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                                  "CPUHP_AP_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         /*
 230          * If we are stepping a pending breakpoint, call the hw_breakpoint
 231          * handler first.
 232          */
 233         if (!reinstall_suspended_bps(regs))
 234                 return 0;
 235
 236         if (user_mode(regs)) {
 237                 send_user_sigtrap(TRAP_TRACE);
 238
 239                 /*
 240                  * ptrace will disable single step unless explicitly
 241                  * asked to re-enable it. For other clients, it makes
 242                  * sense to leave it enabled (i.e. rewind the controls
 243                  * to the active-not-pending state).
 244                  */
 245                 user_rewind_single_step(current);
 246         } else {
 247 #ifdef  CONFIG_KPROBES
 248                 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 249                         return 0;
 250 #endif
 251                 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 252                         return 0;
 253
 254                 pr_warning("Unexpected kernel single-step exception at EL1\n");
 255                 /*
 256                  * Re-enable stepping since we know that we will be
 257                  * returning to regs.
 258                  */
 259                 set_regs_spsr_ss(regs);
 260         }
 261
 262         return 0;
 263 }
 264 NOKPROBE_SYMBOL(single_step_handler);
 265
 266 /*
 267  * Breakpoint handler is re-entrant as another breakpoint can
 268  * hit within breakpoint handler, especically in kprobes.
 269  * Use reader/writer locks instead of plain spinlock.
 270  */
 271 static LIST_HEAD(break_hook);
 272 static DEFINE_SPINLOCK(break_hook_lock);
 273
 274 void register_break_hook(struct break_hook *hook)
 275 {
 276         spin_lock(&break_hook_lock);
 277         list_add_rcu(&hook->node, &break_hook);
 278         spin_unlock(&break_hook_lock);
 279 }
 280
 281 void unregister_break_hook(struct break_hook *hook)
 282 {
 283         spin_lock(&break_hook_lock);
 284         list_del_rcu(&hook->node);
 285         spin_unlock(&break_hook_lock);
 286         synchronize_rcu();
 287 }
 288
 289 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 290 {
 291         struct break_hook *hook;
 292         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 293
 294         rcu_read_lock();
 295         list_for_each_entry_rcu(hook, &break_hook, node)
 296                 if ((esr & hook->esr_mask) == hook->esr_val)
 297                         fn = hook->fn;
 298         rcu_read_unlock();
 299
 300         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 301 }
 302 NOKPROBE_SYMBOL(call_break_hook);
 303
 304 static int brk_handler(unsigned long addr, unsigned int esr,
 305                        struct pt_regs *regs)
 306 {
 307         if (user_mode(regs)) {
 308                 send_user_sigtrap(TRAP_BRKPT);
 309         }
 310 #ifdef  CONFIG_KPROBES
 311         else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 312                 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
 313                         return -EFAULT;
 314         }
 315 #endif
 316         else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
 317                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 318                 return -EFAULT;
 319         }
 320
 321         return 0;
 322 }
 323 NOKPROBE_SYMBOL(brk_handler);
 324
 325 int aarch32_break_handler(struct pt_regs *regs)
 326 {
 327         u32 arm_instr;
 328         u16 thumb_instr;
 329         bool bp = false;
 330         void __user *pc = (void __user *)instruction_pointer(regs);
 331
 332         if (!compat_user_mode(regs))
 333                 return -EFAULT;
 334
 335         if (compat_thumb_mode(regs)) {
 336                 /* get 16-bit Thumb instruction */
 337                 get_user(thumb_instr, (u16 __user *)pc);
 338                 thumb_instr = le16_to_cpu(thumb_instr);
 339                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 340                         /* get second half of 32-bit Thumb-2 instruction */
 341                         get_user(thumb_instr, (u16 __user *)(pc + 2));
 342                         thumb_instr = le16_to_cpu(thumb_instr);
 343                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 344                 } else {
 345                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 346                 }
 347         } else {
 348                 /* 32-bit ARM instruction */
 349                 get_user(arm_instr, (u32 __user *)pc);
 350                 arm_instr = le32_to_cpu(arm_instr);
 351                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 352         }
 353
 354         if (!bp)
 355                 return -EFAULT;
 356
 357         send_user_sigtrap(TRAP_BRKPT);
 358         return 0;
 359 }
 360 NOKPROBE_SYMBOL(aarch32_break_handler);
 361
 362 static int __init debug_traps_init(void)
 363 {
 364         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 365                               TRAP_TRACE, "single-step handler");
 366         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 367                               TRAP_BRKPT, "ptrace BRK handler");
 368         return 0;
 369 }
 370 arch_initcall(debug_traps_init);
 371
 372 /* Re-enable single step for syscall restarting. */
 373 void user_rewind_single_step(struct task_struct *task)
 374 {
 375         /*
 376          * If single step is active for this thread, then set SPSR.SS
 377          * to 1 to avoid returning to the active-pending state.
 378          */
 379         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 380                 set_regs_spsr_ss(task_pt_regs(task));
 381 }
 382 NOKPROBE_SYMBOL(user_rewind_single_step);
 383
 384 void user_fastforward_single_step(struct task_struct *task)
 385 {
 386         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 387                 clear_regs_spsr_ss(task_pt_regs(task));
 388 }
 389
 390 /* Kernel API */
 391 void kernel_enable_single_step(struct pt_regs *regs)
 392 {
 393         WARN_ON(!irqs_disabled());
 394         set_regs_spsr_ss(regs);
 395         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 396         enable_debug_monitors(DBG_ACTIVE_EL1);
 397 }
 398 NOKPROBE_SYMBOL(kernel_enable_single_step);
 399
 400 void kernel_disable_single_step(void)
 401 {
 402         WARN_ON(!irqs_disabled());
 403         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 404         disable_debug_monitors(DBG_ACTIVE_EL1);
 405 }
 406 NOKPROBE_SYMBOL(kernel_disable_single_step);
 407
 408 int kernel_active_single_step(void)
 409 {
 410         WARN_ON(!irqs_disabled());
 411         return mdscr_read() & DBG_MDSCR_SS;
 412 }
 413 NOKPROBE_SYMBOL(kernel_active_single_step);
 414
 415 /* ptrace API */
 416 void user_enable_single_step(struct task_struct *task)
 417 {
 418         struct thread_info *ti = task_thread_info(task);
 419
 420         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 421                 set_regs_spsr_ss(task_pt_regs(task));
 422 }
 423 NOKPROBE_SYMBOL(user_enable_single_step);
 424
 425 void user_disable_single_step(struct task_struct *task)
 426 {
 427         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 428 }
 429 NOKPROBE_SYMBOL(user_disable_single_step);