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         local_dbg_enable();
 155
 156         /* Register hotplug handler. */
 157         __register_cpu_notifier(&os_lock_nb);
 158
 159         cpu_notifier_register_done();
 160         return 0;
 161 }
 162 postcore_initcall(debug_monitors_init);
 163
 164 /*
 165  * Single step API and exception handling.
 166  */
 167 static void set_regs_spsr_ss(struct pt_regs *regs)
 168 {
 169         unsigned long spsr;
 170
 171         spsr = regs->pstate;
 172         spsr &= ~DBG_SPSR_SS;
 173         spsr |= DBG_SPSR_SS;
 174         regs->pstate = spsr;
 175 }
 176
 177 static void clear_regs_spsr_ss(struct pt_regs *regs)
 178 {
 179         unsigned long spsr;
 180
 181         spsr = regs->pstate;
 182         spsr &= ~DBG_SPSR_SS;
 183         regs->pstate = spsr;
 184 }
 185
 186 /* EL1 Single Step Handler hooks */
 187 static LIST_HEAD(step_hook);
 188 static DEFINE_SPINLOCK(step_hook_lock);
 189
 190 void register_step_hook(struct step_hook *hook)
 191 {
 192         spin_lock(&step_hook_lock);
 193         list_add_rcu(&hook->node, &step_hook);
 194         spin_unlock(&step_hook_lock);
 195 }
 196
 197 void unregister_step_hook(struct step_hook *hook)
 198 {
 199         spin_lock(&step_hook_lock);
 200         list_del_rcu(&hook->node);
 201         spin_unlock(&step_hook_lock);
 202         synchronize_rcu();
 203 }
 204
 205 /*
 206  * Call registered single step handlers
 207  * There is no Syndrome info to check for determining the handler.
 208  * So we call all the registered handlers, until the right handler is
 209  * found which returns zero.
 210  */
 211 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 212 {
 213         struct step_hook *hook;
 214         int retval = DBG_HOOK_ERROR;
 215
 216         rcu_read_lock();
 217
 218         list_for_each_entry_rcu(hook, &step_hook, node) {
 219                 retval = hook->fn(regs, esr);
 220                 if (retval == DBG_HOOK_HANDLED)
 221                         break;
 222         }
 223
 224         rcu_read_unlock();
 225
 226         return retval;
 227 }
 228
 229 static void send_user_sigtrap(int si_code)
 230 {
 231         struct pt_regs *regs = current_pt_regs();
 232         siginfo_t info = {
 233                 .si_signo       = SIGTRAP,
 234                 .si_errno       = 0,
 235                 .si_code        = si_code,
 236                 .si_addr        = (void __user *)instruction_pointer(regs),
 237         };
 238
 239         if (WARN_ON(!user_mode(regs)))
 240                 return;
 241
 242         if (interrupts_enabled(regs))
 243                 local_irq_enable();
 244
 245         force_sig_info(SIGTRAP, &info, current);
 246 }
 247
 248 static int single_step_handler(unsigned long addr, unsigned int esr,
 249                                struct pt_regs *regs)
 250 {
 251         /*
 252          * If we are stepping a pending breakpoint, call the hw_breakpoint
 253          * handler first.
 254          */
 255         if (!reinstall_suspended_bps(regs))
 256                 return 0;
 257
 258         if (user_mode(regs)) {
 259                 send_user_sigtrap(TRAP_HWBKPT);
 260
 261                 /*
 262                  * ptrace will disable single step unless explicitly
 263                  * asked to re-enable it. For other clients, it makes
 264                  * sense to leave it enabled (i.e. rewind the controls
 265                  * to the active-not-pending state).
 266                  */
 267                 user_rewind_single_step(current);
 268         } else {
 269                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 270                         return 0;
 271
 272                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 273                 /*
 274                  * Re-enable stepping since we know that we will be
 275                  * returning to regs.
 276                  */
 277                 set_regs_spsr_ss(regs);
 278         }
 279
 280         return 0;
 281 }
 282
 283 /*
 284  * Breakpoint handler is re-entrant as another breakpoint can
 285  * hit within breakpoint handler, especically in kprobes.
 286  * Use reader/writer locks instead of plain spinlock.
