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 /* EL1 Single Step Handler hooks */ 167 static LIST_HEAD(step_hook); 168 static DEFINE_SPINLOCK(step_hook_lock); 169 170 void register_step_hook(struct step_hook *hook) 171 { 172 spin_lock(&step_hook_lock); 173 list_add_rcu(&hook->node, &step_hook); 174 spin_unlock(&step_hook_lock); 175 } 176 177 void unregister_step_hook(struct step_hook *hook) 178 { 179 spin_lock(&step_hook_lock); 180 list_del_rcu(&hook->node); 181 spin_unlock(&step_hook_lock); 182 synchronize_rcu(); 183 } 184 185 /* 186 * Call registered single step handlers 187 * There is no Syndrome info to check for determining the handler. 188 * So we call all the registered handlers, until the right handler is 189 * found which returns zero. 190 */ 191 static int call_step_hook(struct pt_regs *regs, unsigned int esr) 192 { 193 struct step_hook *hook; 194 int retval = DBG_HOOK_ERROR; 195 196 rcu_read_lock(); 197 198 list_for_each_entry_rcu(hook, &step_hook, node) { 199 retval = hook->fn(regs, esr); 200 if (retval == DBG_HOOK_HANDLED) 201 break; 202 } 203 204 rcu_read_unlock(); 205 206 return retval; 207 } 208 NOKPROBE_SYMBOL(call_step_hook); 209 210 static void send_user_sigtrap(int si_code) 211 { 212 struct pt_regs *regs = current_pt_regs(); 213 214 if (WARN_ON(!user_mode(regs))) 215 return; 216 217 if (interrupts_enabled(regs)) 218 local_irq_enable(); 219 220 arm64_force_sig_fault(SIGTRAP, si_code, 221 (void __user *)instruction_pointer(regs), 222 "User debug trap"); 223 } 224 225 static int single_step_handler(unsigned long addr, unsigned int esr, 226 struct pt_regs *regs) 227 { 228 bool handler_found = false; 229 230 /* 231 * If we are stepping a pending breakpoint, call the hw_breakpoint 232 * handler first. 233 */ 234 if (!reinstall_suspended_bps(regs)) 235 return 0; 236 237 #ifdef CONFIG_KPROBES 238 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 239 handler_found = true; 240 #endif 241 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) 242 handler_found = true; 243 244 if (!handler_found && user_mode(regs)) { 245 send_user_sigtrap(TRAP_TRACE); 246 247 /* 248 * ptrace will disable single step unless explicitly 249 * asked to re-enable it. For other clients, it makes 250 * sense to leave it enabled (i.e. rewind the controls 251 * to the active-not-pending state). 252 */ 253 user_rewind_single_step(current); 254 } else if (!handler_found) { 255 pr_warn("Unexpected kernel single-step exception at EL1\n"); 256 /* 257 * Re-enable stepping since we know that we will be 258 * returning to regs. 259 */ 260 set_regs_spsr_ss(regs); 261 } 262 263 return 0; 264 } 265 NOKPROBE_SYMBOL(single_step_handler); 266 267 /* 268 * Breakpoint handler is re-entrant as another breakpoint can 269 * hit within breakpoint handler, especically in kprobes. 270 * Use reader/writer locks instead of plain spinlock. 271 */ 272 static LIST_HEAD(break_hook); 273 static DEFINE_SPINLOCK(break_hook_lock); 274 275 void register_break_hook(struct break_hook *hook) 276 { 277 spin_lock(&break_hook_lock); 278 list_add_rcu(&hook->node, &break_hook); 279 spin_unlock(&break_hook_lock); 280 } 281 282 void unregister_break_hook(struct break_hook *hook) 283 { 284 spin_lock(&break_hook_lock); 285 list_del_rcu(&hook->node); 286 spin_unlock(&break_hook_lock); 287 synchronize_rcu(); 288 } 289 290 static int call_break_hook(struct pt_regs *regs, unsigned int esr) 291 { 292 struct break_hook *hook; 293 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL; 294 295 rcu_read_lock(); 296 list_for_each_entry_rcu(hook, &break_hook, node) 297 if ((esr & hook->esr_mask) == hook->esr_val) 298 fn = hook->fn; 299 rcu_read_unlock(); 300 301 return fn ? fn(regs, esr) : DBG_HOOK_ERROR; 302 } 303 NOKPROBE_SYMBOL(call_break_hook); 304 305 static int brk_handler(unsigned long addr, unsigned int esr, 306 struct pt_regs *regs) 307 { 308 bool handler_found = false; 309 310 #ifdef CONFIG_KPROBES 311 if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) { 312 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED) 313 handler_found = true; 314 } 315 #endif 316 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED) 317 handler_found = true; 318 319 if (!handler_found && user_mode(regs)) { 320 send_user_sigtrap(TRAP_BRKPT); 321 } else if (!handler_found) { 322 pr_warn("Unexpected kernel BRK exception at EL1\n"); 323 return -EFAULT; 324 } 325 326 return 0; 327 } 328 NOKPROBE_SYMBOL(brk_handler); 329 330 int aarch32_break_handler(struct pt_regs *regs) 331 { 332 u32 arm_instr; 333 u16 thumb_instr; 334 bool bp = false; 335 void __user *pc = (void __user *)instruction_pointer(regs); 336 337 if (!compat_user_mode(regs)) 338 return -EFAULT; 339 340 if (compat_thumb_mode(regs)) { 341 /* get 16-bit Thumb instruction */ 342 __le16 instr; 343 get_user(instr, (__le16 __user *)pc); 344 thumb_instr = le16_to_cpu(instr); 345 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 346 /* get second half of 32-bit Thumb-2 instruction */ 347 get_user(instr, (__le16 __user *)(pc + 2)); 348 thumb_instr = le16_to_cpu(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 __le32 instr; 356 get_user(instr, (__le32 __user *)pc); 357 arm_instr = le32_to_cpu(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