1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * ARMv8 single-step debug support and mdscr context switching. 4 * 5 * Copyright (C) 2012 ARM Limited 6 * 7 * Author: Will Deacon <will.deacon@arm.com> 8 */ 9 10 #include <linux/cpu.h> 11 #include <linux/debugfs.h> 12 #include <linux/hardirq.h> 13 #include <linux/init.h> 14 #include <linux/ptrace.h> 15 #include <linux/kprobes.h> 16 #include <linux/stat.h> 17 #include <linux/uaccess.h> 18 #include <linux/sched/task_stack.h> 19 20 #include <asm/cpufeature.h> 21 #include <asm/cputype.h> 22 #include <asm/daifflags.h> 23 #include <asm/debug-monitors.h> 24 #include <asm/exception.h> 25 #include <asm/kgdb.h> 26 #include <asm/kprobes.h> 27 #include <asm/system_misc.h> 28 #include <asm/traps.h> 29 #include <asm/uprobes.h> 30 31 /* Determine debug architecture. */ 32 u8 debug_monitors_arch(void) 33 { 34 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1), 35 ID_AA64DFR0_EL1_DebugVer_SHIFT); 36 } 37 38 /* 39 * MDSCR access routines. 40 */ 41 static void mdscr_write(u64 mdscr) 42 { 43 unsigned long flags; 44 flags = local_daif_save(); 45 write_sysreg(mdscr, mdscr_el1); 46 local_daif_restore(flags); 47 } 48 NOKPROBE_SYMBOL(mdscr_write); 49 50 static u64 mdscr_read(void) 51 { 52 return read_sysreg(mdscr_el1); 53 } 54 NOKPROBE_SYMBOL(mdscr_read); 55 56 /* 57 * Allow root to disable self-hosted debug from userspace. 58 * This is useful if you want to connect an external JTAG debugger. 59 */ 60 static bool debug_enabled = true; 61 62 static int create_debug_debugfs_entry(void) 63 { 64 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled); 65 return 0; 66 } 67 fs_initcall(create_debug_debugfs_entry); 68 69 static int __init early_debug_disable(char *buf) 70 { 71 debug_enabled = false; 72 return 0; 73 } 74 75 early_param("nodebugmon", early_debug_disable); 76 77 /* 78 * Keep track of debug users on each core. 79 * The ref counts are per-cpu so we use a local_t type. 80 */ 81 static DEFINE_PER_CPU(int, mde_ref_count); 82 static DEFINE_PER_CPU(int, kde_ref_count); 83 84 void enable_debug_monitors(enum dbg_active_el el) 85 { 86 u64 mdscr, enable = 0; 87 88 WARN_ON(preemptible()); 89 90 if (this_cpu_inc_return(mde_ref_count) == 1) 91 enable = MDSCR_EL1_MDE; 92 93 if (el == DBG_ACTIVE_EL1 && 94 this_cpu_inc_return(kde_ref_count) == 1) 95 enable |= MDSCR_EL1_KDE; 96 97 if (enable && debug_enabled) { 98 mdscr = mdscr_read(); 99 mdscr |= enable; 100 mdscr_write(mdscr); 101 } 102 } 103 NOKPROBE_SYMBOL(enable_debug_monitors); 104 105 void disable_debug_monitors(enum dbg_active_el el) 106 { 107 u64 mdscr, disable = 0; 108 109 WARN_ON(preemptible()); 110 111 if (this_cpu_dec_return(mde_ref_count) == 0) 112 disable = ~MDSCR_EL1_MDE; 113 114 if (el == DBG_ACTIVE_EL1 && 115 this_cpu_dec_return(kde_ref_count) == 0) 116 disable &= ~MDSCR_EL1_KDE; 117 118 if (disable) { 119 mdscr = mdscr_read(); 120 mdscr &= disable; 121 mdscr_write(mdscr); 122 } 123 } 124 NOKPROBE_SYMBOL(disable_debug_monitors); 125 126 /* 127 * OS lock clearing. 128 */ 129 static int clear_os_lock(unsigned int cpu) 130 { 131 write_sysreg(0, osdlr_el1); 132 write_sysreg(0, oslar_el1); 133 isb(); 134 return 0; 135 } 136 137 static int __init debug_monitors_init(void) 138 { 139 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING, 140 "arm64/debug_monitors:starting", 141 clear_os_lock, NULL); 142 } 143 postcore_initcall(debug_monitors_init); 144 145 /* 146 * Single step API and exception handling. 