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 NOKPROBE_SYMBOL(mdscr_write); 53 54 static u32 mdscr_read(void) 55 { 56 u32 mdscr; 57 asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr)); 58 return mdscr; 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 void clear_os_lock(void *unused) 136 { 137 asm volatile("msr oslar_el1, %0" : : "r" (0)); 138 } 139 140 static int os_lock_notify(struct notifier_block *self, 141 unsigned long action, void *data) 142 { 143 if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE) 144 clear_os_lock(NULL); 145 return NOTIFY_OK; 146 } 147 148 static struct notifier_block os_lock_nb = { 149 .notifier_call = os_lock_notify, 150 }; 151 152 static int debug_monitors_init(void) 153 { 154 cpu_notifier_register_begin(); 155 156 /* Clear the OS lock. */ 157 on_each_cpu(clear_os_lock, NULL, 1); 158 isb(); 159 160 /* Register hotplug handler. */ 161 __register_cpu_notifier(&os_lock_nb); 162 163 cpu_notifier_register_done(); 164 return 0; 165 } 166 postcore_initcall(debug_monitors_init); 167 168 /* 169 * Single step API and exception handling. 170 */ 171 static void set_regs_spsr_ss(struct pt_regs *regs) 172 { 173 regs->pstate |= DBG_SPSR_SS; 174 } 175 NOKPROBE_SYMBOL(set_regs_spsr_ss); 176 177 static void clear_regs_spsr_ss(struct pt_regs *regs) 178 { 179 regs->pstate &= ~DBG_SPSR_SS; 180 } 181 NOKPROBE_SYMBOL(clear_regs_spsr_ss); 182 183 /* EL1 Single Step Handler hooks */ 184 static LIST_HEAD(step_hook); 185 static DEFINE_SPINLOCK(step_hook_lock); 186 187 void register_step_hook(struct step_hook *hook) 188 { 189 spin_lock(&step_hook_lock); 190 list_add_rcu(&hook->node, &step_hook); 191 spin_unlock(&step_hook_lock); 192 } 193 194 void unregister_step_hook(struct step_hook *hook) 195 { 196 spin_lock(&step_hook_lock); 197 list_del_rcu(&hook->node); 198 spin_unlock(&step_hook_lock); 199 synchronize_rcu(); 200 } 201 202 /* 203 * Call registered single step handlers 204 * There is no Syndrome info to check for determining the handler. 205 * So we call all the registered handlers, until the right handler is 206 * found which returns zero. 207 */ 208 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 209 { 210 struct step_hook *hook; 211 int retval = DBG_HOOK_ERROR; 212 213 rcu_read_lock(); 214 215 list_for_each_entry_rcu(hook, &step_hook, node) { 216 retval = hook->fn(regs, esr); 217 if (retval == DBG_HOOK_HANDLED) 218 break; 219 } 220 221 rcu_read_unlock(); 222 223 return retval; 224 } 225 NOKPROBE_SYMBOL(call_step_hook); 226 227 static void send_user_sigtrap(int si_code) 228 { 229 struct pt_regs *regs = current_pt_regs(); 230 siginfo_t info = { 231 .si_signo = SIGTRAP, 232 .si_errno = 0, 233 .si_code = si_code, 234 .si_addr = (void __user *)instruction_pointer(regs), 235 }; 236 237 if (WARN_ON(!user_mode(regs))) 238 return; 239 240 if (interrupts_enabled(regs)) 241 local_irq_enable(); 242 243 force_sig_info(SIGTRAP, &info, current); 244 } 245 246 static int single_step_handler(unsigned long addr, unsigned int esr, 247 struct pt_regs *regs) 248 { 249 /* 250 * If we are stepping a pending breakpoint, call the hw_breakpoint 251 * handler first. 252 */ 253 if (!reinstall_suspended_bps(regs)) 254 return 0; 255 256 if (user_mode(regs)) { 257 send_user_sigtrap(TRAP_HWBKPT); 258 259 /* 260 * ptrace will disable single step unless explicitly 261 * asked to re-enable it. For other clients, it makes 262 * sense to leave it enabled (i.e. rewind the controls 263 * to the active-not-pending state). 264 */ 265 user_rewind_single_step(current); 266 } else { 267 #ifdef CONFIG_KPROBES 268 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 269 return 0; 270 #endif 271 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 272 return 0; 273 274 pr_warning("Unexpected kernel single-step exception at EL1\n"); 275 /* 276 * Re-enable stepping since we know that we will be 277 * returning to regs. 278 */ 279 set_regs_spsr_ss(regs); 280 } 281 282 return 0; 283 } 284 NOKPROBE_SYMBOL(single_step_handler); 285 286 /* 287 * Breakpoint handler is re-entrant as another breakpoint can 288 * hit within breakpoint handler, especically in kprobes. 