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
  37 /* Determine debug architecture. */
  38 u8 debug_monitors_arch(void)
  39 {
  40         return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
  41                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
  42 }
  43
  44 /*
  45  * MDSCR access routines.
  46  */
  47 static void mdscr_write(u32 mdscr)
  48 {
  49         unsigned long flags;
  50         flags = local_daif_save();
  51         write_sysreg(mdscr, mdscr_el1);
  52         local_daif_restore(flags);
  53 }
  54 NOKPROBE_SYMBOL(mdscr_write);
  55
  56 static u32 mdscr_read(void)
  57 {
  58         return read_sysreg(mdscr_el1);
  59 }
  60 NOKPROBE_SYMBOL(mdscr_read);
  61
  62 /*
  63  * Allow root to disable self-hosted debug from userspace.
  64  * This is useful if you want to connect an external JTAG debugger.
  65  */
  66 static bool debug_enabled = true;
  67
  68 static int create_debug_debugfs_entry(void)
  69 {
  70         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
  71         return 0;
  72 }
  73 fs_initcall(create_debug_debugfs_entry);
  74
  75 static int __init early_debug_disable(char *buf)
  76 {
  77         debug_enabled = false;
  78         return 0;
  79 }
  80
  81 early_param("nodebugmon", early_debug_disable);
  82
  83 /*
  84  * Keep track of debug users on each core.
  85  * The ref counts are per-cpu so we use a local_t type.
  86  */
  87 static DEFINE_PER_CPU(int, mde_ref_count);
  88 static DEFINE_PER_CPU(int, kde_ref_count);
  89
  90 void enable_debug_monitors(enum dbg_active_el el)
  91 {
  92         u32 mdscr, enable = 0;
  93
  94         WARN_ON(preemptible());
  95
  96         if (this_cpu_inc_return(mde_ref_count) == 1)
  97                 enable = DBG_MDSCR_MDE;
  98
  99         if (el == DBG_ACTIVE_EL1 &&
 100             this_cpu_inc_return(kde_ref_count) == 1)
 101                 enable |= DBG_MDSCR_KDE;
 102
 103         if (enable && debug_enabled) {
 104                 mdscr = mdscr_read();
 105                 mdscr |= enable;
 106                 mdscr_write(mdscr);
 107         }
 108 }
 109 NOKPROBE_SYMBOL(enable_debug_monitors);
 110
 111 void disable_debug_monitors(enum dbg_active_el el)
 112 {
 113         u32 mdscr, disable = 0;
 114
 115         WARN_ON(preemptible());
 116
 117         if (this_cpu_dec_return(mde_ref_count) == 0)
 118                 disable = ~DBG_MDSCR_MDE;
 119
 120         if (el == DBG_ACTIVE_EL1 &&
 121             this_cpu_dec_return(kde_ref_count) == 0)
 122                 disable &= ~DBG_MDSCR_KDE;
 123
 124         if (disable) {
 125                 mdscr = mdscr_read();
 126                 mdscr &= disable;
 127                 mdscr_write(mdscr);
 128         }
 129 }
 130 NOKPROBE_SYMBOL(disable_debug_monitors);
 131
 132 /*
 133  * OS lock clearing.
 134  */
 135 static int clear_os_lock(unsigned int cpu)
 136 {
 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_regs_spsr_ss(struct pt_regs *regs)
 154 {
 155         regs->pstate |= DBG_SPSR_SS;
 156 }
 157 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 158
 159 static void clear_regs_spsr_ss(struct pt_regs *regs)
 160 {
 161         regs->pstate &= ~DBG_SPSR_SS;
 162 }
 163 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
 164
 165 /* EL1 Single Step Handler hooks */
 166 static LIST_HEAD(step_hook);
 167 static DEFINE_SPINLOCK(step_hook_lock);
 168
 169 void register_step_hook(struct step_hook *hook)
 170 {
 171         spin_lock(&step_hook_lock);
 172         list_add_rcu(&hook->node, &step_hook);
 173         spin_unlock(&step_hook_lock);
 174 }
 175
 176 void unregister_step_hook(struct step_hook *hook)
 177 {
 178         spin_lock(&step_hook_lock);
 179         list_del_rcu(&hook->node);
 180         spin_unlock(&step_hook_lock);
 181         synchronize_rcu();
 182 }
 183
 184 /*
 185  * Call registered single step handlers
 186  * There is no Syndrome info to check for determining the handler.
