1 // SPDX-License-Identifier: GPL-2.0 2 3 #include <linux/context_tracking.h> 4 #include <linux/entry-common.h> 5 #include <linux/livepatch.h> 6 #include <linux/audit.h> 7 8 #define CREATE_TRACE_POINTS 9 #include <trace/events/syscalls.h> 10 11 /** 12 * enter_from_user_mode - Establish state when coming from user mode 13 * 14 * Syscall/interrupt entry disables interrupts, but user mode is traced as 15 * interrupts enabled. Also with NO_HZ_FULL RCU might be idle. 16 * 17 * 1) Tell lockdep that interrupts are disabled 18 * 2) Invoke context tracking if enabled to reactivate RCU 19 * 3) Trace interrupts off state 20 */ 21 static __always_inline void enter_from_user_mode(struct pt_regs *regs) 22 { 23 arch_check_user_regs(regs); 24 lockdep_hardirqs_off(CALLER_ADDR0); 25 26 CT_WARN_ON(ct_state() != CONTEXT_USER); 27 user_exit_irqoff(); 28 29 instrumentation_begin(); 30 trace_hardirqs_off_finish(); 31 instrumentation_end(); 32 } 33 34 static inline void syscall_enter_audit(struct pt_regs *regs, long syscall) 35 { 36 if (unlikely(audit_context())) { 37 unsigned long args[6]; 38 39 syscall_get_arguments(current, regs, args); 40 audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]); 41 } 42 } 43 44 static long syscall_trace_enter(struct pt_regs *regs, long syscall, 45 unsigned long ti_work) 46 { 47 long ret = 0; 48 49 /* Handle ptrace */ 50 if (ti_work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) { 51 ret = arch_syscall_enter_tracehook(regs); 52 if (ret || (ti_work & _TIF_SYSCALL_EMU)) 53 return -1L; 54 } 55 56 /* Do seccomp after ptrace, to catch any tracer changes. */ 57 if (ti_work & _TIF_SECCOMP) { 58 ret = __secure_computing(NULL); 59 if (ret == -1L) 60 return ret; 61 } 62 63 /* Either of the above might have changed the syscall number */ 64 syscall = syscall_get_nr(current, regs); 65 66 if (unlikely(ti_work & _TIF_SYSCALL_TRACEPOINT)) 67 trace_sys_enter(regs, syscall); 68 69 syscall_enter_audit(regs, syscall); 70 71 return ret ? : syscall; 72 } 73 74 static __always_inline long 75 __syscall_enter_from_user_work(struct pt_regs *regs, long syscall) 76 { 77 unsigned long ti_work; 78 79 ti_work = READ_ONCE(current_thread_info()->flags); 80 if (ti_work & SYSCALL_ENTER_WORK) 81 syscall = syscall_trace_enter(regs, syscall, ti_work); 82 83 return syscall; 84 } 85 86 long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall) 87 { 88 return __syscall_enter_from_user_work(regs, syscall); 89 } 90 91 noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall) 92 { 93 long ret; 94 95 enter_from_user_mode(regs); 96 97 instrumentation_begin(); 98 local_irq_enable(); 99 ret = __syscall_enter_from_user_work(regs, syscall); 100 instrumentation_end(); 101 102 return ret; 103 } 104 105 noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs) 106 { 107 enter_from_user_mode(regs); 108 instrumentation_begin(); 109 local_irq_enable(); 110 instrumentation_end(); 111 } 112 113 /** 114 * exit_to_user_mode - Fixup state when exiting to user mode 115 * 116 * Syscall/interupt exit enables interrupts, but the kernel state is 117 * interrupts disabled when this is invoked. Also tell RCU about it. 118 * 119 * 1) Trace interrupts on state 120 * 2) Invoke context tracking if enabled to adjust RCU state 121 * 3) Invoke architecture specific last minute exit code, e.g. speculation 122 * mitigations, etc. 123 * 4) Tell lockdep that interrupts are enabled 124 */ 125 static __always_inline void exit_to_user_mode(void) 126 { 127 instrumentation_begin(); 128 trace_hardirqs_on_prepare(); 129 lockdep_hardirqs_on_prepare(CALLER_ADDR0); 130 instrumentation_end(); 131 132 user_enter_irqoff(); 133 arch_exit_to_user_mode(); 134 lockdep_hardirqs_on(CALLER_ADDR0); 135 } 136 137 /* Workaround to allow gradual conversion of architecture code */ 138 void __weak arch_do_signal(struct pt_regs *regs) { } 139 140 static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, 141 unsigned long ti_work) 142 { 143 /* 144 * Before returning to user space ensure that all pending work 145 * items have been completed. 