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/cpufeature.h>
  30 #include <asm/cputype.h>
  31 #include <asm/debug-monitors.h>
  32 #include <asm/system_misc.h>
  33
  34 /* Determine debug architecture. */
  35 u8 debug_monitors_arch(void)
  36 {
  37         return cpuid_feature_extract_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
  38                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
  39 }
  40
  41 /*
  42  * MDSCR access routines.
  43  */
  44 static void mdscr_write(u32 mdscr)
  45 {
  46         unsigned long flags;
  47         local_dbg_save(flags);
  48         asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
  49         local_dbg_restore(flags);
  50 }
  51
  52 static u32 mdscr_read(void)
  53 {
  54         u32 mdscr;
  55         asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
  56         return mdscr;
  57 }
  58
  59 /*
  60  * Allow root to disable self-hosted debug from userspace.
  61  * This is useful if you want to connect an external JTAG debugger.
  62  */
  63 static bool debug_enabled = true;
  64
  65 static int create_debug_debugfs_entry(void)
  66 {
  67         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  68         return 0;
  69 }
  70 fs_initcall(create_debug_debugfs_entry);
  71
  72 static int __init early_debug_disable(char *buf)
  73 {
  74         debug_enabled = false;
  75         return 0;
  76 }
  77
  78 early_param("nodebugmon", early_debug_disable);
  79
  80 /*
  81  * Keep track of debug users on each core.
  82  * The ref counts are per-cpu so we use a local_t type.
  83  */
  84 static DEFINE_PER_CPU(int, mde_ref_count);
  85 static DEFINE_PER_CPU(int, kde_ref_count);
  86
  87 void enable_debug_monitors(enum dbg_active_el el)
  88 {
  89         u32 mdscr, enable = 0;
  90
  91         WARN_ON(preemptible());
  92
  93         if (this_cpu_inc_return(mde_ref_count) == 1)
  94                 enable = DBG_MDSCR_MDE;
  95
  96         if (el == DBG_ACTIVE_EL1 &&
  97             this_cpu_inc_return(kde_ref_count) == 1)
  98                 enable |= DBG_MDSCR_KDE;
  99
 100         if (enable && debug_enabled) {
 101                 mdscr = mdscr_read();
 102                 mdscr |= enable;
 103                 mdscr_write(mdscr);
 104         }
 105 }
 106
 107 void disable_debug_monitors(enum dbg_active_el el)
 108 {
 109         u32 mdscr, disable = 0;
 110
 111         WARN_ON(preemptible());
 112
 113         if (this_cpu_dec_return(mde_ref_count) == 0)
 114                 disable = ~DBG_MDSCR_MDE;
 115
 116         if (el == DBG_ACTIVE_EL1 &&
 117             this_cpu_dec_return(kde_ref_count) == 0)
 118                 disable &= ~DBG_MDSCR_KDE;
 119
 120         if (disable) {
 121                 mdscr = mdscr_read();
 122                 mdscr &= disable;
 123                 mdscr_write(mdscr);
 124         }
 125 }
 126
 127 /*
 128  * OS lock clearing.
 129  */
 130 static void clear_os_lock(void *unused)
 131 {
 132         asm volatile("msr oslar_el1, %0" : : "r" (0));
 133 }
 134
 135 static int os_lock_notify(struct notifier_block *self,
 136                                     unsigned long action, void *data)
 137 {
 138         int cpu = (unsigned long)data;
 139         if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
 140                 smp_call_function_single(cpu, clear_os_lock, NULL, 1);
 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 int single_step_handler(unsigned long addr, unsigned int esr,
 231                                struct pt_regs *regs)
 232 {
 233         siginfo_t info;
 234
 235         /*
 236          * If we are stepping a pending breakpoint, call the hw_breakpoint
 237          * handler first.
 238          */
 239         if (!reinstall_suspended_bps(regs))
 240                 return 0;
 241
 242         if (user_mode(regs)) {
 243                 info.si_signo = SIGTRAP;
 244                 info.si_errno = 0;
 245                 info.si_code  = TRAP_HWBKPT;
 246                 info.si_addr  = (void __user *)instruction_pointer(regs);
 247                 force_sig_info(SIGTRAP, &info, current);
 248
 249                 /*
 250                  * ptrace will disable single step unless explicitly
 251                  * asked to re-enable it. For other clients, it makes
 252                  * sense to leave it enabled (i.e. rewind the controls
 253                  * to the active-not-pending state).
 254                  */
 255                 user_rewind_single_step(current);
 256         } else {
 257                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 258                         return 0;
 259
 260                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 261                 /*
 262                  * Re-enable stepping since we know that we will be
 263                  * returning to regs.
 264                  */
 265                 set_regs_spsr_ss(regs);
 266         }
 267
 268         return 0;
 269 }
 270
 271 /*
 272  * Breakpoint handler is re-entrant as another breakpoint can
 273  * hit within breakpoint handler, especically in kprobes.
 274  * Use reader/writer locks instead of plain spinlock.
