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, oslar_el1);
 136         isb();
 137         return 0;
 138 }
 139
 140 static int debug_monitors_init(void)
 141 {
 142         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 143                                  "arm64/debug_monitors:starting",
 144                                  clear_os_lock, NULL);
 145 }
 146 postcore_initcall(debug_monitors_init);
 147
 148 /*
 149  * Single step API and exception handling.
 150  */
 151 static void set_regs_spsr_ss(struct pt_regs *regs)
 152 {
 153         regs->pstate |= DBG_SPSR_SS;
 154 }
 155 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 156
 157 static void clear_regs_spsr_ss(struct pt_regs *regs)
 158 {
 159         regs->pstate &= ~DBG_SPSR_SS;
 160 }
 161 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
 162
 163 /* EL1 Single Step Handler hooks */
 164 static LIST_HEAD(step_hook);
 165 static DEFINE_SPINLOCK(step_hook_lock);
 166
 167 void register_step_hook(struct step_hook *hook)
 168 {
 169         spin_lock(&step_hook_lock);
 170         list_add_rcu(&hook->node, &step_hook);
 171         spin_unlock(&step_hook_lock);
 172 }
 173
 174 void unregister_step_hook(struct step_hook *hook)
 175 {
 176         spin_lock(&step_hook_lock);
 177         list_del_rcu(&hook->node);
 178         spin_unlock(&step_hook_lock);
 179         synchronize_rcu();
 180 }
 181
 182 /*
 183  * Call registered single step handlers
 184  * There is no Syndrome info to check for determining the handler.
 185  * So we call all the registered handlers, until the right handler is
 186  * found which returns zero.
 187  */
 188 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 189 {
 190         struct step_hook *hook;
 191         int retval = DBG_HOOK_ERROR;
 192
 193         rcu_read_lock();
 194
 195         list_for_each_entry_rcu(hook, &step_hook, node) {
 196                 retval = hook->fn(regs, esr);
 197                 if (retval == DBG_HOOK_HANDLED)
 198                         break;
 199         }
 200
 201         rcu_read_unlock();
 202
 203         return retval;
 204 }
 205 NOKPROBE_SYMBOL(call_step_hook);
 206
 207 static void send_user_sigtrap(int si_code)
 208 {
 209         struct pt_regs *regs = current_pt_regs();
 210         siginfo_t info = {
 211                 .si_signo       = SIGTRAP,
 212                 .si_errno       = 0,
 213                 .si_code        = si_code,
 214                 .si_addr        = (void __user *)instruction_pointer(regs),
 215         };
 216
 217         if (WARN_ON(!user_mode(regs)))
 218                 return;
 219
 220         if (interrupts_enabled(regs))
 221                 local_irq_enable();
 222
 223         force_sig_info(SIGTRAP, &info, current);
 224 }
 225
 226 static int single_step_handler(unsigned long addr, unsigned int esr,
 227                                struct pt_regs *regs)
 228 {
 229         bool handler_found = false;
 230
 231         /*
 232          * If we are stepping a pending breakpoint, call the hw_breakpoint
 233          * handler first.
 234          */
 235         if (!reinstall_suspended_bps(regs))
 236                 return 0;
 237
 238 #ifdef  CONFIG_KPROBES
 239         if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 240                 handler_found = true;
 241 #endif
 242         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 243                 handler_found = true;
 244
 245         if (!handler_found && user_mode(regs)) {
 246                 send_user_sigtrap(TRAP_TRACE);
 247
 248                 /*
 249                  * ptrace will disable single step unless explicitly
 250                  * asked to re-enable it. For other clients, it makes
 251                  * sense to leave it enabled (i.e. rewind the controls
 252                  * to the active-not-pending state).
 253                  */
 254                 user_rewind_single_step(current);
 255         } else if (!handler_found) {
 256                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 257                 /*
 258                  * Re-enable stepping since we know that we will be
 259                  * returning to regs.
 260                  */
 261                 set_regs_spsr_ss(regs);
 262         }
 263
 264         return 0;
 265 }
 266 NOKPROBE_SYMBOL(single_step_handler);
 267
 268 /*
 269  * Breakpoint handler is re-entrant as another breakpoint can
 270  * hit within breakpoint handler, especically in kprobes.
 271  * Use reader/writer locks instead of plain spinlock.
 272  */
 273 static LIST_HEAD(break_hook);
 274 static DEFINE_SPINLOCK(break_hook_lock);
 275
 276 void register_break_hook(struct break_hook *hook)
 277 {
 278         spin_lock(&break_hook_lock);
 279         list_add_rcu(&hook->node, &break_hook);
 280         spin_unlock(&break_hook_lock);
 281 }
 282
 283 void unregister_break_hook(struct break_hook *hook)
 284 {
 285         spin_lock(&break_hook_lock);
 286         list_del_rcu(&hook->node);
 287         spin_unlock(&break_hook_lock);
 288         synchronize_rcu();
 289 }
 290
 291 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 292 {
 293         struct break_hook *hook;
 294         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 295
 296         rcu_read_lock();
 297         list_for_each_entry_rcu(hook, &break_hook, node)
 298                 if ((esr & hook->esr_mask) == hook->esr_val)
 299                         fn = hook->fn;
 300         rcu_read_unlock();
 301
 302         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 303 }
 304 NOKPROBE_SYMBOL(call_break_hook);
 305
 306 static int brk_handler(unsigned long addr, unsigned int esr,
 307                        struct pt_regs *regs)
 308 {
 309         bool handler_found = false;
 310
 311 #ifdef  CONFIG_KPROBES
 312         if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 313                 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
 314                         handler_found = true;
 315         }
 316 #endif
 317         if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 318                 handler_found = true;
 319
 320         if (!handler_found && user_mode(regs)) {
 321                 send_user_sigtrap(TRAP_BRKPT);
 322         } else if (!handler_found) {
 323                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 324                 return -EFAULT;
 325         }
 326
 327         return 0;
 328 }
 329 NOKPROBE_SYMBOL(brk_handler);
 330
 331 int aarch32_break_handler(struct pt_regs *regs)
 332 {
 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         send_user_sigtrap(TRAP_BRKPT);
 364         return 0;
 365 }
 366 NOKPROBE_SYMBOL(aarch32_break_handler);
 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_TRACE, "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 NOKPROBE_SYMBOL(user_rewind_single_step);
 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 NOKPROBE_SYMBOL(kernel_enable_single_step);
 405
 406 void kernel_disable_single_step(void)
 407 {
 408         WARN_ON(!irqs_disabled());
 409         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 410         disable_debug_monitors(DBG_ACTIVE_EL1);
 411 }
 412 NOKPROBE_SYMBOL(kernel_disable_single_step);
 413
 414 int kernel_active_single_step(void)
 415 {
 416         WARN_ON(!irqs_disabled());
 417         return mdscr_read() & DBG_MDSCR_SS;
 418 }
 419 NOKPROBE_SYMBOL(kernel_active_single_step);
 420
 421 /* ptrace API */
 422 void user_enable_single_step(struct task_struct *task)
 423 {
 424         struct thread_info *ti = task_thread_info(task);
 425
 426         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 427                 set_regs_spsr_ss(task_pt_regs(task));
 428 }
 429 NOKPROBE_SYMBOL(user_enable_single_step);
 430
 431 void user_disable_single_step(struct task_struct *task)
 432 {
 433         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 434 }
 435 NOKPROBE_SYMBOL(user_disable_single_step);