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 #include <linux/sched/task_stack.h>
  30
  31 #include <asm/cpufeature.h>
  32 #include <asm/cputype.h>
  33 #include <asm/daifflags.h>
  34 #include <asm/debug-monitors.h>
  35 #include <asm/system_misc.h>
  36 #include <asm/traps.h>
  37
  38 /* Determine debug architecture. */
  39 u8 debug_monitors_arch(void)
  40 {
  41         return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
  42                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
  43 }
  44
  45 /*
  46  * MDSCR access routines.
  47  */
  48 static void mdscr_write(u32 mdscr)
  49 {
  50         unsigned long flags;
  51         flags = local_daif_save();
  52         write_sysreg(mdscr, mdscr_el1);
  53         local_daif_restore(flags);
  54 }
  55 NOKPROBE_SYMBOL(mdscr_write);
  56
  57 static u32 mdscr_read(void)
  58 {
  59         return read_sysreg(mdscr_el1);
  60 }
  61 NOKPROBE_SYMBOL(mdscr_read);
  62
  63 /*
  64  * Allow root to disable self-hosted debug from userspace.
  65  * This is useful if you want to connect an external JTAG debugger.
  66  */
  67 static bool debug_enabled = true;
  68
  69 static int create_debug_debugfs_entry(void)
  70 {
  71         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  72         return 0;
  73 }
  74 fs_initcall(create_debug_debugfs_entry);
  75
  76 static int __init early_debug_disable(char *buf)
  77 {
  78         debug_enabled = false;
  79         return 0;
  80 }
  81
  82 early_param("nodebugmon", early_debug_disable);
  83
  84 /*
  85  * Keep track of debug users on each core.
  86  * The ref counts are per-cpu so we use a local_t type.
  87  */
  88 static DEFINE_PER_CPU(int, mde_ref_count);
  89 static DEFINE_PER_CPU(int, kde_ref_count);
  90
  91 void enable_debug_monitors(enum dbg_active_el el)
  92 {
  93         u32 mdscr, enable = 0;
  94
  95         WARN_ON(preemptible());
  96
  97         if (this_cpu_inc_return(mde_ref_count) == 1)
  98                 enable = DBG_MDSCR_MDE;
  99
 100         if (el == DBG_ACTIVE_EL1 &&
 101             this_cpu_inc_return(kde_ref_count) == 1)
 102                 enable |= DBG_MDSCR_KDE;
 103
 104         if (enable && debug_enabled) {
 105                 mdscr = mdscr_read();
 106                 mdscr |= enable;
 107                 mdscr_write(mdscr);
 108         }
 109 }
 110 NOKPROBE_SYMBOL(enable_debug_monitors);
 111
 112 void disable_debug_monitors(enum dbg_active_el el)
 113 {
 114         u32 mdscr, disable = 0;
 115
 116         WARN_ON(preemptible());
 117
 118         if (this_cpu_dec_return(mde_ref_count) == 0)
 119                 disable = ~DBG_MDSCR_MDE;
 120
 121         if (el == DBG_ACTIVE_EL1 &&
 122             this_cpu_dec_return(kde_ref_count) == 0)
 123                 disable &= ~DBG_MDSCR_KDE;
 124
 125         if (disable) {
 126                 mdscr = mdscr_read();
 127                 mdscr &= disable;
 128                 mdscr_write(mdscr);
 129         }
 130 }
 131 NOKPROBE_SYMBOL(disable_debug_monitors);
 132
 133 /*
 134  * OS lock clearing.
 135  */
 136 static int clear_os_lock(unsigned int cpu)
 137 {
 138         write_sysreg(0, osdlr_el1);
 139         write_sysreg(0, oslar_el1);
 140         isb();
 141         return 0;
 142 }
 143
 144 static int debug_monitors_init(void)
 145 {
 146         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 147                                  "arm64/debug_monitors:starting",
 148                                  clear_os_lock, NULL);
 149 }
 150 postcore_initcall(debug_monitors_init);
 151
 152 /*
 153  * Single step API and exception handling.
