xref: /kernel/linux/linux-6.6/arch/um/os-Linux/skas/process.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <asm/unistd.h>
#include <as-layout.h>
#include <init.h>
#include <kern_util.h>
#include <mem.h>
#include <os.h>
#include <ptrace_user.h>
#include <registers.h>
#include <skas.h>
#include <sysdep/stub.h>
#include <linux/threads.h>

int is_skas_winch(int pid, int fd, void *data)
{
	return pid == getpgrp();
}

static const char *ptrace_reg_name(int idx)
{
#define R(n) case HOST_##n: return #n

	switch (idx) {
#ifdef __x86_64__
	R(BX);
	R(CX);
	R(DI);
	R(SI);
	R(DX);
	R(BP);
	R(AX);
	R(R8);
	R(R9);
	R(R10);
	R(R11);
	R(R12);
	R(R13);
	R(R14);
	R(R15);
	R(ORIG_AX);
	R(CS);
	R(SS);
	R(EFLAGS);
#elif defined(__i386__)
	R(IP);
	R(SP);
	R(EFLAGS);
	R(AX);
	R(BX);
	R(CX);
	R(DX);
	R(SI);
	R(DI);
	R(BP);
	R(CS);
	R(SS);
	R(DS);
	R(FS);
	R(ES);
	R(GS);
	R(ORIG_AX);
#endif
	}
	return "";
}

static int ptrace_dump_regs(int pid)
{
	unsigned long regs[MAX_REG_NR];
	int i;

	if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
		return -errno;

	printk(UM_KERN_ERR "Stub registers -\n");
	for (i = 0; i < ARRAY_SIZE(regs); i++) {
		const char *regname = ptrace_reg_name(i);

		printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
	}

	return 0;
}

/*
 * Signals that are OK to receive in the stub - we'll just continue it.
 * SIGWINCH will happen when UML is inside a detached screen.
 */
#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))

/* Signals that the stub will finish with - anything else is an error */
#define STUB_DONE_MASK (1 << SIGTRAP)

void wait_stub_done(int pid)
{
	int n, status, err;

	while (1) {
		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
		if ((n < 0) || !WIFSTOPPED(status))
			goto bad_wait;

		if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
			break;

		err = ptrace(PTRACE_CONT, pid, 0, 0);
		if (err) {
			printk(UM_KERN_ERR "%s : continue failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}
	}

	if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
		return;

bad_wait:
	err = ptrace_dump_regs(pid);
	if (err)
		printk(UM_KERN_ERR "Failed to get registers from stub, errno = %d\n",
		       -err);
	printk(UM_KERN_ERR "%s : failed to wait for SIGTRAP, pid = %d, n = %d, errno = %d, status = 0x%x\n",
	       __func__, pid, n, errno, status);
	fatal_sigsegv();
}

extern unsigned long current_stub_stack(void);

static void get_skas_faultinfo(int pid, struct faultinfo *fi, unsigned long *aux_fp_regs)
{
	int err;

	err = get_fp_registers(pid, aux_fp_regs);
	if (err < 0) {
		printk(UM_KERN_ERR "save_fp_registers returned %d\n",
		       err);
		fatal_sigsegv();
	}
	err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
	if (err) {
		printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
		       "errno = %d\n", pid, errno);
		fatal_sigsegv();
	}
	wait_stub_done(pid);

	/*
	 * faultinfo is prepared by the stub_segv_handler at start of
	 * the stub stack page. We just have to copy it.
	 */
	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));

	err = put_fp_registers(pid, aux_fp_regs);
	if (err < 0) {
		printk(UM_KERN_ERR "put_fp_registers returned %d\n",
		       err);
		fatal_sigsegv();
	}
}

static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
{
	get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
	segv(regs->faultinfo, 0, 1, NULL);
}

/*
 * To use the same value of using_sysemu as the caller, ask it that value
 * (in local_using_sysemu
 */
static void handle_trap(int pid, struct uml_pt_regs *regs,
			int local_using_sysemu)
{
	int err, status;

	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
		fatal_sigsegv();

	if (!local_using_sysemu)
	{
		err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
			     __NR_getpid);
		if (err < 0) {
			printk(UM_KERN_ERR "%s - nullifying syscall failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
		if (err < 0) {
			printk(UM_KERN_ERR "%s - continuing to end of syscall failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
		if ((err < 0) || !WIFSTOPPED(status) ||
		    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
			err = ptrace_dump_regs(pid);
			if (err)
				printk(UM_KERN_ERR "Failed to get registers from process, errno = %d\n",
				       -err);
			printk(UM_KERN_ERR "%s - failed to wait at end of syscall, errno = %d, status = %d\n",
			       __func__, errno, status);
			fatal_sigsegv();
		}
	}

	handle_syscall(regs);
}

extern char __syscall_stub_start[];

