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 asm volatile("msr mdscr_el1, %0" :: "r" (mdscr)); 50 local_dbg_restore(flags); 51 } 52 53 static u32 mdscr_read(void) 54 { 55 u32 mdscr; 56 asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr)); 57 return mdscr; 58 } 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 } 107 108 void disable_debug_monitors(enum dbg_active_el el) 109 { 110 u32 mdscr, disable = 0; 111 112 WARN_ON(preemptible()); 113 114 if (this_cpu_dec_return(mde_ref_count) == 0) 115 disable = ~DBG_MDSCR_MDE; 116 117 if (el == DBG_ACTIVE_EL1 && 118 this_cpu_dec_return(kde_ref_count) == 0) 119 disable &= ~DBG_MDSCR_KDE; 120 121 if (disable) { 122 mdscr = mdscr_read(); 123 mdscr &= disable; 124 mdscr_write(mdscr); 125 } 126 } 127 128 /* 129 * OS lock clearing. 130 */ 131 static void clear_os_lock(void *unused) 132 { 133 asm volatile("msr oslar_el1, %0" : : "r" (0)); 134 } 135 136 static int os_lock_notify(struct notifier_block *self, 137 unsigned long action, void *data) 138 { 139 if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE) 140 clear_os_lock(NULL); 141 return NOTIFY_OK; 142 } 143 144 static struct notifier_block os_lock_nb = { 145 .notifier_call = os_lock_notify, 146 }; 147 148 static int debug_monitors_init(void) 149 { 150 cpu_notifier_register_begin(); 151 152 /* Clear the OS lock. */ 153 on_each_cpu(clear_os_lock, NULL, 1); 154 isb(); 155 local_dbg_enable(); 156 157 /* Register hotplug handler. */ 158 __register_cpu_notifier(&os_lock_nb); 159 160 cpu_notifier_register_done(); 161 return 0; 162 } 163 postcore_initcall(debug_monitors_init); 164 165 /* 166 * Single step API and exception handling. 167 */ 168 static void set_regs_spsr_ss(struct pt_regs *regs) 169 { 170 unsigned long spsr; 171 172 spsr = regs->pstate; 173 spsr &= ~DBG_SPSR_SS; 174 spsr |= DBG_SPSR_SS; 175 regs->pstate = spsr; 176 } 177 178 static void clear_regs_spsr_ss(struct pt_regs *regs) 179 { 180 unsigned long spsr; 181 182 spsr = regs->pstate; 183 spsr &= ~DBG_SPSR_SS; 184 regs->pstate = spsr; 185 } 186 187 /* EL1 Single Step Handler hooks */ 188 static LIST_HEAD(step_hook); 189 static DEFINE_SPINLOCK(step_hook_lock); 190 191 void register_step_hook(struct step_hook *hook) 192 { 193 spin_lock(&step_hook_lock); 194 list_add_rcu(&hook->node, &step_hook); 195 spin_unlock(&step_hook_lock); 196 } 197 198 void unregister_step_hook(struct step_hook *hook) 199 { 200 spin_lock(&step_hook_lock); 201 list_del_rcu(&hook->node); 202 spin_unlock(&step_hook_lock); 203 synchronize_rcu(); 204 } 205 206 /* 207 * Call registered single step handlers 208 * There is no Syndrome info to check for determining the handler. 209 * So we call all the registered handlers, until the right handler is 210 * found which returns zero. 211 */ 212 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 213 { 214 struct step_hook *hook; 215 int retval = DBG_HOOK_ERROR; 216 217 rcu_read_lock(); 218 219 list_for_each_entry_rcu(hook, &step_hook, node) { 220 retval = hook->fn(regs, esr); 221 if (retval == DBG_HOOK_HANDLED) 222 break; 223 } 224 225 rcu_read_unlock(); 226 227 return retval; 228 } 229 230 static void send_user_sigtrap(int si_code) 231 { 232 struct pt_regs *regs = current_pt_regs(); 233 siginfo_t info = { 234 .si_signo = SIGTRAP, 235 .si_errno = 0, 236 .si_code = si_code, 237 .si_addr = (void __user *)instruction_pointer(regs), 238 }; 239 240 if (WARN_ON(!user_mode(regs))) 241 return; 242 243 if (interrupts_enabled(regs)) 244 local_irq_enable(); 245 246 force_sig_info(SIGTRAP, &info, current); 247 } 248 249 static int single_step_handler(unsigned long addr, unsigned int esr, 250 struct pt_regs *regs) 251 { 252 /* 253 * If we are stepping a pending breakpoint, call the hw_breakpoint 254 * handler first. 255 */ 256 if (!reinstall_suspended_bps(regs)) 257 return 0; 258 259 if (user_mode(regs)) { 260 send_user_sigtrap(TRAP_HWBKPT); 261 262 /* 263 * ptrace will disable single step unless explicitly 264 * asked to re-enable it. For other clients, it makes 265 * sense to leave it enabled (i.e. rewind the controls 266 * to the active-not-pending state). 267 */ 268 user_rewind_single_step(current); 269 } else { 270 #ifdef CONFIG_KPROBES 271 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 272 return 0; 273 #endif 274 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 275 return 0; 276 277 pr_warning("Unexpected kernel single-step exception at EL1\n"); 278 /* 279 * Re-enable stepping since we know that we will be 280 * returning to regs. 281 */ 282 set_regs_spsr_ss(regs); 283 } 284 285 return 0; 286 } 287 288 /* 289 * Breakpoint handler is re-entrant as another breakpoint can 290 * hit within breakpoint handler, especically in kprobes. 