1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
4 * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
5 */
6
7 #include <stdlib.h>
8 #include <stdbool.h>
9 #include <unistd.h>
10 #include <sched.h>
11 #include <errno.h>
12 #include <string.h>
13 #include <fcntl.h>
14 #include <mem_user.h>
15 #include <sys/mman.h>
16 #include <sys/wait.h>
17 #include <sys/stat.h>
18 #include <asm/unistd.h>
19 #include <as-layout.h>
20 #include <init.h>
21 #include <kern_util.h>
22 #include <mem.h>
23 #include <os.h>
24 #include <ptrace_user.h>
25 #include <registers.h>
26 #include <skas.h>
27 #include <sysdep/stub.h>
28 #include <linux/threads.h>
29 #include <timetravel.h>
30 #include "../internal.h"
31
is_skas_winch(int pid,int fd,void * data)32 int is_skas_winch(int pid, int fd, void *data)
33 {
34 return pid == getpgrp();
35 }
36
ptrace_reg_name(int idx)37 static const char *ptrace_reg_name(int idx)
38 {
39 #define R(n) case HOST_##n: return #n
40
41 switch (idx) {
42 #ifdef __x86_64__
43 R(BX);
44 R(CX);
45 R(DI);
46 R(SI);
47 R(DX);
48 R(BP);
49 R(AX);
50 R(R8);
51 R(R9);
52 R(R10);
53 R(R11);
54 R(R12);
55 R(R13);
56 R(R14);
57 R(R15);
58 R(ORIG_AX);
59 R(CS);
60 R(SS);
61 R(EFLAGS);
62 #elif defined(__i386__)
63 R(IP);
64 R(SP);
65 R(EFLAGS);
66 R(AX);
67 R(BX);
68 R(CX);
69 R(DX);
70 R(SI);
71 R(DI);
72 R(BP);
73 R(CS);
74 R(SS);
75 R(DS);
76 R(FS);
77 R(ES);
78 R(GS);
79 R(ORIG_AX);
80 #endif
81 }
82 return "";
83 }
84
ptrace_dump_regs(int pid)85 static int ptrace_dump_regs(int pid)
86 {
87 unsigned long regs[MAX_REG_NR];
88 int i;
89
90 if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
91 return -errno;
92
93 printk(UM_KERN_ERR "Stub registers -\n");
94 for (i = 0; i < ARRAY_SIZE(regs); i++) {
95 const char *regname = ptrace_reg_name(i);
96
97 printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
98 }
99
100 return 0;
101 }
102
103 /*
104 * Signals that are OK to receive in the stub - we'll just continue it.
105 * SIGWINCH will happen when UML is inside a detached screen.
106 */
107 #define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
108
109 /* Signals that the stub will finish with - anything else is an error */
110 #define STUB_DONE_MASK (1 << SIGTRAP)
111
wait_stub_done(int pid)112 void wait_stub_done(int pid)
113 {
114 int n, status, err;
115
116 while (1) {
117 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
118 if ((n < 0) || !WIFSTOPPED(status))
119 goto bad_wait;
120
121 if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
122 break;
123
124 err = ptrace(PTRACE_CONT, pid, 0, 0);
125 if (err) {
126 printk(UM_KERN_ERR "%s : continue failed, errno = %d\n",
127 __func__, errno);
128 fatal_sigsegv();
129 }
130 }
131
132 if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
133 return;
134
135 bad_wait:
136 err = ptrace_dump_regs(pid);
137 if (err)
138 printk(UM_KERN_ERR "Failed to get registers from stub, errno = %d\n",
139 -err);
140 printk(UM_KERN_ERR "%s : failed to wait for SIGTRAP, pid = %d, n = %d, errno = %d, status = 0x%x\n",
141 __func__, pid, n, errno, status);
142 fatal_sigsegv();
143 }
144
145 extern unsigned long current_stub_stack(void);
146
get_skas_faultinfo(int pid,struct faultinfo * fi)147 static void get_skas_faultinfo(int pid, struct faultinfo *fi)
148 {
149 int err;
150
151 err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
152 if (err) {
153 printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
154 "errno = %d\n", pid, errno);
155 fatal_sigsegv();
156 }
157 wait_stub_done(pid);
158
159 /*
160 * faultinfo is prepared by the stub_segv_handler at start of
161 * the stub stack page. We just have to copy it.
