xref: /openbmc/linux/kernel/entry/common.c (revision 236bdb88)
1 // SPDX-License-Identifier: GPL-2.0
2 
3 #include <linux/context_tracking.h>
4 #include <linux/entry-common.h>
5 #include <linux/resume_user_mode.h>
6 #include <linux/highmem.h>
7 #include <linux/jump_label.h>
8 #include <linux/kmsan.h>
9 #include <linux/livepatch.h>
10 #include <linux/audit.h>
11 #include <linux/tick.h>
12 
13 #include "common.h"
14 
15 #define CREATE_TRACE_POINTS
16 #include <trace/events/syscalls.h>
17 
18 /* See comment for enter_from_user_mode() in entry-common.h */
19 static __always_inline void __enter_from_user_mode(struct pt_regs *regs)
20 {
21 	arch_enter_from_user_mode(regs);
22 	lockdep_hardirqs_off(CALLER_ADDR0);
23 
24 	CT_WARN_ON(ct_state() != CONTEXT_USER);
25 	user_exit_irqoff();
26 
27 	instrumentation_begin();
28 	kmsan_unpoison_entry_regs(regs);
29 	trace_hardirqs_off_finish();
30 	instrumentation_end();
31 }
32 
33 void noinstr enter_from_user_mode(struct pt_regs *regs)
34 {
35 	__enter_from_user_mode(regs);
36 }
37 
38 static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
39 {
40 	if (unlikely(audit_context())) {
41 		unsigned long args[6];
42 
43 		syscall_get_arguments(current, regs, args);
44 		audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
45 	}
46 }
47 
48 static long syscall_trace_enter(struct pt_regs *regs, long syscall,
49 				unsigned long work)
50 {
51 	long ret = 0;
52 
53 	/*
54 	 * Handle Syscall User Dispatch.  This must comes first, since
55 	 * the ABI here can be something that doesn't make sense for
56 	 * other syscall_work features.
57 	 */
58 	if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) {
59 		if (syscall_user_dispatch(regs))
60 			return -1L;
61 	}
62 
63 	/* Handle ptrace */
64 	if (work & (SYSCALL_WORK_SYSCALL_TRACE | SYSCALL_WORK_SYSCALL_EMU)) {
65 		ret = ptrace_report_syscall_entry(regs);
66 		if (ret || (work & SYSCALL_WORK_SYSCALL_EMU))
67 			return -1L;
68 	}
69 
70 	/* Do seccomp after ptrace, to catch any tracer changes. */
71 	if (work & SYSCALL_WORK_SECCOMP) {
72 		ret = __secure_computing(NULL);
73 		if (ret == -1L)
74 			return ret;
75 	}
76 
77 	/* Either of the above might have changed the syscall number */
78 	syscall = syscall_get_nr(current, regs);
79 
80 	if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT))
81 		trace_sys_enter(regs, syscall);
82 
83 	syscall_enter_audit(regs, syscall);
84 
85 	return ret ? : syscall;
86 }
87 
88 static __always_inline long
89 __syscall_enter_from_user_work(struct pt_regs *regs, long syscall)
90 {
91 	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
92 
93 	if (work & SYSCALL_WORK_ENTER)
94 		syscall = syscall_trace_enter(regs, syscall, work);
95 
96 	return syscall;
97 }
98 
99 long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall)
100 {
101 	return __syscall_enter_from_user_work(regs, syscall);
102 }
103 
104 noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
105 {
106 	long ret;
107 
108 	__enter_from_user_mode(regs);
109 
110 	instrumentation_begin();
111 	local_irq_enable();
112 	ret = __syscall_enter_from_user_work(regs, syscall);
113 	instrumentation_end();
114 
115 	return ret;
116 }
117 
118 noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
119 {
120 	__enter_from_user_mode(regs);
121 	instrumentation_begin();
122 	local_irq_enable();
123 	instrumentation_end();
124 }
125 
126 /* See comment for exit_to_user_mode() in entry-common.h */
127 static __always_inline void __exit_to_user_mode(void)
128 {
129 	instrumentation_begin();
130 	trace_hardirqs_on_prepare();
131 	lockdep_hardirqs_on_prepare();
132 	instrumentation_end();
133 
134 	user_enter_irqoff();
135 	arch_exit_to_user_mode();
136 	lockdep_hardirqs_on(CALLER_ADDR0);
137 }
138 
139 void noinstr exit_to_user_mode(void)
140 {
141 	__exit_to_user_mode();
142 }
143 
144 /* Workaround to allow gradual conversion of architecture code */
145 void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
146 
147 static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
148 					    unsigned long ti_work)
149 {
150 	/*
151 	 * Before returning to user space ensure that all pending work
152 	 * items have been completed.
