1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * ARMv8 single-step debug support and mdscr context switching. 4 * 5 * Copyright (C) 2012 ARM Limited 6 * 7 * Author: Will Deacon <will.deacon@arm.com> 8 */ 9 10 #include <linux/cpu.h> 11 #include <linux/debugfs.h> 12 #include <linux/hardirq.h> 13 #include <linux/init.h> 14 #include <linux/ptrace.h> 15 #include <linux/kprobes.h> 16 #include <linux/stat.h> 17 #include <linux/uaccess.h> 18 #include <linux/sched/task_stack.h> 19 20 #include <asm/cpufeature.h> 21 #include <asm/cputype.h> 22 #include <asm/daifflags.h> 23 #include <asm/debug-monitors.h> 24 #include <asm/system_misc.h> 25 #include <asm/traps.h> 26 27 /* Determine debug architecture. */ 28 u8 debug_monitors_arch(void) 29 { 30 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1), 31 ID_AA64DFR0_DEBUGVER_SHIFT); 32 } 33 34 /* 35 * MDSCR access routines. 36 */ 37 static void mdscr_write(u32 mdscr) 38 { 39 unsigned long flags; 40 flags = local_daif_save(); 41 write_sysreg(mdscr, mdscr_el1); 42 local_daif_restore(flags); 43 } 44 NOKPROBE_SYMBOL(mdscr_write); 45 46 static u32 mdscr_read(void) 47 { 48 return read_sysreg(mdscr_el1); 49 } 50 NOKPROBE_SYMBOL(mdscr_read); 51 52 /* 53 * Allow root to disable self-hosted debug from userspace. 54 * This is useful if you want to connect an external JTAG debugger. 55 */ 56 static bool debug_enabled = true; 57 58 static int create_debug_debugfs_entry(void) 59 { 60 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled); 61 return 0; 62 } 63 fs_initcall(create_debug_debugfs_entry); 64 65 static int __init early_debug_disable(char *buf) 66 { 67 debug_enabled = false; 68 return 0; 69 } 70 71 early_param("nodebugmon", early_debug_disable); 72 73 /* 74 * Keep track of debug users on each core. 75 * The ref counts are per-cpu so we use a local_t type. 76 */ 77 static DEFINE_PER_CPU(int, mde_ref_count); 78 static DEFINE_PER_CPU(int, kde_ref_count); 79 80 void enable_debug_monitors(enum dbg_active_el el) 81 { 82 u32 mdscr, enable = 0; 83 84 WARN_ON(preemptible()); 85 86 if (this_cpu_inc_return(mde_ref_count) == 1) 87 enable = DBG_MDSCR_MDE; 88 89 if (el == DBG_ACTIVE_EL1 && 90 this_cpu_inc_return(kde_ref_count) == 1) 91 enable |= DBG_MDSCR_KDE; 92 93 if (enable && debug_enabled) { 94 mdscr = mdscr_read(); 95 mdscr |= enable; 96 mdscr_write(mdscr); 97 } 98 } 99 NOKPROBE_SYMBOL(enable_debug_monitors); 100 101 void disable_debug_monitors(enum dbg_active_el el) 102 { 103 u32 mdscr, disable = 0; 104 105 WARN_ON(preemptible()); 106 107 if (this_cpu_dec_return(mde_ref_count) == 0) 108 disable = ~DBG_MDSCR_MDE; 109 110 if (el == DBG_ACTIVE_EL1 && 111 this_cpu_dec_return(kde_ref_count) == 0) 112 disable &= ~DBG_MDSCR_KDE; 113 114 if (disable) { 115 mdscr = mdscr_read(); 116 mdscr &= disable; 117 mdscr_write(mdscr); 118 } 119 } 120 NOKPROBE_SYMBOL(disable_debug_monitors); 121 122 /* 123 * OS lock clearing. 124 */ 125 static int clear_os_lock(unsigned int cpu) 126 { 127 write_sysreg(0, osdlr_el1); 128 write_sysreg(0, oslar_el1); 129 isb(); 130 return 0; 131 } 132 133 static int __init debug_monitors_init(void) 134 { 135 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING, 136 "arm64/debug_monitors:starting", 137 clear_os_lock, NULL); 138 } 139 postcore_initcall(debug_monitors_init); 140 141 /* 142 * Single step API and exception handling. 143 */ 144 static void set_user_regs_spsr_ss(struct user_pt_regs *regs) 145 { 146 regs->pstate |= DBG_SPSR_SS; 147 } 148 NOKPROBE_SYMBOL(set_user_regs_spsr_ss); 149 150 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs) 151 { 152 regs->pstate &= ~DBG_SPSR_SS; 153 } 154 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss); 155 156 #define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs) 157 #define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs) 158 159 static DEFINE_SPINLOCK(debug_hook_lock); 160 static LIST_HEAD(user_step_hook); 161 static LIST_HEAD(kernel_step_hook); 