162 */
163 memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
164 }
165
handle_segv(int pid,struct uml_pt_regs * regs)166 static void handle_segv(int pid, struct uml_pt_regs *regs)
167 {
168 get_skas_faultinfo(pid, ®s->faultinfo);
169 segv(regs->faultinfo, 0, 1, NULL);
170 }
171
handle_trap(int pid,struct uml_pt_regs * regs)172 static void handle_trap(int pid, struct uml_pt_regs *regs)
173 {
174 if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
175 fatal_sigsegv();
176
177 handle_syscall(regs);
178 }
179
180 extern char __syscall_stub_start[];
181
182 static int stub_exe_fd;
183
184 #ifndef CLOSE_RANGE_CLOEXEC
185 #define CLOSE_RANGE_CLOEXEC (1U << 2)
186 #endif
187
userspace_tramp(void * stack)188 static int userspace_tramp(void *stack)
189 {
190 char *const argv[] = { "uml-userspace", NULL };
191 int pipe_fds[2];
192 unsigned long long offset;
193 struct stub_init_data init_data = {
194 .stub_start = STUB_START,
195 .segv_handler = STUB_CODE +
196 (unsigned long) stub_segv_handler -
197 (unsigned long) __syscall_stub_start,
198 };
199 struct iomem_region *iomem;
200 int ret;
201
202 init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
203 &offset);
204 init_data.stub_code_offset = MMAP_OFFSET(offset);
205
206 init_data.stub_data_fd = phys_mapping(uml_to_phys(stack), &offset);
207 init_data.stub_data_offset = MMAP_OFFSET(offset);
208
209 /*
210 * Avoid leaking unneeded FDs to the stub by setting CLOEXEC on all FDs
211 * and then unsetting it on all memory related FDs.
212 * This is not strictly necessary from a safety perspective.
213 */
214 syscall(__NR_close_range, 0, ~0U, CLOSE_RANGE_CLOEXEC);
215
216 fcntl(init_data.stub_data_fd, F_SETFD, 0);
217 for (iomem = iomem_regions; iomem; iomem = iomem->next)
218 fcntl(iomem->fd, F_SETFD, 0);
219
220 /* Create a pipe for init_data (no CLOEXEC) and dup2 to STDIN */
221 if (pipe(pipe_fds))
222 exit(2);
223
224 if (dup2(pipe_fds[0], 0) < 0)
225 exit(3);
226 close(pipe_fds[0]);
227
228 /* Write init_data and close write side */
229 ret = write(pipe_fds[1], &init_data, sizeof(init_data));
230 close(pipe_fds[1]);
231
232 if (ret != sizeof(init_data))
233 exit(4);
234
235 /* Raw execveat for compatibility with older libc versions */
236 syscall(__NR_execveat, stub_exe_fd, (unsigned long)"",
237 (unsigned long)argv, NULL, AT_EMPTY_PATH);
238
239 exit(5);
240 }
241
242 extern char stub_exe_start[];
243 extern char stub_exe_end[];
244
245 extern char *tempdir;
246
247 #define STUB_EXE_NAME_TEMPLATE "/uml-userspace-XXXXXX"
248
249 #ifndef MFD_EXEC
250 #define MFD_EXEC 0x0010U
251 #endif
252
init_stub_exe_fd(void)253 static int __init init_stub_exe_fd(void)
254 {
255 size_t written = 0;
256 char *tmpfile = NULL;
257
258 stub_exe_fd = memfd_create("uml-userspace",
259 MFD_EXEC | MFD_CLOEXEC | MFD_ALLOW_SEALING);
260
261 if (stub_exe_fd < 0) {
262 printk(UM_KERN_INFO "Could not create executable memfd, using temporary file!");
263
264 tmpfile = malloc(strlen(tempdir) +
265 strlen(STUB_EXE_NAME_TEMPLATE) + 1);
266 if (tmpfile == NULL)
267 panic("Failed to allocate memory for stub binary name");
268
269 strcpy(tmpfile, tempdir);
270 strcat(tmpfile, STUB_EXE_NAME_TEMPLATE);
271
272 stub_exe_fd = mkstemp(tmpfile);
273 if (stub_exe_fd < 0)
274 panic("Could not create temporary file for stub binary: %d",
275 -errno);
276 }
277
278 while (written < stub_exe_end - stub_exe_start) {
279 ssize_t res = write(stub_exe_fd, stub_exe_start + written,
280 stub_exe_end - stub_exe_start - written);
281 if (res < 0) {
282 if (errno == EINTR)
283 continue;
284
285 if (tmpfile)
286 unlink(tmpfile);
287 panic("Failed write stub binary: %d", -errno);
288 }
289
290 written += res;
