process.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
  4 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  5 * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  6 */
  7
  8#include <stdlib.h>
  9#include <stdbool.h>
 10#include <unistd.h>
 11#include <sched.h>
 12#include <errno.h>
 13#include <string.h>
 14#include <fcntl.h>
 15#include <mem_user.h>
 16#include <sys/mman.h>
 17#include <sys/wait.h>
 18#include <sys/stat.h>
 19#include <sys/socket.h>
 20#include <asm/unistd.h>
 21#include <as-layout.h>
 22#include <init.h>
 23#include <kern_util.h>
 24#include <mem.h>
 25#include <os.h>
 26#include <ptrace_user.h>
 27#include <registers.h>
 28#include <skas.h>
 29#include <sysdep/stub.h>
 30#include <sysdep/mcontext.h>
 31#include <linux/futex.h>
 32#include <linux/threads.h>
 33#include <timetravel.h>
 34#include <asm-generic/rwonce.h>
 35#include "../internal.h"
 36
 37int is_skas_winch(int pid, int fd, void *data)
 38{
 39	return pid == getpgrp();
 40}
 41
 42static const char *ptrace_reg_name(int idx)
 43{
 44#define R(n) case HOST_##n: return #n
 45
 46	switch (idx) {
 47#ifdef __x86_64__
 48	R(BX);
 49	R(CX);
 50	R(DI);
 51	R(SI);
 52	R(DX);
 53	R(BP);
 54	R(AX);
 55	R(R8);
 56	R(R9);
 57	R(R10);
 58	R(R11);
 59	R(R12);
 60	R(R13);
 61	R(R14);
 62	R(R15);
 63	R(ORIG_AX);
 64	R(CS);
 65	R(SS);
 66	R(EFLAGS);
 67#elif defined(__i386__)
 68	R(IP);
 69	R(SP);
 70	R(EFLAGS);
 71	R(AX);
 72	R(BX);
 73	R(CX);
 74	R(DX);
 75	R(SI);
 76	R(DI);
 77	R(BP);
 78	R(CS);
 79	R(SS);
 80	R(DS);
 81	R(FS);
 82	R(ES);
 83	R(GS);
 84	R(ORIG_AX);
 85#endif
 86	}
 87	return "";
 88}
 89
 90static int ptrace_dump_regs(int pid)
 91{
 92	unsigned long regs[MAX_REG_NR];
 93	int i;
 94
 95	if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
 96		return -errno;
 97
 98	printk(UM_KERN_ERR "Stub registers -\n");
 99	for (i = 0; i < ARRAY_SIZE(regs); i++) {
100		const char *regname = ptrace_reg_name(i);
101
102		printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
103	}
104
105	return 0;
106}
107
108/*
109 * Signals that are OK to receive in the stub - we'll just continue it.
110 * SIGWINCH will happen when UML is inside a detached screen.
111 */
112#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
113
114/* Signals that the stub will finish with - anything else is an error */
115#define STUB_DONE_MASK (1 << SIGTRAP)
116
117void wait_stub_done(int pid)
118{
119	int n, status, err;
120
121	while (1) {
122		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
123		if ((n < 0) || !WIFSTOPPED(status))
124			goto bad_wait;
125
126		if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
127			break;
128
129		err = ptrace(PTRACE_CONT, pid, 0, 0);
130		if (err) {
131			printk(UM_KERN_ERR "%s : continue failed, errno = %d\n",
132			       __func__, errno);
133			fatal_sigsegv();
134		}
135	}
136
137	if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
138		return;
139
140bad_wait:
141	err = ptrace_dump_regs(pid);
142	if (err)
143		printk(UM_KERN_ERR "Failed to get registers from stub, errno = %d\n",
144		       -err);
145	printk(UM_KERN_ERR "%s : failed to wait for SIGTRAP, pid = %d, n = %d, errno = %d, status = 0x%x\n",
146	       __func__, pid, n, errno, status);
147	fatal_sigsegv();
148}
149
150void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys)
151{
