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/kprobes.h>
  27 #include <linux/stat.h>
  28 #include <linux/uaccess.h>
  29
  30 #include <asm/cpufeature.h>
  31 #include <asm/cputype.h>
  32 #include <asm/debug-monitors.h>
  33 #include <asm/system_misc.h>
  34
  35 /* Determine debug architecture. */
  36 u8 debug_monitors_arch(void)
  37 {
  38         return cpuid_feature_extract_unsigned_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
  39                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
  40 }
  41
  42 /*
  43  * MDSCR access routines.
  44  */
  45 static void mdscr_write(u32 mdscr)
  46 {
  47         unsigned long flags;
  48         local_dbg_save(flags);
  49         asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
  50         local_dbg_restore(flags);
  51 }
  52
  53 static u32 mdscr_read(void)
  54 {
  55         u32 mdscr;
  56         asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
  57         return mdscr;
  58 }
  59
  60 /*
  61  * Allow root to disable self-hosted debug from userspace.
  62  * This is useful if you want to connect an external JTAG debugger.
  63  */
  64 static bool debug_enabled = true;
  65
  66 static int create_debug_debugfs_entry(void)
  67 {
  68         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  69         return 0;
  70 }
  71 fs_initcall(create_debug_debugfs_entry);
  72
  73 static int __init early_debug_disable(char *buf)
  74 {
  75         debug_enabled = false;
  76         return 0;
  77 }
  78
  79 early_param("nodebugmon", early_debug_disable);
  80
  81 /*
  82  * Keep track of debug users on each core.
  83  * The ref counts are per-cpu so we use a local_t type.
  84  */
  85 static DEFINE_PER_CPU(int, mde_ref_count);
  86 static DEFINE_PER_CPU(int, kde_ref_count);
  87
  88 void enable_debug_monitors(enum dbg_active_el el)
  89 {
  90         u32 mdscr, enable = 0;
  91
  92         WARN_ON(preemptible());
  93
  94         if (this_cpu_inc_return(mde_ref_count) == 1)
  95                 enable = DBG_MDSCR_MDE;
  96
  97         if (el == DBG_ACTIVE_EL1 &&
  98             this_cpu_inc_return(kde_ref_count) == 1)
  99                 enable |= DBG_MDSCR_KDE;
 100
 101         if (enable && debug_enabled) {
 102                 mdscr = mdscr_read();
 103                 mdscr |= enable;
 104                 mdscr_write(mdscr);
 105         }
 106 }
 107
 108 void disable_debug_monitors(enum dbg_active_el el)
 109 {
 110         u32 mdscr, disable = 0;
 111
 112         WARN_ON(preemptible());
 113
 114         if (this_cpu_dec_return(mde_ref_count) == 0)
 115                 disable = ~DBG_MDSCR_MDE;
 116
 117         if (el == DBG_ACTIVE_EL1 &&
 118             this_cpu_dec_return(kde_ref_count) == 0)
 119                 disable &= ~DBG_MDSCR_KDE;
 120
 121         if (disable) {
 122                 mdscr = mdscr_read();
 123                 mdscr &= disable;
 124                 mdscr_write(mdscr);
 125         }
 126 }
 127
 128 /*
 129  * OS lock clearing.
 130  */
 131 static void clear_os_lock(void *unused)
 132 {
 133         asm volatile("msr oslar_el1, %0" : : "r" (0));
 134 }
 135
 136 static int os_lock_notify(struct notifier_block *self,
 137                                     unsigned long action, void *data)
 138 {
 139         if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
 140                 clear_os_lock(NULL);
 141         return NOTIFY_OK;
 142 }
 143
 144 static struct notifier_block os_lock_nb = {
 145         .notifier_call = os_lock_notify,
 146 };
 147
 148 static int debug_monitors_init(void)
 149 {
 150         cpu_notifier_register_begin();
 151
 152         /* Clear the OS lock. */
 153         on_each_cpu(clear_os_lock, NULL, 1);
 154         isb();
 155         local_dbg_enable();
 156
 157         /* Register hotplug handler. */
 158         __register_cpu_notifier(&os_lock_nb);
 159
 160         cpu_notifier_register_done();
 161         return 0;
 162 }
 163 postcore_initcall(debug_monitors_init);
 164
 165 /*
 166  * Single step API and exception handling.