291 }
292
293 if (!tmpfile) {
294 fcntl(stub_exe_fd, F_ADD_SEALS,
295 F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_SEAL);
296 } else {
297 if (fchmod(stub_exe_fd, 00500) < 0) {
298 unlink(tmpfile);
299 panic("Could not make stub binary executable: %d",
300 -errno);
301 }
302
303 close(stub_exe_fd);
304 stub_exe_fd = open(tmpfile, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
305 if (stub_exe_fd < 0) {
306 unlink(tmpfile);
307 panic("Could not reopen stub binary: %d", -errno);
308 }
309
310 unlink(tmpfile);
311 free(tmpfile);
312 }
313
314 return 0;
315 }
316 __initcall(init_stub_exe_fd);
317
318 int userspace_pid[NR_CPUS];
319
320 /**
321 * start_userspace() - prepare a new userspace process
322 * @stub_stack: pointer to the stub stack.
323 *
324 * Setups a new temporary stack page that is used while userspace_tramp() runs
325 * Clones the kernel process into a new userspace process, with FDs only.
326 *
327 * Return: When positive: the process id of the new userspace process,
328 * when negative: an error number.
329 * FIXME: can PIDs become negative?!
330 */
start_userspace(unsigned long stub_stack)331 int start_userspace(unsigned long stub_stack)
332 {
333 void *stack;
334 unsigned long sp;
335 int pid, status, n, err;
336
337 /* setup a temporary stack page */
338 stack = mmap(NULL, UM_KERN_PAGE_SIZE,
339 PROT_READ | PROT_WRITE | PROT_EXEC,
340 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
341 if (stack == MAP_FAILED) {
342 err = -errno;
343 printk(UM_KERN_ERR "%s : mmap failed, errno = %d\n",
344 __func__, errno);
345 return err;
346 }
347
348 /* set stack pointer to the end of the stack page, so it can grow downwards */
349 sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;
350
351 /* clone into new userspace process */
352 pid = clone(userspace_tramp, (void *) sp,
353 CLONE_VFORK | CLONE_VM | SIGCHLD,
354 (void *)stub_stack);
355 if (pid < 0) {
356 err = -errno;
357 printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
358 __func__, errno);
359 return err;
360 }
361
362 do {
363 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
364 if (n < 0) {
365 err = -errno;
366 printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
367 __func__, errno);
368 goto out_kill;
369 }
370 } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
371
372 if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
373 err = -EINVAL;
374 printk(UM_KERN_ERR "%s : expected SIGSTOP, got status = %d\n",
375 __func__, status);
376 goto out_kill;
377 }
378
379 if (ptrace(PTRACE_SETOPTIONS, pid, NULL,
380 (void *) PTRACE_O_TRACESYSGOOD) < 0) {
381 err = -errno;
382 printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
383 __func__, errno);
384 goto out_kill;
385 }
386
387 if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
388 err = -errno;
389 printk(UM_KERN_ERR "%s : munmap failed, errno = %d\n",
390 __func__, errno);
391 goto out_kill;
392 }
393
394 return pid;
395
396 out_kill:
397 os_kill_ptraced_process(pid, 1);
398 return err;
399 }
400
401 int unscheduled_userspace_iterations;
402 extern unsigned long tt_extra_sched_jiffies;
403
userspace(struct uml_pt_regs * regs)404 void userspace(struct uml_pt_regs *regs)
405 {
406 int err, status, op, pid = userspace_pid[0];
407 siginfo_t si;
408
409 /* Handle any immediate reschedules or signals */
410 interrupt_end();
411
412 while (1) {
413 /*
414 * When we are in time-travel mode, userspace can theoretically
415 * do a *lot* of work without being scheduled. The problem with
416 * this is that it will prevent kernel bookkeeping (primarily
417 * the RCU) from running and this can for example cause OOM
418 * situations.
