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         write_sysreg(mdscr, mdscr_el1);
  50         local_dbg_restore(flags);
  51 }
  52 NOKPROBE_SYMBOL(mdscr_write);
  53
  54 static u32 mdscr_read(void)
  55 {
  56         return read_sysreg(mdscr_el1);
  57 }
  58 NOKPROBE_SYMBOL(mdscr_read);
  59
  60 /*
  61  * Allow root to disable self-hosted debug from userspace.
  62  * This is useful if you want to connect an external JTAG debugger.
  63  */
  64 static bool debug_enabled = true;
  65
  66 static int create_debug_debugfs_entry(void)
  67 {
  68         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  69         return 0;
  70 }
  71 fs_initcall(create_debug_debugfs_entry);
  72
  73 static int __init early_debug_disable(char *buf)
  74 {
  75         debug_enabled = false;
  76         return 0;
  77 }
  78
  79 early_param("nodebugmon", early_debug_disable);
  80
  81 /*
  82  * Keep track of debug users on each core.
  83  * The ref counts are per-cpu so we use a local_t type.
  84  */
  85 static DEFINE_PER_CPU(int, mde_ref_count);
  86 static DEFINE_PER_CPU(int, kde_ref_count);
  87
  88 void enable_debug_monitors(enum dbg_active_el el)
  89 {
  90         u32 mdscr, enable = 0;
  91
  92         WARN_ON(preemptible());
  93
  94         if (this_cpu_inc_return(mde_ref_count) == 1)
  95                 enable = DBG_MDSCR_MDE;
  96
  97         if (el == DBG_ACTIVE_EL1 &&
  98             this_cpu_inc_return(kde_ref_count) == 1)
  99                 enable |= DBG_MDSCR_KDE;
 100
 101         if (enable && debug_enabled) {
 102                 mdscr = mdscr_read();
 103                 mdscr |= enable;
 104                 mdscr_write(mdscr);
 105         }
 106 }
 107 NOKPROBE_SYMBOL(enable_debug_monitors);
 108
 109 void disable_debug_monitors(enum dbg_active_el el)
 110 {
 111         u32 mdscr, disable = 0;
 112
 113         WARN_ON(preemptible());
 114
 115         if (this_cpu_dec_return(mde_ref_count) == 0)
 116                 disable = ~DBG_MDSCR_MDE;
 117
 118         if (el == DBG_ACTIVE_EL1 &&
 119             this_cpu_dec_return(kde_ref_count) == 0)
 120                 disable &= ~DBG_MDSCR_KDE;
 121
 122         if (disable) {
 123                 mdscr = mdscr_read();
 124                 mdscr &= disable;
 125                 mdscr_write(mdscr);
 126         }
 127 }
 128 NOKPROBE_SYMBOL(disable_debug_monitors);
 129
 130 /*
 131  * OS lock clearing.
 132  */
 133 static int clear_os_lock(unsigned int cpu)
 134 {
 135         write_sysreg(0, osdlr_el1);
 136         write_sysreg(0, oslar_el1);
 137         isb();
 138         return 0;
 139 }
 140
 141 static int debug_monitors_init(void)
 142 {
 143         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 144                                  "CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING",
 145                                  clear_os_lock, NULL);
 146 }
 147 postcore_initcall(debug_monitors_init);
 148
 149 /*
 150  * Single step API and exception handling.
 151  */
 152 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
 153 {
 154         regs->pstate |= DBG_SPSR_SS;
 155 }
 156 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
 157
 158 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
 159 {
 160         regs->pstate &= ~DBG_SPSR_SS;
 161 }
 162 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
 163
 164 #define set_regs_spsr_ss(r)     set_user_regs_spsr_ss(&(r)->user_regs)
 165 #define clear_regs_spsr_ss(r)   clear_user_regs_spsr_ss(&(r)->user_regs)
 166
 167 /* EL1 Single Step Handler hooks */
 168 static LIST_HEAD(step_hook);
 169 static DEFINE_SPINLOCK(step_hook_lock);
 170
 171 void register_step_hook(struct step_hook *hook)
 172 {
 173         spin_lock(&step_hook_lock);
 174         list_add_rcu(&hook->node, &step_hook);
 175         spin_unlock(&step_hook_lock);
 176 }
 177
 178 void unregister_step_hook(struct step_hook *hook)
 179 {
 180         spin_lock(&step_hook_lock);
 181         list_del_rcu(&hook->node);
 182         spin_unlock(&step_hook_lock);
 183         synchronize_rcu();
 184 }
 185
 186 /*
 187  * Call registered single step handlers
 188  * There is no Syndrome info to check for determining the handler.
