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 NOKPROBE_SYMBOL(mdscr_write);
  53
  54 static u32 mdscr_read(void)
  55 {
  56         u32 mdscr;
  57         asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
  58         return mdscr;
  59 }
  60 NOKPROBE_SYMBOL(mdscr_read);
  61
  62 /*
  63  * Allow root to disable self-hosted debug from userspace.
  64  * This is useful if you want to connect an external JTAG debugger.
  65  */
  66 static bool debug_enabled = true;
  67
  68 static int create_debug_debugfs_entry(void)
  69 {
  70         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  71         return 0;
  72 }
  73 fs_initcall(create_debug_debugfs_entry);
  74
  75 static int __init early_debug_disable(char *buf)
  76 {
  77         debug_enabled = false;
  78         return 0;
  79 }
  80
  81 early_param("nodebugmon", early_debug_disable);
  82
  83 /*
  84  * Keep track of debug users on each core.
  85  * The ref counts are per-cpu so we use a local_t type.
  86  */
  87 static DEFINE_PER_CPU(int, mde_ref_count);
  88 static DEFINE_PER_CPU(int, kde_ref_count);
  89
  90 void enable_debug_monitors(enum dbg_active_el el)
  91 {
  92         u32 mdscr, enable = 0;
  93
  94         WARN_ON(preemptible());
  95
  96         if (this_cpu_inc_return(mde_ref_count) == 1)
  97                 enable = DBG_MDSCR_MDE;
  98
  99         if (el == DBG_ACTIVE_EL1 &&
 100             this_cpu_inc_return(kde_ref_count) == 1)
 101                 enable |= DBG_MDSCR_KDE;
 102
 103         if (enable && debug_enabled) {
 104                 mdscr = mdscr_read();
 105                 mdscr |= enable;
 106                 mdscr_write(mdscr);
 107         }
 108 }
 109 NOKPROBE_SYMBOL(enable_debug_monitors);
 110
 111 void disable_debug_monitors(enum dbg_active_el el)
 112 {
 113         u32 mdscr, disable = 0;
 114
 115         WARN_ON(preemptible());
 116
 117         if (this_cpu_dec_return(mde_ref_count) == 0)
 118                 disable = ~DBG_MDSCR_MDE;
 119
 120         if (el == DBG_ACTIVE_EL1 &&
 121             this_cpu_dec_return(kde_ref_count) == 0)
 122                 disable &= ~DBG_MDSCR_KDE;
 123
 124         if (disable) {
 125                 mdscr = mdscr_read();
 126                 mdscr &= disable;
 127                 mdscr_write(mdscr);
 128         }
 129 }
 130 NOKPROBE_SYMBOL(disable_debug_monitors);
 131
 132 /*
 133  * OS lock clearing.
 134  */
 135 static void clear_os_lock(void *unused)
 136 {
 137         asm volatile("msr oslar_el1, %0" : : "r" (0));
 138 }
 139
 140 static int os_lock_notify(struct notifier_block *self,
 141                                     unsigned long action, void *data)
 142 {
 143         if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
 144                 clear_os_lock(NULL);
 145         return NOTIFY_OK;
 146 }
 147
 148 static struct notifier_block os_lock_nb = {
 149         .notifier_call = os_lock_notify,
 150 };
 151
 152 static int debug_monitors_init(void)
 153 {
 154         cpu_notifier_register_begin();
 155
 156         /* Clear the OS lock. */
 157         on_each_cpu(clear_os_lock, NULL, 1);
 158         isb();
 159
 160         /* Register hotplug handler. */
 161         __register_cpu_notifier(&os_lock_nb);
 162
 163         cpu_notifier_register_done();
 164         return 0;
 165 }
 166 postcore_initcall(debug_monitors_init);
 167
 168 /*
 169  * Single step API and exception handling.