152	struct stub_data *data = (void *)mm_idp->stack;
153	int ret;
154
155	do {
156		const char byte = 0;
157		struct iovec iov = {
158			.iov_base = (void *)&byte,
159			.iov_len = sizeof(byte),
160		};
161		union {
162			char data[CMSG_SPACE(sizeof(mm_idp->syscall_fd_map))];
163			struct cmsghdr align;
164		} ctrl;
165		struct msghdr msgh = {
166			.msg_iov = &iov,
167			.msg_iovlen = 1,
168		};
169
170		if (!running) {
171			if (mm_idp->syscall_fd_num) {
172				unsigned int fds_size =
173					sizeof(int) * mm_idp->syscall_fd_num;
174				struct cmsghdr *cmsg;
175
176				msgh.msg_control = ctrl.data;
177				msgh.msg_controllen = CMSG_SPACE(fds_size);
178				cmsg = CMSG_FIRSTHDR(&msgh);
179				cmsg->cmsg_level = SOL_SOCKET;
180				cmsg->cmsg_type = SCM_RIGHTS;
181				cmsg->cmsg_len = CMSG_LEN(fds_size);
182				memcpy(CMSG_DATA(cmsg), mm_idp->syscall_fd_map,
183				       fds_size);
184
185				CATCH_EINTR(syscall(__NR_sendmsg, mm_idp->sock,
186						&msgh, 0));
187			}
188
189			data->signal = 0;
190			data->futex = FUTEX_IN_CHILD;
191			CATCH_EINTR(syscall(__NR_futex, &data->futex,
192					    FUTEX_WAKE, 1, NULL, NULL, 0));
193		}
194
195		do {
196			/*
197			 * We need to check whether the child is still alive
198			 * before and after the FUTEX_WAIT call. Before, in
199			 * case it just died but we still updated data->futex
200			 * to FUTEX_IN_CHILD. And after, in case it died while
201			 * we were waiting (and SIGCHLD woke us up, see the
202			 * IRQ handler in mmu.c).
203			 *
204			 * Either way, if PID is negative, then we have no
205			 * choice but to kill the task.
206			 */
207			if (__READ_ONCE(mm_idp->pid) < 0)
208				goto out_kill;
209
210			ret = syscall(__NR_futex, &data->futex,
211				      FUTEX_WAIT, FUTEX_IN_CHILD,
212				      NULL, NULL, 0);
213			if (ret < 0 && errno != EINTR && errno != EAGAIN) {
214				printk(UM_KERN_ERR "%s : FUTEX_WAIT failed, errno = %d\n",
215				       __func__, errno);
216				goto out_kill;
217			}
218		} while (data->futex == FUTEX_IN_CHILD);
219
220		if (__READ_ONCE(mm_idp->pid) < 0)
221			goto out_kill;
222
223		running = 0;
224
225		/* We may receive a SIGALRM before SIGSYS, iterate again. */
226	} while (wait_sigsys && data->signal == SIGALRM);
227
228	if (data->mctx_offset > sizeof(data->sigstack) - sizeof(mcontext_t)) {
229		printk(UM_KERN_ERR "%s : invalid mcontext offset", __func__);
230		goto out_kill;
231	}
232
233	if (wait_sigsys && data->signal != SIGSYS) {
234		printk(UM_KERN_ERR "%s : expected SIGSYS but got %d",
235		       __func__, data->signal);
236		goto out_kill;
237	}
238
239	return;
240
241out_kill:
242	printk(UM_KERN_ERR "%s : failed to wait for stub, pid = %d, errno = %d\n",
243	       __func__, mm_idp->pid, errno);
244	/* This is not true inside start_userspace */
245	if (current_mm_id() == mm_idp)
246		fatal_sigsegv();
247}
248
249extern unsigned long current_stub_stack(void);
250
251static void get_skas_faultinfo(int pid, struct faultinfo *fi)
252{
253	int err;
254
255	err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
256	if (err) {
257		printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
258		       "errno = %d\n", pid, errno);
259		fatal_sigsegv();
260	}
261	wait_stub_done(pid);
262
263	/*
264	 * faultinfo is prepared by the stub_segv_handler at start of
265	 * the stub stack page. We just have to copy it.