 189  * So we call all the registered handlers, until the right handler is
 190  * found which returns zero.
 191  */
 192 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 193 {
 194         struct step_hook *hook;
 195         int retval = DBG_HOOK_ERROR;
 196
 197         rcu_read_lock();
 198
 199         list_for_each_entry_rcu(hook, &step_hook, node) {
 200                 retval = hook->fn(regs, esr);
 201                 if (retval == DBG_HOOK_HANDLED)
 202                         break;
 203         }
 204
 205         rcu_read_unlock();
 206
 207         return retval;
 208 }
 209 NOKPROBE_SYMBOL(call_step_hook);
 210
 211 static void send_user_sigtrap(int si_code)
 212 {
 213         struct pt_regs *regs = current_pt_regs();
 214         siginfo_t info = {
 215                 .si_signo       = SIGTRAP,
 216                 .si_errno       = 0,
 217                 .si_code        = si_code,
 218                 .si_addr        = (void __user *)instruction_pointer(regs),
 219         };
 220
 221         if (WARN_ON(!user_mode(regs)))
 222                 return;
 223
 224         if (interrupts_enabled(regs))
 225                 local_irq_enable();
 226
 227         force_sig_info(SIGTRAP, &info, current);
 228 }
 229
 230 static int single_step_handler(unsigned long addr, unsigned int esr,
 231                                struct pt_regs *regs)
 232 {
 233         /*
 234          * If we are stepping a pending breakpoint, call the hw_breakpoint
 235          * handler first.
 236          */
 237         if (!reinstall_suspended_bps(regs))
 238                 return 0;
 239
 240         if (user_mode(regs)) {
 241                 send_user_sigtrap(TRAP_TRACE);
 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 #ifdef  CONFIG_KPROBES
 252                 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 253                         return 0;
 254 #endif
 255                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 256                         return 0;
 257
 258                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 259                 /*
 260                  * Re-enable stepping since we know that we will be
 261                  * returning to regs.
 262                  */
 263                 set_regs_spsr_ss(regs);
 264         }
 265
 266         return 0;
 267 }
 268 NOKPROBE_SYMBOL(single_step_handler);
 269
 270 /*
 271  * Breakpoint handler is re-entrant as another breakpoint can
 272  * hit within breakpoint handler, especically in kprobes.
 273  * Use reader/writer locks instead of plain spinlock.
 274  */
 275 static LIST_HEAD(break_hook);
 276 static DEFINE_SPINLOCK(break_hook_lock);
 277
 278 void register_break_hook(struct break_hook *hook)
 279 {
 280         spin_lock(&break_hook_lock);
 281         list_add_rcu(&hook->node, &break_hook);
 282         spin_unlock(&break_hook_lock);
 283 }
 284
 285 void unregister_break_hook(struct break_hook *hook)
 286 {
 287         spin_lock(&break_hook_lock);
 288         list_del_rcu(&hook->node);
 289         spin_unlock(&break_hook_lock);
 290         synchronize_rcu();
 291 }
 292
 293 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 294 {
 295         struct break_hook *hook;
 296         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 297
 298         rcu_read_lock();
 299         list_for_each_entry_rcu(hook, &break_hook, node)
 300                 if ((esr & hook->esr_mask) == hook->esr_val)
 301                         fn = hook->fn;
 302         rcu_read_unlock();
 303
 304         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 305 }
 306 NOKPROBE_SYMBOL(call_break_hook);
 307
 308 static int brk_handler(unsigned long addr, unsigned int esr,
 309                        struct pt_regs *regs)
 310 {
 311         if (user_mode(regs)) {
 312                 send_user_sigtrap(TRAP_BRKPT);
 313         }
 314 #ifdef  CONFIG_KPROBES
 315         else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 316                 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
 317                         return -EFAULT;
 318         }
 319 #endif
 320         else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 321                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 322                 return -EFAULT;
 323         }