146 */ 147 while (ti_work & EXIT_TO_USER_MODE_WORK) { 148 149 local_irq_enable_exit_to_user(ti_work); 150 151 if (ti_work & _TIF_NEED_RESCHED) 152 schedule(); 153 154 if (ti_work & _TIF_UPROBE) 155 uprobe_notify_resume(regs); 156 157 if (ti_work & _TIF_PATCH_PENDING) 158 klp_update_patch_state(current); 159 160 if (ti_work & _TIF_SIGPENDING) 161 arch_do_signal(regs); 162 163 if (ti_work & _TIF_NOTIFY_RESUME) { 164 clear_thread_flag(TIF_NOTIFY_RESUME); 165 tracehook_notify_resume(regs); 166 rseq_handle_notify_resume(NULL, regs); 167 } 168 169 /* Architecture specific TIF work */ 170 arch_exit_to_user_mode_work(regs, ti_work); 171 172 /* 173 * Disable interrupts and reevaluate the work flags as they 174 * might have changed while interrupts and preemption was 175 * enabled above. 176 */ 177 local_irq_disable_exit_to_user(); 178 ti_work = READ_ONCE(current_thread_info()->flags); 179 } 180 181 /* Return the latest work state for arch_exit_to_user_mode() */ 182 return ti_work; 183 } 184 185 static void exit_to_user_mode_prepare(struct pt_regs *regs) 186 { 187 unsigned long ti_work = READ_ONCE(current_thread_info()->flags); 188 189 lockdep_assert_irqs_disabled(); 190 191 if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) 192 ti_work = exit_to_user_mode_loop(regs, ti_work); 193 194 arch_exit_to_user_mode_prepare(regs, ti_work); 195 196 /* Ensure that the address limit is intact and no locks are held */ 197 addr_limit_user_check(); 198 lockdep_assert_irqs_disabled(); 199 lockdep_sys_exit(); 200 } 201 202 #ifndef _TIF_SINGLESTEP 203 static inline bool report_single_step(unsigned long ti_work) 204 { 205 return false; 206 } 207 #else 208 /* 209 * If TIF_SYSCALL_EMU is set, then the only reason to report is when 210 * TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall 211 * instruction has been already reported in syscall_enter_from_usermode(). 212 */ 213 #define SYSEMU_STEP (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU) 214 215 static inline bool report_single_step(unsigned long ti_work) 216 { 217 return (ti_work & SYSEMU_STEP) == _TIF_SINGLESTEP; 218 } 219 #endif 220 221 static void syscall_exit_work(struct pt_regs *regs, unsigned long ti_work) 222 { 223 bool step; 224 225 audit_syscall_exit(regs); 226 227 if (ti_work & _TIF_SYSCALL_TRACEPOINT) 228 trace_sys_exit(regs, syscall_get_return_value(current, regs)); 229 230 step = report_single_step(ti_work); 231 if (step || ti_work & _TIF_SYSCALL_TRACE) 232 arch_syscall_exit_tracehook(regs, step); 233 } 234 235 /* 236 * Syscall specific exit to user mode preparation. Runs with interrupts 237 * enabled. 238 */ 239 static void syscall_exit_to_user_mode_prepare(struct pt_regs *regs) 240 { 241 u32 cached_flags = READ_ONCE(current_thread_info()->flags); 242 unsigned long nr = syscall_get_nr(current, regs); 243 244 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 245 246 if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { 247 if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr)) 248 local_irq_enable(); 249 } 250 251 rseq_syscall(regs); 252 253 /* 254 * Do one-time syscall specific work. If these work items are 255 * enabled, we want to run them exactly once per syscall exit with 256 * interrupts enabled. 