153 	 */
154 	while (ti_work & EXIT_TO_USER_MODE_WORK) {
155 
156 		local_irq_enable_exit_to_user(ti_work);
157 
158 		if (ti_work & _TIF_NEED_RESCHED)
159 			schedule();
160 
161 		if (ti_work & _TIF_UPROBE)
162 			uprobe_notify_resume(regs);
163 
164 		if (ti_work & _TIF_PATCH_PENDING)
165 			klp_update_patch_state(current);
166 
167 		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
168 			arch_do_signal_or_restart(regs);
169 
170 		if (ti_work & _TIF_NOTIFY_RESUME)
171 			resume_user_mode_work(regs);
172 
173 		/* Architecture specific TIF work */
174 		arch_exit_to_user_mode_work(regs, ti_work);
175 
176 		/*
177 		 * Disable interrupts and reevaluate the work flags as they
178 		 * might have changed while interrupts and preemption was
179 		 * enabled above.
180 		 */
181 		local_irq_disable_exit_to_user();
182 
183 		/* Check if any of the above work has queued a deferred wakeup */
184 		tick_nohz_user_enter_prepare();
185 
186 		ti_work = read_thread_flags();
187 	}
188 
189 	/* Return the latest work state for arch_exit_to_user_mode() */
190 	return ti_work;
191 }
192 
193 static void exit_to_user_mode_prepare(struct pt_regs *regs)
194 {
195 	unsigned long ti_work = read_thread_flags();
196 
197 	lockdep_assert_irqs_disabled();
198 
199 	/* Flush pending rcuog wakeup before the last need_resched() check */
200 	tick_nohz_user_enter_prepare();
201 
202 	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
203 		ti_work = exit_to_user_mode_loop(regs, ti_work);
204 
205 	arch_exit_to_user_mode_prepare(regs, ti_work);
206 
207 	/* Ensure that the address limit is intact and no locks are held */
208 	addr_limit_user_check();
209 	kmap_assert_nomap();
210 	lockdep_assert_irqs_disabled();
211 	lockdep_sys_exit();
212 }
213 
214 /*
215  * If SYSCALL_EMU is set, then the only reason to report is when
216  * SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall
217  * instruction has been already reported in syscall_enter_from_user_mode().
218  */
219 static inline bool report_single_step(unsigned long work)
220 {
221 	if (work & SYSCALL_WORK_SYSCALL_EMU)
222 		return false;
223 
224 	return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
225 }
226 
227 static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
228 {
229 	bool step;
230 
231 	/*
232 	 * If the syscall was rolled back due to syscall user dispatching,
233 	 * then the tracers below are not invoked for the same reason as
234 	 * the entry side was not invoked in syscall_trace_enter(): The ABI
235 	 * of these syscalls is unknown.
236 	 */
237 	if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) {
238 		if (unlikely(current->syscall_dispatch.on_dispatch)) {
239 			current->syscall_dispatch.on_dispatch = false;
240 			return;
241 		}
242 	}
243 
244 	audit_syscall_exit(regs);
245 
246 	if (work & SYSCALL_WORK_SYSCALL_TRACEPOINT)
247 		trace_sys_exit(regs, syscall_get_return_value(current, regs));
248 
249 	step = report_single_step(work);
250 	if (step || work & SYSCALL_WORK_SYSCALL_TRACE)
251 		ptrace_report_syscall_exit(regs, step);
252 }
253 
254 /*
255  * Syscall specific exit to user mode preparation. Runs with interrupts
256  * enabled.
257  */
258 static void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
259 {
260 	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
261 	unsigned long nr = syscall_get_nr(current, regs);
262 
263 	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
264 
265 	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
266 		if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr))
267 			local_irq_enable();
268 	}
269 
270 	rseq_syscall(regs);
271 
272 	/*
273 	 * Do one-time syscall specific work. If these work items are
274 	 * enabled, we want to run them exactly once per syscall exit with
275 	 * interrupts enabled.
276 	 */
277 	if (unlikely(work & SYSCALL_WORK_EXIT))
278 		syscall_exit_work(regs, work);
279 }
280 
281 static __always_inline void __syscall_exit_to_user_mode_work(struct pt_regs *regs)
282 {
283 	syscall_exit_to_user_mode_prepare(regs);
284 	local_irq_disable_exit_to_user();
285 	exit_to_user_mode_prepare(regs);
286 }
287 
288 void syscall_exit_to_user_mode_work(struct pt_regs *regs)
289 {
290 	__syscall_exit_to_user_mode_work(regs);
291 }
292 
293 __visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
294 {
295 	instrumentation_begin();
296 	__syscall_exit_to_user_mode_work(regs);
297 	instrumentation_end();
298 	__exit_to_user_mode();
299 }
300 
301 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
302 {
303 	__enter_from_user_mode(regs);
304 }
305 
306 noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
307 {
308 	instrumentation_begin();
309 	exit_to_user_mode_prepare(regs);
310 	instrumentation_end();
311 	__exit_to_user_mode();
312 }
313 
314 noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
315 {
316 	irqentry_state_t ret = {
317 		.exit_rcu = false,
318 	};
319 
320 	if (user_mode(regs)) {
321 		irqentry_enter_from_user_mode(regs);
322 		return ret;
323 	}
324 
325 	/*
326 	 * If this entry hit the idle task invoke ct_irq_enter() whether
327 	 * RCU is watching or not.
328 	 *
329 	 * Interrupts can nest when the first interrupt invokes softirq
330 	 * processing on return which enables interrupts.