419 *
420 * This code accounts a jiffie against the scheduling clock
421 * after the defined userspace iterations in the same thread.
422 * By doing so the situation is effectively prevented.
423 */
424 if (time_travel_mode == TT_MODE_INFCPU ||
425 time_travel_mode == TT_MODE_EXTERNAL) {
426 #ifdef CONFIG_UML_MAX_USERSPACE_ITERATIONS
427 if (CONFIG_UML_MAX_USERSPACE_ITERATIONS &&
428 unscheduled_userspace_iterations++ >
429 CONFIG_UML_MAX_USERSPACE_ITERATIONS) {
430 tt_extra_sched_jiffies += 1;
431 unscheduled_userspace_iterations = 0;
432 }
433 #endif
434 }
435
436 time_travel_print_bc_msg();
437
438 current_mm_sync();
439
440 /* Flush out any pending syscalls */
441 err = syscall_stub_flush(current_mm_id());
442 if (err) {
443 if (err == -ENOMEM)
444 report_enomem();
445
446 printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
447 __func__, -err);
448 fatal_sigsegv();
449 }
450
451 /*
452 * This can legitimately fail if the process loads a
453 * bogus value into a segment register. It will
454 * segfault and PTRACE_GETREGS will read that value
455 * out of the process. However, PTRACE_SETREGS will
456 * fail. In this case, there is nothing to do but
457 * just kill the process.
458 */
459 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
460 printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
461 __func__, errno);
462 fatal_sigsegv();
463 }
464
465 if (put_fp_registers(pid, regs->fp)) {
466 printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
467 __func__, errno);
468 fatal_sigsegv();
469 }
470
471 if (singlestepping())
472 op = PTRACE_SYSEMU_SINGLESTEP;
473 else
474 op = PTRACE_SYSEMU;
475
476 if (ptrace(op, pid, 0, 0)) {
477 printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
478 __func__, op, errno);
479 fatal_sigsegv();
480 }
481
482 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
483 if (err < 0) {
484 printk(UM_KERN_ERR "%s - wait failed, errno = %d\n",
485 __func__, errno);
486 fatal_sigsegv();
487 }
488
489 regs->is_user = 1;
490 if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
491 printk(UM_KERN_ERR "%s - PTRACE_GETREGS failed, errno = %d\n",
492 __func__, errno);
493 fatal_sigsegv();
494 }
495
496 if (get_fp_registers(pid, regs->fp)) {
497 printk(UM_KERN_ERR "%s - get_fp_registers failed, errno = %d\n",
498 __func__, errno);
499 fatal_sigsegv();
500 }
501
502 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
503
504 if (WIFSTOPPED(status)) {
505 int sig = WSTOPSIG(status);
506
507 /* These signal handlers need the si argument.
508 * The SIGIO and SIGALARM handlers which constitute the
509 * majority of invocations, do not use it.
