xref: /freebsd-11-stable/sys/kern/subr_syscall.c

/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (C) 1994, David Greenman
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 * Copyright (C) 2010 Konstantin Belousov <kib@freebsd.org>
 *
 * This code is derived from software contributed to Berkeley by
 * the University of Utah, and William Jolitz.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	from: @(#)trap.c	7.4 (Berkeley) 5/13/91
 */

#include "opt_capsicum.h"
#include "opt_ktrace.h"

__FBSDID("$FreeBSD: stable/11/sys/kern/subr_syscall.c 331017 2018-03-15 19:08:33Z kevans $");

#include <sys/capsicum.h>
#include <sys/ktr.h>
#include <sys/vmmeter.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <security/audit/audit.h>

static inline int
syscallenter(struct thread *td)
{
	struct proc *p;
	struct syscall_args *sa;
	int error, traced;

	PCPU_INC(cnt.v_syscall);
	p = td->td_proc;
	sa = &td->td_sa;

	td->td_pticks = 0;
	if (td->td_cowgen != p->p_cowgen)
		thread_cow_update(td);
	traced = (p->p_flag & P_TRACED) != 0;
	if (traced || td->td_dbgflags & TDB_USERWR) {
		PROC_LOCK(p);
		td->td_dbgflags &= ~TDB_USERWR;
		if (traced)
			td->td_dbgflags |= TDB_SCE;
		PROC_UNLOCK(p);
	}
	error = (p->p_sysent->sv_fetch_syscall_args)(td);
#ifdef KTRACE
	if (KTRPOINT(td, KTR_SYSCALL))
		ktrsyscall(sa->code, sa->narg, sa->args);
#endif
	KTR_START4(KTR_SYSC, "syscall", syscallname(p, sa->code),
	    (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "arg0:%p", sa->args[0],
	    "arg1:%p", sa->args[1], "arg2:%p", sa->args[2]);

	if (error == 0) {

		STOPEVENT(p, S_SCE, sa->narg);
		if (p->p_flag & P_TRACED) {
			PROC_LOCK(p);
			if (p->p_ptevents & PTRACE_SCE)
				ptracestop((td), SIGTRAP, NULL);
			PROC_UNLOCK(p);
		}
		if (td->td_dbgflags & TDB_USERWR) {
			/*
			 * Reread syscall number and arguments if
			 * debugger modified registers or memory.
			 */
			error = (p->p_sysent->sv_fetch_syscall_args)(td);
#ifdef KTRACE
			if (KTRPOINT(td, KTR_SYSCALL))
				ktrsyscall(sa->code, sa->narg, sa->args);
#endif
			if (error != 0)
				goto retval;
		}

#ifdef CAPABILITY_MODE
		/*
		 * In capability mode, we only allow access to system calls
		 * flagged with SYF_CAPENABLED.
		 */
		if (IN_CAPABILITY_MODE(td) &&
		    !(sa->callp->sy_flags & SYF_CAPENABLED)) {
			error = ECAPMODE;
			goto retval;
		}
#endif

		error = syscall_thread_enter(td, sa->callp);
		if (error != 0)
			goto retval;

#ifdef KDTRACE_HOOKS
		/* Give the syscall:::entry DTrace probe a chance to fire. */
		if (systrace_probe_func != NULL && sa->callp->sy_entry != 0)
			(*systrace_probe_func)(sa, SYSTRACE_ENTRY, 0);
#endif

		AUDIT_SYSCALL_ENTER(sa->code, td);
		error = (sa->callp->sy_call)(td, sa->args);
		AUDIT_SYSCALL_EXIT(error, td);

		/* Save the latest error return value. */
		if ((td->td_pflags & TDP_NERRNO) == 0)
			td->td_errno = error;