266	 */
267	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
268}
269
270static void handle_trap(struct uml_pt_regs *regs)
271{
272	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
273		fatal_sigsegv();
274
275	handle_syscall(regs);
276}
277
278extern char __syscall_stub_start[];
279
280static int stub_exe_fd;
281
282struct tramp_data {
283	struct stub_data *stub_data;
284	/* 0 is inherited, 1 is the kernel side */
285	int sockpair[2];
286};
287
288#ifndef CLOSE_RANGE_CLOEXEC
289#define CLOSE_RANGE_CLOEXEC	(1U << 2)
290#endif
291
292static int userspace_tramp(void *data)
293{
294	struct tramp_data *tramp_data = data;
295	char *const argv[] = { "uml-userspace", NULL };
296	unsigned long long offset;
297	struct stub_init_data init_data = {
298		.seccomp = using_seccomp,
299		.stub_start = STUB_START,
300	};
301	int ret;
302
303	if (using_seccomp) {
304		init_data.signal_handler = STUB_CODE +
305					   (unsigned long) stub_signal_interrupt -
306					   (unsigned long) __syscall_stub_start;
307		init_data.signal_restorer = STUB_CODE +
308					   (unsigned long) stub_signal_restorer -
309					   (unsigned long) __syscall_stub_start;
310	} else {
311		init_data.signal_handler = STUB_CODE +
312					   (unsigned long) stub_segv_handler -
313					   (unsigned long) __syscall_stub_start;
314		init_data.signal_restorer = 0;
315	}
316
317	init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
318					      &offset);
319	init_data.stub_code_offset = MMAP_OFFSET(offset);
320
321	init_data.stub_data_fd = phys_mapping(uml_to_phys(tramp_data->stub_data),
322					      &offset);
323	init_data.stub_data_offset = MMAP_OFFSET(offset);
324
325	/*
326	 * Avoid leaking unneeded FDs to the stub by setting CLOEXEC on all FDs
327	 * and then unsetting it on all memory related FDs.
328	 * This is not strictly necessary from a safety perspective.
329	 */
330	syscall(__NR_close_range, 0, ~0U, CLOSE_RANGE_CLOEXEC);
331
332	fcntl(init_data.stub_data_fd, F_SETFD, 0);
333
334	/* dup2 signaling FD/socket to STDIN */
335	if (dup2(tramp_data->sockpair[0], 0) < 0)
336		exit(3);
337	close(tramp_data->sockpair[0]);
338
339	/* Write init_data and close write side */
340	ret = write(tramp_data->sockpair[1], &init_data, sizeof(init_data));
341	close(tramp_data->sockpair[1]);
342
343	if (ret != sizeof(init_data))
344		exit(4);
345
346	/* Raw execveat for compatibility with older libc versions */
347	syscall(__NR_execveat, stub_exe_fd, (unsigned long)"",
348		(unsigned long)argv, NULL, AT_EMPTY_PATH);
349
350	exit(5);
351}
352
353extern char stub_exe_start[];
354extern char stub_exe_end[];
355
356extern char *tempdir;
357
358#define STUB_EXE_NAME_TEMPLATE "/uml-userspace-XXXXXX"
359
360#ifndef MFD_EXEC
361#define MFD_EXEC 0x0010U
362#endif
363
364static int __init init_stub_exe_fd(void)
365{
366	size_t written = 0;
367	char *tmpfile = NULL;
368
369	stub_exe_fd = memfd_create("uml-userspace",
370				   MFD_EXEC | MFD_CLOEXEC | MFD_ALLOW_SEALING);
371
372	if (stub_exe_fd < 0) {
373		printk(UM_KERN_INFO "Could not create executable memfd, using temporary file!");
374
375		tmpfile = malloc(strlen(tempdir) +
376				  strlen(STUB_EXE_NAME_TEMPLATE) + 1);
377		if (tmpfile == NULL)
378			panic("Failed to allocate memory for stub binary name");
379
380		strcpy(tmpfile, tempdir);
381		strcat(tmpfile, STUB_EXE_NAME_TEMPLATE);
382
383		stub_exe_fd = mkstemp(tmpfile);
384		if (stub_exe_fd < 0)
385			panic("Could not create temporary file for stub binary: %d",
386			      -errno);
387	}
388
389	while (written < stub_exe_end - stub_exe_start) {
390		ssize_t res = write(stub_exe_fd, stub_exe_start + written,