 170  */
 171 static void set_regs_spsr_ss(struct pt_regs *regs)
 172 {
 173         regs->pstate |= DBG_SPSR_SS;
 174 }
 175 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 176
 177 static void clear_regs_spsr_ss(struct pt_regs *regs)
 178 {
 179         regs->pstate &= ~DBG_SPSR_SS;
 180 }
 181 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
 182
 183 /* EL1 Single Step Handler hooks */
 184 static LIST_HEAD(step_hook);
 185 static DEFINE_SPINLOCK(step_hook_lock);
 186
 187 void register_step_hook(struct step_hook *hook)
 188 {
 189         spin_lock(&step_hook_lock);
 190         list_add_rcu(&hook->node, &step_hook);
 191         spin_unlock(&step_hook_lock);
 192 }
 193
 194 void unregister_step_hook(struct step_hook *hook)
 195 {
 196         spin_lock(&step_hook_lock);
 197         list_del_rcu(&hook->node);
 198         spin_unlock(&step_hook_lock);
 199         synchronize_rcu();
 200 }
 201
 202 /*
 203  * Call registered single step handlers
 204  * There is no Syndrome info to check for determining the handler.
 205  * So we call all the registered handlers, until the right handler is
 206  * found which returns zero.
 207  */
 208 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 209 {
 210         struct step_hook *hook;
 211         int retval = DBG_HOOK_ERROR;
 212
 213         rcu_read_lock();
 214
 215         list_for_each_entry_rcu(hook, &step_hook, node) {
 216                 retval = hook->fn(regs, esr);
 217                 if (retval == DBG_HOOK_HANDLED)
 218                         break;
 219         }
 220
 221         rcu_read_unlock();
 222
 223         return retval;
 224 }
 225 NOKPROBE_SYMBOL(call_step_hook);
 226
 227 static void send_user_sigtrap(int si_code)
 228 {
 229         struct pt_regs *regs = current_pt_regs();
 230         siginfo_t info = {
 231                 .si_signo       = SIGTRAP,
 232                 .si_errno       = 0,
 233                 .si_code        = si_code,
 234                 .si_addr        = (void __user *)instruction_pointer(regs),
 235         };
 236
 237         if (WARN_ON(!user_mode(regs)))
 238                 return;
 239
 240         if (interrupts_enabled(regs))
 241                 local_irq_enable();
 242
 243         force_sig_info(SIGTRAP, &info, current);
 244 }
 245
 246 static int single_step_handler(unsigned long addr, unsigned int esr,
 247                                struct pt_regs *regs)
 248 {
 249         /*
 250          * If we are stepping a pending breakpoint, call the hw_breakpoint
 251          * handler first.
 252          */
 253         if (!reinstall_suspended_bps(regs))
 254                 return 0;
 255
 256         if (user_mode(regs)) {
 257                 send_user_sigtrap(TRAP_HWBKPT);
 258
 259                 /*
 260                  * ptrace will disable single step unless explicitly
 261                  * asked to re-enable it. For other clients, it makes
 262                  * sense to leave it enabled (i.e. rewind the controls
 263                  * to the active-not-pending state).
 264                  */
 265                 user_rewind_single_step(current);
 266         } else {
 267 #ifdef  CONFIG_KPROBES
 268                 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 269                         return 0;
 270 #endif
 271                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 272                         return 0;
 273
 274                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 275                 /*
 276                  * Re-enable stepping since we know that we will be
 277                  * returning to regs.
 278                  */
 279                 set_regs_spsr_ss(regs);
 280         }
 281
 282         return 0;
 283 }
 284 NOKPROBE_SYMBOL(single_step_handler);
 285
 286 /*
 287  * Breakpoint handler is re-entrant as another breakpoint can
 288  * hit within breakpoint handler, especically in kprobes.
 289  * Use reader/writer locks instead of plain spinlock.
