arch/powerpc/kernel/hw_breakpoint.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
   4  * using the CPU's debug registers. Derived from
   5  * "arch/x86/kernel/hw_breakpoint.c"
   6  *
   7  * Copyright 2010 IBM Corporation
   8  * Author: K.Prasad <prasad@linux.vnet.ibm.com>
   9  */
  10
  11 #include <linux/hw_breakpoint.h>
  12 #include <linux/notifier.h>
  13 #include <linux/kprobes.h>
  14 #include <linux/percpu.h>
  15 #include <linux/kernel.h>
  16 #include <linux/sched.h>
  17 #include <linux/smp.h>
  18 #include <linux/debugfs.h>
  19 #include <linux/init.h>
  20
  21 #include <asm/hw_breakpoint.h>
  22 #include <asm/processor.h>
  23 #include <asm/sstep.h>
  24 #include <asm/debug.h>
  25 #include <asm/debugfs.h>
  26 #include <asm/hvcall.h>
  27 #include <linux/uaccess.h>
  28
  29 /*
  30  * Stores the breakpoints currently in use on each breakpoint address
  31  * register for every cpu
  32  */
  33 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
  34
  35 /*
  36  * Returns total number of data or instruction breakpoints available.
  37  */
  38 int hw_breakpoint_slots(int type)
  39 {
  40         if (type == TYPE_DATA)
  41                 return HBP_NUM;
  42         return 0;               /* no instruction breakpoints available */
  43 }
  44
  45 /*
  46  * Install a perf counter breakpoint.
  47  *
  48  * We seek a free debug address register and use it for this
  49  * breakpoint.
  50  *
  51  * Atomic: we hold the counter->ctx->lock and we only handle variables
  52  * and registers local to this cpu.
  53  */
  54 int arch_install_hw_breakpoint(struct perf_event *bp)
  55 {
  56         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
  57         struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
  58
  59         *slot = bp;
  60
  61         /*
  62          * Do not install DABR values if the instruction must be single-stepped.
  63          * If so, DABR will be populated in single_step_dabr_instruction().
  64          */
  65         if (current->thread.last_hit_ubp != bp)
  66                 __set_breakpoint(info);
  67
  68         return 0;
  69 }
  70
  71 /*
  72  * Uninstall the breakpoint contained in the given counter.
  73  *
  74  * First we search the debug address register it uses and then we disable
  75  * it.
  76  *
  77  * Atomic: we hold the counter->ctx->lock and we only handle variables
  78  * and registers local to this cpu.
  79  */
  80 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
  81 {
  82         struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
  83
  84         if (*slot != bp) {
  85                 WARN_ONCE(1, "Can't find the breakpoint");
  86                 return;
  87         }
  88
  89         *slot = NULL;
  90         hw_breakpoint_disable();
  91 }
  92
  93 /*
  94  * Perform cleanup of arch-specific counters during unregistration
  95  * of the perf-event
  96  */
  97 void arch_unregister_hw_breakpoint(struct perf_event *bp)
  98 {
  99         /*
 100          * If the breakpoint is unregistered between a hw_breakpoint_handler()
 101          * and the single_step_dabr_instruction(), then cleanup the breakpoint
 102          * restoration variables to prevent dangling pointers.
 103          * FIXME, this should not be using bp->ctx at all! Sayeth peterz.
 104          */
 105         if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L))
 106                 bp->ctx->task->thread.last_hit_ubp = NULL;
 107 }
 108
 109 /*
 110  * Check for virtual address in kernel space.