 154  */
 155 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
 156 {
 157         regs->pstate |= DBG_SPSR_SS;
 158 }
 159 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
 160
 161 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
 162 {
 163         regs->pstate &= ~DBG_SPSR_SS;
 164 }
 165 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
 166
 167 #define set_regs_spsr_ss(r)     set_user_regs_spsr_ss(&(r)->user_regs)
 168 #define clear_regs_spsr_ss(r)   clear_user_regs_spsr_ss(&(r)->user_regs)
 169
 170 /* EL1 Single Step Handler hooks */
 171 static LIST_HEAD(step_hook);
 172 static DEFINE_SPINLOCK(step_hook_lock);
 173
 174 void register_step_hook(struct step_hook *hook)
 175 {
 176         spin_lock(&step_hook_lock);
 177         list_add_rcu(&hook->node, &step_hook);
 178         spin_unlock(&step_hook_lock);
 179 }
 180
 181 void unregister_step_hook(struct step_hook *hook)
 182 {
 183         spin_lock(&step_hook_lock);
 184         list_del_rcu(&hook->node);
 185         spin_unlock(&step_hook_lock);
 186         synchronize_rcu();
 187 }
 188
 189 /*
 190  * Call registered single step handlers
 191  * There is no Syndrome info to check for determining the handler.
 192  * So we call all the registered handlers, until the right handler is
 193  * found which returns zero.
 194  */
 195 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 196 {
 197         struct step_hook *hook;
 198         int retval = DBG_HOOK_ERROR;
 199
 200         rcu_read_lock();
 201
 202         list_for_each_entry_rcu(hook, &step_hook, node) {
 203                 retval = hook->fn(regs, esr);
 204                 if (retval == DBG_HOOK_HANDLED)
 205                         break;
 206         }
 207
 208         rcu_read_unlock();
 209
 210         return retval;
 211 }
 212 NOKPROBE_SYMBOL(call_step_hook);
 213
 214 static void send_user_sigtrap(int si_code)
 215 {
 216         struct pt_regs *regs = current_pt_regs();
 217         siginfo_t info;
 218
 219         clear_siginfo(&info);
 220         info.si_signo   = SIGTRAP;
 221         info.si_errno   = 0;
 222         info.si_code    = si_code;
 223         info.si_addr    = (void __user *)instruction_pointer(regs);
 224
 225         if (WARN_ON(!user_mode(regs)))
 226                 return;
 227
 228         if (interrupts_enabled(regs))
 229                 local_irq_enable();
 230
 231         arm64_force_sig_info(&info, "User debug trap", current);
 232 }
 233
 234 static int single_step_handler(unsigned long addr, unsigned int esr,
 235                                struct pt_regs *regs)
 236 {
 237         bool handler_found = false;
 238
 239         /*
 240          * If we are stepping a pending breakpoint, call the hw_breakpoint
 241          * handler first.
 242          */
 243         if (!reinstall_suspended_bps(regs))
 244                 return 0;
 245
 246 #ifdef  CONFIG_KPROBES
 247         if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 248                 handler_found = true;
 249 #endif
 250         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 251                 handler_found = true;
 252
 253         if (!handler_found && user_mode(regs)) {
 254                 send_user_sigtrap(TRAP_TRACE);
 255
 256                 /*
 257                  * ptrace will disable single step unless explicitly
 258                  * asked to re-enable it. For other clients, it makes
 259                  * sense to leave it enabled (i.e. rewind the controls
 260                  * to the active-not-pending state).
 261                  */
 262                 user_rewind_single_step(current);
 263         } else if (!handler_found) {
 264                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 265                 /*
 266                  * Re-enable stepping since we know that we will be
 267                  * returning to regs.
 268                  */
 269                 set_regs_spsr_ss(regs);
 270         }
 271
 272         return 0;
 273 }
 274 NOKPROBE_SYMBOL(single_step_handler);
 275
 276 /*
 277  * Breakpoint handler is re-entrant as another breakpoint can
 278  * hit within breakpoint handler, especically in kprobes.
 279  * Use reader/writer locks instead of plain spinlock.
