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