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 37 /* Determine debug architecture. */ 38 u8 debug_monitors_arch(void) 39 { 40 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1), 41 ID_AA64DFR0_DEBUGVER_SHIFT); 42 } 43 44 /* 45 * MDSCR access routines. 46 */ 47 static void mdscr_write(u32 mdscr) 48 { 49 unsigned long flags; 50 flags = local_daif_save(); 51 write_sysreg(mdscr, mdscr_el1); 52 local_daif_restore(flags); 53 } 54 NOKPROBE_SYMBOL(mdscr_write); 55 56 static u32 mdscr_read(void) 57 { 58 return read_sysreg(mdscr_el1); 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 int clear_os_lock(unsigned int cpu) 136 { 137 write_sysreg(0, oslar_el1); 138 isb(); 139 return 0; 140 } 141 142 static int debug_monitors_init(void) 143 { 144 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING, 145 "arm64/debug_monitors:starting", 146 clear_os_lock, NULL); 147 } 148 postcore_initcall(debug_monitors_init); 149 150 /* 151 * Single step API and exception handling. 152 */ 153 static void set_regs_spsr_ss(struct pt_regs *regs) 154 { 155 regs->pstate |= DBG_SPSR_SS; 156 } 157 NOKPROBE_SYMBOL(set_regs_spsr_ss); 158 159 static void clear_regs_spsr_ss(struct pt_regs *regs) 160 { 161 regs->pstate &= ~DBG_SPSR_SS; 162 } 163 NOKPROBE_SYMBOL(clear_regs_spsr_ss); 164 165 /* EL1 Single Step Handler hooks */ 166 static LIST_HEAD(step_hook); 167 static DEFINE_SPINLOCK(step_hook_lock); 168 169 void register_step_hook(struct step_hook *hook) 170 { 171 spin_lock(&step_hook_lock); 172 list_add_rcu(&hook->node, &step_hook); 173 spin_unlock(&step_hook_lock); 174 } 175 176 void unregister_step_hook(struct step_hook *hook) 177 { 178 spin_lock(&step_hook_lock); 179 list_del_rcu(&hook->node); 180 spin_unlock(&step_hook_lock); 181 synchronize_rcu(); 182 } 183 184 /* 185 * Call registered single step handlers 186 * There is no Syndrome info to check for determining the handler. 187 * So we call all the registered handlers, until the right handler is 188 * found which returns zero. 189 */ 190 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 191 { 192 struct step_hook *hook; 193 int retval = DBG_HOOK_ERROR; 194 195 rcu_read_lock(); 196 197 list_for_each_entry_rcu(hook, &step_hook, node) { 198 retval = hook->fn(regs, esr); 199 if (retval == DBG_HOOK_HANDLED) 200 break; 201 } 202 203 rcu_read_unlock(); 204 205 return retval; 206 } 207 NOKPROBE_SYMBOL(call_step_hook); 208 209 static void send_user_sigtrap(int si_code) 210 { 211 struct pt_regs *regs = current_pt_regs(); 212 siginfo_t info; 213 214 clear_siginfo(&info); 215 info.si_signo = SIGTRAP; 216 info.si_errno = 0; 217 info.si_code = si_code; 218 info.si_addr = (void __user *)instruction_pointer(regs); 219 220 if (WARN_ON(!user_mode(regs))) 221 return; 222 223 if (interrupts_enabled(regs)) 224 local_irq_enable(); 225 226 force_sig_info(SIGTRAP, &info, current); 227 } 228 229 static int single_step_handler(unsigned long addr, unsigned int esr, 230 struct pt_regs *regs) 231 { 232 bool handler_found = false; 233 234 /* 235 * If we are stepping a pending breakpoint, call the hw_breakpoint 236 * handler first. 237 */ 238 if (!reinstall_suspended_bps(regs)) 239 return 0; 240 241 #ifdef CONFIG_KPROBES 242 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 243 handler_found = true; 244 #endif 245 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 246 handler_found = true; 247 248 if (!handler_found && user_mode(regs)) { 249 send_user_sigtrap(TRAP_TRACE); 250 251 /* 252 * ptrace will disable single step unless explicitly 253 * asked to re-enable it. For other clients, it makes 254 * sense to leave it enabled (i.e. rewind the controls 255 * to the active-not-pending state). 256 */ 257 user_rewind_single_step(current); 258 } else if (!handler_found) { 259 pr_warn("Unexpected kernel single-step exception at EL1\n"); 260 /* 261 * Re-enable stepping since we know that we will be 262 * returning to regs. 263 */ 264 set_regs_spsr_ss(regs); 265 } 266 267 return 0; 268 } 269 NOKPROBE_SYMBOL(single_step_handler); 270 271 /* 272 * Breakpoint handler is re-entrant as another breakpoint can 273 * hit within breakpoint handler, especically in kprobes. 274 * Use reader/writer locks instead of plain spinlock. 