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, oslar_el1);
 139         isb();
 140         return 0;
 141 }
 142
 143 static int debug_monitors_init(void)
 144 {
 145         return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 146                                  "arm64/debug_monitors:starting",
 147                                  clear_os_lock, NULL);
 148 }
 149 postcore_initcall(debug_monitors_init);
 150
 151 /*
 152  * Single step API and exception handling.
 153  */
 154 static void set_regs_spsr_ss(struct pt_regs *regs)
 155 {
 156         regs->pstate |= DBG_SPSR_SS;
 157 }
 158 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 159
 160 static void clear_regs_spsr_ss(struct pt_regs *regs)
 161 {
 162         regs->pstate &= ~DBG_SPSR_SS;
 163 }
 164 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
 165
 166 /* EL1 Single Step Handler hooks */
 167 static LIST_HEAD(step_hook);
 168 static DEFINE_SPINLOCK(step_hook_lock);
 169
 170 void register_step_hook(struct step_hook *hook)
 171 {
 172         spin_lock(&step_hook_lock);
 173         list_add_rcu(&hook->node, &step_hook);
 174         spin_unlock(&step_hook_lock);
 175 }
 176
 177 void unregister_step_hook(struct step_hook *hook)
 178 {
 179         spin_lock(&step_hook_lock);
 180         list_del_rcu(&hook->node);
 181         spin_unlock(&step_hook_lock);
 182         synchronize_rcu();
 183 }
 184
 185 /*
 186  * Call registered single step handlers
 187  * There is no Syndrome info to check for determining the handler.
 188  * So we call all the registered handlers, until the right handler is
 189  * found which returns zero.
 190  */
 191 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 192 {
 193         struct step_hook *hook;
 194         int retval = DBG_HOOK_ERROR;
 195
 196         rcu_read_lock();
 197
 198         list_for_each_entry_rcu(hook, &step_hook, node) {
 199                 retval = hook->fn(regs, esr);
 200                 if (retval == DBG_HOOK_HANDLED)
 201                         break;
 202         }
 203
 204         rcu_read_unlock();
 205
 206         return retval;
 207 }
 208 NOKPROBE_SYMBOL(call_step_hook);
 209
 210 static void send_user_sigtrap(int si_code)
 211 {
 212         struct pt_regs *regs = current_pt_regs();
 213
 214         if (WARN_ON(!user_mode(regs)))
 215                 return;
 216
 217         if (interrupts_enabled(regs))
 218                 local_irq_enable();
 219
 220         arm64_force_sig_fault(SIGTRAP, si_code,
 221                              (void __user *)instruction_pointer(regs),
 222                              "User debug trap");
 223 }
 224
 225 static int single_step_handler(unsigned long addr, unsigned int esr,
 226                                struct pt_regs *regs)
 227 {
 228         bool handler_found = false;
 229
 230         /*
 231          * If we are stepping a pending breakpoint, call the hw_breakpoint
 232          * handler first.
 233          */
 234         if (!reinstall_suspended_bps(regs))
 235                 return 0;
 236
 237 #ifdef  CONFIG_KPROBES
 238         if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 239                 handler_found = true;
 240 #endif
 241         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 242                 handler_found = true;
 243
 244         if (!handler_found && user_mode(regs)) {
 245                 send_user_sigtrap(TRAP_TRACE);
 246
 247                 /*
 248                  * ptrace will disable single step unless explicitly
 249                  * asked to re-enable it. For other clients, it makes
 250                  * sense to leave it enabled (i.e. rewind the controls
 251                  * to the active-not-pending state).
 252                  */
 253                 user_rewind_single_step(current);
 254         } else if (!handler_found) {
 255                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 256                 /*
 257                  * Re-enable stepping since we know that we will be
 258                  * returning to regs.
 259                  */
 260                 set_regs_spsr_ss(regs);
 261         }
 262
 263         return 0;
 264 }
 265 NOKPROBE_SYMBOL(single_step_handler);
 266
 267 /*
 268  * Breakpoint handler is re-entrant as another breakpoint can
 269  * hit within breakpoint handler, especically in kprobes.
 270  * Use reader/writer locks instead of plain spinlock.