289 * Use reader/writer locks instead of plain spinlock. 290 */ 291 static LIST_HEAD(break_hook); 292 static DEFINE_SPINLOCK(break_hook_lock); 293 294 void register_break_hook(struct break_hook *hook) 295 { 296 spin_lock(&break_hook_lock); 297 list_add_rcu(&hook->node, &break_hook); 298 spin_unlock(&break_hook_lock); 299 } 300 301 void unregister_break_hook(struct break_hook *hook) 302 { 303 spin_lock(&break_hook_lock); 304 list_del_rcu(&hook->node); 305 spin_unlock(&break_hook_lock); 306 synchronize_rcu(); 307 } 308 309 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 310 { 311 struct break_hook *hook; 312 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 313 314 rcu_read_lock(); 315 list_for_each_entry_rcu(hook, &break_hook, node) 316 if ((esr & hook->esr_mask) == hook->esr_val) 317 fn = hook->fn; 318 rcu_read_unlock(); 319 320 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 321 } 322 NOKPROBE_SYMBOL(call_break_hook); 323 324 static int brk_handler(unsigned long addr, unsigned int esr, 325 struct pt_regs *regs) 326 { 327 if (user_mode(regs)) { 328 send_user_sigtrap(TRAP_BRKPT); 329 } 330 #ifdef CONFIG_KPROBES 331 else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) { 332 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED) 333 return -EFAULT; 334 } 335 #endif 336 else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) { 337 pr_warn("Unexpected kernel BRK exception at EL1\n"); 338 return -EFAULT; 339 } 340 341 return 0; 342 } 343 NOKPROBE_SYMBOL(brk_handler); 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 NOKPROBE_SYMBOL(aarch32_break_handler); 381 382 static int __init debug_traps_init(void) 383 { 384 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 385 TRAP_HWBKPT, "single-step handler"); 386 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 387 TRAP_BRKPT, "ptrace BRK handler"); 388 return 0; 389 } 390 arch_initcall(debug_traps_init); 391 392 /* Re-enable single step for syscall restarting. */ 393 void user_rewind_single_step(struct task_struct *task) 394 { 395 /* 396 * If single step is active for this thread, then set SPSR.SS 397 * to 1 to avoid returning to the active-pending state. 398 */ 399 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 400 set_regs_spsr_ss(task_pt_regs(task)); 401 } 402 NOKPROBE_SYMBOL(user_rewind_single_step); 403 404 void user_fastforward_single_step(struct task_struct *task) 405 { 406 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 407 clear_regs_spsr_ss(task_pt_regs(task)); 408 } 409 410 /* Kernel API */ 411 void kernel_enable_single_step(struct pt_regs *regs) 412 { 413 WARN_ON(!irqs_disabled()); 414 set_regs_spsr_ss(regs); 415 mdscr_write(mdscr_read() | DBG_MDSCR_SS); 416 enable_debug_monitors(DBG_ACTIVE_EL1); 417 } 418 NOKPROBE_SYMBOL(kernel_enable_single_step); 419 420 void kernel_disable_single_step(void) 421 { 422 WARN_ON(!irqs_disabled()); 423 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); 424 disable_debug_monitors(DBG_ACTIVE_EL1); 425 } 426 NOKPROBE_SYMBOL(kernel_disable_single_step); 427 428 int kernel_active_single_step(void) 429 { 430 WARN_ON(!irqs_disabled()); 431 return mdscr_read() & DBG_MDSCR_SS; 432 } 433 NOKPROBE_SYMBOL(kernel_active_single_step); 434 435 /* ptrace API */ 436 void user_enable_single_step(struct task_struct *task) 437 { 438 set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 439 set_regs_spsr_ss(task_pt_regs(task)); 440 } 441 NOKPROBE_SYMBOL(user_enable_single_step); 442 443 void user_disable_single_step(struct task_struct *task) 444 { 445 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 446 } 447 NOKPROBE_SYMBOL(user_disable_single_step); 448