391				    stub_exe_end - stub_exe_start - written);
392		if (res < 0) {
393			if (errno == EINTR)
394				continue;
395
396			if (tmpfile)
397				unlink(tmpfile);
398			panic("Failed write stub binary: %d", -errno);
399		}
400
401		written += res;
402	}
403
404	if (!tmpfile) {
405		fcntl(stub_exe_fd, F_ADD_SEALS,
406		      F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_SEAL);
407	} else {
408		if (fchmod(stub_exe_fd, 00500) < 0) {
409			unlink(tmpfile);
410			panic("Could not make stub binary executable: %d",
411			      -errno);
412		}
413
414		close(stub_exe_fd);
415		stub_exe_fd = open(tmpfile, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
416		if (stub_exe_fd < 0) {
417			unlink(tmpfile);
418			panic("Could not reopen stub binary: %d", -errno);
419		}
420
421		unlink(tmpfile);
422		free(tmpfile);
423	}
424
425	return 0;
426}
427__initcall(init_stub_exe_fd);
428
429int using_seccomp;
430
431/**
432 * start_userspace() - prepare a new userspace process
433 * @mm_id: The corresponding struct mm_id
434 *
435 * Setups a new temporary stack page that is used while userspace_tramp() runs
436 * Clones the kernel process into a new userspace process, with FDs only.
437 *
438 * Return: When positive: the process id of the new userspace process,
439 *         when negative: an error number.
440 * FIXME: can PIDs become negative?!
441 */
442int start_userspace(struct mm_id *mm_id)
443{
444	struct stub_data *proc_data = (void *)mm_id->stack;
445	struct tramp_data tramp_data = {
446		.stub_data = proc_data,
447	};
448	void *stack;
449	unsigned long sp;
450	int status, n, err;
451
452	/* setup a temporary stack page */
453	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
454		     PROT_READ | PROT_WRITE | PROT_EXEC,
455		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
456	if (stack == MAP_FAILED) {
457		err = -errno;
458		printk(UM_KERN_ERR "%s : mmap failed, errno = %d\n",
459		       __func__, errno);
460		return err;
461	}
462
463	/* set stack pointer to the end of the stack page, so it can grow downwards */
464	sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;
465
466	/* socket pair for init data and SECCOMP FD passing (no CLOEXEC here) */
467	if (socketpair(AF_UNIX, SOCK_STREAM, 0, tramp_data.sockpair)) {
468		err = -errno;
469		printk(UM_KERN_ERR "%s : socketpair failed, errno = %d\n",
470		       __func__, errno);
471		return err;
472	}
473
474	if (using_seccomp)
475		proc_data->futex = FUTEX_IN_CHILD;
476
477	mm_id->pid = clone(userspace_tramp, (void *) sp,
478		    CLONE_VFORK | CLONE_VM | SIGCHLD,
479		    (void *)&tramp_data);
480	if (mm_id->pid < 0) {
481		err = -errno;
482		printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
483		       __func__, errno);
484		goto out_close;
485	}
486
487	if (using_seccomp) {
488		wait_stub_done_seccomp(mm_id, 1, 1);
489	} else {
490		do {
491			CATCH_EINTR(n = waitpid(mm_id->pid, &status,
492						WUNTRACED | __WALL));
493			if (n < 0) {
494				err = -errno;
495				printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
496				       __func__, errno);
497				goto out_kill;
498			}
499		} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
500
501		if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
502			err = -EINVAL;
503			printk(UM_KERN_ERR "%s : expected SIGSTOP, got status = %d\n",
504			       __func__, status);
505			goto out_kill;
506		}
507
508		if (ptrace(PTRACE_SETOPTIONS, mm_id->pid, NULL,
509			   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
510			err = -errno;
511			printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
