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