147 */ 148 static void set_user_regs_spsr_ss(struct user_pt_regs *regs) 149 { 150 regs->pstate |= DBG_SPSR_SS; 151 } 152 NOKPROBE_SYMBOL(set_user_regs_spsr_ss); 153 154 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs) 155 { 156 regs->pstate &= ~DBG_SPSR_SS; 157 } 158 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss); 159 160 #define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs) 161 #define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs) 162 163 static void send_user_sigtrap(int si_code) 164 { 165 struct pt_regs *regs = current_pt_regs(); 166 167 if (WARN_ON(!user_mode(regs))) 168 return; 169 170 if (interrupts_enabled(regs)) 171 local_irq_enable(); 172 173 arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs), 174 "User debug trap"); 175 } 176 177 /* 178 * We have already unmasked interrupts and enabled preemption 179 * when calling do_el0_softstep() from entry-common.c. 180 */ 181 void do_el0_softstep(unsigned long esr, struct pt_regs *regs) 182 { 183 if (uprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 184 return; 185 186 send_user_sigtrap(TRAP_TRACE); 187 /* 188 * ptrace will disable single step unless explicitly 189 * asked to re-enable it. For other clients, it makes 190 * sense to leave it enabled (i.e. rewind the controls 191 * to the active-not-pending state). 192 */ 193 user_rewind_single_step(current); 194 } 195 196 void do_el1_softstep(unsigned long esr, struct pt_regs *regs) 197 { 198 if (kgdb_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) 199 return; 200 201 pr_warn("Unexpected kernel single-step exception at EL1\n"); 202 /* 203 * Re-enable stepping since we know that we will be 204 * returning to regs. 205 */ 206 set_regs_spsr_ss(regs); 207 } 208 NOKPROBE_SYMBOL(do_el1_softstep); 209 210 static int call_el1_break_hook(struct pt_regs *regs, unsigned long esr) 211 { 212 if (esr_brk_comment(esr) == BUG_BRK_IMM) 213 return bug_brk_handler(regs, esr); 214 215 if (IS_ENABLED(CONFIG_CFI_CLANG) && esr_is_cfi_brk(esr)) 216 return cfi_brk_handler(regs, esr); 217 218 if (esr_brk_comment(esr) == FAULT_BRK_IMM) 219 return reserved_fault_brk_handler(regs, esr); 220 221 if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && 222 (esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM) 223 return kasan_brk_handler(regs, esr); 224 225 if (IS_ENABLED(CONFIG_UBSAN_TRAP) && esr_is_ubsan_brk(esr)) 226 return ubsan_brk_handler(regs, esr); 227 228 if (IS_ENABLED(CONFIG_KGDB)) { 229 if (esr_brk_comment(esr) == KGDB_DYN_DBG_BRK_IMM) 230 return kgdb_brk_handler(regs, esr); 231 if (esr_brk_comment(esr) == KGDB_COMPILED_DBG_BRK_IMM) 232 return kgdb_compiled_brk_handler(regs, esr); 233 } 234 235 if (IS_ENABLED(CONFIG_KPROBES)) { 236 if (esr_brk_comment(esr) == KPROBES_BRK_IMM) 237 return kprobe_brk_handler(regs, esr); 238 if (esr_brk_comment(esr) == KPROBES_BRK_SS_IMM) 239 return kprobe_ss_brk_handler(regs, esr); 240 } 241 242 if (IS_ENABLED(CONFIG_KRETPROBES) && 243 esr_brk_comment(esr) == KRETPROBES_BRK_IMM) 244 return kretprobe_brk_handler(regs, esr); 245 246 return DBG_HOOK_ERROR; 247 } 248 NOKPROBE_SYMBOL(call_el1_break_hook); 249 250 /* 251 * We have already unmasked interrupts and enabled preemption 252 * when calling do_el0_brk64() from entry-common.c. 253 */ 254 void do_el0_brk64(unsigned long esr, struct pt_regs *regs) 255 { 256 if (IS_ENABLED(CONFIG_UPROBES) && 257 esr_brk_comment(esr) == UPROBES_BRK_IMM && 258 uprobe_brk_handler(regs, esr) == DBG_HOOK_HANDLED) 259 return; 260 261 send_user_sigtrap(TRAP_BRKPT); 262 } 263 264 void do_el1_brk64(unsigned long esr, struct pt_regs *regs) 265 { 266 if (call_el1_break_hook(regs, esr) == DBG_HOOK_HANDLED) 267 return; 268 269 die("Oops - BRK", regs, esr); 270 } 271 NOKPROBE_SYMBOL(do_el1_brk64); 272 273 #ifdef CONFIG_COMPAT 274 void do_bkpt32(unsigned long esr, struct pt_regs *regs) 275 { 276 arm64_notify_die("aarch32 BKPT", regs, SIGTRAP, TRAP_BRKPT, regs->pc, esr); 277 } 278 #endif /* CONFIG_COMPAT */ 279 280 bool try_handle_aarch32_break(struct pt_regs *regs) 281 { 282 u32 arm_instr; 283 u16 thumb_instr; 284 bool bp = false; 285 void __user *pc = (void __user *)instruction_pointer(regs); 286 287 if (!compat_user_mode(regs)) 288 return false; 289 290 if (compat_thumb_mode(regs)) { 291 /* get 16-bit Thumb instruction */ 292 __le16 instr; 293 get_user(instr, (__le16 __user *)pc); 294 thumb_instr = le16_to_cpu(instr); 295 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) { 296 /* get second half of 32-bit Thumb-2 instruction */ 297 get_user(instr, (__le16 __user *)(pc + 2)); 298 thumb_instr = le16_to_cpu(instr); 299 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI; 300 } else { 301 bp = thumb_instr == AARCH32_BREAK_THUMB; 302 } 303 } else { 304 /* 32-bit ARM instruction */ 305 __le32 instr; 306 get_user(instr, (__le32 __user *)pc); 307 arm_instr = le32_to_cpu(instr); 308 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM; 309 } 310 311 if (!bp) 312 return false; 313 314 send_user_sigtrap(TRAP_BRKPT); 315 return true; 316 } 317 NOKPROBE_SYMBOL(try_handle_aarch32_break); 318 319 /* Re-enable single step for syscall restarting. */ 320 void user_rewind_single_step(struct task_struct *task) 321 { 322 /* 323 * If single step is active for this thread, then set SPSR.SS 324 * to 1 to avoid returning to the active-pending state. 325 */ 326 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 327 set_regs_spsr_ss(task_pt_regs(task)); 328 } 329 NOKPROBE_SYMBOL(user_rewind_single_step); 330 331 void user_fastforward_single_step(struct task_struct *task) 332 { 333 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 334 clear_regs_spsr_ss(task_pt_regs(task)); 335 } 336 337 void user_regs_reset_single_step(struct user_pt_regs *regs, 338 struct task_struct *task) 339 { 340 if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) 341 set_user_regs_spsr_ss(regs); 342 else 343 clear_user_regs_spsr_ss(regs); 344 } 345 346 /* Kernel API */ 347 void kernel_enable_single_step(struct pt_regs *regs) 348 { 349 WARN_ON(!irqs_disabled()); 350 set_regs_spsr_ss(regs); 351 mdscr_write(mdscr_read() | MDSCR_EL1_SS); 352 enable_debug_monitors(DBG_ACTIVE_EL1); 353 } 354 NOKPROBE_SYMBOL(kernel_enable_single_step); 355 356 void kernel_disable_single_step(void) 357 { 358 WARN_ON(!irqs_disabled()); 359 mdscr_write(mdscr_read() & ~MDSCR_EL1_SS); 360 disable_debug_monitors(DBG_ACTIVE_EL1); 361 } 362 NOKPROBE_SYMBOL(kernel_disable_single_step); 363 364 int kernel_active_single_step(void) 365 { 366 WARN_ON(!irqs_disabled()); 367 return mdscr_read() & MDSCR_EL1_SS; 368 } 369 NOKPROBE_SYMBOL(kernel_active_single_step); 370 371 void kernel_rewind_single_step(struct pt_regs *regs) 372 { 373 set_regs_spsr_ss(regs); 374 } 375 376 void kernel_fastforward_single_step(struct pt_regs *regs) 377 { 378 clear_regs_spsr_ss(regs); 379 } 380 381 /* ptrace API */ 382 void user_enable_single_step(struct task_struct *task) 383 { 384 struct thread_info *ti = task_thread_info(task); 385 386 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) 387 set_regs_spsr_ss(task_pt_regs(task)); 388 } 389 NOKPROBE_SYMBOL(user_enable_single_step); 390 391 void user_disable_single_step(struct task_struct *task) 392 { 393 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); 394 } 395 NOKPROBE_SYMBOL(user_disable_single_step); 396