Return to kern_syscall.c CVS log

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Allow syscall_establish() to install new syscalls when the existing
entry-point is either sys_nomodule or sys_nosys.  Update the
makesyscalls.sh script to create a const array of bits to allow
syscall_disestablish() to properly restore the original entry-point.
Update all the initializers of struct emul to initialize the pointer
to the bit array struct emul.

XXX Regen of all files created by makesyscalls.sh will come soon,
XXX followed by a kernel version bump (since struct emul is being
XXX modified).

This commit should address PR kern/45781 and also removes the need
for the work-around for that PR in file

	sys/arch/usermode/modules/syscallemu/syscallemu.c

/*	$NetBSD: kern_syscall.c,v 1.17 2018/08/10 21:44:59 pgoyette Exp $	*/

/*-
 * Copyright (c) 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software developed for The NetBSD Foundation
 * by Andrew Doran.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_syscall.c,v 1.17 2018/08/10 21:44:59 pgoyette Exp $");

#ifdef _KERNEL_OPT
#include "opt_modular.h"
#include "opt_syscall_debug.h"
#include "opt_ktrace.h"
#include "opt_ptrace.h"
#include "opt_dtrace.h"
#endif

/* XXX To get syscall prototypes. */
#define SYSVSHM
#define SYSVSEM
#define SYSVMSG

#include <sys/param.h>
#include <sys/module.h>
#include <sys/sched.h>
#include <sys/syscall.h>
#include <sys/syscallargs.h>
#include <sys/syscallvar.h>
#include <sys/systm.h>
#include <sys/xcall.h>
#include <sys/ktrace.h>
#include <sys/ptrace.h>

int
sys_nomodule(struct lwp *l, const void *v, register_t *retval)
{
#ifdef MODULAR

	const struct sysent *sy;
	const struct emul *em;
	const struct sc_autoload *auto_list;
	u_int code;

	/*
	 * Restart the syscall if we interrupted a module unload that
	 * failed.  Acquiring kernconfig_lock delays us until any unload
	 * has been completed or rolled back.
	 */
	kernconfig_lock();
	sy = l->l_sysent;
	if (sy->sy_call != sys_nomodule) {
		kernconfig_unlock();
		return ERESTART;
	}
	/*
	 * Try to autoload a module to satisfy the request.  If it 
	 * works, retry the request.
	 */
	em = l->l_proc->p_emul;
	code = sy - em->e_sysent;

	if ((auto_list = em->e_sc_autoload) != NULL)
		for (; auto_list->al_code > 0; auto_list++) {
			if (auto_list->al_code != code) {
				continue;
			}
			if (module_autoload(auto_list->al_module,
			    MODULE_CLASS_ANY) != 0 ||
			    sy->sy_call == sys_nomodule) {
			    	break;
			}
			kernconfig_unlock();
			return ERESTART;
		}
	kernconfig_unlock();
#endif	/* MODULAR */

	return sys_nosys(l, v, retval);
}

int
syscall_establish(const struct emul *em, const struct syscall_package *sp)
{
	struct sysent *sy;
	int i;

	KASSERT(kernconfig_is_held());

	if (em == NULL) {
		em = &emul_netbsd;
	}
	sy = em->e_sysent;

	/*
	 * Ensure that all preconditions are valid, since this is
	 * an all or nothing deal.  Once a system call is entered,
	 * it can become busy and we could be unable to remove it
	 * on error.
	 */
	for (i = 0; sp[i].sp_call != NULL; i++) {
		if (sp[i].sp_code >= SYS_NSYSENT)
			return EINVAL;
		if (sy[sp[i].sp_code].sy_call != sys_nomodule &&
		    sy[sp[i].sp_code].sy_call != sys_nosys) {
#ifdef DIAGNOSTIC
			printf("syscall %d is busy\n", sp[i].sp_code);
#endif
			return EBUSY;
		}
	}
	/* Everything looks good, patch them in. */
	for (i = 0; sp[i].sp_call != NULL; i++) {
		sy[sp[i].sp_code].sy_call = sp[i].sp_call;
	}

	return 0;
}

int
syscall_disestablish(const struct emul *em, const struct syscall_package *sp)
{
	struct sysent *sy;
	const uint32_t *sb;
	uint64_t where;
	lwp_t *l;
	int i;