510 */
511 switch (sig) {
512 case SIGSEGV:
513 case SIGTRAP:
514 case SIGILL:
515 case SIGBUS:
516 case SIGFPE:
517 case SIGWINCH:
518 ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
519 break;
520 }
521
522 switch (sig) {
523 case SIGSEGV:
524 if (PTRACE_FULL_FAULTINFO) {
525 get_skas_faultinfo(pid,
526 ®s->faultinfo);
527 (*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
528 regs);
529 }
530 else handle_segv(pid, regs);
531 break;
532 case SIGTRAP + 0x80:
533 handle_trap(pid, regs);
534 break;
535 case SIGTRAP:
536 relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
537 break;
538 case SIGALRM:
539 break;
540 case SIGIO:
541 case SIGILL:
542 case SIGBUS:
543 case SIGFPE:
544 case SIGWINCH:
545 block_signals_trace();
546 (*sig_info[sig])(sig, (struct siginfo *)&si, regs);
547 unblock_signals_trace();
548 break;
549 default:
550 printk(UM_KERN_ERR "%s - child stopped with signal %d\n",
551 __func__, sig);
552 fatal_sigsegv();
553 }
554 pid = userspace_pid[0];
555 interrupt_end();
556
557 /* Avoid -ERESTARTSYS handling in host */
558 if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
559 PT_SYSCALL_NR(regs->gp) = -1;
560 }
561 }
562 }
563
new_thread(void * stack,jmp_buf * buf,void (* handler)(void))564 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
565 {
566 (*buf)[0].JB_IP = (unsigned long) handler;
567 (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
568 sizeof(void *);
569 }
570
571 #define INIT_JMP_NEW_THREAD 0
572 #define INIT_JMP_CALLBACK 1
573 #define INIT_JMP_HALT 2
574 #define INIT_JMP_REBOOT 3
575
switch_threads(jmp_buf * me,jmp_buf * you)576 void switch_threads(jmp_buf *me, jmp_buf *you)
577 {
578 unscheduled_userspace_iterations = 0;
579
580 if (UML_SETJMP(me) == 0)
581 UML_LONGJMP(you, 1);
582 }
583
584 static jmp_buf initial_jmpbuf;
585
586 /* XXX Make these percpu */
587 static void (*cb_proc)(void *arg);
588 static void *cb_arg;
589 static jmp_buf *cb_back;
590
start_idle_thread(void * stack,jmp_buf * switch_buf)591 int start_idle_thread(void *stack, jmp_buf *switch_buf)
592 {
593 int n;
594
595 set_handler(SIGWINCH);
596
597 /*
598 * Can't use UML_SETJMP or UML_LONGJMP here because they save
599 * and restore signals, with the possible side-effect of
600 * trying to handle any signals which came when they were
601 * blocked, which can't be done on this stack.
602 * Signals must be blocked when jumping back here and restored
603 * after returning to the jumper.
604 */
605 n = setjmp(initial_jmpbuf);
606 switch (n) {
607 case INIT_JMP_NEW_THREAD:
608 (*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
609 (*switch_buf)[0].JB_SP = (unsigned long) stack +
610 UM_THREAD_SIZE - sizeof(void *);
611 break;
612 case INIT_JMP_CALLBACK:
613 (*cb_proc)(cb_arg);
614 longjmp(*cb_back, 1);
615 break;
616 case INIT_JMP_HALT:
617 kmalloc_ok = 0;
618 return 0;
619 case INIT_JMP_REBOOT:
620 kmalloc_ok = 0;
621 return 1;
622 default:
623 printk(UM_KERN_ERR "Bad sigsetjmp return in %s - %d\n",
624 __func__, n);
625 fatal_sigsegv();
626 }
627 longjmp(*switch_buf, 1);
628
629 /* unreachable */
630 printk(UM_KERN_ERR "impossible long jump!");
631 fatal_sigsegv();
632 return 0;
633 }
634
initial_thread_cb_skas(void (* proc)(void *),void * arg)635 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
636 {
637 jmp_buf here;
638
639 cb_proc = proc;
640 cb_arg = arg;
641 cb_back = &here;
642
643 block_signals_trace();
644 if (UML_SETJMP(&here) == 0)
645 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
646 unblock_signals_trace();
647
648 cb_proc = NULL;
649 cb_arg = NULL;
650 cb_back = NULL;
651 }
652
halt_skas(void)653 void halt_skas(void)
654 {
655 block_signals_trace();
656 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
657 }
658
659 static bool noreboot;
660
noreboot_cmd_param(char * str,int * add)661 static int __init noreboot_cmd_param(char *str, int *add)
662 {
663 *add = 0;
664 noreboot = true;
665 return 0;
666 }
667
668 __uml_setup("noreboot", noreboot_cmd_param,
669 "noreboot\n"
670 " Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
671 " This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
672 " crashes in CI\n");
673
reboot_skas(void)674 void reboot_skas(void)
675 {
676 block_signals_trace();
677 UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
678 }
679
__switch_mm(struct mm_id * mm_idp)680 void __switch_mm(struct mm_id *mm_idp)
681 {
682 userspace_pid[0] = mm_idp->pid;
683 }
684