 111  */
 112 int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
 113 {
 114         return is_kernel_addr(hw->address);
 115 }
 116
 117 int arch_bp_generic_fields(int type, int *gen_bp_type)
 118 {
 119         *gen_bp_type = 0;
 120         if (type & HW_BRK_TYPE_READ)
 121                 *gen_bp_type |= HW_BREAKPOINT_R;
 122         if (type & HW_BRK_TYPE_WRITE)
 123                 *gen_bp_type |= HW_BREAKPOINT_W;
 124         if (*gen_bp_type == 0)
 125                 return -EINVAL;
 126         return 0;
 127 }
 128
 129 /*
 130  * Validate the arch-specific HW Breakpoint register settings
 131  */
 132 int hw_breakpoint_arch_parse(struct perf_event *bp,
 133                              const struct perf_event_attr *attr,
 134                              struct arch_hw_breakpoint *hw)
 135 {
 136         int ret = -EINVAL, length_max;
 137
 138         if (!bp)
 139                 return ret;
 140
 141         hw->type = HW_BRK_TYPE_TRANSLATE;
 142         if (attr->bp_type & HW_BREAKPOINT_R)
 143                 hw->type |= HW_BRK_TYPE_READ;
 144         if (attr->bp_type & HW_BREAKPOINT_W)
 145                 hw->type |= HW_BRK_TYPE_WRITE;
 146         if (hw->type == HW_BRK_TYPE_TRANSLATE)
 147                 /* must set alteast read or write */
 148                 return ret;
 149         if (!attr->exclude_user)
 150                 hw->type |= HW_BRK_TYPE_USER;
 151         if (!attr->exclude_kernel)
 152                 hw->type |= HW_BRK_TYPE_KERNEL;
 153         if (!attr->exclude_hv)
 154                 hw->type |= HW_BRK_TYPE_HYP;
 155         hw->address = attr->bp_addr;
 156         hw->len = attr->bp_len;
 157
 158         /*
 159          * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
 160          * and breakpoint addresses are aligned to nearest double-word
 161          * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
 162          * 'symbolsize' should satisfy the check below.
 163          */
 164         if (!ppc_breakpoint_available())
 165                 return -ENODEV;
 166         length_max = 8; /* DABR */
 167         if (dawr_enabled()) {
 168                 length_max = 512 ; /* 64 doublewords */
 169                 /* DAWR region can't cross 512 boundary */
 170                 if ((attr->bp_addr >> 9) !=
 171                     ((attr->bp_addr + attr->bp_len - 1) >> 9))
 172                         return -EINVAL;
 173         }
 174         if (hw->len >
 175             (length_max - (hw->address & HW_BREAKPOINT_ALIGN)))
 176                 return -EINVAL;
 177         return 0;
 178 }
 179
 180 /*
 181  * Restores the breakpoint on the debug registers.
 182  * Invoke this function if it is known that the execution context is
 183  * about to change to cause loss of MSR_SE settings.
 184  */
 185 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 186 {
 187         struct arch_hw_breakpoint *info;
 188
 189         if (likely(!tsk->thread.last_hit_ubp))
 190                 return;
 191
 192         info = counter_arch_bp(tsk->thread.last_hit_ubp);
 193         regs->msr &= ~MSR_SE;
 194         __set_breakpoint(info);
 195         tsk->thread.last_hit_ubp = NULL;
 196 }
 197
 198 /*
 199  * Handle debug exception notifications.
 200  */
 201 int hw_breakpoint_handler(struct die_args *args)
 202 {
 203         int rc = NOTIFY_STOP;
 204         struct perf_event *bp;
 205         struct pt_regs *regs = args->regs;
 206 #ifndef CONFIG_PPC_8xx
 207         int stepped = 1;
 208         unsigned int instr;
 209 #endif
 210         struct arch_hw_breakpoint *info;
 211         unsigned long dar = regs->dar;
 212
 213         /* Disable breakpoints during exception handling */
 214         hw_breakpoint_disable();
 215
 216         /*
 217          * The counter may be concurrently released but that can only
 218          * occur from a call_rcu() path. We can then safely fetch
 219          * the breakpoint, use its callback, touch its counter
 220          * while we are in an rcu_read_lock() path.
 221          */
 222         rcu_read_lock();
 223
 224         bp = __this_cpu_read(bp_per_reg);
 225         if (!bp) {
 226                 rc = NOTIFY_DONE;
 227                 goto out;
 228         }
 229         info = counter_arch_bp(bp);
 230
 231         /*
 232          * Return early after invoking user-callback function without restoring
 233          * DABR if the breakpoint is from ptrace which always operates in
 234          * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
 235          * generated in do_dabr().
 236          */
 237         if (bp->overflow_handler == ptrace_triggered) {
 238                 perf_bp_event(bp, regs);
 239                 rc = NOTIFY_DONE;
 240                 goto out;
 241         }
 242
 243         /*
 244          * Verify if dar lies within the address range occupied by the symbol
 245          * being watched to filter extraneous exceptions.  If it doesn't,
 246          * we still need to single-step the instruction, but we don't
 247          * generate an event.