 167  */
 168 static void set_regs_spsr_ss(struct pt_regs *regs)
 169 {
 170         unsigned long spsr;
 171
 172         spsr = regs->pstate;
 173         spsr &= ~DBG_SPSR_SS;
 174         spsr |= DBG_SPSR_SS;
 175         regs->pstate = spsr;
 176 }
 177
 178 static void clear_regs_spsr_ss(struct pt_regs *regs)
 179 {
 180         unsigned long spsr;
 181
 182         spsr = regs->pstate;
 183         spsr &= ~DBG_SPSR_SS;
 184         regs->pstate = spsr;
 185 }
 186
 187 /* EL1 Single Step Handler hooks */
 188 static LIST_HEAD(step_hook);
 189 static DEFINE_SPINLOCK(step_hook_lock);
 190
 191 void register_step_hook(struct step_hook *hook)
 192 {
 193         spin_lock(&step_hook_lock);
 194         list_add_rcu(&hook->node, &step_hook);
 195         spin_unlock(&step_hook_lock);
 196 }
 197
 198 void unregister_step_hook(struct step_hook *hook)
 199 {
 200         spin_lock(&step_hook_lock);
 201         list_del_rcu(&hook->node);
 202         spin_unlock(&step_hook_lock);
 203         synchronize_rcu();
 204 }
 205
 206 /*
 207  * Call registered single step handlers
 208  * There is no Syndrome info to check for determining the handler.
 209  * So we call all the registered handlers, until the right handler is
 210  * found which returns zero.
 211  */
 212 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 213 {
 214         struct step_hook *hook;
 215         int retval = DBG_HOOK_ERROR;
 216
 217         rcu_read_lock();
 218
 219         list_for_each_entry_rcu(hook, &step_hook, node) {
 220                 retval = hook->fn(regs, esr);
 221                 if (retval == DBG_HOOK_HANDLED)
 222                         break;
 223         }
 224
 225         rcu_read_unlock();
 226
 227         return retval;
 228 }
 229
 230 static void send_user_sigtrap(int si_code)
 231 {
 232         struct pt_regs *regs = current_pt_regs();
 233         siginfo_t info = {
 234                 .si_signo       = SIGTRAP,
 235                 .si_errno       = 0,
 236                 .si_code        = si_code,
 237                 .si_addr        = (void __user *)instruction_pointer(regs),
 238         };
 239
 240         if (WARN_ON(!user_mode(regs)))
 241                 return;
 242
 243         if (interrupts_enabled(regs))
 244                 local_irq_enable();
 245
 246         force_sig_info(SIGTRAP, &info, current);
 247 }
 248
 249 static int single_step_handler(unsigned long addr, unsigned int esr,
 250                                struct pt_regs *regs)
 251 {
 252         /*
 253          * If we are stepping a pending breakpoint, call the hw_breakpoint
 254          * handler first.
 255          */
 256         if (!reinstall_suspended_bps(regs))
 257                 return 0;
 258
 259         if (user_mode(regs)) {
 260                 send_user_sigtrap(TRAP_HWBKPT);
 261
 262                 /*
 263                  * ptrace will disable single step unless explicitly
 264                  * asked to re-enable it. For other clients, it makes
 265                  * sense to leave it enabled (i.e. rewind the controls
 266                  * to the active-not-pending state).
 267                  */
 268                 user_rewind_single_step(current);
 269         } else {
 270 #ifdef  CONFIG_KPROBES
 271                 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 272                         return 0;
 273 #endif
 274                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 275                         return 0;
 276
 277                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 278                 /*
 279                  * Re-enable stepping since we know that we will be
 280                  * returning to regs.
 281                  */
 282                 set_regs_spsr_ss(regs);
 283         }
 284
 285         return 0;
 286 }
 287
 288 /*
 289  * Breakpoint handler is re-entrant as another breakpoint can
 290  * hit within breakpoint handler, especically in kprobes.
 291  * Use reader/writer locks instead of plain spinlock.