/**
 * userspace_tramp() - userspace trampoline
 * @stack:	pointer to the new userspace stack page, can be NULL, if? FIXME:
 *
 * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
 * This function will run on a temporary stack page.
 * It ptrace()'es itself, then
 * Two pages are mapped into the userspace address space:
 * - STUB_CODE (with EXEC), which contains the skas stub code
 * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
 * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
 * And last the process stops itself to give control to the UML kernel for this userspace process.
 *
 * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
 */
static int userspace_tramp(void *stack)
{
	void *addr;
	int fd;
	unsigned long long offset;

	ptrace(PTRACE_TRACEME, 0, 0, 0);

	signal(SIGTERM, SIG_DFL);
	signal(SIGWINCH, SIG_IGN);

	fd = phys_mapping(uml_to_phys(__syscall_stub_start), &offset);
	addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
		      PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
	if (addr == MAP_FAILED) {
		printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, errno = %d\n",
		       STUB_CODE, errno);
		exit(1);
	}

	if (stack != NULL) {
		fd = phys_mapping(uml_to_phys(stack), &offset);
		addr = mmap((void *) STUB_DATA,
			    STUB_DATA_PAGES * UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
			    MAP_FIXED | MAP_SHARED, fd, offset);
		if (addr == MAP_FAILED) {
			printk(UM_KERN_ERR "mapping segfault stack at 0x%lx failed, errno = %d\n",
			       STUB_DATA, errno);
			exit(1);
		}
	}
	if (stack != NULL) {
		struct sigaction sa;

		unsigned long v = STUB_CODE +
				  (unsigned long) stub_segv_handler -
				  (unsigned long) __syscall_stub_start;

		set_sigstack((void *) STUB_DATA, STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
		sigemptyset(&sa.sa_mask);
		sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
		sa.sa_sigaction = (void *) v;
		sa.sa_restorer = NULL;
		if (sigaction(SIGSEGV, &sa, NULL) < 0) {
			printk(UM_KERN_ERR "%s - setting SIGSEGV handler failed - errno = %d\n",
			       __func__, errno);
			exit(1);
		}
	}

	kill(os_getpid(), SIGSTOP);
	return 0;
}

int userspace_pid[NR_CPUS];
int kill_userspace_mm[NR_CPUS];

/**
 * start_userspace() - prepare a new userspace process
 * @stub_stack:	pointer to the stub stack. Can be NULL, if? FIXME:
 *
 * Setups a new temporary stack page that is used while userspace_tramp() runs
 * Clones the kernel process into a new userspace process, with FDs only.
 *
 * Return: When positive: the process id of the new userspace process,
 *         when negative: an error number.
 * FIXME: can PIDs become negative?!
 */
int start_userspace(unsigned long stub_stack)
{
	void *stack;
	unsigned long sp;
	int pid, status, n, flags, err;

	/* setup a temporary stack page */
	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
		     PROT_READ | PROT_WRITE | PROT_EXEC,
		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if (stack == MAP_FAILED) {
		err = -errno;
		printk(UM_KERN_ERR "%s : mmap failed, errno = %d\n",
		       __func__, errno);
		return err;
	}

	/* set stack pointer to the end of the stack page, so it can grow downwards */
	sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;

	flags = CLONE_FILES | SIGCHLD;

	/* clone into new userspace process */
	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
	if (pid < 0) {
		err = -errno;
		printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
		       __func__, errno);
		return err;
	}

	do {
		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
		if (n < 0) {
			err = -errno;
			printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
			       __func__, errno);
			goto out_kill;
		}
	} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));

	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
		err = -EINVAL;
		printk(UM_KERN_ERR "%s : expected SIGSTOP, got status = %d\n",
		       __func__, status);
		goto out_kill;
	}

	if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
		   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
		err = -errno;
		printk(UM_KERN_ERR "%s : PTRACE_OLDSETOPTIONS failed, errno = %d\n",
		       __func__, errno);
		goto out_kill;
	}

	if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
		err = -errno;
		printk(UM_KERN_ERR "%s : munmap failed, errno = %d\n",
		       __func__, errno);
		goto out_kill;
	}

	return pid;

 out_kill:
	os_kill_ptraced_process(pid, 1);
	return err;
}

void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
{
	int err, status, op, pid = userspace_pid[0];
	/* To prevent races if using_sysemu changes under us.*/
	int local_using_sysemu;
	siginfo_t si;

