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/debug-monitors.h> 34 #include <asm/system_misc.h> 35 36 /* Determine debug architecture. */ 37 u8 debug_monitors_arch(void) 38 { 39 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1), 40 ID_AA64DFR0_DEBUGVER_SHIFT); 41 } 42 43 /* 44 * MDSCR access routines. 45 */ 46 static void mdscr_write(u32 mdscr) 47 { 48 unsigned long flags; 49 local_dbg_save(flags); 50 write_sysreg(mdscr, mdscr_el1); 51 local_dbg_restore(flags); 52 } 53 NOKPROBE_SYMBOL(mdscr_write); 54 55 static u32 mdscr_read(void) 56 { 57 return read_sysreg(mdscr_el1); 58 } 59 NOKPROBE_SYMBOL(mdscr_read); 60 61 /* 62 * Allow root to disable self-hosted debug from userspace. 63 * This is useful if you want to connect an external JTAG debugger. 64 */ 65 static bool debug_enabled = true; 66 67 static int create_debug_debugfs_entry(void) 68 { 69 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled); 70 return 0; 71 } 72 fs_initcall(create_debug_debugfs_entry); 73 74 static int __init early_debug_disable(char *buf) 75 { 76 debug_enabled = false; 77 return 0; 78 } 79 80 early_param("nodebugmon", early_debug_disable); 81 82 /* 83 * Keep track of debug users on each core. 84 * The ref counts are per-cpu so we use a local_t type. 85 */ 86 static DEFINE_PER_CPU(int, mde_ref_count); 87 static DEFINE_PER_CPU(int, kde_ref_count); 88 89 void enable_debug_monitors(enum dbg_active_el el) 90 { 91 u32 mdscr, enable = 0; 92 93 WARN_ON(preemptible()); 94 95 if (this_cpu_inc_return(mde_ref_count) == 1) 96 enable = DBG_MDSCR_MDE; 97 98 if (el == DBG_ACTIVE_EL1 && 99 this_cpu_inc_return(kde_ref_count) == 1) 100 enable |= DBG_MDSCR_KDE; 101 102 if (enable && debug_enabled) { 103 mdscr = mdscr_read(); 104 mdscr |= enable; 105 mdscr_write(mdscr); 106 } 107 } 108 NOKPROBE_SYMBOL(enable_debug_monitors); 109 110 void disable_debug_monitors(enum dbg_active_el el) 111 { 112 u32 mdscr, disable = 0; 113 114 WARN_ON(preemptible()); 115 116 if (this_cpu_dec_return(mde_ref_count) == 0) 117 disable = ~DBG_MDSCR_MDE; 118 119 if (el == DBG_ACTIVE_EL1 && 120 this_cpu_dec_return(kde_ref_count) == 0) 121 disable &= ~DBG_MDSCR_KDE; 122 123 if (disable) { 124 mdscr = mdscr_read(); 125 mdscr &= disable; 126 mdscr_write(mdscr); 127 } 128 } 129 NOKPROBE_SYMBOL(disable_debug_monitors); 130 131 /* 132 * OS lock clearing. 133 */ 134 static int clear_os_lock(unsigned int cpu) 135 { 136 write_sysreg(0, oslar_el1); 137 isb(); 138 return 0; 139 } 140 141 static int debug_monitors_init(void) 142 { 143 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING, 144 "arm64/debug_monitors:starting", 145 clear_os_lock, NULL); 146 } 147 postcore_initcall(debug_monitors_init); 148 149 /* 150 * Single step API and exception handling. 151 */ 152 static void set_regs_spsr_ss(struct pt_regs *regs) 153 { 154 regs->pstate |= DBG_SPSR_SS; 155 } 156 NOKPROBE_SYMBOL(set_regs_spsr_ss); 157 158 static void clear_regs_spsr_ss(struct pt_regs *regs) 159 { 160 regs->pstate &= ~DBG_SPSR_SS; 161 } 162 NOKPROBE_SYMBOL(clear_regs_spsr_ss); 163 164 /* EL1 Single Step Handler hooks */ 165 static LIST_HEAD(step_hook); 166 static DEFINE_SPINLOCK(step_hook_lock); 167 168 void register_step_hook(struct step_hook *hook) 169 { 170 spin_lock(&step_hook_lock); 171 list_add_rcu(&hook->node, &step_hook); 172 spin_unlock(&step_hook_lock); 173 } 174 175 void unregister_step_hook(struct step_hook *hook) 176 { 177 spin_lock(&step_hook_lock); 178 list_del_rcu(&hook->node); 179 spin_unlock(&step_hook_lock); 180 synchronize_rcu(); 181 } 182 183 /* 184 * Call registered single step handlers 185 * There is no Syndrome info to check for determining the handler. 