162 163 static void register_debug_hook(struct list_head *node, struct list_head *list) 164 { 165 spin_lock(&debug_hook_lock); 166 list_add_rcu(node, list); 167 spin_unlock(&debug_hook_lock); 168 169 } 170 171 static void unregister_debug_hook(struct list_head *node) 172 { 173 spin_lock(&debug_hook_lock); 174 list_del_rcu(node); 175 spin_unlock(&debug_hook_lock); 176 synchronize_rcu(); 177 } 178 179 void register_user_step_hook(struct step_hook *hook) 180 { 181 register_debug_hook(&hook->node, &user_step_hook); 182 } 183 184 void unregister_user_step_hook(struct step_hook *hook) 185 { 186 unregister_debug_hook(&hook->node); 187 } 188 189 void register_kernel_step_hook(struct step_hook *hook) 190 { 191 register_debug_hook(&hook->node, &kernel_step_hook); 192 } 193 194 void unregister_kernel_step_hook(struct step_hook *hook) 195 { 196 unregister_debug_hook(&hook->node); 197 } 198 199 /* 200 * Call registered single step handlers 201 * There is no Syndrome info to check for determining the handler. 202 * So we call all the registered handlers, until the right handler is 203 * found which returns zero. 204 */ 205 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 206 { 207 struct step_hook *hook; 208 struct list_head *list; 209 int retval = DBG_HOOK_ERROR; 210 211 list = user_mode(regs) ? &user_step_hook : &kernel_step_hook; 212 213 /* 214 * Since single-step exception disables interrupt, this function is 215 * entirely not preemptible, and we can use rcu list safely here. 216 */ 217 list_for_each_entry_rcu(hook, list, node) { 218 retval = hook->fn(regs, esr); 219 if (retval == DBG_HOOK_HANDLED) 220 break; 221 } 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(); 230 231 if (WARN_ON(!user_mode(regs))) 232 return; 233 234 if (interrupts_enabled(regs)) 235 local_irq_enable(); 236 237 arm64_force_sig_fault(SIGTRAP, si_code, 238 (void __user *)instruction_pointer(regs), 239 "User debug trap"); 240 } 241 242 static int single_step_handler(unsigned long unused, unsigned int esr, 243 struct pt_regs *regs) 244 { 245 bool handler_found = false; 246 247 /* 248 * If we are stepping a pending breakpoint, call the hw_breakpoint 249 * handler first. 250 */ 251 if (!reinstall_suspended_bps(regs)) 252 return 0; 253 254 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 255 handler_found = true; 256 257 if (!handler_found && user_mode(regs)) { 258 send_user_sigtrap(TRAP_TRACE); 259 260 /* 261 * ptrace will disable single step unless explicitly 262 * asked to re-enable it. For other clients, it makes 263 * sense to leave it enabled (i.e. rewind the controls 264 * to the active-not-pending state). 265 */ 266 user_rewind_single_step(current); 267 } else if (!handler_found) { 268 pr_warn("Unexpected kernel single-step exception at EL1\n"); 269 /* 270 * Re-enable stepping since we know that we will be 271 * returning to regs. 272 */ 273 set_regs_spsr_ss(regs); 274 } 275 276 return 0; 277 } 278 NOKPROBE_SYMBOL(single_step_handler); 279 280 static LIST_HEAD(user_break_hook); 281 static LIST_HEAD(kernel_break_hook); 282 283 void register_user_break_hook(struct break_hook *hook) 284 { 285 register_debug_hook(&hook->node, &user_break_hook); 286 } 287 288 void unregister_user_break_hook(struct break_hook *hook) 289 { 290 unregister_debug_hook(&hook->node); 291 } 292 293 void register_kernel_break_hook(struct break_hook *hook) 294 { 295 register_debug_hook(&hook->node, &kernel_break_hook); 296 } 297 298 void unregister_kernel_break_hook(struct break_hook *hook) 299 { 300 unregister_debug_hook(&hook->node); 301 } 302 303 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 304 { 305 struct break_hook *hook; 306 struct list_head *list; 307 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 308 309 list = user_mode(regs) ? &user_break_hook : &kernel_break_hook; 310 311 /* 312 * Since brk exception disables interrupt, this function is 313 * entirely not preemptible, and we can