arch/arm64/kernel/debug-monitors.c

   1 /*
   2  * ARMv8 single-step debug support and mdscr context switching.
   3  *
   4  * Copyright (C) 2012 ARM Limited
   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 version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  *
  18  * Author: Will Deacon <will.deacon@arm.com>
  19  */
  20
  21 #include <linux/cpu.h>
  22 #include <linux/debugfs.h>
  23 #include <linux/hardirq.h>
  24 #include <linux/init.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/stat.h>
  27 #include <linux/uaccess.h>
  28
  29 #include <asm/debug-monitors.h>
  30 #include <asm/cputype.h>
  31 #include <asm/system_misc.h>
  32
  33 /* Determine debug architecture. */
  34 u8 debug_monitors_arch(void)
  35 {
  36         return read_cpuid(ID_AA64DFR0_EL1) & 0xf;
  37 }
  38
  39 /*
  40  * MDSCR access routines.
  41  */
  42 static void mdscr_write(u32 mdscr)
  43 {
  44         unsigned long flags;
  45         local_dbg_save(flags);
  46         asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
  47         local_dbg_restore(flags);
  48 }
  49
  50 static u32 mdscr_read(void)
  51 {
  52         u32 mdscr;
  53         asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
  54         return mdscr;
  55 }
  56
  57 /*
  58  * Allow root to disable self-hosted debug from userspace.
  59  * This is useful if you want to connect an external JTAG debugger.
  60  */
  61 static u32 debug_enabled = 1;
  62
  63 static int create_debug_debugfs_entry(void)
  64 {
  65         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  66         return 0;
  67 }
  68 fs_initcall(create_debug_debugfs_entry);
  69
  70 static int __init early_debug_disable(char *buf)
  71 {
  72         debug_enabled = 0;
  73         return 0;
  74 }
  75
  76 early_param("nodebugmon", early_debug_disable);
  77
  78 /*
  79  * Keep track of debug users on each core.
  80  * The ref counts are per-cpu so we use a local_t type.
  81  */
  82 static DEFINE_PER_CPU(int, mde_ref_count);
  83 static DEFINE_PER_CPU(int, kde_ref_count);
  84
  85 void enable_debug_monitors(enum dbg_active_el el)
  86 {
  87         u32 mdscr, enable = 0;
  88
  89         WARN_ON(preemptible());
  90
  91         if (this_cpu_inc_return(mde_ref_count) == 1)
  92                 enable = DBG_MDSCR_MDE;
  93
  94         if (el == DBG_ACTIVE_EL1 &&
  95             this_cpu_inc_return(kde_ref_count) == 1)
  96                 enable |= DBG_MDSCR_KDE;
  97
  98         if (enable && debug_enabled) {
  99                 mdscr = mdscr_read();
 100                 mdscr |= enable;
 101                 mdscr_write(mdscr);
 102         }
 103 }
 104
 105 void disable_debug_monitors(enum dbg_active_el el)
 106 {
 107         u32 mdscr, disable = 0;
 108
 109         WARN_ON(preemptible());
 110
 111         if (this_cpu_dec_return(mde_ref_count) == 0)
 112                 disable = ~DBG_MDSCR_MDE;
 113
 114         if (el == DBG_ACTIVE_EL1 &&
 115             this_cpu_dec_return(kde_ref_count) == 0)
 116                 disable &= ~DBG_MDSCR_KDE;
 117
 118         if (disable) {
 119                 mdscr = mdscr_read();
 120                 mdscr &= disable;
 121                 mdscr_write(mdscr);
 122         }
 123 }
 124
 125 /*
 126  * OS lock clearing.
 127  */
 128 static void clear_os_lock(void *unused)
 129 {
 130         asm volatile("msr oslar_el1, %0" : : "r" (0));
 131 }
 132
 133 static int os_lock_notify(struct notifier_block *self,
 134                                     unsigned long action, void *data)
 135 {
 136         int cpu = (unsigned long)data;
 137         if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
 138                 smp_call_function_single(cpu, clear_os_lock, NULL, 1);
 139         return NOTIFY_OK;
 140 }
 141
 142 static struct notifier_block os_lock_nb = {
 143         .notifier_call = os_lock_notify,
 144 };
 145
 146 static int debug_monitors_init(void)
 147 {
 148         cpu_notifier_register_begin();
 149
 150         /* Clear the OS lock. */
 151         on_each_cpu(clear_os_lock, NULL, 1);
 152         isb();
 153         local_dbg_enable();
 154
 155         /* Register hotplug handler. */
 156         __register_cpu_notifier(&os_lock_nb);
 157
 158         cpu_notifier_register_done();
 159         return 0;
 160 }
 161 postcore_initcall(debug_monitors_init);
 162
 163 /*
 164  * Single step API and exception handling.