186 * So we call all the registered handlers, until the right handler is 187 * found which returns zero. 188 */ 189 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 190 { 191 struct step_hook *hook; 192 int retval = DBG_HOOK_ERROR; 193 194 rcu_read_lock(); 195 196 list_for_each_entry_rcu(hook, &step_hook, node) { 197 retval = hook->fn(regs, esr); 198 if (retval == DBG_HOOK_HANDLED) 199 break; 200 } 201 202 rcu_read_unlock(); 203 204 return retval; 205 } 206 NOKPROBE_SYMBOL(call_step_hook); 207 208 static void send_user_sigtrap(int si_code) 209 { 210 struct pt_regs *regs = current_pt_regs(); 211 siginfo_t info = { 212 .si_signo = SIGTRAP, 213 .si_errno = 0, 214 .si_code = si_code, 215 .si_addr = (void __user *)instruction_pointer(regs), 216 }; 217 218 if (WARN_ON(!user_mode(regs))) 219 return; 220 221 if (interrupts_enabled(regs)) 222 local_irq_enable(); 223 224 force_sig_info(SIGTRAP, &info, current); 225 } 226 227 static int single_step_handler(unsigned long addr, unsigned int esr, 228 struct pt_regs *regs) 229 { 230 bool handler_found = false; 231 232 /* 233 * If we are stepping a pending breakpoint, call the hw_breakpoint 234 * handler first. 235 */ 236 if (!reinstall_suspended_bps(regs)) 237 return 0; 238 239 #ifdef CONFIG_KPROBES 240 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 241 handler_found = true; 242 #endif 243 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 244 handler_found = true; 245 246 if (!handler_found && user_mode(regs)) { 247 send_user_sigtrap(TRAP_TRACE); 248 249 /* 250 * ptrace will disable single step unless explicitly 251 * asked to re-enable it. For other clients, it makes 252 * sense to leave it enabled (i.e. rewind the controls 253 * to the active-not-pending state). 254 */ 255 user_rewind_single_step(current); 256 } else if (!handler_found) { 257 pr_warn("Unexpected kernel single-step exception at EL1\n"); 258 /* 259 * Re-enable stepping since we know that we will be 260 * returning to regs. 261 */ 262 set_regs_spsr_ss(regs); 263 } 264 265 return 0; 266 } 267 NOKPROBE_SYMBOL(single_step_handler); 268 269 /* 270 * Breakpoint handler is re-entrant as another breakpoint can 271 * hit within breakpoint handler, especically in kprobes. 272 * Use reader/writer locks instead of plain spinlock. 273 */ 274 static LIST_HEAD(break_hook); 275 static DEFINE_SPINLOCK(break_hook_lock); 276 277 void register_break_hook(struct break_hook *hook) 278 { 279 spin_lock(&break_hook_lock); 280 list_add_rcu(&hook->node, &break_hook); 281 spin_unlock(&break_hook_lock); 282 } 283 284 void unregister_break_hook(struct break_hook *hook) 285 { 286 spin_lock(&break_hook_lock); 287 list_del_rcu(&hook->node); 288 spin_unlock(&break_hook_lock); 289 synchronize_rcu(); 290 } 291 292 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 293 { 294 struct break_hook *hook; 295 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 296 297 rcu_read_lock(); 298 list_for_each_entry_rcu(hook, &break_hook, node) 299 if ((esr & hook->esr_mask) == hook->esr_val) 300 fn = hook->fn; 301 rcu_read_unlock(); 302 303 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 304 } 305 NOKPROBE_SYMBOL(call_break_hook); 306 307 static int brk_handler(unsigned long addr, unsigned int esr, 308 struct pt_regs *regs) 309 { 310 bool handler_found = false; 311 312 #ifdef CONFIG_KPROBES 313 if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) { 314 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED) 315 