512			       __func__, errno);
513			goto out_kill;
514		}
515	}
516
517	if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
518		err = -errno;
519		printk(UM_KERN_ERR "%s : munmap failed, errno = %d\n",
520		       __func__, errno);
521		goto out_kill;
522	}
523
524	close(tramp_data.sockpair[0]);
525	if (using_seccomp)
526		mm_id->sock = tramp_data.sockpair[1];
527	else
528		close(tramp_data.sockpair[1]);
529
530	return 0;
531
532out_kill:
533	os_kill_ptraced_process(mm_id->pid, 1);
534out_close:
535	close(tramp_data.sockpair[0]);
536	close(tramp_data.sockpair[1]);
537
538	mm_id->pid = -1;
539
540	return err;
541}
542
543static int unscheduled_userspace_iterations;
544extern unsigned long tt_extra_sched_jiffies;
545
546void userspace(struct uml_pt_regs *regs)
547{
548	int err, status, op;
549	siginfo_t si_local;
550	siginfo_t *si;
551	int sig;
552
553	/* Handle any immediate reschedules or signals */
554	interrupt_end();
555
556	while (1) {
557		struct mm_id *mm_id = current_mm_id();
558
559		/*
560		 * At any given time, only one CPU thread can enter the
561		 * turnstile to operate on the same stub process, including
562		 * executing stub system calls (mmap and munmap).
563		 */
564		enter_turnstile(mm_id);
565
566		/*
567		 * When we are in time-travel mode, userspace can theoretically
568		 * do a *lot* of work without being scheduled. The problem with
569		 * this is that it will prevent kernel bookkeeping (primarily
570		 * the RCU) from running and this can for example cause OOM
571		 * situations.
572		 *
573		 * This code accounts a jiffie against the scheduling clock
574		 * after the defined userspace iterations in the same thread.
575		 * By doing so the situation is effectively prevented.
576		 */
577		if (time_travel_mode == TT_MODE_INFCPU ||
578		    time_travel_mode == TT_MODE_EXTERNAL) {
579#ifdef CONFIG_UML_MAX_USERSPACE_ITERATIONS
580			if (CONFIG_UML_MAX_USERSPACE_ITERATIONS &&
581			    unscheduled_userspace_iterations++ >
582			    CONFIG_UML_MAX_USERSPACE_ITERATIONS) {
583				tt_extra_sched_jiffies += 1;
584				unscheduled_userspace_iterations = 0;
585			}
586#endif
587		}
588
589		time_travel_print_bc_msg();
590
591		current_mm_sync();
592
593		if (using_seccomp) {
594			struct stub_data *proc_data = (void *) mm_id->stack;
595
596			err = set_stub_state(regs, proc_data, singlestepping());
597			if (err) {
598				printk(UM_KERN_ERR "%s - failed to set regs: %d",
599				       __func__, err);
600				fatal_sigsegv();
601			}
602
603			/* Must have been reset by the syscall caller */
604			if (proc_data->restart_wait != 0)
605				panic("Programming error: Flag to only run syscalls in child was not cleared!");
606
607			/* Mark pending syscalls for flushing */
608			proc_data->syscall_data_len = mm_id->syscall_data_len;
609
610			wait_stub_done_seccomp(mm_id, 0, 0);
611
612			sig = proc_data->signal;
613
614			if (sig == SIGTRAP && proc_data->err != 0) {
615				printk(UM_KERN_ERR "%s - Error flushing stub syscalls",
616				       __func__);
617				syscall_stub_dump_error(mm_id);
618				mm_id->syscall_data_len = proc_data->err;
619				fatal_sigsegv();
620			}
621
622			mm_id->syscall_data_len = 0;
623			mm_id->syscall_fd_num = 0;
624
625			err = get_stub_state(regs, proc_data, NULL);
626			if (err) {
627				printk(UM_KERN_ERR "%s - failed to get regs: %d",
628				       __func__, err);
629				fatal_sigsegv();
630			}
631
632			if (proc_data->si_offset > sizeof(proc_data->sigstack) - sizeof(*si))
633				panic("%s - Invalid siginfo offset from child", __func__);
634
635			si = &si_local;