 165  */
 166 static void set_regs_spsr_ss(struct pt_regs *regs)
 167 {
 168         unsigned long spsr;
 169
 170         spsr = regs->pstate;
 171         spsr &= ~DBG_SPSR_SS;
 172         spsr |= DBG_SPSR_SS;
 173         regs->pstate = spsr;
 174 }
 175
 176 static void clear_regs_spsr_ss(struct pt_regs *regs)
 177 {
 178         unsigned long spsr;
 179
 180         spsr = regs->pstate;
 181         spsr &= ~DBG_SPSR_SS;
 182         regs->pstate = spsr;
 183 }
 184
 185 /* EL1 Single Step Handler hooks */
 186 static LIST_HEAD(step_hook);
 187 static DEFINE_RWLOCK(step_hook_lock);
 188
 189 void register_step_hook(struct step_hook *hook)
 190 {
 191         write_lock(&step_hook_lock);
 192         list_add(&hook->node, &step_hook);
 193         write_unlock(&step_hook_lock);
 194 }
 195
 196 void unregister_step_hook(struct step_hook *hook)
 197 {
 198         write_lock(&step_hook_lock);
 199         list_del(&hook->node);
 200         write_unlock(&step_hook_lock);
 201 }
 202
 203 /*
 204  * Call registered single step handers
 205  * There is no Syndrome info to check for determining the handler.
 206  * So we call all the registered handlers, until the right handler is
 207  * found which returns zero.
 208  */
 209 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 210 {
 211         struct step_hook *hook;
 212         int retval = DBG_HOOK_ERROR;
 213
 214         read_lock(&step_hook_lock);
 215
 216         list_for_each_entry(hook, &step_hook, node)     {
 217                 retval = hook->fn(regs, esr);
 218                 if (retval == DBG_HOOK_HANDLED)
 219                         break;
 220         }
 221
 222         read_unlock(&step_hook_lock);
 223
 224         return retval;
 225 }
 226
 227 static int single_step_handler(unsigned long addr, unsigned int esr,
 228                                struct pt_regs *regs)
 229 {
 230         siginfo_t info;
 231
 232         /*
 233          * If we are stepping a pending breakpoint, call the hw_breakpoint
 234          * handler first.
 235          */
 236         if (!reinstall_suspended_bps(regs))
 237                 return 0;
 238
 239         if (user_mode(regs)) {
 240                 info.si_signo = SIGTRAP;
 241                 info.si_errno = 0;
 242                 info.si_code  = TRAP_HWBKPT;
 243                 info.si_addr  = (void __user *)instruction_pointer(regs);
 244                 force_sig_info(SIGTRAP, &info, current);
 245
 246                 /*
 247                  * ptrace will disable single step unless explicitly
 248                  * asked to re-enable it. For other clients, it makes
 249                  * sense to leave it enabled (i.e. rewind the controls
 250                  * to the active-not-pending state).
 251                  */
 252                 user_rewind_single_step(current);
 253         } else {
 254                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 255                         return 0;
 256
 257                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 258                 /*
 259                  * Re-enable stepping since we know that we will be
 260                  * returning to regs.
 261                  */
 262                 set_regs_spsr_ss(regs);
 263         }
 264
 265         return 0;
 266 }
 267
 268 /*
 269  * Breakpoint handler is re-entrant as another breakpoint can
 270  * hit within breakpoint handler, especically in kprobes.
 271  * Use reader/writer locks instead of plain spinlock.