257 */ 258 if (unlikely(cached_flags & SYSCALL_EXIT_WORK)) 259 syscall_exit_work(regs, cached_flags); 260 } 261 262 __visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs) 263 { 264 instrumentation_begin(); 265 syscall_exit_to_user_mode_prepare(regs); 266 local_irq_disable_exit_to_user(); 267 exit_to_user_mode_prepare(regs); 268 instrumentation_end(); 269 exit_to_user_mode(); 270 } 271 272 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs) 273 { 274 enter_from_user_mode(regs); 275 } 276 277 noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs) 278 { 279 instrumentation_begin(); 280 exit_to_user_mode_prepare(regs); 281 instrumentation_end(); 282 exit_to_user_mode(); 283 } 284 285 noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs) 286 { 287 irqentry_state_t ret = { 288 .exit_rcu = false, 289 }; 290 291 if (user_mode(regs)) { 292 irqentry_enter_from_user_mode(regs); 293 return ret; 294 } 295 296 /* 297 * If this entry hit the idle task invoke rcu_irq_enter() whether 298 * RCU is watching or not. 299 * 300 * Interupts can nest when the first interrupt invokes softirq 301 * processing on return which enables interrupts. 302 * 303 * Scheduler ticks in the idle task can mark quiescent state and 304 * terminate a grace period, if and only if the timer interrupt is 305 * not nested into another interrupt. 306 * 307 * Checking for __rcu_is_watching() here would prevent the nesting 308 * interrupt to invoke rcu_irq_enter(). If that nested interrupt is 309 * the tick then rcu_flavor_sched_clock_irq() would wrongfully 310 * assume that it is the first interupt and eventually claim 311 * quiescient state and end grace periods prematurely. 312 * 313 * Unconditionally invoke rcu_irq_enter() so RCU state stays 314 * consistent. 315 * 316 * TINY_RCU does not support EQS, so let the compiler eliminate 317 * this part when enabled. 318 */ 319 if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) { 320 /* 321 * If RCU is not watching then the same careful 322 * sequence vs. lockdep and tracing is required 323 * as in irq_enter_from_user_mode(). 324 */ 325 lockdep_hardirqs_off(CALLER_ADDR0); 326 rcu_irq_enter(); 327 instrumentation_begin(); 328 trace_hardirqs_off_finish(); 329 instrumentation_end(); 330 331 ret.exit_rcu = true; 332 return ret; 333 } 334 335 /* 336 * If RCU is watching then RCU only wants to check whether it needs 337 * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick() 338 * already contains a warning when RCU is not watching, so no point 339 * in having another one here. 340 */ 341 instrumentation_begin(); 342 rcu_irq_enter_check_tick(); 343 /* Use the combo lockdep/tracing function */ 344 trace_hardirqs_off(); 345 instrumentation_end(); 346 347 return ret; 348 } 349 350 void irqentry_exit_cond_resched(void) 351 { 352 if (!preempt_count()) { 353 /* Sanity check RCU and thread stack */ 354 rcu_irq_exit_check_preempt(); 355 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 356 WARN_ON_ONCE(!on_thread_stack()); 357 if (need_resched()) 358 preempt_schedule_irq(); 359 } 360 } 361 362 noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state) 363 { 364 lockdep_assert_irqs_disabled(); 365 366 /* Check whether this returns to user mode */ 367 if (user_mode(regs)) { 368 irqentry_exit_to_user_mode(regs); 369 } else if (!regs_irqs_disabled(regs)) { 370 /* 371 * If RCU was not watching on entry this needs to be done 372 * carefully and needs the same ordering of lockdep/tracing 373 * and RCU as the return to user mode path. 374 */ 375 if (state.exit_rcu) { 376 instrumentation_begin(); 377 /* Tell the tracer that IRET will enable interrupts */ 378 trace_hardirqs_on_prepare(); 379 lockdep_hardirqs_on_prepare(CALLER_ADDR0); 380 instrumentation_end(); 381 rcu_irq_exit(); 382 lockdep_hardirqs_on(CALLER_ADDR0); 383 return; 384 } 385 386 instrumentation_begin(); 387 if (IS_ENABLED(CONFIG_PREEMPTION)) 388 irqentry_exit_cond_resched(); 389 /* Covers both tracing and lockdep */ 390 trace_hardirqs_on(); 391 instrumentation_end(); 392 } else { 393 /* 394 * IRQ flags state is correct already. Just tell RCU if it 395 * was not watching on entry. 396 */ 397 if (state.exit_rcu) 398 rcu_irq_exit(); 399 } 400 } 401