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_unsigned_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         if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
 139                 clear_os_lock(NULL);
 140         return NOTIFY_OK;
 141 }
 142
 143 static struct notifier_block os_lock_nb = {
 144         .notifier_call = os_lock_notify,
 145 };
 146
 147 static int debug_monitors_init(void)
 148 {
 149         cpu_notifier_register_begin();
 150
 151         /* Clear the OS lock. */
 152         on_each_cpu(clear_os_lock, NULL, 1);
 153         isb();
 154
 155         /* Register hotplug handler. */
 156         __register_cpu_notifier(&os_lock_nb);
 157
 158         cpu_notifier_register_done();
 159         return 0;
 160 }
 161 postcore_initcall(debug_monitors_init);
 162
 163 /*
 164  * Single step API and exception handling.
 165  */
 166 static void set_regs_spsr_ss(struct pt_regs *regs)
 167 {
 168         unsigned long spsr;
 169
 170         spsr = regs->pstate;
 171         spsr &= ~DBG_SPSR_SS;
 172         spsr |= DBG_SPSR_SS;
 173         regs->pstate = spsr;
 174 }
 175
 176 static void clear_regs_spsr_ss(struct pt_regs *regs)
 177 {
 178         unsigned long spsr;
 179
 180         spsr = regs->pstate;
 181         spsr &= ~DBG_SPSR_SS;
 182         regs->pstate = spsr;
 183 }
 184
 185 /* EL1 Single Step Handler hooks */
 186 static LIST_HEAD(step_hook);
 187 static DEFINE_SPINLOCK(step_hook_lock);
 188
 189 void register_step_hook(struct step_hook *hook)
 190 {
 191         spin_lock(&step_hook_lock);
 192         list_add_rcu(&hook->node, &step_hook);
 193         spin_unlock(&step_hook_lock);
 194 }
 195
 196 void unregister_step_hook(struct step_hook *hook)
 197 {
 198         spin_lock(&step_hook_lock);
 199         list_del_rcu(&hook->node);
 200         spin_unlock(&step_hook_lock);
 201         synchronize_rcu();
 202 }
 203
 204 /*
 205  * Call registered single step handlers
 206  * There is no Syndrome info to check for determining the handler.
 207  * So we call all the registered handlers, until the right handler is
 208  * found which returns zero.
 209  */
 210 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 211 {
 212         struct step_hook *hook;
 213         int retval = DBG_HOOK_ERROR;
 214
 215         rcu_read_lock();
 216
 217         list_for_each_entry_rcu(hook, &step_hook, node) {
 218                 retval = hook->fn(regs, esr);
 219                 if (retval == DBG_HOOK_HANDLED)
 220                         break;
 221         }
 222
 223         rcu_read_unlock();
 224
 225         return retval;
 226 }
 227
 228 static void send_user_sigtrap(int si_code)
 229 {
 230         struct pt_regs *regs = current_pt_regs();
 231         siginfo_t info = {
 232                 .si_signo       = SIGTRAP,
 233                 .si_errno       = 0,
 234                 .si_code        = si_code,
 235                 .si_addr        = (void __user *)instruction_pointer(regs),
 236         };
 237
 238         if (WARN_ON(!user_mode(regs)))
 239                 return;
 240
 241         if (interrupts_enabled(regs))
 242                 local_irq_enable();
 243
 244         force_sig_info(SIGTRAP, &info, current);
 245 }
 246
 247 static int single_step_handler(unsigned long addr, unsigned int esr,
 248                                struct pt_regs *regs)
 249 {
 250         /*
 251          * If we are stepping a pending breakpoint, call the hw_breakpoint
 252          * handler first.
 253          */
 254         if (!reinstall_suspended_bps(regs))
 255                 return 0;
 256
 257         if (user_mode(regs)) {
 258                 send_user_sigtrap(TRAP_HWBKPT);
 259
 260                 /*
 261                  * ptrace will disable single step unless explicitly
 262                  * asked to re-enable it. For other clients, it makes
 263                  * sense to leave it enabled (i.e. rewind the controls
 264                  * to the active-not-pending state).
 265                  */
 266                 user_rewind_single_step(current);
 267         } else {
 268                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 269                         return 0;
 270
 271                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 272                 /*
 273                  * Re-enable stepping since we know that we will be
 274                  * returning to regs.
 275                  */
 276                 set_regs_spsr_ss(regs);
 277         }
 278
 279         return 0;
 280 }
 281
 282 /*
 283  * Breakpoint handler is re-entrant as another breakpoint can
 284  * hit within breakpoint handler, especically in kprobes.