275 */ 276 static LIST_HEAD(break_hook); 277 static DEFINE_SPINLOCK(break_hook_lock); 278 279 void register_break_hook(struct break_hook *hook) 280 { 281 spin_lock(&break_hook_lock); 282 list_add_rcu(&hook->node, &break_hook); 283 spin_unlock(&break_hook_lock); 284 } 285 286 void unregister_break_hook(struct break_hook *hook) 287 { 288 spin_lock(&break_hook_lock); 289 list_del_rcu(&hook->node); 290 spin_unlock(&break_hook_lock); 291 synchronize_rcu(); 292 } 293 294 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 295 { 296 struct break_hook *hook; 297 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 298 299 rcu_read_lock(); 300 list_for_each_entry_rcu(hook, &break_hook, node) 301 if ((esr & hook->esr_mask) == hook->esr_val) 302 fn = hook->fn; 303 rcu_read_unlock(); 304 305 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 306 } 307 NOKPROBE_SYMBOL(call_break_hook); 308 309 static int brk_handler(unsigned long addr, unsigned int esr, 310 struct pt_regs *regs) 311 { 312 bool handler_found = false; 313 314 #ifdef CONFIG_KPROBES 315 if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) { 316 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED) 317 handler_found = true; 318 } 319 #endif 320 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED) 321 handler_found = true; 322 323 if (!handler_found && user_mode(regs)) { 324 send_user_sigtrap(TRAP_BRKPT); 325 } else if (!handler_found) { 326 pr_warn("Unexpected kernel BRK exception at EL1\n"); 327 return -EFAULT; 328 } 329 330 return 0; 331 } 332 NOKPROBE_SYMBOL(brk_handler); 333 334 int aarch32_break_handler(struct pt_regs *regs) 335 { 336 u32 arm_instr; 337 u16 thumb_instr; 338 bool bp = false; 339 void __user *pc = (void __user *)instruction_pointer(regs); 340 341 if (!compat_user_mode(regs)) 342 return -EFAULT; 343 344 if (compat_thumb_mode(regs)) { 345 /* get 16-bit Thumb instruction */ 346 __le16 instr; 347 get_user(instr, (__le16 __user *)pc); 348 thumb_instr = le16_to_cpu(instr); 349 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 350 /* get second half of 32-bit Thumb-2 instruction */ 351 get_user(instr, (__le16 __user *)(pc + 2)); 352 thumb_instr = le16_to_cpu(instr); 353 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 354 } else { 355 bp = thumb_instr == AARCH32_BREAK_THUMB; 356 } 357 } else { 358 /* 32-bit ARM instruction */ 359 __le32 instr; 360 get_user(instr, (__le32 __user *)pc); 361 arm_instr = le32_to_cpu(instr); 362 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM; 363 } 364 365 if (!bp) 366 return -EFAULT; 367 368 send_user_sigtrap(TRAP_BRKPT); 369 return 0; 370 } 371 NOKPROBE_SYMBOL(aarch32_break_handler); 372 373 static int __init debug_traps_init(void) 374 { 375 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, 376 TRAP_TRACE, "single-step handler"); 377 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, 378 TRAP_BRKPT, "ptrace BRK handler"); 379 return 0; 380 } 381 arch_initcall(debug_traps_init); 382 383 /* Re-enable single step for syscall restarting. */ 384 void user_rewind_single_step(struct task_struct *task) 385 { 386 /* 387 * If single step is active for this thread, then set SPSR.SS 388 * to 1 to avoid returning to the active-pending state. 389 */ 390 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 391 set_regs_spsr_ss(task_pt_regs(task)); 392 } 393 NOKPROBE_SYMBOL(user_rewind_single_step); 394 395 void user_fastforward_single_step(struct task_struct *task) 396 { 397 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) 398 clear_regs_spsr_ss(task_pt_regs(task)); 399 } 400 401 /* Kernel API */ 402 void kernel_enable_single_step(struct pt_regs *regs) 403 { 404 WARN_ON(!irqs_disabled()); 405 set_regs_spsr_ss(regs); 406 mdscr_write(mdscr_read() | DBG_MDSCR_SS); 407 enable_debug_monitors(DBG_ACTIVE_EL1); 408 } 409 NOKPROBE_SYMBOL(kernel_enable_single_step); 410 411 void kernel_disable_single_step(void) 412 { 413 WARN_ON(!irqs_disabled()); 414 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); 415 disable_debug_monitors(DBG_ACTIVE_EL1); 416 } 417 NOKPROBE_SYMBOL(kernel_disable_single_step); 418 419 int kernel_active_single_step(void) 420 { 421 WARN_ON(!irqs_disabled()); 422 return mdscr_read() & DBG_MDSCR_SS; 423 } 424 NOKPROBE_SYMBOL(kernel_active_single_step); 425 426 /* ptrace API */ 427 void user_enable_single_step(struct task_struct *task) 428 { 429 struct thread_info *ti = task_thread_info(task); 430 431 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) 432 set_regs_spsr_ss(task_pt_regs(task)); 433 } 434 NOKPROBE_SYMBOL(user_enable_single_step); 435 436 void user_disable_single_step(struct task_struct *task) 437 { 438 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 439 } 440 NOKPROBE_SYMBOL(user_disable_single_step); 441