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 /* Low-level stepping controls. */
  34 #define DBG_MDSCR_SS            (1 << 0)
  35 #define DBG_SPSR_SS             (1 << 21)
  36
  37 /* MDSCR_EL1 enabling bits */
  38 #define DBG_MDSCR_KDE           (1 << 13)
  39 #define DBG_MDSCR_MDE           (1 << 15)
  40 #define DBG_MDSCR_MASK          ~(DBG_MDSCR_KDE | DBG_MDSCR_MDE)
  41
  42 /* Determine debug architecture. */
  43 u8 debug_monitors_arch(void)
  44 {
  45         return read_cpuid(ID_AA64DFR0_EL1) & 0xf;
  46 }
  47
  48 /*
  49  * MDSCR access routines.
  50  */
  51 static void mdscr_write(u32 mdscr)
  52 {
  53         unsigned long flags;
  54         local_dbg_save(flags);
  55         asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
  56         local_dbg_restore(flags);
  57 }
  58
  59 static u32 mdscr_read(void)
  60 {
  61         u32 mdscr;
  62         asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
  63         return mdscr;
  64 }
  65
  66 /*
  67  * Allow root to disable self-hosted debug from userspace.
  68  * This is useful if you want to connect an external JTAG debugger.
  69  */
  70 static u32 debug_enabled = 1;
  71
  72 static int create_debug_debugfs_entry(void)
  73 {
  74         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  75         return 0;
  76 }
  77 fs_initcall(create_debug_debugfs_entry);
  78
  79 static int __init early_debug_disable(char *buf)
  80 {
  81         debug_enabled = 0;
  82         return 0;
  83 }
  84
  85 early_param("nodebugmon", early_debug_disable);
  86
  87 /*
  88  * Keep track of debug users on each core.
  89  * The ref counts are per-cpu so we use a local_t type.
  90  */
  91 static DEFINE_PER_CPU(int, mde_ref_count);
  92 static DEFINE_PER_CPU(int, kde_ref_count);
  93
  94 void enable_debug_monitors(enum debug_el el)
  95 {
  96         u32 mdscr, enable = 0;
  97
  98         WARN_ON(preemptible());
  99
 100         if (this_cpu_inc_return(mde_ref_count) == 1)
 101                 enable = DBG_MDSCR_MDE;
 102
 103         if (el == DBG_ACTIVE_EL1 &&
 104             this_cpu_inc_return(kde_ref_count) == 1)
 105                 enable |= DBG_MDSCR_KDE;
 106
 107         if (enable && debug_enabled) {
 108                 mdscr = mdscr_read();
 109                 mdscr |= enable;
 110                 mdscr_write(mdscr);
 111         }
 112 }
 113
 114 void disable_debug_monitors(enum debug_el el)
 115 {
 116         u32 mdscr, disable = 0;
 117
 118         WARN_ON(preemptible());
 119
 120         if (this_cpu_dec_return(mde_ref_count) == 0)
 121                 disable = ~DBG_MDSCR_MDE;
 122
 123         if (el == DBG_ACTIVE_EL1 &&
 124             this_cpu_dec_return(kde_ref_count) == 0)
 125                 disable &= ~DBG_MDSCR_KDE;
 126
 127         if (disable) {
 128                 mdscr = mdscr_read();
 129                 mdscr &= disable;
 130                 mdscr_write(mdscr);
 131         }
 132 }
 133
 134 /*
 135  * OS lock clearing.
 136  */
 137 static void clear_os_lock(void *unused)
 138 {
 139         asm volatile("msr oslar_el1, %0" : : "r" (0));
 140 }
 141
 142 static int os_lock_notify(struct notifier_block *self,
 143                                     unsigned long action, void *data)
 144 {
 145         int cpu = (unsigned long)data;
 146         if (action == CPU_ONLINE)
 147                 smp_call_function_single(cpu, clear_os_lock, NULL, 1);
 148         return NOTIFY_OK;
 149 }
 150
 151 static struct notifier_block os_lock_nb = {
 152         .notifier_call = os_lock_notify,
 153 };
 154
 155 static int debug_monitors_init(void)
 156 {
 157         cpu_notifier_register_begin();
 158
 159         /* Clear the OS lock. */
 160         on_each_cpu(clear_os_lock, NULL, 1);
 161         isb();
 162
 163         /* Register hotplug handler. */
 164         __register_cpu_notifier(&os_lock_nb);
 165
 166         cpu_notifier_register_done();
 167         return 0;
 168 }
 169 postcore_initcall(debug_monitors_init);
 170
 171 /*
 172  * Single step API and exception handling.