 272  */
 273 static LIST_HEAD(break_hook);
 274 static DEFINE_RWLOCK(break_hook_lock);
 275
 276 void register_break_hook(struct break_hook *hook)
 277 {
 278         write_lock(&break_hook_lock);
 279         list_add(&hook->node, &break_hook);
 280         write_unlock(&break_hook_lock);
 281 }
 282
 283 void unregister_break_hook(struct break_hook *hook)
 284 {
 285         write_lock(&break_hook_lock);
 286         list_del(&hook->node);
 287         write_unlock(&break_hook_lock);
 288 }
 289
 290 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 291 {
 292         struct break_hook *hook;
 293         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 294
 295         read_lock(&break_hook_lock);
 296         list_for_each_entry(hook, &break_hook, node)
 297                 if ((esr & hook->esr_mask) == hook->esr_val)
 298                         fn = hook->fn;
 299         read_unlock(&break_hook_lock);
 300
 301         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 302 }
 303
 304 static int brk_handler(unsigned long addr, unsigned int esr,
 305                        struct pt_regs *regs)
 306 {
 307         siginfo_t info;
 308
 309         if (user_mode(regs)) {
 310                 info = (siginfo_t) {
 311                         .si_signo = SIGTRAP,
 312                         .si_errno = 0,
 313                         .si_code  = TRAP_BRKPT,
 314                         .si_addr  = (void __user *)instruction_pointer(regs),
 315                 };
 316
 317                 force_sig_info(SIGTRAP, &info, current);
 318         } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 319                 pr_warning("Unexpected kernel BRK exception at EL1\n");
 320                 return -EFAULT;
 321         }
 322
 323         return 0;
 324 }
 325
 326 int aarch32_break_handler(struct pt_regs *regs)
 327 {
 328         siginfo_t info;
 329         u32 arm_instr;
 330         u16 thumb_instr;
 331         bool bp = false;
 332         void __user *pc = (void __user *)instruction_pointer(regs);
 333
 334         if (!compat_user_mode(regs))
 335                 return -EFAULT;
 336
 337         if (compat_thumb_mode(regs)) {
 338                 /* get 16-bit Thumb instruction */
 339                 get_user(thumb_instr, (u16 __user *)pc);
 340                 thumb_instr = le16_to_cpu(thumb_instr);
 341                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 342                         /* get second half of 32-bit Thumb-2 instruction */
 343                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 344                         thumb_instr = le16_to_cpu(thumb_instr);
 345                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 346                 } else {
 347                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 348                 }
 349         } else {
 350                 /* 32-bit ARM instruction */
 351                 get_user(arm_instr, (u32 __user *)pc);
 352                 arm_instr = le32_to_cpu(arm_instr);
 353                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 354         }
 355
 356         if (!bp)
 357                 return -EFAULT;
 358
 359         info = (siginfo_t) {
 360                 .si_signo = SIGTRAP,
 361                 .si_errno = 0,
 362                 .si_code  = TRAP_BRKPT,
 363                 .si_addr  = pc,
 364         };
 365
 366         force_sig_info(SIGTRAP, &info, current);
 367         return 0;
 368 }
 369
 370 static int __init debug_traps_init(void)
 371 {
 372         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 373                               TRAP_HWBKPT, "single-step handler");
 374         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 375                               TRAP_BRKPT, "ptrace BRK handler");
 376         return 0;
 377 }
 378 arch_initcall(debug_traps_init);
 379
 380 /* Re-enable single step for syscall restarting. */
 381 void user_rewind_single_step(struct task_struct *task)
 382 {
 383         /*
 384          * If single step is active for this thread, then set SPSR.SS
 385          * to 1 to avoid returning to the active-pending state.
 386          */
 387         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 388                 set_regs_spsr_ss(task_pt_regs(task));
 389 }
 390
 391 void user_fastforward_single_step(struct task_struct *task)
 392 {
 393         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 394                 clear_regs_spsr_ss(task_pt_regs(task));
 395 }
 396
 397 /* Kernel API */
 398 void kernel_enable_single_step(struct pt_regs *regs)
 399 {
 400         WARN_ON(!irqs_disabled());
 401         set_regs_spsr_ss(regs);
 402         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 403         enable_debug_monitors(DBG_ACTIVE_EL1);
 404 }
 405
 406 void kernel_disable_single_step(void)
 407 {
 408         WARN_ON(!irqs_disabled());
 409         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 410         disable_debug_monitors(DBG_ACTIVE_EL1);
 411 }
 412
 413 int kernel_active_single_step(void)
 414 {
 415         WARN_ON(!irqs_disabled());
 416         return mdscr_read() & DBG_MDSCR_SS;
 417 }
 418
 419 /* ptrace API */
 420 void user_enable_single_step(struct task_struct *task)
 421 {
 422         set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 423         set_regs_spsr_ss(task_pt_regs(task));
 424 }
 425
 426 void user_disable_single_step(struct task_struct *task)
 427 {
 428         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 429 }