 271  */
 272 static LIST_HEAD(break_hook);
 273 static DEFINE_SPINLOCK(break_hook_lock);
 274
 275 void register_break_hook(struct break_hook *hook)
 276 {
 277         spin_lock(&break_hook_lock);
 278         list_add_rcu(&hook->node, &break_hook);
 279         spin_unlock(&break_hook_lock);
 280 }
 281
 282 void unregister_break_hook(struct break_hook *hook)
 283 {
 284         spin_lock(&break_hook_lock);
 285         list_del_rcu(&hook->node);
 286         spin_unlock(&break_hook_lock);
 287         synchronize_rcu();
 288 }
 289
 290 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 291 {
 292         struct break_hook *hook;
 293         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 294
 295         rcu_read_lock();
 296         list_for_each_entry_rcu(hook, &break_hook, node)
 297                 if ((esr & hook->esr_mask) == hook->esr_val)
 298                         fn = hook->fn;
 299         rcu_read_unlock();
 300
 301         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 302 }
 303 NOKPROBE_SYMBOL(call_break_hook);
 304
 305 static int brk_handler(unsigned long addr, unsigned int esr,
 306                        struct pt_regs *regs)
 307 {
 308         bool handler_found = false;
 309
 310 #ifdef  CONFIG_KPROBES
 311         if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 312                 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
 313                         handler_found = true;
 314         }
 315 #endif
 316         if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 317                 handler_found = true;
 318
 319         if (!handler_found && user_mode(regs)) {
 320                 send_user_sigtrap(TRAP_BRKPT);
 321         } else if (!handler_found) {
 322                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 323                 return -EFAULT;
 324         }
 325
 326         return 0;
 327 }
 328 NOKPROBE_SYMBOL(brk_handler);
 329
 330 int aarch32_break_handler(struct pt_regs *regs)
 331 {
 332         u32 arm_instr;
 333         u16 thumb_instr;
 334         bool bp = false;
 335         void __user *pc = (void __user *)instruction_pointer(regs);
 336
 337         if (!compat_user_mode(regs))
 338                 return -EFAULT;
 339
 340         if (compat_thumb_mode(regs)) {
 341                 /* get 16-bit Thumb instruction */
 342                 __le16 instr;
 343                 get_user(instr, (__le16 __user *)pc);
 344                 thumb_instr = le16_to_cpu(instr);
 345                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 346                         /* get second half of 32-bit Thumb-2 instruction */
 347                         get_user(instr, (__le16 __user *)(pc + 2));
 348                         thumb_instr = le16_to_cpu(instr);
 349                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 350                 } else {
 351                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 352                 }
 353         } else {
 354                 /* 32-bit ARM instruction */
 355                 __le32 instr;
 356                 get_user(instr, (__le32 __user *)pc);
 357                 arm_instr = le32_to_cpu(instr);
 358                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 359         }
 360
 361         if (!bp)
 362                 return -EFAULT;
 363
 364         send_user_sigtrap(TRAP_BRKPT);
 365         return 0;
 366 }
 367 NOKPROBE_SYMBOL(aarch32_break_handler);
 368
 369 static int __init debug_traps_init(void)
 370 {
 371         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 372                               TRAP_TRACE, "single-step handler");
 373         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 374                               TRAP_BRKPT, "ptrace BRK handler");
 375         return 0;
 376 }
 377 arch_initcall(debug_traps_init);
 378
 379 /* Re-enable single step for syscall restarting. */
 380 void user_rewind_single_step(struct task_struct *task)
 381 {
 382         /*
 383          * If single step is active for this thread, then set SPSR.SS
 384          * to 1 to avoid returning to the active-pending state.
 385          */
 386         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 387                 set_regs_spsr_ss(task_pt_regs(task));
 388 }
 389 NOKPROBE_SYMBOL(user_rewind_single_step);
 390
 391 void user_fastforward_single_step(struct task_struct *task)
 392 {
 393         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 394                 clear_regs_spsr_ss(task_pt_regs(task));
 395 }
 396
 397 /* Kernel API */
 398 void kernel_enable_single_step(struct pt_regs *regs)
 399 {
 400         WARN_ON(!irqs_disabled());
 401         set_regs_spsr_ss(regs);
 402         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 403         enable_debug_monitors(DBG_ACTIVE_EL1);
 404 }
 405 NOKPROBE_SYMBOL(kernel_enable_single_step);
 406
 407 void kernel_disable_single_step(void)
 408 {
 409         WARN_ON(!irqs_disabled());
 410         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 411         disable_debug_monitors(DBG_ACTIVE_EL1);
 412 }
 413 NOKPROBE_SYMBOL(kernel_disable_single_step);
 414
 415 int kernel_active_single_step(void)
 416 {
 417         WARN_ON(!irqs_disabled());
 418         return mdscr_read() & DBG_MDSCR_SS;
 419 }
 420 NOKPROBE_SYMBOL(kernel_active_single_step);
 421
 422 /* ptrace API */
 423 void user_enable_single_step(struct task_struct *task)
 424 {
 425         struct thread_info *ti = task_thread_info(task);
 426
 427         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 428                 set_regs_spsr_ss(task_pt_regs(task));
 429 }
 430 NOKPROBE_SYMBOL(user_enable_single_step);
 431
 432 void user_disable_single_step(struct task_struct *task)
 433 {
 434         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 435 }
 436 NOKPROBE_SYMBOL(user_disable_single_step);