use rcu list safely here. 314 */ 315 list_for_each_entry_rcu(hook, list, node) { 316 unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK; 317 318 if ((comment & ~hook->mask) == hook->imm) 319 fn = hook->fn; 320 } 321 322 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 323 } 324 NOKPROBE_SYMBOL(call_break_hook); 325 326 static int brk_handler(unsigned long unused, unsigned int esr, 327 struct pt_regs *regs) 328 { 329 if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED) 330 return 0; 331 332 if (user_mode(regs)) { 333 send_user_sigtrap(TRAP_BRKPT); 334 } else { 335 pr_warn("Unexpected kernel BRK exception at EL1\n"); 336 return -EFAULT; 337 } 338 339 return 0; 340 } 341 NOKPROBE_SYMBOL(brk_handler); 342 343 int aarch32_break_handler(struct pt_regs *regs) 344 { 345 u32 arm_instr; 346 u16 thumb_instr; 347 bool bp = false; 348 void __user *pc = (void __user *)instruction_pointer(regs); 349 350 if (!compat_user_mode(regs)) 351 return -EFAULT; 352 353 if (compat_thumb_mode(regs)) { 354 /* get 16-bit Thumb instruction */ 355 __le16 instr; 356 get_user(instr, (__le16 __user *)pc); 357 thumb_instr = le16_to_cpu(instr); 358 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 359 /* get second half of 32-bit Thumb-2 instruction */ 360 get_user(instr, (__le16 __user *)(pc + 2)); 361 thumb_instr = le16_to_cpu(instr); 362 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 363 } else { 364 bp = thumb_instr == AARCH32_BREAK_THUMB; 365 } 366 } else { 367 /* 32-bit ARM instruction */ 368 __le32 instr; 369 get_user(instr, (__le32 __user *)pc); 370 arm_instr = le32_to_cpu(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 void __init debug_traps_init(void) 383 { 384 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 385 TRAP_TRACE, "single-step handler"); 386 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 387 TRAP_BRKPT, "ptrace BRK handler"); 388 } 389 390 /* Re-enable single step for syscall restarting. */ 391 void user_rewind_single_step(struct task_struct *task) 392 { 393 /* 394 * If single step is active for this thread, then set SPSR.SS 395 * to 1 to avoid returning to the active-pending state. 396 */ 397 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 398 set_regs_spsr_ss(task_pt_regs(task)); 399 } 400 NOKPROBE_SYMBOL(user_rewind_single_step); 401 402 void user_fastforward_single_step(struct task_struct *task) 403 { 404 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 405 clear_regs_spsr_ss(task_pt_regs(task)); 406 } 407 408 void user_regs_reset_single_step(struct user_pt_regs *regs, 409 struct task_struct *task) 410 { 411 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 412 set_user_regs_spsr_ss(regs); 413 else 414 clear_user_regs_spsr_ss(regs); 415 } 416 417 /* Kernel API */ 418 void kernel_enable_single_step(struct pt_regs *regs) 419 { 420 WARN_ON(!irqs_disabled()); 421 set_regs_spsr_ss(regs); 422 mdscr_write(mdscr_read() | DBG_MDSCR_SS); 423 enable_debug_monitors(DBG_ACTIVE_EL1); 424 } 425 NOKPROBE_SYMBOL(kernel_enable_single_step); 426 427 void kernel_disable_single_step(void) 428 { 429 WARN_ON(!irqs_disabled()); 430 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); 431 disable_debug_monitors(DBG_ACTIVE_EL1); 432 } 433 NOKPROBE_SYMBOL(kernel_disable_single_step); 434 435 int kernel_active_single_step(void) 436 { 437 WARN_ON(!irqs_disabled()); 438 return mdscr_read() & DBG_MDSCR_SS; 439 } 440 NOKPROBE_SYMBOL(kernel_active_single_step); 441 442 /* ptrace API */ 443 void user_enable_single_step(struct task_struct *task) 444 { 445 struct thread_info *ti = task_thread_info(task); 446 447 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) 448 set_regs_spsr_ss(task_pt_regs(task)); 449 } 450 NOKPROBE_SYMBOL(user_enable_single_step); 451 452 void user_disable_single_step(struct task_struct *task) 453 { 454 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 455 } 456 NOKPROBE_SYMBOL(user_disable_single_step); 457