 285  * Use reader/writer locks instead of plain spinlock.
 286  */
 287 static LIST_HEAD(break_hook);
 288 static DEFINE_SPINLOCK(break_hook_lock);
 289
 290 void register_break_hook(struct break_hook *hook)
 291 {
 292         spin_lock(&break_hook_lock);
 293         list_add_rcu(&hook->node, &break_hook);
 294         spin_unlock(&break_hook_lock);
 295 }
 296
 297 void unregister_break_hook(struct break_hook *hook)
 298 {
 299         spin_lock(&break_hook_lock);
 300         list_del_rcu(&hook->node);
 301         spin_unlock(&break_hook_lock);
 302         synchronize_rcu();
 303 }
 304
 305 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 306 {
 307         struct break_hook *hook;
 308         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 309
 310         rcu_read_lock();
 311         list_for_each_entry_rcu(hook, &break_hook, node)
 312                 if ((esr & hook->esr_mask) == hook->esr_val)
 313                         fn = hook->fn;
 314         rcu_read_unlock();
 315
 316         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 317 }
 318
 319 static int brk_handler(unsigned long addr, unsigned int esr,
 320                        struct pt_regs *regs)
 321 {
 322         if (user_mode(regs)) {
 323                 send_user_sigtrap(TRAP_BRKPT);
 324         } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 325                 pr_warning("Unexpected kernel BRK exception at EL1\n");
 326                 return -EFAULT;
 327         }
 328
 329         return 0;
 330 }
 331
 332 int aarch32_break_handler(struct pt_regs *regs)
 333 {
 334         u32 arm_instr;
 335         u16 thumb_instr;
 336         bool bp = false;
 337         void __user *pc = (void __user *)instruction_pointer(regs);
 338
 339         if (!compat_user_mode(regs))
 340                 return -EFAULT;
 341
 342         if (compat_thumb_mode(regs)) {
 343                 /* get 16-bit Thumb instruction */
 344                 get_user(thumb_instr, (u16 __user *)pc);
 345                 thumb_instr = le16_to_cpu(thumb_instr);
 346                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 347                         /* get second half of 32-bit Thumb-2 instruction */
 348                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 349                         thumb_instr = le16_to_cpu(thumb_instr);
 350                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 351                 } else {
 352                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 353                 }
 354         } else {
 355                 /* 32-bit ARM instruction */
 356                 get_user(arm_instr, (u32 __user *)pc);
 357                 arm_instr = le32_to_cpu(arm_instr);
 358                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 359         }
 360
 361         if (!bp)
 362                 return -EFAULT;
 363
 364         send_user_sigtrap(TRAP_BRKPT);
 365         return 0;
 366 }
 367
 368 static int __init debug_traps_init(void)
 369 {
 370         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 371                               TRAP_HWBKPT, "single-step handler");
 372         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 373                               TRAP_BRKPT, "ptrace BRK handler");
 374         return 0;
 375 }
 376 arch_initcall(debug_traps_init);
 377
 378 /* Re-enable single step for syscall restarting. */
 379 void user_rewind_single_step(struct task_struct *task)
 380 {
 381         /*
 382          * If single step is active for this thread, then set SPSR.SS
 383          * to 1 to avoid returning to the active-pending state.
 384          */
 385         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 386                 set_regs_spsr_ss(task_pt_regs(task));
 387 }
 388
 389 void user_fastforward_single_step(struct task_struct *task)
 390 {
 391         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 392                 clear_regs_spsr_ss(task_pt_regs(task));
 393 }
 394
 395 /* Kernel API */
 396 void kernel_enable_single_step(struct pt_regs *regs)
 397 {
 398         WARN_ON(!irqs_disabled());
 399         set_regs_spsr_ss(regs);
 400         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 401         enable_debug_monitors(DBG_ACTIVE_EL1);
 402 }
 403
 404 void kernel_disable_single_step(void)
 405 {
 406         WARN_ON(!irqs_disabled());
 407         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 408         disable_debug_monitors(DBG_ACTIVE_EL1);
 409 }
 410
 411 int kernel_active_single_step(void)
 412 {
 413         WARN_ON(!irqs_disabled());
 414         return mdscr_read() & DBG_MDSCR_SS;
 415 }
 416
 417 /* ptrace API */
 418 void user_enable_single_step(struct task_struct *task)
 419 {
 420         set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 421         set_regs_spsr_ss(task_pt_regs(task));
 422 }
 423
 424 void user_disable_single_step(struct task_struct *task)
 425 {
 426         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 427 }