#ifdef KDTRACE_HOOKS
		/* Give the syscall:::return DTrace probe a chance to fire. */
		if (systrace_probe_func != NULL && sa->callp->sy_return != 0)
			(*systrace_probe_func)(sa, SYSTRACE_RETURN,
			    error ? -1 : td->td_retval[0]);
#endif
		syscall_thread_exit(td, sa->callp);
	}
 retval:
	KTR_STOP4(KTR_SYSC, "syscall", syscallname(p, sa->code),
	    (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "error:%d", error,
	    "retval0:%#lx", td->td_retval[0], "retval1:%#lx",
	    td->td_retval[1]);
	if (traced) {
		PROC_LOCK(p);
		td->td_dbgflags &= ~TDB_SCE;
		PROC_UNLOCK(p);
	}
	(p->p_sysent->sv_set_syscall_retval)(td, error);
	return (error);
}

static inline void
syscallret(struct thread *td, int error)
{
	struct proc *p, *p2;
	struct syscall_args *sa;
	ksiginfo_t ksi;
	int traced, error1;

	KASSERT((td->td_pflags & TDP_FORKING) == 0,
	    ("fork() did not clear TDP_FORKING upon completion"));

	p = td->td_proc;
	sa = &td->td_sa;
	if ((trap_enotcap || (p->p_flag2 & P2_TRAPCAP) != 0) &&
	    IN_CAPABILITY_MODE(td)) {
		error1 = (td->td_pflags & TDP_NERRNO) == 0 ? error :
		    td->td_errno;
		if (error1 == ENOTCAPABLE || error1 == ECAPMODE) {
			ksiginfo_init_trap(&ksi);
			ksi.ksi_signo = SIGTRAP;
			ksi.ksi_errno = error1;
			ksi.ksi_code = TRAP_CAP;
			trapsignal(td, &ksi);
		}
	}

	/*
	 * Handle reschedule and other end-of-syscall issues
	 */
	userret(td, td->td_frame);

#ifdef KTRACE
	if (KTRPOINT(td, KTR_SYSRET)) {
		ktrsysret(sa->code, (td->td_pflags & TDP_NERRNO) == 0 ?
		    error : td->td_errno, td->td_retval[0]);
	}
#endif
	td->td_pflags &= ~TDP_NERRNO;

	if (p->p_flag & P_TRACED) {
		traced = 1;
		PROC_LOCK(p);
		td->td_dbgflags |= TDB_SCX;
		PROC_UNLOCK(p);
	} else
		traced = 0;
	/*
	 * This works because errno is findable through the
	 * register set.  If we ever support an emulation where this
	 * is not the case, this code will need to be revisited.
	 */
	STOPEVENT(p, S_SCX, sa->code);
	if (traced || (td->td_dbgflags & (TDB_EXEC | TDB_FORK)) != 0) {
		PROC_LOCK(p);
		/*
		 * If tracing the execed process, trap to the debugger
		 * so that breakpoints can be set before the program
		 * executes.  If debugger requested tracing of syscall
		 * returns, do it now too.
		 */
		if (traced &&
		    ((td->td_dbgflags & (TDB_FORK | TDB_EXEC)) != 0 ||
		    (p->p_ptevents & PTRACE_SCX) != 0))
			ptracestop(td, SIGTRAP, NULL);
		td->td_dbgflags &= ~(TDB_SCX | TDB_EXEC | TDB_FORK);
		PROC_UNLOCK(p);
	}

	if (td->td_pflags & TDP_RFPPWAIT) {
		/*
		 * Preserve synchronization semantics of vfork.  If
		 * waiting for child to exec or exit, fork set
		 * P_PPWAIT on child, and there we sleep on our proc
		 * (in case of exit).
		 *
		 * Do it after the ptracestop() above is finished, to
		 * not block our debugger until child execs or exits
		 * to finish vfork wait.
		 */
		td->td_pflags &= ~TDP_RFPPWAIT;
		p2 = td->td_rfppwait_p;
again:
		PROC_LOCK(p2);
		while (p2->p_flag & P_PPWAIT) {
			PROC_LOCK(p);
			if (thread_suspend_check_needed()) {
				PROC_UNLOCK(p2);
				thread_suspend_check(0);
				PROC_UNLOCK(p);
				goto again;
			} else {
				PROC_UNLOCK(p);
			}
			cv_timedwait(&p2->p_pwait, &p2->p_mtx, hz);
		}
		PROC_UNLOCK(p2);

		if (td->td_dbgflags & TDB_VFORK) {
			PROC_LOCK(p);
			if (p->p_ptevents & PTRACE_VFORK)
				ptracestop(td, SIGTRAP, NULL);
			td->td_dbgflags &= ~TDB_VFORK;
			PROC_UNLOCK(p);
		}
	}
}