arch/arm64/kernel/debug-monitors.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * ARMv8 single-step debug support and mdscr context switching.
   4  *
   5  * Copyright (C) 2012 ARM Limited
   6  *
   7  * Author: Will Deacon <will.deacon@arm.com>
   8  */
   9
  10 #include <linux/cpu.h>
  11 #include <linux/debugfs.h>
  12 #include <linux/hardirq.h>
  13 #include <linux/init.h>
  14 #include <linux/ptrace.h>
  15 #include <linux/kprobes.h>
  16 #include <linux/stat.h>
  17 #include <linux/uaccess.h>
  18 #include <linux/sched/task_stack.h>
  19
  20 #include <asm/cpufeature.h>
  21 #include <asm/cputype.h>
  22 #include <asm/daifflags.h>
  23 #include <asm/debug-monitors.h>
  24 #include <asm/system_misc.h>
  25 #include <asm/traps.h>
  26
  27 /* Determine debug architecture. */
  28 u8 debug_monitors_arch(void)
  29 {
  30         return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
  31                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
  32 }
  33
  34 /*
  35  * MDSCR access routines.
  36  */
  37 static void mdscr_write(u32 mdscr)
  38 {
  39         unsigned long flags;
  40         flags = local_daif_save();
  41         write_sysreg(mdscr, mdscr_el1);
  42         local_daif_restore(flags);
  43 }
  44 NOKPROBE_SYMBOL(mdscr_write);
  45
  46 static u32 mdscr_read(void)
  47 {
  48         return read_sysreg(mdscr_el1);
  49 }
  50 NOKPROBE_SYMBOL(mdscr_read);
  51
  52 /*
  53  * Allow root to disable self-hosted debug from userspace.
  54  * This is useful if you want to connect an external JTAG debugger.
  55  */
  56 static bool debug_enabled = true;
  57
  58 static int create_debug_debugfs_entry(void)
  59 {
  60         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  61         return 0;
  62 }
  63 fs_initcall(create_debug_debugfs_entry);
  64
  65 static int __init early_debug_disable(char *buf)
  66 {
  67         debug_enabled = false;
  68         return 0;
  69 }
  70
  71 early_param("nodebugmon", early_debug_disable);
  72
  73 /*
  74  * Keep track of debug users on each core.
  75  * The ref counts are per-cpu so we use a local_t type.
  76  */
  77 static DEFINE_PER_CPU(int, mde_ref_count);
  78 static DEFINE_PER_CPU(int, kde_ref_count);
  79
  80 void enable_debug_monitors(enum dbg_active_el el)
  81 {
  82         u32 mdscr, enable = 0;
  83
  84         WARN_ON(preemptible());
  85
  86         if (this_cpu_inc_return(mde_ref_count) == 1)
  87                 enable = DBG_MDSCR_MDE;
  88
  89         if (el == DBG_ACTIVE_EL1 &&
  90             this_cpu_inc_return(kde_ref_count) == 1)
  91                 enable |= DBG_MDSCR_KDE;
  92
  93         if (enable && debug_enabled) {
  94                 mdscr = mdscr_read();
  95                 mdscr |= enable;
  96                 mdscr_write(mdscr);
  97         }
  98 }
  99 NOKPROBE_SYMBOL(enable_debug_monitors);
 100
 101 void disable_debug_monitors(enum dbg_active_el el)
 102 {
 103         u32 mdscr, disable = 0;
 104
 105         WARN_ON(preemptible());
 106
 107         if (this_cpu_dec_return(mde_ref_count) == 0)
 108                 disable = ~DBG_MDSCR_MDE;
 109
 110         if (el == DBG_ACTIVE_EL1 &&
 111             this_cpu_dec_return(kde_ref_count) == 0)
 112                 disable &= ~DBG_MDSCR_KDE;
 113
 114         if (disable) {
 115                 mdscr = mdscr_read();
 116                 mdscr &= disable;
 117                 mdscr_write(mdscr);
 118         }
 119 }
 120 NOKPROBE_SYMBOL(disable_debug_monitors);
 121
 122 /*
 123  * OS lock clearing.
 124  */
 125 static int clear_os_lock(unsigned int cpu)
 126 {
 127         write_sysreg(0, osdlr_el1);
 128         write_sysreg(0, oslar_el1);
 129         isb();
 130         return 0;
 131 }
 132
 133 static int __init debug_monitors_init(void)
 134 {
 135         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 136                                  "arm64/debug_monitors:starting",
 137                                  clear_os_lock, NULL);
 138 }
 139 postcore_initcall(debug_monitors_init);
 140
 141 /*
 142  * Single step API and exception handling.