291 * Use reader/writer locks instead of plain spinlock. 292 */ 293 static LIST_HEAD(break_hook); 294 static DEFINE_SPINLOCK(break_hook_lock); 295 296 void register_break_hook(struct break_hook *hook) 297 { 298 spin_lock(&break_hook_lock); 299 list_add_rcu(&hook->node, &break_hook); 300 spin_unlock(&break_hook_lock); 301 } 302 303 void unregister_break_hook(struct break_hook *hook) 304 { 305 spin_lock(&break_hook_lock); 306 list_del_rcu(&hook->node); 307 spin_unlock(&break_hook_lock); 308 synchronize_rcu(); 309 } 310 311 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 312 { 313 struct break_hook *hook; 314 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 315 316 rcu_read_lock(); 317 list_for_each_entry_rcu(hook, &break_hook, node) 318 if ((esr & hook->esr_mask) == hook->esr_val) 319 fn = hook->fn; 320 rcu_read_unlock(); 321 322 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 323 } 324 325 static int brk_handler(unsigned long addr, unsigned int esr, 326 struct pt_regs *regs) 327 { 328 if (user_mode(regs)) { 329 send_user_sigtrap(TRAP_BRKPT); 330 } 331 #ifdef CONFIG_KPROBES 332 else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) { 333 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED) 334 return -EFAULT; 335 } 336 #endif 337 else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) { 338 pr_warn("Unexpected kernel BRK exception at EL1\n"); 339 return -EFAULT; 340 } 341 342 return 0; 343 } 344 345 int aarch32_break_handler(struct pt_regs *regs) 346 { 347 u32 arm_instr; 348 u16 thumb_instr; 349 bool bp = false; 350 void __user *pc = (void __user *)instruction_pointer(regs); 351 352 if (!compat_user_mode(regs)) 353 return -EFAULT; 354 355 if (compat_thumb_mode(regs)) { 356 /* get 16-bit Thumb instruction */ 357 get_user(thumb_instr, (u16 __user *)pc); 358 thumb_instr = le16_to_cpu(thumb_instr); 359 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 360 /* get second half of 32-bit Thumb-2 instruction */ 361 get_user(thumb_instr, (u16 __user *)(pc + 2)); 362 thumb_instr = le16_to_cpu(thumb_instr); 363 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 364 } else { 365 bp = thumb_instr == AARCH32_BREAK_THUMB; 366 } 367 } else { 368 /* 32-bit ARM instruction */ 369 get_user(arm_instr, (u32 __user *)pc); 370 arm_instr = le32_to_cpu(arm_instr); 371 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM; 372 } 373 374 if (!bp) 375 return -EFAULT; 376 377 send_user_sigtrap(TRAP_BRKPT); 378 return 0; 379 } 380 381 static int __init debug_traps_init(void) 382 { 383 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 384 TRAP_HWBKPT, "single-step handler"); 385 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 386 TRAP_BRKPT, "ptrace BRK handler"); 387 return 0; 388 } 389 arch_initcall(debug_traps_init); 390 391 /* Re-enable single step for syscall restarting. */ 392 void user_rewind_single_step(struct task_struct *task) 393 { 394 /* 395 * If single step is active for this thread, then set SPSR.SS 396 * to 1 to avoid returning to the active-pending state. 397 */ 398 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 399 set_regs_spsr_ss(task_pt_regs(task)); 400 } 401 402 void user_fastforward_single_step(struct task_struct *task) 403 { 404 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 405 clear_regs_spsr_ss(task_pt_regs(task)); 406 } 407 408 /* Kernel API */ 409 void kernel_enable_single_step(struct pt_regs *regs) 410 { 411 WARN_ON(!irqs_disabled()); 412 set_regs_spsr_ss(regs); 413 mdscr_write(mdscr_read() | DBG_MDSCR_SS); 414 enable_debug_monitors(DBG_ACTIVE_EL1); 415 } 416 417 void kernel_disable_single_step(void) 418 { 419 WARN_ON(!irqs_disabled()); 420 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); 421 disable_debug_monitors(DBG_ACTIVE_EL1); 422 } 423 424 int kernel_active_single_step(void) 425 { 426 WARN_ON(!irqs_disabled()); 427 return mdscr_read() & DBG_MDSCR_SS; 428 } 429 430 /* ptrace API */ 431 void user_enable_single_step(struct task_struct *task) 432 { 433 set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 434 set_regs_spsr_ss(task_pt_regs(task)); 435 } 436 437 void user_disable_single_step(struct task_struct *task) 438 { 439 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 440 } 441