 357         struct thread_struct *t = &tsk->thread;
 358
 359         unregister_hw_breakpoint(t->ptrace_bps[0]);
 360         t->ptrace_bps[0] = NULL;
 361 }
 362
 363 void hw_breakpoint_pmu_read(struct perf_event *bp)
 364 {
 365         /* TODO */
 366 }