331 	 *
332 	 * Scheduler ticks in the idle task can mark quiescent state and
333 	 * terminate a grace period, if and only if the timer interrupt is
334 	 * not nested into another interrupt.
335 	 *
336 	 * Checking for rcu_is_watching() here would prevent the nesting
337 	 * interrupt to invoke ct_irq_enter(). If that nested interrupt is
338 	 * the tick then rcu_flavor_sched_clock_irq() would wrongfully
339 	 * assume that it is the first interrupt and eventually claim
340 	 * quiescent state and end grace periods prematurely.
341 	 *
342 	 * Unconditionally invoke ct_irq_enter() so RCU state stays
343 	 * consistent.
344 	 *
345 	 * TINY_RCU does not support EQS, so let the compiler eliminate
346 	 * this part when enabled.
347 	 */
348 	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
349 		/*
350 		 * If RCU is not watching then the same careful
351 		 * sequence vs. lockdep and tracing is required
352 		 * as in irqentry_enter_from_user_mode().
353 		 */
354 		lockdep_hardirqs_off(CALLER_ADDR0);
355 		ct_irq_enter();
356 		instrumentation_begin();
357 		kmsan_unpoison_entry_regs(regs);
358 		trace_hardirqs_off_finish();
359 		instrumentation_end();
360 
361 		ret.exit_rcu = true;
362 		return ret;
363 	}
364 
365 	/*
366 	 * If RCU is watching then RCU only wants to check whether it needs
367 	 * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick()
368 	 * already contains a warning when RCU is not watching, so no point
369 	 * in having another one here.
370 	 */
371 	lockdep_hardirqs_off(CALLER_ADDR0);
372 	instrumentation_begin();
373 	kmsan_unpoison_entry_regs(regs);
374 	rcu_irq_enter_check_tick();
375 	trace_hardirqs_off_finish();
376 	instrumentation_end();
377 
378 	return ret;
379 }
380 
381 void raw_irqentry_exit_cond_resched(void)
382 {
383 	if (!preempt_count()) {
384 		/* Sanity check RCU and thread stack */
385 		rcu_irq_exit_check_preempt();
386 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
387 			WARN_ON_ONCE(!on_thread_stack());
388 		if (need_resched())
389 			preempt_schedule_irq();
390 	}
391 }
392 #ifdef CONFIG_PREEMPT_DYNAMIC
393 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
394 DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
395 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
396 DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
397 void dynamic_irqentry_exit_cond_resched(void)
398 {
399 	if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
400 		return;
401 	raw_irqentry_exit_cond_resched();
402 }
403 #endif
404 #endif
405 
406 noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
407 {
408 	lockdep_assert_irqs_disabled();
409 
410 	/* Check whether this returns to user mode */
411 	if (user_mode(regs)) {
412 		irqentry_exit_to_user_mode(regs);
413 	} else if (!regs_irqs_disabled(regs)) {
414 		/*
415 		 * If RCU was not watching on entry this needs to be done
416 		 * carefully and needs the same ordering of lockdep/tracing
417 		 * and RCU as the return to user mode path.
418 		 */
419 		if (state.exit_rcu) {
420 			instrumentation_begin();
421 			/* Tell the tracer that IRET will enable interrupts */
422 			trace_hardirqs_on_prepare();
423 			lockdep_hardirqs_on_prepare();
424 			instrumentation_end();
425 			ct_irq_exit();
426 			lockdep_hardirqs_on(CALLER_ADDR0);
427 			return;
428 		}
429 
430 		instrumentation_begin();
431 		if (IS_ENABLED(CONFIG_PREEMPTION))
432 			irqentry_exit_cond_resched();
433 
434 		/* Covers both tracing and lockdep */
435 		trace_hardirqs_on();
436 		instrumentation_end();
437 	} else {
438 		/*
439 		 * IRQ flags state is correct already. Just tell RCU if it
440 		 * was not watching on entry.
441 		 */
442 		if (state.exit_rcu)
443 			ct_irq_exit();
444 	}
445 }
446 
447 irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)
448 {
449 	irqentry_state_t irq_state;
450 
451 	irq_state.lockdep = lockdep_hardirqs_enabled();
452 
453 	__nmi_enter();
454 	lockdep_hardirqs_off(CALLER_ADDR0);
455 	lockdep_hardirq_enter();
456 	ct_nmi_enter();
457 
458 	instrumentation_begin();
459 	kmsan_unpoison_entry_regs(regs);
460 	trace_hardirqs_off_finish();
461 	ftrace_nmi_enter();
462 	instrumentation_end();
463 
464 	return irq_state;
465 }
466 
467 void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state)
468 {
469 	instrumentation_begin();
470 	ftrace_nmi_exit();
471 	if (irq_state.lockdep) {
472 		trace_hardirqs_on_prepare();
473 		lockdep_hardirqs_on_prepare();
474 	}
475 	instrumentation_end();
476 
477 	ct_nmi_exit();
478 	lockdep_hardirq_exit();
479 	if (irq_state.lockdep)
480 		lockdep_hardirqs_on(CALLER_ADDR0);
481 	__nmi_exit();
482 }
483