 287  */
 288 static LIST_HEAD(break_hook);
 289 static DEFINE_SPINLOCK(break_hook_lock);
 290
 291 void register_break_hook(struct break_hook *hook)
 292 {
 293         spin_lock(&break_hook_lock);
 294         list_add_rcu(&hook->node, &break_hook);
 295         spin_unlock(&break_hook_lock);
 296 }
 297
 298 void unregister_break_hook(struct break_hook *hook)
 299 {
 300         spin_lock(&break_hook_lock);
 301         list_del_rcu(&hook->node);
 302         spin_unlock(&break_hook_lock);
 303         synchronize_rcu();
 304 }
 305
 306 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 307 {
 308         struct break_hook *hook;
 309         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 310
 311         rcu_read_lock();
 312         list_for_each_entry_rcu(hook, &break_hook, node)
 313                 if ((esr & hook->esr_mask) == hook->esr_val)
 314                         fn = hook->fn;
 315         rcu_read_unlock();
 316
 317         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 318 }
 319
 320 static int brk_handler(unsigned long addr, unsigned int esr,
 321                        struct pt_regs *regs)
 322 {
 323         if (user_mode(regs)) {
 324                 send_user_sigtrap(TRAP_BRKPT);
 325         } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 326                 pr_warning("Unexpected kernel BRK exception at EL1\n");
 327                 return -EFAULT;
 328         }
 329
 330         return 0;
 331 }
 332
 333 int aarch32_break_handler(struct pt_regs *regs)
 334 {
 335         u32 arm_instr;
 336         u16 thumb_instr;
 337         bool bp = false;
 338         void __user *pc = (void __user *)instruction_pointer(regs);
 339
 340         if (!compat_user_mode(regs))
 341                 return -EFAULT;
 342
 343         if (compat_thumb_mode(regs)) {
 344                 /* get 16-bit Thumb instruction */
 345                 get_user(thumb_instr, (u16 __user *)pc);
 346                 thumb_instr = le16_to_cpu(thumb_instr);
 347                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 348                         /* get second half of 32-bit Thumb-2 instruction */
 349                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 350                         thumb_instr = le16_to_cpu(thumb_instr);
 351                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 352                 } else {
 353                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 354                 }
 355         } else {
 356                 /* 32-bit ARM instruction */
 357                 get_user(arm_instr, (u32 __user *)pc);
 358                 arm_instr = le32_to_cpu(arm_instr);
 359                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 360         }
 361
 362         if (!bp)
 363                 return -EFAULT;
 364
 365         send_user_sigtrap(TRAP_BRKPT);
 366         return 0;
 367 }
 368
 369 static int __init debug_traps_init(void)
 370 {
 371         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 372                               TRAP_HWBKPT, "single-step handler");
 373         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 374                               TRAP_BRKPT, "ptrace BRK handler");
 375         return 0;
 376 }
 377 arch_initcall(debug_traps_init);
 378
 379 /* Re-enable single step for syscall restarting. */
 380 void user_rewind_single_step(struct task_struct *task)
 381 {
 382         /*
 383          * If single step is active for this thread, then set SPSR.SS
 384          * to 1 to avoid returning to the active-pending state.
 385          */
 386         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 387                 set_regs_spsr_ss(task_pt_regs(task));
 388 }
 389
 390 void user_fastforward_single_step(struct task_struct *task)
 391 {
 392         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 393                 clear_regs_spsr_ss(task_pt_regs(task));
 394 }
 395
 396 /* Kernel API */
 397 void kernel_enable_single_step(struct pt_regs *regs)
 398 {
 399         WARN_ON(!irqs_disabled());
 400         set_regs_spsr_ss(regs);
 401         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 402         enable_debug_monitors(DBG_ACTIVE_EL1);
 403 }
 404
 405 void kernel_disable_single_step(void)
 406 {
 407         WARN_ON(!irqs_disabled());
 408         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 409         disable_debug_monitors(DBG_ACTIVE_EL1);
 410 }
 411
 412 int kernel_active_single_step(void)
 413 {
 414         WARN_ON(!irqs_disabled());
 415         return mdscr_read() & DBG_MDSCR_SS;
 416 }
 417
 418 /* ptrace API */
 419 void user_enable_single_step(struct task_struct *task)
 420 {
 421         set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 422         set_regs_spsr_ss(task_pt_regs(task));
 423 }
 424
 425 void user_disable_single_step(struct task_struct *task)
 426 {
 427         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 428 }