636			memcpy(si, &proc_data->sigstack[proc_data->si_offset], sizeof(*si));
637
638			regs->is_user = 1;
639
640			/* Fill in ORIG_RAX and extract fault information */
641			PT_SYSCALL_NR(regs->gp) = si->si_syscall;
642			if (sig == SIGSEGV) {
643				mcontext_t *mcontext = (void *)&proc_data->sigstack[proc_data->mctx_offset];
644
645				GET_FAULTINFO_FROM_MC(regs->faultinfo, mcontext);
646			}
647		} else {
648			int pid = mm_id->pid;
649
650			/* Flush out any pending syscalls */
651			err = syscall_stub_flush(mm_id);
652			if (err) {
653				if (err == -ENOMEM)
654					report_enomem();
655
656				printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
657					__func__, -err);
658				fatal_sigsegv();
659			}
660
661			/*
662			 * This can legitimately fail if the process loads a
663			 * bogus value into a segment register.  It will
664			 * segfault and PTRACE_GETREGS will read that value
665			 * out of the process.  However, PTRACE_SETREGS will
666			 * fail.  In this case, there is nothing to do but
667			 * just kill the process.
668			 */
669			if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
670				printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
671				       __func__, errno);
672				fatal_sigsegv();
673			}
674
675			if (put_fp_registers(pid, regs->fp)) {
676				printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
677				       __func__, errno);
678				fatal_sigsegv();
679			}
680
681			if (singlestepping())
682				op = PTRACE_SYSEMU_SINGLESTEP;
683			else
684				op = PTRACE_SYSEMU;
685
686			if (ptrace(op, pid, 0, 0)) {
687				printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
688				       __func__, op, errno);
689				fatal_sigsegv();
690			}
691
692			CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
693			if (err < 0) {
694				printk(UM_KERN_ERR "%s - wait failed, errno = %d\n",
695				       __func__, errno);
696				fatal_sigsegv();
697			}
698
699			regs->is_user = 1;
700			if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
701				printk(UM_KERN_ERR "%s - PTRACE_GETREGS failed, errno = %d\n",
702				       __func__, errno);
703				fatal_sigsegv();
704			}
705
706			if (get_fp_registers(pid, regs->fp)) {
707				printk(UM_KERN_ERR "%s -  get_fp_registers failed, errno = %d\n",
708				       __func__, errno);
709				fatal_sigsegv();
710			}
711
712			if (WIFSTOPPED(status)) {
713				sig = WSTOPSIG(status);
714
715				/*
716				 * These signal handlers need the si argument
717				 * and SIGSEGV needs the faultinfo.
718				 * The SIGIO and SIGALARM handlers which constitute
719				 * the majority of invocations, do not use it.
720				 */
721				switch (sig) {
722				case SIGSEGV:
723					get_skas_faultinfo(pid,
724							   &regs->faultinfo);
725					fallthrough;
726				case SIGTRAP:
727				case SIGILL:
728				case SIGBUS:
729				case SIGFPE:
730				case SIGWINCH:
731					ptrace(PTRACE_GETSIGINFO, pid, 0,
732					       (struct siginfo *)&si_local);
733					si = &si_local;
734					break;
735				default:
736					si = NULL;
737					break;
738				}
739			} else {
740				sig = 0;
741			}
742		}
743
744		exit_turnstile(mm_id);
745
746		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
747
748		if (sig) {
749			switch (sig) {
750			case SIGSEGV:
751				if (using_seccomp || PTRACE_FULL_FAULTINFO)
752					(*sig_info[SIGSEGV])(SIGSEGV,
753							     (struct siginfo *)si,
754							     regs, NULL);
755				else
756					segv(regs->faultinfo, 0, 1, NULL, NULL);
757
758				break;
759			case SIGSYS:
760				handle_syscall(regs);
761				break;
762			case SIGTRAP + 0x80:
763				handle_trap(regs);
764				break;