 292  */
 293 static LIST_HEAD(break_hook);
 294 static DEFINE_SPINLOCK(break_hook_lock);
 295
 296 void register_break_hook(struct break_hook *hook)
 297 {
 298         spin_lock(&break_hook_lock);
 299         list_add_rcu(&hook->node, &break_hook);
 300         spin_unlock(&break_hook_lock);
 301 }
 302
 303 void unregister_break_hook(struct break_hook *hook)
 304 {
 305         spin_lock(&break_hook_lock);
 306         list_del_rcu(&hook->node);
 307         spin_unlock(&break_hook_lock);
 308         synchronize_rcu();
 309 }
 310
 311 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 312 {
 313         struct break_hook *hook;
 314         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 315
 316         rcu_read_lock();
 317         list_for_each_entry_rcu(hook, &break_hook, node)
 318                 if ((esr & hook->esr_mask) == hook->esr_val)
 319                         fn = hook->fn;
 320         rcu_read_unlock();
 321
 322         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 323 }
 324
 325 static int brk_handler(unsigned long addr, unsigned int esr,
 326                        struct pt_regs *regs)
 327 {
 328         if (user_mode(regs)) {
 329                 send_user_sigtrap(TRAP_BRKPT);
 330         }
 331 #ifdef  CONFIG_KPROBES
 332         else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 333                 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
 334                         return -EFAULT;
 335         }
 336 #endif
 337         else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 338                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 339                 return -EFAULT;
 340         }
 341
 342         return 0;
 343 }
 344
 345 int aarch32_break_handler(struct pt_regs *regs)
 346 {
 347         u32 arm_instr;
 348         u16 thumb_instr;
 349         bool bp = false;
 350         void __user *pc = (void __user *)instruction_pointer(regs);
 351
 352         if (!compat_user_mode(regs))
 353                 return -EFAULT;
 354
 355         if (compat_thumb_mode(regs)) {
 356                 /* get 16-bit Thumb instruction */
 357                 get_user(thumb_instr, (u16 __user *)pc);
 358                 thumb_instr = le16_to_cpu(thumb_instr);
 359                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 360                         /* get second half of 32-bit Thumb-2 instruction */
 361                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 362                         thumb_instr = le16_to_cpu(thumb_instr);
 363                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 364                 } else {
 365                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 366                 }
 367         } else {
 368                 /* 32-bit ARM instruction */
 369                 get_user(arm_instr, (u32 __user *)pc);
 370                 arm_instr = le32_to_cpu(arm_instr);
 371                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 372         }
 373
 374         if (!bp)
 375                 return -EFAULT;
 376
 377         send_user_sigtrap(TRAP_BRKPT);
 378         return 0;
 379 }
 380
 381 static int __init debug_traps_init(void)
 382 {
 383         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 384                               TRAP_HWBKPT, "single-step handler");
 385         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 386                               TRAP_BRKPT, "ptrace BRK handler");
 387         return 0;
 388 }
 389 arch_initcall(debug_traps_init);
 390
 391 /* Re-enable single step for syscall restarting. */
 392 void user_rewind_single_step(struct task_struct *task)
 393 {
 394         /*
 395          * If single step is active for this thread, then set SPSR.SS
 396          * to 1 to avoid returning to the active-pending state.
 397          */
 398         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 399                 set_regs_spsr_ss(task_pt_regs(task));
 400 }
 401
 402 void user_fastforward_single_step(struct task_struct *task)
 403 {
 404         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 405                 clear_regs_spsr_ss(task_pt_regs(task));
 406 }
 407
 408 /* Kernel API */
 409 void kernel_enable_single_step(struct pt_regs *regs)
 410 {
 411         WARN_ON(!irqs_disabled());
 412         set_regs_spsr_ss(regs);
 413         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 414         enable_debug_monitors(DBG_ACTIVE_EL1);
 415 }
 416
 417 void kernel_disable_single_step(void)
 418 {
 419         WARN_ON(!irqs_disabled());
 420         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 421         disable_debug_monitors(DBG_ACTIVE_EL1);
 422 }
 423
 424 int kernel_active_single_step(void)
 425 {
 426         WARN_ON(!irqs_disabled());
 427         return mdscr_read() & DBG_MDSCR_SS;
 428 }
 429
 430 /* ptrace API */
 431 void user_enable_single_step(struct task_struct *task)
 432 {
 433         set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 434         set_regs_spsr_ss(task_pt_regs(task));
 435 }
 436
 437 void user_disable_single_step(struct task_struct *task)
 438 {
 439         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 440 }