 173  */
 174 static void set_regs_spsr_ss(struct pt_regs *regs)
 175 {
 176         unsigned long spsr;
 177
 178         spsr = regs->pstate;
 179         spsr &= ~DBG_SPSR_SS;
 180         spsr |= DBG_SPSR_SS;
 181         regs->pstate = spsr;
 182 }
 183
 184 static void clear_regs_spsr_ss(struct pt_regs *regs)
 185 {
 186         unsigned long spsr;
 187
 188         spsr = regs->pstate;
 189         spsr &= ~DBG_SPSR_SS;
 190         regs->pstate = spsr;
 191 }
 192
 193 /* EL1 Single Step Handler hooks */
 194 static LIST_HEAD(step_hook);
 195 static DEFINE_RWLOCK(step_hook_lock);
 196
 197 void register_step_hook(struct step_hook *hook)
 198 {
 199         write_lock(&step_hook_lock);
 200         list_add(&hook->node, &step_hook);
 201         write_unlock(&step_hook_lock);
 202 }
 203
 204 void unregister_step_hook(struct step_hook *hook)
 205 {
 206         write_lock(&step_hook_lock);
 207         list_del(&hook->node);
 208         write_unlock(&step_hook_lock);
 209 }
 210
 211 /*
 212  * Call registered single step handers
 213  * There is no Syndrome info to check for determining the handler.
 214  * So we call all the registered handlers, until the right handler is
 215  * found which returns zero.
 216  */
 217 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 218 {
 219         struct step_hook *hook;
 220         int retval = DBG_HOOK_ERROR;
 221
 222         read_lock(&step_hook_lock);
 223
 224         list_for_each_entry(hook, &step_hook, node)     {
 225                 retval = hook->fn(regs, esr);
 226                 if (retval == DBG_HOOK_HANDLED)
 227                         break;
 228         }
 229
 230         read_unlock(&step_hook_lock);
 231
 232         return retval;
 233 }
 234
 235 static int single_step_handler(unsigned long addr, unsigned int esr,
 236                                struct pt_regs *regs)
 237 {
 238         siginfo_t info;
 239
 240         /*
 241          * If we are stepping a pending breakpoint, call the hw_breakpoint
 242          * handler first.
 243          */
 244         if (!reinstall_suspended_bps(regs))
 245                 return 0;
 246
 247         if (user_mode(regs)) {
 248                 info.si_signo = SIGTRAP;
 249                 info.si_errno = 0;
 250                 info.si_code  = TRAP_HWBKPT;
 251                 info.si_addr  = (void __user *)instruction_pointer(regs);
 252                 force_sig_info(SIGTRAP, &info, current);
 253
 254                 /*
 255                  * ptrace will disable single step unless explicitly
 256                  * asked to re-enable it. For other clients, it makes
 257                  * sense to leave it enabled (i.e. rewind the controls
 258                  * to the active-not-pending state).
 259                  */
 260                 user_rewind_single_step(current);
 261         } else {
 262                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 263                         return 0;
 264
 265                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 266                 /*
 267                  * Re-enable stepping since we know that we will be
 268                  * returning to regs.
 269                  */
 270                 set_regs_spsr_ss(regs);
 271         }
 272
 273         return 0;
 274 }
 275
 276 /*
 277  * Breakpoint handler is re-entrant as another breakpoint can
 278  * hit within breakpoint handler, especically in kprobes.
 279  * Use reader/writer locks instead of plain spinlock.