handler_found = true; 316 } 317 #endif 318 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED) 319 handler_found = true; 320 321 if (!handler_found && user_mode(regs)) { 322 send_user_sigtrap(TRAP_BRKPT); 323 } else if (!handler_found) { 324 pr_warn("Unexpected kernel BRK exception at EL1\n"); 325 return -EFAULT; 326 } 327 328 return 0; 329 } 330 NOKPROBE_SYMBOL(brk_handler); 331 332 int aarch32_break_handler(struct pt_regs *regs) 333 { 334 u32 arm_instr; 335 u16 thumb_instr; 336 bool bp = false; 337 void __user *pc = (void __user *)instruction_pointer(regs); 338 339 if (!compat_user_mode(regs)) 340 return -EFAULT; 341 342 if (compat_thumb_mode(regs)) { 343 /* get 16-bit Thumb instruction */ 344 get_user(thumb_instr, (u16 __user *)pc); 345 thumb_instr = le16_to_cpu(thumb_instr); 346 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 347 /* get second half of 32-bit Thumb-2 instruction */ 348 get_user(thumb_instr, (u16 __user *)(pc + 2)); 349 thumb_instr = le16_to_cpu(thumb_instr); 350 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 351 } else { 352 bp = thumb_instr == AARCH32_BREAK_THUMB; 353 } 354 } else { 355 /* 32-bit ARM instruction */ 356 get_user(arm_instr, (u32 __user *)pc); 357 arm_instr = le32_to_cpu(arm_instr); 358 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM; 359 } 360 361 if (!bp) 362 return -EFAULT; 363 364 send_user_sigtrap(TRAP_BRKPT); 365 return 0; 366 } 367 NOKPROBE_SYMBOL(aarch32_break_handler); 368 369 static int __init debug_traps_init(void) 370 { 371 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 372 TRAP_TRACE, "single-step handler"); 373 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 374 TRAP_BRKPT, "ptrace BRK handler"); 375 return 0; 376 } 377 arch_initcall(debug_traps_init); 378 379 /* Re-enable single step for syscall restarting. */ 380 void user_rewind_single_step(struct task_struct *task) 381 { 382 /* 383 * If single step is active for this thread, then set SPSR.SS 384 * to 1 to avoid returning to the active-pending state. 385 */ 386 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 387 set_regs_spsr_ss(task_pt_regs(task)); 388 } 389 NOKPROBE_SYMBOL(user_rewind_single_step); 390 391 void user_fastforward_single_step(struct task_struct *task) 392 { 393 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 394 clear_regs_spsr_ss(task_pt_regs(task)); 395 } 396 397 /* Kernel API */ 398 void kernel_enable_single_step(struct pt_regs *regs) 399 { 400 WARN_ON(!irqs_disabled()); 401 set_regs_spsr_ss(regs); 402 mdscr_write(mdscr_read() | DBG_MDSCR_SS); 403 enable_debug_monitors(DBG_ACTIVE_EL1); 404 } 405 NOKPROBE_SYMBOL(kernel_enable_single_step); 406 407 void kernel_disable_single_step(void) 408 { 409 WARN_ON(!irqs_disabled()); 410 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); 411 disable_debug_monitors(DBG_ACTIVE_EL1); 412 } 413 NOKPROBE_SYMBOL(kernel_disable_single_step); 414 415 int kernel_active_single_step(void) 416 { 417 WARN_ON(!irqs_disabled()); 418 return mdscr_read() & DBG_MDSCR_SS; 419 } 420 NOKPROBE_SYMBOL(kernel_active_single_step); 421 422 /* ptrace API */ 423 void user_enable_single_step(struct task_struct *task) 424 { 425 struct thread_info *ti = task_thread_info(task); 426 427 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) 428 set_regs_spsr_ss(task_pt_regs(task)); 429 } 430 NOKPROBE_SYMBOL(user_enable_single_step); 431 432 void user_disable_single_step(struct task_struct *task) 433 { 434 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 435 } 436 NOKPROBE_SYMBOL(user_disable_single_step); 437