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, osdlr_el1);
 137         write_sysreg(0, oslar_el1);
 138         isb();
 139         return 0;
 140 }
 141
 142 static int debug_monitors_init(void)
 143 {
 144         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 145                                  "arm64/debug_monitors:starting",
 146                                  clear_os_lock, NULL);
 147 }
 148 postcore_initcall(debug_monitors_init);
 149
 150 /*
 151  * Single step API and exception handling.
 152  */
 153 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
 154 {
 155         regs->pstate |= DBG_SPSR_SS;
 156 }
 157 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
 158
 159 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
 160 {
 161         regs->pstate &= ~DBG_SPSR_SS;
 162 }
 163 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
 164
 165 #define set_regs_spsr_ss(r)     set_user_regs_spsr_ss(&(r)->user_regs)
 166 #define clear_regs_spsr_ss(r)   clear_user_regs_spsr_ss(&(r)->user_regs)
 167
 168 /* EL1 Single Step Handler hooks */
 169 static LIST_HEAD(step_hook);
 170 static DEFINE_SPINLOCK(step_hook_lock);
 171
 172 void register_step_hook(struct step_hook *hook)
 173 {
 174         spin_lock(&step_hook_lock);
 175         list_add_rcu(&hook->node, &step_hook);
 176         spin_unlock(&step_hook_lock);
 177 }
 178
 179 void unregister_step_hook(struct step_hook *hook)
 180 {
 181         spin_lock(&step_hook_lock);
 182         list_del_rcu(&hook->node);
 183         spin_unlock(&step_hook_lock);
 184         synchronize_rcu();
 185 }
 186
 187 /*
 188  * Call registered single step handlers
 189  * There is no Syndrome info to check for determining the handler.
 190  * So we call all the registered handlers, until the right handler is
 191  * found which returns zero.
 192  */
 193 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 194 {
 195         struct step_hook *hook;
 196         int retval = DBG_HOOK_ERROR;
 197
 198         rcu_read_lock();
 199
 200         list_for_each_entry_rcu(hook, &step_hook, node) {
 201                 retval = hook->fn(regs, esr);
 202                 if (retval == DBG_HOOK_HANDLED)
 203                         break;
 204         }
 205
 206         rcu_read_unlock();
 207
 208         return retval;
 209 }
 210 NOKPROBE_SYMBOL(call_step_hook);
 211
 212 static void send_user_sigtrap(int si_code)
 213 {
 214         struct pt_regs *regs = current_pt_regs();
 215         siginfo_t info = {
 216                 .si_signo       = SIGTRAP,
 217                 .si_errno       = 0,
 218                 .si_code        = si_code,
 219                 .si_addr        = (void __user *)instruction_pointer(regs),
 220         };
 221
 222         if (WARN_ON(!user_mode(regs)))
 223                 return;
 224
 225         if (interrupts_enabled(regs))
 226                 local_irq_enable();
 227
 228         force_sig_info(SIGTRAP, &info, current);
 229 }
 230
 231 static int single_step_handler(unsigned long addr, unsigned int esr,
 232                                struct pt_regs *regs)
 233 {
 234         bool handler_found = false;
 235
 236         /*
 237          * If we are stepping a pending breakpoint, call the hw_breakpoint
 238          * handler first.
 239          */
 240         if (!reinstall_suspended_bps(regs))
 241                 return 0;
 242
 243 #ifdef  CONFIG_KPROBES
 244         if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 245                 handler_found = true;
 246 #endif
 247         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 248                 handler_found = true;
 249
 250         if (!handler_found && user_mode(regs)) {
 251                 send_user_sigtrap(TRAP_TRACE);
 252
 253                 /*
 254                  * ptrace will disable single step unless explicitly
 255                  * asked to re-enable it. For other clients, it makes
 256                  * sense to leave it enabled (i.e. rewind the controls
 257                  * to the active-not-pending state).
 258                  */
 259                 user_rewind_single_step(current);
 260         } else if (!handler_found) {
 261                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 262                 /*
 263                  * Re-enable stepping since we know that we will be
 264                  * returning to regs.
 265                  */
 266                 set_regs_spsr_ss(regs);
 267         }
 268
 269         return 0;
 270 }
 271 NOKPROBE_SYMBOL(single_step_handler);
 272
 273 /*
 274  * Breakpoint handler is re-entrant as another breakpoint can
 275  * hit within breakpoint handler, especically in kprobes.
 276  * Use reader/writer locks instead of plain spinlock.