 143  */
 144 static void set_regs_spsr_ss(struct pt_regs *regs)
 145 {
 146         regs->pstate |= DBG_SPSR_SS;
 147 }
 148 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 149
 150 static void clear_regs_spsr_ss(struct pt_regs *regs)
 151 {
 152         regs->pstate &= ~DBG_SPSR_SS;
 153 }
 154 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
 155
 156 static DEFINE_SPINLOCK(debug_hook_lock);
 157 static LIST_HEAD(user_step_hook);
 158 static LIST_HEAD(kernel_step_hook);
 159
 160 static void register_debug_hook(struct list_head *node, struct list_head *list)
 161 {
 162         spin_lock(&debug_hook_lock);
 163         list_add_rcu(node, list);
 164         spin_unlock(&debug_hook_lock);
 165
 166 }
 167
 168 static void unregister_debug_hook(struct list_head *node)
 169 {
 170         spin_lock(&debug_hook_lock);
 171         list_del_rcu(node);
 172         spin_unlock(&debug_hook_lock);
 173         synchronize_rcu();
 174 }
 175
 176 void register_user_step_hook(struct step_hook *hook)
 177 {
 178         register_debug_hook(&hook->node, &user_step_hook);
 179 }
 180
 181 void unregister_user_step_hook(struct step_hook *hook)
 182 {
 183         unregister_debug_hook(&hook->node);
 184 }
 185
 186 void register_kernel_step_hook(struct step_hook *hook)
 187 {
 188         register_debug_hook(&hook->node, &kernel_step_hook);
 189 }
 190
 191 void unregister_kernel_step_hook(struct step_hook *hook)
 192 {
 193         unregister_debug_hook(&hook->node);
 194 }
 195
 196 /*
 197  * Call registered single step handlers
 198  * There is no Syndrome info to check for determining the handler.
 199  * So we call all the registered handlers, until the right handler is
 200  * found which returns zero.
 201  */
 202 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 203 {
 204         struct step_hook *hook;
 205         struct list_head *list;
 206         int retval = DBG_HOOK_ERROR;
 207
 208         list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
 209
 210         /*
 211          * Since single-step exception disables interrupt, this function is
 212          * entirely not preemptible, and we can use rcu list safely here.
 213          */
 214         list_for_each_entry_rcu(hook, list, node)       {
 215                 retval = hook->fn(regs, esr);
 216                 if (retval == DBG_HOOK_HANDLED)
 217                         break;
 218         }
 219
 220         return retval;
 221 }
 222 NOKPROBE_SYMBOL(call_step_hook);
 223
 224 static void send_user_sigtrap(int si_code)
 225 {
 226         struct pt_regs *regs = current_pt_regs();
 227
 228         if (WARN_ON(!user_mode(regs)))
 229                 return;
 230
 231         if (interrupts_enabled(regs))
 232                 local_irq_enable();
 233
 234         arm64_force_sig_fault(SIGTRAP, si_code,
 235                              (void __user *)instruction_pointer(regs),
 236                              "User debug trap");
 237 }
 238
 239 static int single_step_handler(unsigned long unused, unsigned int esr,
 240                                struct pt_regs *regs)
 241 {
 242         bool handler_found = false;
 243
 244         /*
 245          * If we are stepping a pending breakpoint, call the hw_breakpoint
 246          * handler first.
 247          */
 248         if (!reinstall_suspended_bps(regs))
 249                 return 0;
 250
 251         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 252                 handler_found = true;
 253
 254         if (!handler_found && user_mode(regs)) {
 255                 send_user_sigtrap(TRAP_TRACE);
 256
 257                 /*
 258                  * ptrace will disable single step unless explicitly
 259                  * asked to re-enable it. For other clients, it makes
 260                  * sense to leave it enabled (i.e. rewind the controls
 261                  * to the active-not-pending state).
 262                  */
 263                 user_rewind_single_step(current);
 264         } else if (!handler_found) {
 265                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 266                 /*
 267                  * Re-enable stepping since we know that we will be
 268                  * returning to regs.
 269                  */
 270                 set_regs_spsr_ss(regs);
 271         }
 272
 273         return 0;
 274 }
 275 NOKPROBE_SYMBOL(single_step_handler);
 276
 277 static LIST_HEAD(user_break_hook);
 278 static LIST_HEAD(kernel_break_hook);
 279
 280 void register_user_break_hook(struct break_hook *hook)
 281 {
 282         register_debug_hook(&hook->node, &user_break_hook);
 283 }
 284
 285 void unregister_user_break_hook(struct break_hook *hook)
 286 {
 287         unregister_debug_hook(&hook->node);
 288 }
 289
 290 void register_kernel_break_hook(struct break_hook *hook)
 291 {
 292         register_debug_hook(&hook->node, &kernel_break_hook);
 293 }
 294
 295 void unregister_kernel_break_hook(struct break_hook *hook)
 296 {
 297         unregister_debug_hook(&hook->node);
 298 }
 299
 300 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 301 {
 302         struct break_hook *hook;
 303         struct list_head *list;
 304         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 305
 306         list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
 307
 308         /*
 309          * Since brk exception disables interrupt, this function is
 310          * entirely not preemptible, and we can use rcu list safely here.