 280  */
 281 static LIST_HEAD(break_hook);
 282 static DEFINE_SPINLOCK(break_hook_lock);
 283
 284 void register_break_hook(struct break_hook *hook)
 285 {
 286         spin_lock(&break_hook_lock);
 287         list_add_rcu(&hook->node, &break_hook);
 288         spin_unlock(&break_hook_lock);
 289 }
 290
 291 void unregister_break_hook(struct break_hook *hook)
 292 {
 293         spin_lock(&break_hook_lock);
 294         list_del_rcu(&hook->node);
 295         spin_unlock(&break_hook_lock);
 296         synchronize_rcu();
 297 }
 298
 299 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 300 {
 301         struct break_hook *hook;
 302         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 303
 304         rcu_read_lock();
 305         list_for_each_entry_rcu(hook, &break_hook, node)
 306                 if ((esr & hook->esr_mask) == hook->esr_val)
 307                         fn = hook->fn;
 308         rcu_read_unlock();
 309
 310         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 311 }
 312 NOKPROBE_SYMBOL(call_break_hook);
 313
 314 static int brk_handler(unsigned long addr, unsigned int esr,
 315                        struct pt_regs *regs)
 316 {
 317         bool handler_found = false;
 318
 319 #ifdef  CONFIG_KPROBES
 320         if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 321                 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
 322                         handler_found = true;
 323         }
 324 #endif
 325         if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 326                 handler_found = true;
 327
 328         if (!handler_found && user_mode(regs)) {
 329                 send_user_sigtrap(TRAP_BRKPT);
 330         } else if (!handler_found) {
 331                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 332                 return -EFAULT;
 333         }
 334
 335         return 0;
 336 }
 337 NOKPROBE_SYMBOL(brk_handler);
 338
 339 int aarch32_break_handler(struct pt_regs *regs)
 340 {
 341         u32 arm_instr;
 342         u16 thumb_instr;
 343         bool bp = false;
 344         void __user *pc = (void __user *)instruction_pointer(regs);
 345
 346         if (!compat_user_mode(regs))
 347                 return -EFAULT;
 348
 349         if (compat_thumb_mode(regs)) {
 350                 /* get 16-bit Thumb instruction */
 351                 __le16 instr;
 352                 get_user(instr, (__le16 __user *)pc);
 353                 thumb_instr = le16_to_cpu(instr);
 354                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 355                         /* get second half of 32-bit Thumb-2 instruction */
 356                         get_user(instr, (__le16 __user *)(pc + 2));
 357                         thumb_instr = le16_to_cpu(instr);
 358                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 359                 } else {
 360                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 361                 }
 362         } else {
 363                 /* 32-bit ARM instruction */
 364                 __le32 instr;
 365                 get_user(instr, (__le32 __user *)pc);
 366                 arm_instr = le32_to_cpu(instr);
 367                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 368         }
 369
 370         if (!bp)
 371                 return -EFAULT;
 372
 373         send_user_sigtrap(TRAP_BRKPT);
 374         return 0;
 375 }
 376 NOKPROBE_SYMBOL(aarch32_break_handler);
 377
 378 static int __init debug_traps_init(void)
 379 {
 380         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 381                               TRAP_TRACE, "single-step handler");
 382         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 383                               TRAP_BRKPT, "ptrace BRK handler");
 384         return 0;
 385 }
 386 arch_initcall(debug_traps_init);
 387
 388 /* Re-enable single step for syscall restarting. */
 389 void user_rewind_single_step(struct task_struct *task)
 390 {
 391         /*
 392          * If single step is active for this thread, then set SPSR.SS
 393          * to 1 to avoid returning to the active-pending state.
 394          */
 395         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 396                 set_regs_spsr_ss(task_pt_regs(task));
 397 }
 398 NOKPROBE_SYMBOL(user_rewind_single_step);
 399
 400 void user_fastforward_single_step(struct task_struct *task)
 401 {
 402         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 403                 clear_regs_spsr_ss(task_pt_regs(task));
 404 }
 405
 406 void user_regs_reset_single_step(struct user_pt_regs *regs,
 407                                  struct task_struct *task)
 408 {
 409         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 410                 set_user_regs_spsr_ss(regs);
 411         else
 412                 clear_user_regs_spsr_ss(regs);
 413 }
 414
 415 /* Kernel API */
 416 void kernel_enable_single_step(struct pt_regs *regs)
 417 {
 418         WARN_ON(!irqs_disabled());
 419         set_regs_spsr_ss(regs);
 420         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 421         enable_debug_monitors(DBG_ACTIVE_EL1);
 422 }
 423 NOKPROBE_SYMBOL(kernel_enable_single_step);
 424
 425 void kernel_disable_single_step(void)
 426 {
 427         WARN_ON(!irqs_disabled());
 428         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 429         disable_debug_monitors(DBG_ACTIVE_EL1);
 430 }
 431 NOKPROBE_SYMBOL(kernel_disable_single_step);
 432
 433 int kernel_active_single_step(void)
 434 {
 435         WARN_ON(!irqs_disabled());
 436         return mdscr_read() & DBG_MDSCR_SS;
 437 }
 438 NOKPROBE_SYMBOL(kernel_active_single_step);
 439
 440 void kernel_rewind_single_step(struct pt_regs *regs)
 441 {
 442         set_regs_spsr_ss(regs);
 443 }
 444
 445 /* ptrace API */
 446 void user_enable_single_step(struct task_struct *task)
 447 {
 448         struct thread_info *ti = task_thread_info(task);
 449
 450         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 451                 set_regs_spsr_ss(task_pt_regs(task));
 452 }
 453 NOKPROBE_SYMBOL(user_enable_single_step);
 454
 455 void user_disable_single_step(struct task_struct *task)
 456 {
 457         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 458 }
 459 NOKPROBE_SYMBOL(user_disable_single_step);