 277  */
 278 static LIST_HEAD(break_hook);
 279 static DEFINE_SPINLOCK(break_hook_lock);
 280
 281 void register_break_hook(struct break_hook *hook)
 282 {
 283         spin_lock(&break_hook_lock);
 284         list_add_rcu(&hook->node, &break_hook);
 285         spin_unlock(&break_hook_lock);
 286 }
 287
 288 void unregister_break_hook(struct break_hook *hook)
 289 {
 290         spin_lock(&break_hook_lock);
 291         list_del_rcu(&hook->node);
 292         spin_unlock(&break_hook_lock);
 293         synchronize_rcu();
 294 }
 295
 296 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 297 {
 298         struct break_hook *hook;
 299         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 300
 301         rcu_read_lock();
 302         list_for_each_entry_rcu(hook, &break_hook, node)
 303                 if ((esr & hook->esr_mask) == hook->esr_val)
 304                         fn = hook->fn;
 305         rcu_read_unlock();
 306
 307         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 308 }
 309 NOKPROBE_SYMBOL(call_break_hook);
 310
 311 static int brk_handler(unsigned long addr, unsigned int esr,
 312                        struct pt_regs *regs)
 313 {
 314         bool handler_found = false;
 315
 316 #ifdef  CONFIG_KPROBES
 317         if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 318                 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
 319                         handler_found = true;
 320         }
 321 #endif
 322         if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 323                 handler_found = true;
 324
 325         if (!handler_found && user_mode(regs)) {
 326                 send_user_sigtrap(TRAP_BRKPT);
 327         } else if (!handler_found) {
 328                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 329                 return -EFAULT;
 330         }
 331
 332         return 0;
 333 }
 334 NOKPROBE_SYMBOL(brk_handler);
 335
 336 int aarch32_break_handler(struct pt_regs *regs)
 337 {
 338         u32 arm_instr;
 339         u16 thumb_instr;
 340         bool bp = false;
 341         void __user *pc = (void __user *)instruction_pointer(regs);
 342
 343         if (!compat_user_mode(regs))
 344                 return -EFAULT;
 345
 346         if (compat_thumb_mode(regs)) {
 347                 /* get 16-bit Thumb instruction */
 348                 __le16 instr;
 349                 get_user(instr, (__le16 __user *)pc);
 350                 thumb_instr = le16_to_cpu(instr);
 351                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 352                         /* get second half of 32-bit Thumb-2 instruction */
 353                         get_user(instr, (__le16 __user *)(pc + 2));
 354                         thumb_instr = le16_to_cpu(instr);
 355                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 356                 } else {
 357                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 358                 }
 359         } else {
 360                 /* 32-bit ARM instruction */
 361                 __le32 instr;
 362                 get_user(instr, (__le32 __user *)pc);
 363                 arm_instr = le32_to_cpu(instr);
 364                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 365         }
 366
 367         if (!bp)
 368                 return -EFAULT;
 369
 370         send_user_sigtrap(TRAP_BRKPT);
 371         return 0;
 372 }
 373 NOKPROBE_SYMBOL(aarch32_break_handler);
 374
 375 static int __init debug_traps_init(void)
 376 {
 377         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 378                               TRAP_TRACE, "single-step handler");
 379         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 380                               TRAP_BRKPT, "ptrace BRK handler");
 381         return 0;
 382 }
 383 arch_initcall(debug_traps_init);
 384
 385 /* Re-enable single step for syscall restarting. */
 386 void user_rewind_single_step(struct task_struct *task)
 387 {
 388         /*
 389          * If single step is active for this thread, then set SPSR.SS
 390          * to 1 to avoid returning to the active-pending state.
 391          */
 392         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 393                 set_regs_spsr_ss(task_pt_regs(task));
 394 }
 395 NOKPROBE_SYMBOL(user_rewind_single_step);
 396
 397 void user_fastforward_single_step(struct task_struct *task)
 398 {
 399         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 400                 clear_regs_spsr_ss(task_pt_regs(task));
 401 }
 402
 403 void user_regs_reset_single_step(struct user_pt_regs *regs,
 404                                  struct task_struct *task)
 405 {
 406         if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
 407                 set_user_regs_spsr_ss(regs);
 408         else
 409                 clear_user_regs_spsr_ss(regs);
 410 }
 411
 412 /* Kernel API */
 413 void kernel_enable_single_step(struct pt_regs *regs)
 414 {
 415         WARN_ON(!irqs_disabled());
 416         set_regs_spsr_ss(regs);
 417         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 418         enable_debug_monitors(DBG_ACTIVE_EL1);
 419 }
 420 NOKPROBE_SYMBOL(kernel_enable_single_step);
 421
 422 void kernel_disable_single_step(void)
 423 {
 424         WARN_ON(!irqs_disabled());
 425         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 426         disable_debug_monitors(DBG_ACTIVE_EL1);
 427 }
 428 NOKPROBE_SYMBOL(kernel_disable_single_step);
 429
 430 int kernel_active_single_step(void)
 431 {
 432         WARN_ON(!irqs_disabled());
 433         return mdscr_read() & DBG_MDSCR_SS;
 434 }
 435 NOKPROBE_SYMBOL(kernel_active_single_step);
 436
 437 /* ptrace API */
 438 void user_enable_single_step(struct task_struct *task)
 439 {
 440         struct thread_info *ti = task_thread_info(task);
 441
 442         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 443                 set_regs_spsr_ss(task_pt_regs(task));
 444 }
 445 NOKPROBE_SYMBOL(user_enable_single_step);
 446
 447 void user_disable_single_step(struct task_struct *task)
 448 {
 449         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 450 }
 451 NOKPROBE_SYMBOL(user_disable_single_step);