 275  */
 276 static LIST_HEAD(break_hook);
 277 static DEFINE_SPINLOCK(break_hook_lock);
 278
 279 void register_break_hook(struct break_hook *hook)
 280 {
 281         spin_lock(&break_hook_lock);
 282         list_add_rcu(&hook->node, &break_hook);
 283         spin_unlock(&break_hook_lock);
 284 }
 285
 286 void unregister_break_hook(struct break_hook *hook)
 287 {
 288         spin_lock(&break_hook_lock);
 289         list_del_rcu(&hook->node);
 290         spin_unlock(&break_hook_lock);
 291         synchronize_rcu();
 292 }
 293
 294 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 295 {
 296         struct break_hook *hook;
 297         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 298
 299         rcu_read_lock();
 300         list_for_each_entry_rcu(hook, &break_hook, node)
 301                 if ((esr & hook->esr_mask) == hook->esr_val)
 302                         fn = hook->fn;
 303         rcu_read_unlock();
 304
 305         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 306 }
 307
 308 static int brk_handler(unsigned long addr, unsigned int esr,
 309                        struct pt_regs *regs)
 310 {
 311         siginfo_t info;
 312
 313         if (user_mode(regs)) {
 314                 info = (siginfo_t) {
 315                         .si_signo = SIGTRAP,
 316                         .si_errno = 0,
 317                         .si_code  = TRAP_BRKPT,
 318                         .si_addr  = (void __user *)instruction_pointer(regs),
 319                 };
 320
 321                 force_sig_info(SIGTRAP, &info, current);
 322         } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 323                 pr_warning("Unexpected kernel BRK exception at EL1\n");
 324                 return -EFAULT;
 325         }
 326
 327         return 0;
 328 }
 329
 330 int aarch32_break_handler(struct pt_regs *regs)
 331 {
 332         siginfo_t info;
 333         u32 arm_instr;
 334         u16 thumb_instr;
 335         bool bp = false;
 336         void __user *pc = (void __user *)instruction_pointer(regs);
 337
 338         if (!compat_user_mode(regs))
 339                 return -EFAULT;
 340
 341         if (compat_thumb_mode(regs)) {
 342                 /* get 16-bit Thumb instruction */
 343                 get_user(thumb_instr, (u16 __user *)pc);
 344                 thumb_instr = le16_to_cpu(thumb_instr);
 345                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 346                         /* get second half of 32-bit Thumb-2 instruction */
 347                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 348                         thumb_instr = le16_to_cpu(thumb_instr);
 349                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 350                 } else {
 351                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 352                 }
 353         } else {
 354                 /* 32-bit ARM instruction */
 355                 get_user(arm_instr, (u32 __user *)pc);
 356                 arm_instr = le32_to_cpu(arm_instr);
 357                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 358         }
 359
 360         if (!bp)
 361                 return -EFAULT;
 362
 363         info = (siginfo_t) {
 364                 .si_signo = SIGTRAP,
 365                 .si_errno = 0,
 366                 .si_code  = TRAP_BRKPT,
 367                 .si_addr  = pc,
 368         };
 369
 370         force_sig_info(SIGTRAP, &info, current);
 371         return 0;
 372 }
 373
 374 static int __init debug_traps_init(void)
 375 {
 376         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 377                               TRAP_HWBKPT, "single-step handler");
 378         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 379                               TRAP_BRKPT, "ptrace BRK handler");
 380         return 0;
 381 }
 382 arch_initcall(debug_traps_init);
 383
 384 /* Re-enable single step for syscall restarting. */
 385 void user_rewind_single_step(struct task_struct *task)
 386 {
 387         /*
 388          * If single step is active for this thread, then set SPSR.SS
 389          * to 1 to avoid returning to the active-pending state.
 390          */
 391         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 392                 set_regs_spsr_ss(task_pt_regs(task));
 393 }
 394
 395 void user_fastforward_single_step(struct task_struct *task)
 396 {
 397         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 398                 clear_regs_spsr_ss(task_pt_regs(task));
 399 }
 400
 401 /* Kernel API */
 402 void kernel_enable_single_step(struct pt_regs *regs)
 403 {
 404         WARN_ON(!irqs_disabled());
 405         set_regs_spsr_ss(regs);
 406         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 407         enable_debug_monitors(DBG_ACTIVE_EL1);
 408 }
 409
 410 void kernel_disable_single_step(void)
 411 {
 412         WARN_ON(!irqs_disabled());
 413         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 414         disable_debug_monitors(DBG_ACTIVE_EL1);
 415 }
 416
 417 int kernel_active_single_step(void)
 418 {
 419         WARN_ON(!irqs_disabled());
 420         return mdscr_read() & DBG_MDSCR_SS;
 421 }
 422
 423 /* ptrace API */
 424 void user_enable_single_step(struct task_struct *task)
 425 {
 426         set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 427         set_regs_spsr_ss(task_pt_regs(task));
 428 }
 429
 430 void user_disable_single_step(struct task_struct *task)
 431 {
 432         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 433 }