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 static DEFINE_SPINLOCK(debug_hook_lock); 167 static LIST_HEAD(user_step_hook); 168 static LIST_HEAD(kernel_step_hook); 169 170 static void register_debug_hook(struct list_head *node, struct list_head *list) 171 { 172 spin_lock(&debug_hook_lock); 173 list_add_rcu(node, list); 174 spin_unlock(&debug_hook_lock); 175 176 } 177 178 static void unregister_debug_hook(struct list_head *node) 179 { 180 spin_lock(&debug_hook_lock); 181 list_del_rcu(node); 182 spin_unlock(&debug_hook_lock); 183 synchronize_rcu(); 184 } 185 186 void register_user_step_hook(struct step_hook *hook) 187 { 188 register_debug_hook(&hook->node, &user_step_hook); 189 } 190 191 void unregister_user_step_hook(struct step_hook *hook) 192 { 193 unregister_debug_hook(&hook->node); 194 } 195 196 void register_kernel_step_hook(struct step_hook *hook) 197 { 198 register_debug_hook(&hook->node, &kernel_step_hook); 199 } 200 201 void unregister_kernel_step_hook(struct step_hook *hook) 202 { 203 unregister_debug_hook(&hook->node); 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 struct list_head *list; 216 int retval = DBG_HOOK_ERROR; 217 218 list = user_mode(regs) ? &user_step_hook : &kernel_step_hook; 219 220 rcu_read_lock(); 221 222 list_for_each_entry_rcu(hook, list, node) { 223 retval = hook->fn(regs, esr); 224 if (retval == DBG_HOOK_HANDLED) 225 break; 226 } 227 228 rcu_read_unlock(); 229 230 return retval; 231 } 232 NOKPROBE_SYMBOL(call_step_hook); 233 234 static void send_user_sigtrap(int si_code) 235 { 236 struct pt_regs *regs = current_pt_regs(); 237 238 if (WARN_ON(!user_mode(regs))) 239 return; 240 241 if (interrupts_enabled(regs)) 242 local_irq_enable(); 243 244 arm64_force_sig_fault(SIGTRAP, si_code, 245 (void __user *)instruction_pointer(regs), 246 "User debug trap"); 247 } 248 249 static int single_step_handler(unsigned long unused, unsigned int esr, 250 struct pt_regs *regs) 251 { 252 bool handler_found = false; 253 254 /* 255 * If we are stepping a pending breakpoint, call the hw_breakpoint 256 * handler first. 257 */ 258 if (!reinstall_suspended_bps(regs)) 259 return 0; 260 261 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 262 handler_found = true; 263 264 if (!handler_found && user_mode(regs)) { 265 send_user_sigtrap(TRAP_TRACE); 266 267 /* 268 * ptrace will disable single step unless explicitly 269 * asked to re-enable it. For other clients, it makes 270 * sense to leave it enabled (i.e. rewind the controls 271 * to the active-not-pending state). 272 */ 273 user_rewind_single_step(current); 274 } else if (!handler_found) { 275 pr_warn("Unexpected kernel single-step exception at EL1\n"); 276 /* 277 * Re-enable stepping since we know that we will be 278 * returning to regs. 279 */ 280 set_regs_spsr_ss(regs); 281 } 282 283 return 0; 284 } 285 NOKPROBE_SYMBOL(single_step_handler); 286 287 static LIST_HEAD(user_break_hook); 288 static LIST_HEAD(kernel_break_hook); 289 290 void register_user_break_hook(struct break_hook *hook) 291 { 292 register_debug_hook(&hook->node, &user_break_hook); 293 } 294 295 void unregister_user_break_hook(struct break_hook *hook) 296 { 297 unregister_debug_hook(&hook->node); 298 } 299 300 void register_kernel_break_hook(struct break_hook *hook) 301 { 302 register_debug_hook(&hook->node, &kernel_break_hook); 303 } 304 305 void unregister_kernel_break_hook(struct break_hook *hook) 306 { 307 unregister_debug_hook(&hook->node); 308 } 309 310 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 311 { 312 struct break_hook *hook; 313 struct list_head *list; 314 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 315 316 list = user_mode(regs) ? &user_break_hook : &kernel_break_hook; 317 318 rcu_read_lock(); 319 list_for_each_entry_rcu(hook, list, node) { 320 unsigned int comment = esr & BRK64_ESR_MASK; 321 322 if ((comment & ~hook->mask) == hook->imm) 323 fn = hook->fn; 324 } 325 rcu_read_unlock(); 326 327 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 328 } 329 NOKPROBE_SYMBOL(call_break_hook); 330 331 static int brk_handler(unsigned long unused, unsigned int esr, 332 struct pt_regs *regs) 333 { 334 bool handler_found = false; 335 336 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED) 337 handler_found = true; 338 339 if (!handler_found && user_mode(regs)) { 340 send_user_sigtrap(TRAP_BRKPT); 341 } else if (!handler_found) { 342 pr_warn("Unexpected kernel BRK exception at EL1\n"); 343 return -EFAULT; 344 } 345 346 return 0; 347 } 348 NOKPROBE_SYMBOL(brk_handler); 349 350 int aarch32_break_handler(struct pt_regs *regs) 351 { 352 u32 arm_instr; 353 u16 thumb_instr; 354 bool bp = false; 355 void __user *pc = (void __user *)instruction_pointer(regs); 356 357 if (!compat_user_mode(regs)) 358 return -EFAULT; 359 360 if (compat_thumb_mode(regs)) { 361 /* get 16-bit Thumb instruction */ 362 __le16 instr; 363 get_user(instr, (__le16 __user *)pc); 364 thumb_instr = le16_to_cpu(instr); 365 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 366 /* get second half of 32-bit Thumb-2 instruction */ 367 get_user(instr, (__le16 __user *)(pc + 2)); 368 thumb_instr = le16_to_cpu(instr); 369 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 370 } else { 371 bp = thumb_instr == AARCH32_BREAK_THUMB; 372 } 373 } else { 374 /* 32-bit ARM instruction */ 375 __le32 instr; 376 get_user(instr, (__le32 __user *)pc); 377 arm_instr = le32_to_cpu(instr); 378 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM; 379 } 380 381 if (!bp) 382 return -EFAULT; 383 384 send_user_sigtrap(TRAP_BRKPT); 385 return 0; 386 } 387 NOKPROBE_SYMBOL(aarch32_break_handler); 388 389 static int __init debug_traps_init(void) 390 { 391 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 392 TRAP_TRACE, "single-step handler"); 393 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 394 TRAP_BRKPT, "ptrace BRK handler"); 395 return 0; 396 } 397 arch_initcall(debug_traps_init); 398 399 /* Re-enable single step for syscall restarting. */ 400 void user_rewind_single_step(struct task_struct *task) 401 { 402 /* 403 * If single step is active for this thread, then set SPSR.SS 404 * to 1 to avoid returning to the active-pending state. 405 */ 406 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 407 set_regs_spsr_ss(task_pt_regs(task)); 408 } 409 NOKPROBE_SYMBOL(user_rewind_single_step); 410 411 void user_fastforward_single_step(struct task_struct *task) 412 { 413 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 414 clear_regs_spsr_ss(task_pt_regs(task)); 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