 187  * So we call all the registered handlers, until the right handler is
 188  * found which returns zero.
 189  */
 190 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 191 {
 192         struct step_hook *hook;
 193         int retval = DBG_HOOK_ERROR;
 194
 195         rcu_read_lock();
 196
 197         list_for_each_entry_rcu(hook, &step_hook, node) {
 198                 retval = hook->fn(regs, esr);
 199                 if (retval == DBG_HOOK_HANDLED)
 200                         break;
 201         }
 202
 203         rcu_read_unlock();
 204
 205         return retval;
 206 }
 207 NOKPROBE_SYMBOL(call_step_hook);
 208
 209 static void send_user_sigtrap(int si_code)
 210 {
 211         struct pt_regs *regs = current_pt_regs();
 212         siginfo_t info = {
 213                 .si_signo       = SIGTRAP,
 214                 .si_errno       = 0,
 215                 .si_code        = si_code,
 216                 .si_addr        = (void __user *)instruction_pointer(regs),
 217         };
 218
 219         if (WARN_ON(!user_mode(regs)))
 220                 return;
 221
 222         if (interrupts_enabled(regs))
 223                 local_irq_enable();
 224
 225         force_sig_info(SIGTRAP, &info, current);
 226 }
 227
 228 static int single_step_handler(unsigned long addr, unsigned int esr,
 229                                struct pt_regs *regs)
 230 {
 231         bool handler_found = false;
 232
 233         /*
 234          * If we are stepping a pending breakpoint, call the hw_breakpoint
 235          * handler first.
 236          */
 237         if (!reinstall_suspended_bps(regs))
 238                 return 0;
 239
 240 #ifdef  CONFIG_KPROBES
 241         if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
 242                 handler_found = true;
 243 #endif
 244         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
 245                 handler_found = true;
 246
 247         if (!handler_found && user_mode(regs)) {
 248                 send_user_sigtrap(TRAP_TRACE);
 249
 250                 /*
 251                  * ptrace will disable single step unless explicitly
 252                  * asked to re-enable it. For other clients, it makes
 253                  * sense to leave it enabled (i.e. rewind the controls
 254                  * to the active-not-pending state).
 255                  */
 256                 user_rewind_single_step(current);
 257         } else if (!handler_found) {
 258                 pr_warn("Unexpected kernel single-step exception at EL1\n");
 259                 /*
 260                  * Re-enable stepping since we know that we will be
 261                  * returning to regs.
 262                  */
 263                 set_regs_spsr_ss(regs);
 264         }
 265
 266         return 0;
 267 }
 268 NOKPROBE_SYMBOL(single_step_handler);
 269
 270 /*
 271  * Breakpoint handler is re-entrant as another breakpoint can
 272  * hit within breakpoint handler, especically in kprobes.
 273  * Use reader/writer locks instead of plain spinlock.
 274  */
 275 static LIST_HEAD(break_hook);
 276 static DEFINE_SPINLOCK(break_hook_lock);
 277
 278 void register_break_hook(struct break_hook *hook)
 279 {
 280         spin_lock(&break_hook_lock);
 281         list_add_rcu(&hook->node, &break_hook);
 282         spin_unlock(&break_hook_lock);
 283 }
 284
 285 void unregister_break_hook(struct break_hook *hook)
 286 {
 287         spin_lock(&break_hook_lock);
 288         list_del_rcu(&hook->node);
 289         spin_unlock(&break_hook_lock);
 290         synchronize_rcu();
 291 }
 292
 293 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 294 {
 295         struct break_hook *hook;
 296         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
 297
 298         rcu_read_lock();
 299         list_for_each_entry_rcu(hook, &break_hook, node)
 300                 if ((esr & hook->esr_mask) == hook->esr_val)
 301                         fn = hook->fn;
 302         rcu_read_unlock();
 303
 304         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 305 }
 306 NOKPROBE_SYMBOL(call_break_hook);
 307
 308 static int brk_handler(unsigned long addr, unsigned int esr,
 309                        struct pt_regs *regs)
 310 {
 311         bool handler_found = false;
 312
 313 #ifdef  CONFIG_KPROBES
 314         if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
 315                 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
 316                         handler_found = true;
