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