765			case SIGTRAP:
766				relay_signal(SIGTRAP, (struct siginfo *)si, regs, NULL);
767				break;
768			case SIGALRM:
769				break;
770			case SIGIO:
771			case SIGILL:
772			case SIGBUS:
773			case SIGFPE:
774			case SIGWINCH:
775				block_signals_trace();
776				(*sig_info[sig])(sig, (struct siginfo *)si, regs, NULL);
777				unblock_signals_trace();
778				break;
779			default:
780				printk(UM_KERN_ERR "%s - child stopped with signal %d\n",
781				       __func__, sig);
782				fatal_sigsegv();
783			}
784			interrupt_end();
785
786			/* Avoid -ERESTARTSYS handling in host */
787			if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
788				PT_SYSCALL_NR(regs->gp) = -1;
789		}
790	}
791}
792
793void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
794{
795	(*buf)[0].JB_IP = (unsigned long) handler;
796	(*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
797		sizeof(void *);
798}
799
800#define INIT_JMP_NEW_THREAD 0
801#define INIT_JMP_CALLBACK 1
802#define INIT_JMP_HALT 2
803#define INIT_JMP_REBOOT 3
804
805void switch_threads(jmp_buf *me, jmp_buf *you)
806{
807	unscheduled_userspace_iterations = 0;
808
809	if (UML_SETJMP(me) == 0)
810		UML_LONGJMP(you, 1);
811}
812
813static jmp_buf initial_jmpbuf;
814
815static __thread void (*cb_proc)(void *arg);
816static __thread void *cb_arg;
817static __thread jmp_buf *cb_back;
818
819int start_idle_thread(void *stack, jmp_buf *switch_buf)
820{
821	int n;
822
823	set_handler(SIGWINCH);
824
825	/*
826	 * Can't use UML_SETJMP or UML_LONGJMP here because they save
827	 * and restore signals, with the possible side-effect of
828	 * trying to handle any signals which came when they were
829	 * blocked, which can't be done on this stack.
830	 * Signals must be blocked when jumping back here and restored
831	 * after returning to the jumper.
832	 */
833	n = setjmp(initial_jmpbuf);
834	switch (n) {
835	case INIT_JMP_NEW_THREAD:
836		(*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
837		(*switch_buf)[0].JB_SP = (unsigned long) stack +
838			UM_THREAD_SIZE - sizeof(void *);
839		break;
840	case INIT_JMP_CALLBACK:
841		(*cb_proc)(cb_arg);
842		longjmp(*cb_back, 1);
843		break;
844	case INIT_JMP_HALT:
845		kmalloc_ok = 0;
846		return 0;
847	case INIT_JMP_REBOOT:
848		kmalloc_ok = 0;
849		return 1;
850	default:
851		printk(UM_KERN_ERR "Bad sigsetjmp return in %s - %d\n",
852		       __func__, n);
853		fatal_sigsegv();
854	}
855	longjmp(*switch_buf, 1);
856
857	/* unreachable */
858	printk(UM_KERN_ERR "impossible long jump!");
859	fatal_sigsegv();
860	return 0;
861}
862
863void initial_thread_cb_skas(void (*proc)(void *), void *arg)
864{
865	jmp_buf here;
866
867	cb_proc = proc;
868	cb_arg = arg;
869	cb_back = &here;
870
871	initial_jmpbuf_lock();
872	if (UML_SETJMP(&here) == 0)
873		UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
874	initial_jmpbuf_unlock();
875
876	cb_proc = NULL;
877	cb_arg = NULL;
878	cb_back = NULL;
879}
880
881void halt_skas(void)
882{
883	initial_jmpbuf_lock();
884	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
885	/* unreachable */
886}
887
888static bool noreboot;
889
890static int __init noreboot_cmd_param(char *str, int *add)
891{
892	*add = 0;
893	noreboot = true;
894	return 0;
895}
896
897__uml_setup("noreboot", noreboot_cmd_param,
898"noreboot\n"
899"    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
900"    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
901"    crashes in CI\n\n");
902
903void reboot_skas(void)
904{
905	initial_jmpbuf_lock();
906	UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
907	/* unreachable */
908}