	/* Handle any immediate reschedules or signals */
	interrupt_end();

	while (1) {
		if (kill_userspace_mm[0])
			fatal_sigsegv();

		/*
		 * This can legitimately fail if the process loads a
		 * bogus value into a segment register.  It will
		 * segfault and PTRACE_GETREGS will read that value
		 * out of the process.  However, PTRACE_SETREGS will
		 * fail.  In this case, there is nothing to do but
		 * just kill the process.
		 */
		if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
			printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		if (put_fp_registers(pid, regs->fp)) {
			printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		/* Now we set local_using_sysemu to be used for one loop */
		local_using_sysemu = get_using_sysemu();

		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
					     singlestepping(NULL));

		if (ptrace(op, pid, 0, 0)) {
			printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
			       __func__, op, errno);
			fatal_sigsegv();
		}

		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
		if (err < 0) {
			printk(UM_KERN_ERR "%s - wait failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		regs->is_user = 1;
		if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
			printk(UM_KERN_ERR "%s - PTRACE_GETREGS failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		if (get_fp_registers(pid, regs->fp)) {
			printk(UM_KERN_ERR "%s -  get_fp_registers failed, errno = %d\n",
			       __func__, errno);
			fatal_sigsegv();
		}

		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */

		if (WIFSTOPPED(status)) {
			int sig = WSTOPSIG(status);

			/* These signal handlers need the si argument.
			 * The SIGIO and SIGALARM handlers which constitute the
			 * majority of invocations, do not use it.
			 */
			switch (sig) {
			case SIGSEGV:
			case SIGTRAP:
			case SIGILL:
			case SIGBUS:
			case SIGFPE:
			case SIGWINCH:
				ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
				break;
			}

			switch (sig) {
			case SIGSEGV:
				if (PTRACE_FULL_FAULTINFO) {
					get_skas_faultinfo(pid,
							   &regs->faultinfo, aux_fp_regs);
					(*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
							     regs);
				}
				else handle_segv(pid, regs, aux_fp_regs);
				break;
			case SIGTRAP + 0x80:
			        handle_trap(pid, regs, local_using_sysemu);
				break;
			case SIGTRAP:
				relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
				break;
			case SIGALRM:
				break;
			case SIGIO:
			case SIGILL:
			case SIGBUS:
			case SIGFPE:
			case SIGWINCH:
				block_signals_trace();
				(*sig_info[sig])(sig, (struct siginfo *)&si, regs);
				unblock_signals_trace();
				break;
			default:
				printk(UM_KERN_ERR "%s - child stopped with signal %d\n",
				       __func__, sig);
				fatal_sigsegv();
			}
			pid = userspace_pid[0];
			interrupt_end();

			/* Avoid -ERESTARTSYS handling in host */
			if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
				PT_SYSCALL_NR(regs->gp) = -1;
		}
	}
}

static unsigned long thread_regs[MAX_REG_NR];
static unsigned long thread_fp_regs[FP_SIZE];

static int __init init_thread_regs(void)
{
	get_safe_registers(thread_regs, thread_fp_regs);
	/* Set parent's instruction pointer to start of clone-stub */
	thread_regs[REGS_IP_INDEX] = STUB_CODE +
				(unsigned long) stub_clone_handler -
				(unsigned long) __syscall_stub_start;
	thread_regs[REGS_SP_INDEX] = STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE -
		sizeof(void *);
#ifdef __SIGNAL_FRAMESIZE
	thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
#endif
	return 0;
}

__initcall(init_thread_regs);

int copy_context_skas0(unsigned long new_stack, int pid)
{
	int err;
	unsigned long current_stack = current_stub_stack();
	struct stub_data *data = (struct stub_data *) current_stack;
	struct stub_data *child_data = (struct stub_data *) new_stack;
	unsigned long long new_offset;
	int new_fd = phys_mapping(uml_to_phys((void *)new_stack), &new_offset);

	/*
	 * prepare offset and fd of child's stack as argument for parent's
	 * and child's mmap2 calls
	 */
	*data = ((struct stub_data) {
		.offset	= MMAP_OFFSET(new_offset),
		.fd     = new_fd,
		.parent_err = -ESRCH,
		.child_err = 0,
	});

	*child_data = ((struct stub_data) {
		.child_err = -ESRCH,
	});

	err = ptrace_setregs(pid, thread_regs);
	if (err < 0) {
		err = -errno;
		printk(UM_KERN_ERR "%s : PTRACE_SETREGS failed, pid = %d, errno = %d\n",
		      __func__, pid, -err);
		return err;
	}

	err = put_fp_registers(pid, thread_fp_regs);
	if (err < 0) {
		printk(UM_KERN_ERR "%s : put_fp_registers failed, pid = %d, err = %d\n",
		       __func__, pid, err);
		return err;
	}

