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