 290  */
 291 static LIST_HEAD(break_hook);
 292 static DEFINE_SPINLOCK(break_hook_lock);
 293
 294 void register_break_hook(struct break_hook *hook)
 295 {
 296         spin_lock(&break_hook_lock);
 297         list_add_rcu(&hook->node, &break_hook);
 298         spin_unlock(&break_hook_lock);
 299 }
 300
 301 void unregister_break_hook(struct break_hook *hook)
 302 {
 303         spin_lock(&break_hook_lock);
 304         list_del_rcu(&hook->node);
 305         spin_unlock(&break_hook_lock);
 306         synchronize_rcu();
 307 }
 308
 309 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 310 {
 311         struct break_hook *hook;
 312         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 313
 314         rcu_read_lock();
 315         list_for_each_entry_rcu(hook, &break_hook, node)
 316                 if ((esr & hook->esr_mask) == hook->esr_val)
 317                         fn = hook->fn;
 318         rcu_read_unlock();
 319
 320         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 321 }
 322 NOKPROBE_SYMBOL(call_break_hook);
 323
 324 static int brk_handler(unsigned long addr, unsigned int esr,
 325                        struct pt_regs *regs)
 326 {
 327         if (user_mode(regs)) {
 328                 send_user_sigtrap(TRAP_BRKPT);
 329         }
 330 #ifdef  CONFIG_KPROBES
 331         else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 332                 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
 333                         return -EFAULT;
 334         }
 335 #endif
 336         else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 337                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 338                 return -EFAULT;
 339         }
 340
 341         return 0;
 342 }
 343 NOKPROBE_SYMBOL(brk_handler);
 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 NOKPROBE_SYMBOL(aarch32_break_handler);
 381
 382 static int __init debug_traps_init(void)
 383 {
 384         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 385                               TRAP_HWBKPT, "single-step handler");
 386         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 387                               TRAP_BRKPT, "ptrace BRK handler");
 388         return 0;
 389 }
 390 arch_initcall(debug_traps_init);
 391
 392 /* Re-enable single step for syscall restarting. */
 393 void user_rewind_single_step(struct task_struct *task)
 394 {
 395         /*
 396          * If single step is active for this thread, then set SPSR.SS
 397          * to 1 to avoid returning to the active-pending state.
 398          */
 399         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 400                 set_regs_spsr_ss(task_pt_regs(task));
 401 }
 402 NOKPROBE_SYMBOL(user_rewind_single_step);
 403
 404 void user_fastforward_single_step(struct task_struct *task)
 405 {
 406         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 407                 clear_regs_spsr_ss(task_pt_regs(task));
 408 }
 409
 410 /* Kernel API */
 411 void kernel_enable_single_step(struct pt_regs *regs)
 412 {
 413         WARN_ON(!irqs_disabled());
 414         set_regs_spsr_ss(regs);
 415         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 416         enable_debug_monitors(DBG_ACTIVE_EL1);
 417 }
 418 NOKPROBE_SYMBOL(kernel_enable_single_step);
 419
 420 void kernel_disable_single_step(void)
 421 {
 422         WARN_ON(!irqs_disabled());
 423         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 424         disable_debug_monitors(DBG_ACTIVE_EL1);
 425 }
 426 NOKPROBE_SYMBOL(kernel_disable_single_step);
 427
 428 int kernel_active_single_step(void)
 429 {
 430         WARN_ON(!irqs_disabled());
 431         return mdscr_read() & DBG_MDSCR_SS;
 432 }
 433 NOKPROBE_SYMBOL(kernel_active_single_step);
 434
 435 /* ptrace API */
 436 void user_enable_single_step(struct task_struct *task)
 437 {
 438         struct thread_info *ti = task_thread_info(task);
 439
 440         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 441                 set_regs_spsr_ss(task_pt_regs(task));
 442 }
 443 NOKPROBE_SYMBOL(user_enable_single_step);
 444
 445 void user_disable_single_step(struct task_struct *task)
 446 {
 447         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 448 }
 449 NOKPROBE_SYMBOL(user_disable_single_step);