 280  */
 281 static LIST_HEAD(break_hook);
 282 static DEFINE_RWLOCK(break_hook_lock);
 283
 284 void register_break_hook(struct break_hook *hook)
 285 {
 286         write_lock(&break_hook_lock);
 287         list_add(&hook->node, &break_hook);
 288         write_unlock(&break_hook_lock);
 289 }
 290
 291 void unregister_break_hook(struct break_hook *hook)
 292 {
 293         write_lock(&break_hook_lock);
 294         list_del(&hook->node);
 295         write_unlock(&break_hook_lock);
 296 }
 297
 298 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 299 {
 300         struct break_hook *hook;
 301         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 302
 303         read_lock(&break_hook_lock);
 304         list_for_each_entry(hook, &break_hook, node)
 305                 if ((esr & hook->esr_mask) == hook->esr_val)
 306                         fn = hook->fn;
 307         read_unlock(&break_hook_lock);
 308
 309         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 310 }
 311
 312 static int brk_handler(unsigned long addr, unsigned int esr,
 313                        struct pt_regs *regs)
 314 {
 315         siginfo_t info;
 316
 317         if (user_mode(regs)) {
 318                 info = (siginfo_t) {
 319                         .si_signo = SIGTRAP,
 320                         .si_errno = 0,
 321                         .si_code  = TRAP_BRKPT,
 322                         .si_addr  = (void __user *)instruction_pointer(regs),
 323                 };
 324
 325                 force_sig_info(SIGTRAP, &info, current);
 326         } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 327                 pr_warning("Unexpected kernel BRK exception at EL1\n");
 328                 return -EFAULT;
 329         }
 330
 331         return 0;
 332 }
 333
 334 int aarch32_break_handler(struct pt_regs *regs)
 335 {
 336         siginfo_t info;
 337         u32 arm_instr;
 338         u16 thumb_instr;
 339         bool bp = false;
 340         void __user *pc = (void __user *)instruction_pointer(regs);
 341
 342         if (!compat_user_mode(regs))
 343                 return -EFAULT;
 344
 345         if (compat_thumb_mode(regs)) {
 346                 /* get 16-bit Thumb instruction */
 347                 get_user(thumb_instr, (u16 __user *)pc);
 348                 thumb_instr = le16_to_cpu(thumb_instr);
 349                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 350                         /* get second half of 32-bit Thumb-2 instruction */
 351                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 352                         thumb_instr = le16_to_cpu(thumb_instr);
 353                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 354                 } else {
 355                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 356                 }
 357         } else {
 358                 /* 32-bit ARM instruction */
 359                 get_user(arm_instr, (u32 __user *)pc);
 360                 arm_instr = le32_to_cpu(arm_instr);
 361                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 362         }
 363
 364         if (!bp)
 365                 return -EFAULT;
 366
 367         info = (siginfo_t) {
 368                 .si_signo = SIGTRAP,
 369                 .si_errno = 0,
 370                 .si_code  = TRAP_BRKPT,
 371                 .si_addr  = pc,
 372         };
 373
 374         force_sig_info(SIGTRAP, &info, current);
 375         return 0;
 376 }
 377
 378 static int __init debug_traps_init(void)
 379 {
 380         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 381                               TRAP_HWBKPT, "single-step handler");
 382         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 383                               TRAP_BRKPT, "ptrace BRK handler");
 384         return 0;
 385 }
 386 arch_initcall(debug_traps_init);
 387
 388 /* Re-enable single step for syscall restarting. */
 389 void user_rewind_single_step(struct task_struct *task)
 390 {
 391         /*
 392          * If single step is active for this thread, then set SPSR.SS
 393          * to 1 to avoid returning to the active-pending state.
 394          */
 395         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 396                 set_regs_spsr_ss(task_pt_regs(task));
 397 }
 398
 399 void user_fastforward_single_step(struct task_struct *task)
 400 {
 401         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 402                 clear_regs_spsr_ss(task_pt_regs(task));
 403 }
 404
 405 /* Kernel API */
 406 void kernel_enable_single_step(struct pt_regs *regs)
 407 {
 408         WARN_ON(!irqs_disabled());
 409         set_regs_spsr_ss(regs);
 410         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 411         enable_debug_monitors(DBG_ACTIVE_EL1);
 412 }
 413
 414 void kernel_disable_single_step(void)
 415 {
 416         WARN_ON(!irqs_disabled());
 417         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 418         disable_debug_monitors(DBG_ACTIVE_EL1);
 419 }
 420
 421 int kernel_active_single_step(void)
 422 {
 423         WARN_ON(!irqs_disabled());
 424         return mdscr_read() & DBG_MDSCR_SS;
 425 }
 426
 427 /* ptrace API */
 428 void user_enable_single_step(struct task_struct *task)
 429 {
 430         struct thread_info *ti = task_thread_info(task);
 431
 432         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 433                 set_regs_spsr_ss(task_pt_regs(task));
 434 }
 435
 436 void user_disable_single_step(struct task_struct *task)
 437 {
 438         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 439 }