 311          */
 312         list_for_each_entry_rcu(hook, list, node) {
 313                 unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
 314
 315                 if ((comment & ~hook->mask) == hook->imm)
 316                         fn = hook->fn;
 317         }
 318
 319         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 320 }
 321 NOKPROBE_SYMBOL(call_break_hook);
 322
 323 static int brk_handler(unsigned long unused, unsigned int esr,
 324                        struct pt_regs *regs)
 325 {
 326         if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 327                 return 0;
 328
 329         if (user_mode(regs)) {
 330                 send_user_sigtrap(TRAP_BRKPT);
 331         } else {
 332                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 333                 return -EFAULT;
 334         }
 335
 336         return 0;
 337 }
 338 NOKPROBE_SYMBOL(brk_handler);
 339
 340 int aarch32_break_handler(struct pt_regs *regs)
 341 {
 342         u32 arm_instr;
 343         u16 thumb_instr;
 344         bool bp = false;
 345         void __user *pc = (void __user *)instruction_pointer(regs);
 346
 347         if (!compat_user_mode(regs))
 348                 return -EFAULT;
 349
 350         if (compat_thumb_mode(regs)) {
 351                 /* get 16-bit Thumb instruction */
 352                 __le16 instr;
 353                 get_user(instr, (__le16 __user *)pc);
 354                 thumb_instr = le16_to_cpu(instr);
 355                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 356                         /* get second half of 32-bit Thumb-2 instruction */
 357                         get_user(instr, (__le16 __user *)(pc + 2));
 358                         thumb_instr = le16_to_cpu(instr);
 359                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 360                 } else {
 361                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 362                 }
 363         } else {
 364                 /* 32-bit ARM instruction */
 365                 __le32 instr;
 366                 get_user(instr, (__le32 __user *)pc);
 367                 arm_instr = le32_to_cpu(instr);
 368                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 369         }
 370
 371         if (!bp)
 372                 return -EFAULT;
 373
 374         send_user_sigtrap(TRAP_BRKPT);
 375         return 0;
 376 }
 377 NOKPROBE_SYMBOL(aarch32_break_handler);
 378
 379 void __init debug_traps_init(void)
 380 {
 381         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 382                               TRAP_TRACE, "single-step handler");
 383         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 384                               TRAP_BRKPT, "ptrace BRK handler");
 385 }
 386
 387 /* Re-enable single step for syscall restarting. */
 388 void user_rewind_single_step(struct task_struct *task)
 389 {
 390         /*
 391          * If single step is active for this thread, then set SPSR.SS
 392          * to 1 to avoid returning to the active-pending state.
 393          */
 394         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 395                 set_regs_spsr_ss(task_pt_regs(task));
 396 }
 397 NOKPROBE_SYMBOL(user_rewind_single_step);
 398
 399 void user_fastforward_single_step(struct task_struct *task)
 400 {
 401         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 402                 clear_regs_spsr_ss(task_pt_regs(task));
 403 }
 404
 405 /* Kernel API */
 406 void kernel_enable_single_step(struct pt_regs *regs)
 407 {
 408         WARN_ON(!irqs_disabled());
 409         set_regs_spsr_ss(regs);
 410         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 411         enable_debug_monitors(DBG_ACTIVE_EL1);
 412 }
 413 NOKPROBE_SYMBOL(kernel_enable_single_step);
 414
 415 void kernel_disable_single_step(void)
 416 {
 417         WARN_ON(!irqs_disabled());
 418         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 419         disable_debug_monitors(DBG_ACTIVE_EL1);
 420 }
 421 NOKPROBE_SYMBOL(kernel_disable_single_step);
 422
 423 int kernel_active_single_step(void)
 424 {
 425         WARN_ON(!irqs_disabled());
 426         return mdscr_read() & DBG_MDSCR_SS;
 427 }
 428 NOKPROBE_SYMBOL(kernel_active_single_step);
 429
 430 /* ptrace API */
 431 void user_enable_single_step(struct task_struct *task)
 432 {
 433         struct thread_info *ti = task_thread_info(task);
 434
 435         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 436                 set_regs_spsr_ss(task_pt_regs(task));
 437 }
 438 NOKPROBE_SYMBOL(user_enable_single_step);
 439
 440 void user_disable_single_step(struct task_struct *task)
 441 {
 442         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 443 }
 444 NOKPROBE_SYMBOL(user_disable_single_step);