 317         }
 318 #endif
 319         if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 320                 handler_found = true;
 321
 322         if (!handler_found && user_mode(regs)) {
 323                 send_user_sigtrap(TRAP_BRKPT);
 324         } else if (!handler_found) {
 325                 pr_warn("Unexpected kernel BRK exception at EL1\n");
 326                 return -EFAULT;
 327         }
 328
 329         return 0;
 330 }
 331 NOKPROBE_SYMBOL(brk_handler);
 332
 333 int aarch32_break_handler(struct pt_regs *regs)
 334 {
 335         u32 arm_instr;
 336         u16 thumb_instr;
 337         bool bp = false;
 338         void __user *pc = (void __user *)instruction_pointer(regs);
 339
 340         if (!compat_user_mode(regs))
 341                 return -EFAULT;
 342
 343         if (compat_thumb_mode(regs)) {
 344                 /* get 16-bit Thumb instruction */
 345                 __le16 instr;
 346                 get_user(instr, (__le16 __user *)pc);
 347                 thumb_instr = le16_to_cpu(instr);
 348                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
 349                         /* get second half of 32-bit Thumb-2 instruction */
 350                         get_user(instr, (__le16 __user *)(pc + 2));
 351                         thumb_instr = le16_to_cpu(instr);
 352                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
 353                 } else {
 354                         bp = thumb_instr == AARCH32_BREAK_THUMB;
 355                 }
 356         } else {
 357                 /* 32-bit ARM instruction */
 358                 __le32 instr;
 359                 get_user(instr, (__le32 __user *)pc);
 360                 arm_instr = le32_to_cpu(instr);
 361                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
 362         }
 363
 364         if (!bp)
 365                 return -EFAULT;
 366
 367         send_user_sigtrap(TRAP_BRKPT);
 368         return 0;
 369 }
 370 NOKPROBE_SYMBOL(aarch32_break_handler);
 371
 372 static int __init debug_traps_init(void)
 373 {
 374         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
 375                               TRAP_TRACE, "single-step handler");
 376         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
 377                               TRAP_BRKPT, "ptrace BRK handler");
 378         return 0;
 379 }
 380 arch_initcall(debug_traps_init);
 381
 382 /* Re-enable single step for syscall restarting. */
 383 void user_rewind_single_step(struct task_struct *task)
 384 {
 385         /*
 386          * If single step is active for this thread, then set SPSR.SS
 387          * to 1 to avoid returning to the active-pending state.
 388          */
 389         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 390                 set_regs_spsr_ss(task_pt_regs(task));
 391 }
 392 NOKPROBE_SYMBOL(user_rewind_single_step);
 393
 394 void user_fastforward_single_step(struct task_struct *task)
 395 {
 396         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
 397                 clear_regs_spsr_ss(task_pt_regs(task));
 398 }
 399
 400 /* Kernel API */
 401 void kernel_enable_single_step(struct pt_regs *regs)
 402 {
 403         WARN_ON(!irqs_disabled());
 404         set_regs_spsr_ss(regs);
 405         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
 406         enable_debug_monitors(DBG_ACTIVE_EL1);
 407 }
 408 NOKPROBE_SYMBOL(kernel_enable_single_step);
 409
 410 void kernel_disable_single_step(void)
 411 {
 412         WARN_ON(!irqs_disabled());
 413         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
 414         disable_debug_monitors(DBG_ACTIVE_EL1);
 415 }
 416 NOKPROBE_SYMBOL(kernel_disable_single_step);
 417
 418 int kernel_active_single_step(void)
 419 {
 420         WARN_ON(!irqs_disabled());
 421         return mdscr_read() & DBG_MDSCR_SS;
 422 }
 423 NOKPROBE_SYMBOL(kernel_active_single_step);
 424
 425 /* ptrace API */
 426 void user_enable_single_step(struct task_struct *task)
 427 {
 428         struct thread_info *ti = task_thread_info(task);
 429
 430         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
 431                 set_regs_spsr_ss(task_pt_regs(task));
 432 }
 433 NOKPROBE_SYMBOL(user_enable_single_step);
 434
 435 void user_disable_single_step(struct task_struct *task)
 436 {
 437         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
 438 }
 439 NOKPROBE_SYMBOL(user_disable_single_step);