 248          */
 249         info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
 250         if (!((bp->attr.bp_addr <= dar) &&
 251               (dar - bp->attr.bp_addr < bp->attr.bp_len)))
 252                 info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
 253
 254 #ifndef CONFIG_PPC_8xx
 255         /* Do not emulate user-space instructions, instead single-step them */
 256         if (user_mode(regs)) {
 257                 current->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_inatomic(bp);
 276                 goto out;
 277         }
 278 #endif
 279         /*
 280          * As a policy, the callback is invoked in a 'trigger-after-execute'
 281          * fashion
 282          */
 283         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
 284                 perf_bp_event(bp, regs);
 285
 286         __set_breakpoint(info);
 287 out:
 288         rcu_read_unlock();
 289         return rc;
 290 }
 291 NOKPROBE_SYMBOL(hw_breakpoint_handler);
 292
 293 /*
 294  * Handle single-step exceptions following a DABR hit.
 295  */
 296 static int 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 NOKPROBE_SYMBOL(single_step_dabr_instruction);
 332
 333 /*
 334  * Handle debug exception notifications.
 335  */
 336 int hw_breakpoint_exceptions_notify(
 337                 struct notifier_block *unused, unsigned long val, void *data)
 338 {
 339         int ret = NOTIFY_DONE;
 340
 341         switch (val) {
 342         case DIE_DABR_MATCH:
 343                 ret = hw_breakpoint_handler(data);
 344                 break;
 345         case DIE_SSTEP:
 346                 ret = single_step_dabr_instruction(data);
 347                 break;
 348         }
 349
 350         return ret;
 351 }
 352 NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify);
 353
 354 /*
 355  * Release the user breakpoints used by ptrace
 356  */
 357 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 358 {
 359         struct thread_struct *t = &tsk->thread;
 360
 361         unregister_hw_breakpoint(t->ptrace_bps[0]);
 362         t->ptrace_bps[0] = NULL;
 363 }
 364
 365 void hw_breakpoint_pmu_read(struct perf_event *bp)
 366 {
 367         /* TODO */
 368 }
 369
 370 bool dawr_force_enable;
 371 EXPORT_SYMBOL_GPL(dawr_force_enable);
 372
 373 static ssize_t dawr_write_file_bool(struct file *file,
 374                                     const char __user *user_buf,
 375                                     size_t count, loff_t *ppos)
 376 {
 377         struct arch_hw_breakpoint null_brk = {0, 0, 0};
 378         size_t rc;
 379
 380         /* Send error to user if they hypervisor won't allow us to write DAWR */
 381         if ((!dawr_force_enable) &&
 382             (firmware_has_feature(FW_FEATURE_LPAR)) &&
 383             (set_dawr(&null_brk) != H_SUCCESS))
 384                 return -1;
 385
 386         rc = debugfs_write_file_bool(file, user_buf, count, ppos);
 387         if (rc)
 388                 return rc;
 389
 390         /* If we are clearing, make sure all CPUs have the DAWR cleared */
 391         if (!dawr_force_enable)
 392                 smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
 393
 394         return rc;
 395 }
 396
 397 static const struct file_operations dawr_enable_fops = {
 398         .read =         debugfs_read_file_bool,
 399         .write =        dawr_write_file_bool,
 400         .open =         simple_open,
 401         .llseek =       default_llseek,
 402 };
 403
 404 static int __init dawr_force_setup(void)
 405 {
 406         dawr_force_enable = false;
 407
 408         if (cpu_has_feature(CPU_FTR_DAWR)) {
 409                 /* Don't setup sysfs file for user control on P8 */
 410                 dawr_force_enable = true;
 411                 return 0;
 412         }
 413
 414         if (PVR_VER(mfspr(SPRN_PVR)) == PVR_POWER9) {
 415                 /* Turn DAWR off by default, but allow admin to turn it on */
 416                 dawr_force_enable = false;
 417                 debugfs_create_file_unsafe("dawr_enable_dangerous", 0600,
 418                                            powerpc_debugfs_root,
 419                                            &dawr_force_enable,
 420                                            &dawr_enable_fops);
 421         }
 422         return 0;
 423 }
 424 arch_initcall(dawr_force_setup);