 324
 325         return 0;
 326 }
 327 NOKPROBE_SYMBOL(brk_handler);
 328
 329 int aarch32_break_handler(struct pt_regs *regs)
 330 {
 331         u32 arm_instr;
 332         u16 thumb_instr;
 333         bool bp = false;
 334         void __user *pc = (void __user *)instruction_pointer(regs);
 335
 336         if (!compat_user_mode(regs))
 337                 return -EFAULT;
 338
 339         if (compat_thumb_mode(regs)) {
 340                 /* get 16-bit Thumb instruction */
 341                 get_user(thumb_instr, (u16 __user *)pc);
 342                 thumb_instr = le16_to_cpu(thumb_instr);
 343                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 344                         /* get second half of 32-bit Thumb-2 instruction */
 345                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 346                         thumb_instr = le16_to_cpu(thumb_instr);
 347                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 348                 } else {
 349                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 350                 }
 351         } else {
 352                 /* 32-bit ARM instruction */
 353                 get_user(arm_instr, (u32 __user *)pc);
 354                 arm_instr = le32_to_cpu(arm_instr);
 355                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 356         }
 357
 358         if (!bp)
 359                 return -EFAULT;
 360
 361         send_user_sigtrap(TRAP_BRKPT);
 362         return 0;
 363 }
 364 NOKPROBE_SYMBOL(aarch32_break_handler);
 365
 366 static int __init debug_traps_init(void)
 367 {
 368         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 369                               TRAP_TRACE, "single-step handler");
 370         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 371                               TRAP_BRKPT, "ptrace BRK handler");
 372         return 0;
 373 }
 374 arch_initcall(debug_traps_init);
 375
 376 /* Re-enable single step for syscall restarting. */
 377 void user_rewind_single_step(struct task_struct *task)
 378 {
 379         /*
 380          * If single step is active for this thread, then set SPSR.SS
 381          * to 1 to avoid returning to the active-pending state.
 382          */
 383         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 384                 set_regs_spsr_ss(task_pt_regs(task));
 385 }
 386 NOKPROBE_SYMBOL(user_rewind_single_step);
 387
 388 void user_fastforward_single_step(struct task_struct *task)
 389 {
 390         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 391                 clear_regs_spsr_ss(task_pt_regs(task));
 392 }
 393
 394 void user_regs_reset_single_step(struct user_pt_regs *regs,
 395                                  struct task_struct *task)
 396 {
 397         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 398                 set_user_regs_spsr_ss(regs);
 399         else
 400                 clear_user_regs_spsr_ss(regs);
 401 }
 402
 403 /* Kernel API */
 404 void kernel_enable_single_step(struct pt_regs *regs)
 405 {
 406         WARN_ON(!irqs_disabled());
 407         set_regs_spsr_ss(regs);
 408         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 409         enable_debug_monitors(DBG_ACTIVE_EL1);
 410 }
 411 NOKPROBE_SYMBOL(kernel_enable_single_step);
 412
 413 void kernel_disable_single_step(void)
 414 {
 415         WARN_ON(!irqs_disabled());
 416         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 417         disable_debug_monitors(DBG_ACTIVE_EL1);
 418 }
 419 NOKPROBE_SYMBOL(kernel_disable_single_step);
 420
 421 int kernel_active_single_step(void)
 422 {
 423         WARN_ON(!irqs_disabled());
 424         return mdscr_read() & DBG_MDSCR_SS;
 425 }
 426 NOKPROBE_SYMBOL(kernel_active_single_step);
 427
 428 /* ptrace API */
 429 void user_enable_single_step(struct task_struct *task)
 430 {
 431         struct thread_info *ti = task_thread_info(task);
 432
 433         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 434                 set_regs_spsr_ss(task_pt_regs(task));
 435 }
 436 NOKPROBE_SYMBOL(user_enable_single_step);
 437
 438 void user_disable_single_step(struct task_struct *task)
 439 {
 440         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 441 }
 442 NOKPROBE_SYMBOL(user_disable_single_step);