	/*
	 * Wait, until parent has finished its work: read child's pid from
	 * parent's stack, and check, if bad result.
	 */
	err = ptrace(PTRACE_CONT, pid, 0, 0);
	if (err) {
		err = -errno;
		printk(UM_KERN_ERR "Failed to continue new process, pid = %d, errno = %d\n",
		       pid, errno);
		return err;
	}

	wait_stub_done(pid);

	pid = data->parent_err;
	if (pid < 0) {
		printk(UM_KERN_ERR "%s - stub-parent reports error %d\n",
		      __func__, -pid);
		return pid;
	}

	/*
	 * Wait, until child has finished too: read child's result from
	 * child's stack and check it.
	 */
	wait_stub_done(pid);
	if (child_data->child_err != STUB_DATA) {
		printk(UM_KERN_ERR "%s - stub-child %d reports error %ld\n",
		       __func__, pid, data->child_err);
		err = data->child_err;
		goto out_kill;
	}

	if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
		   (void *)PTRACE_O_TRACESYSGOOD) < 0) {
		err = -errno;
		printk(UM_KERN_ERR "%s : PTRACE_OLDSETOPTIONS failed, errno = %d\n",
		       __func__, errno);
		goto out_kill;
	}

	return pid;

 out_kill:
	os_kill_ptraced_process(pid, 1);
	return err;
}

void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
{
	(*buf)[0].JB_IP = (unsigned long) handler;
	(*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
		sizeof(void *);
}

#define INIT_JMP_NEW_THREAD 0
#define INIT_JMP_CALLBACK 1
#define INIT_JMP_HALT 2
#define INIT_JMP_REBOOT 3

void switch_threads(jmp_buf *me, jmp_buf *you)
{
	if (UML_SETJMP(me) == 0)
		UML_LONGJMP(you, 1);
}

static jmp_buf initial_jmpbuf;

/* XXX Make these percpu */
static void (*cb_proc)(void *arg);
static void *cb_arg;
static jmp_buf *cb_back;

int start_idle_thread(void *stack, jmp_buf *switch_buf)
{
	int n;

	set_handler(SIGWINCH);

	/*
	 * Can't use UML_SETJMP or UML_LONGJMP here because they save
	 * and restore signals, with the possible side-effect of
	 * trying to handle any signals which came when they were
	 * blocked, which can't be done on this stack.
	 * Signals must be blocked when jumping back here and restored
	 * after returning to the jumper.
	 */
	n = setjmp(initial_jmpbuf);
	switch (n) {
	case INIT_JMP_NEW_THREAD:
		(*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
		(*switch_buf)[0].JB_SP = (unsigned long) stack +
			UM_THREAD_SIZE - sizeof(void *);
		break;
	case INIT_JMP_CALLBACK:
		(*cb_proc)(cb_arg);
		longjmp(*cb_back, 1);
		break;
	case INIT_JMP_HALT:
		kmalloc_ok = 0;
		return 0;
	case INIT_JMP_REBOOT:
		kmalloc_ok = 0;
		return 1;
	default:
		printk(UM_KERN_ERR "Bad sigsetjmp return in %s - %d\n",
		       __func__, n);
		fatal_sigsegv();
	}
	longjmp(*switch_buf, 1);

	/* unreachable */
	printk(UM_KERN_ERR "impossible long jump!");
	fatal_sigsegv();
	return 0;
}

void initial_thread_cb_skas(void (*proc)(void *), void *arg)
{
	jmp_buf here;

	cb_proc = proc;
	cb_arg = arg;
	cb_back = &here;

	block_signals_trace();
	if (UML_SETJMP(&here) == 0)
		UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
	unblock_signals_trace();

	cb_proc = NULL;
	cb_arg = NULL;
	cb_back = NULL;
}

void halt_skas(void)
{
	block_signals_trace();
	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
}

static bool noreboot;

static int __init noreboot_cmd_param(char *str, int *add)
{
	noreboot = true;
	return 0;
}

__uml_setup("noreboot", noreboot_cmd_param,
"noreboot\n"
"    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
"    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
"    crashes in CI\n");

void reboot_skas(void)
{
	block_signals_trace();
	UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
}

void __switch_mm(struct mm_id *mm_idp)
{
	userspace_pid[0] = mm_idp->u.pid;
	kill_userspace_mm[0] = mm_idp->kill;
}