	KASSERT(kernconfig_is_held());

	if (em == NULL) {
		em = &emul_netbsd;
	}
	sy = em->e_sysent;
	sb = em->e_nomodbits;

	/*
	 * First, patch the system calls to sys_nomodule or sys_nosys
	 * to gate further activity.
	 */
	for (i = 0; sp[i].sp_call != NULL; i++) {
		KASSERT(sy[sp[i].sp_code].sy_call == sp[i].sp_call);
		sy[sp[i].sp_code].sy_call =
		    sb[sp[i].sp_code / 32] & (1 << (sp[i].sp_code % 32)) ?
		      sys_nomodule : sys_nosys;
	}

	/*
	 * Run a cross call to cycle through all CPUs.  This does two
	 * things: lock activity provides a barrier and makes our update
	 * of sy_call visible to all CPUs, and upon return we can be sure
	 * that we see pertinent values of l_sysent posted by remote CPUs.
	 */
	where = xc_broadcast(0, (xcfunc_t)nullop, NULL, NULL);
	xc_wait(where);

	/*
	 * Now it's safe to check l_sysent.  Run through all LWPs and see
	 * if anyone is still using the system call.
	 */
	for (i = 0; sp[i].sp_call != NULL; i++) {
		mutex_enter(proc_lock);
		LIST_FOREACH(l, &alllwp, l_list) {
			if (l->l_sysent == &sy[sp[i].sp_code]) {
				break;
			}
		}
		mutex_exit(proc_lock);
		if (l == NULL) {
			continue;
		}
		/*
		 * We lose: one or more calls are still in use.  Put back
		 * the old entrypoints and act like nothing happened.
		 * When we drop kernconfig_lock, any system calls held in
		 * sys_nomodule() will be restarted.
		 */
		for (i = 0; sp[i].sp_call != NULL; i++) {
			sy[sp[i].sp_code].sy_call = sp[i].sp_call;
		}
		return EBUSY;
	}

	return 0;
}

/*
 * Return true if system call tracing is enabled for the specified process.
 */
bool
trace_is_enabled(struct proc *p)
{
#ifdef SYSCALL_DEBUG
	return (true);
#endif
#ifdef KTRACE
	if (ISSET(p->p_traceflag, (KTRFAC_SYSCALL | KTRFAC_SYSRET)))
		return (true);
#endif
#ifdef PTRACE
	if (ISSET(p->p_slflag, PSL_SYSCALL))
		return (true);
#endif

	return (false);
}

/*
 * Start trace of particular system call. If process is being traced,
 * this routine is called by MD syscall dispatch code just before
 * a system call is actually executed.
 */
int
trace_enter(register_t code, const struct sysent *sy, const void *args)
{
	int error = 0;

#ifdef KDTRACE_HOOKS
	if (sy->sy_entry) {
		struct emul *e = curlwp->l_proc->p_emul;
		(*e->e_dtrace_syscall)(sy->sy_entry, code, sy, args, NULL, 0);
	}
#endif

#ifdef SYSCALL_DEBUG
	scdebug_call(code, args);
#endif /* SYSCALL_DEBUG */

	ktrsyscall(code, args, sy->sy_narg);

#ifdef PTRACE
	if ((curlwp->l_proc->p_slflag & (PSL_SYSCALL|PSL_TRACED)) ==
	    (PSL_SYSCALL|PSL_TRACED)) {
		proc_stoptrace(TRAP_SCE);
		if (curlwp->l_proc->p_slflag & PSL_SYSCALLEMU) {
			/* tracer will emulate syscall for us */
			error = EJUSTRETURN;
		}
	}
#endif
	return error;
}

/*
 * End trace of particular system call. If process is being traced,
 * this routine is called by MD syscall dispatch code just after
 * a system call finishes.
 * MD caller guarantees the passed 'code' is within the supported
 * system call number range for emulation the process runs under.
 */
void
trace_exit(register_t code, const struct sysent *sy, const void *args,
    register_t rval[], int error)
{
#if defined(PTRACE) || defined(KDTRACE_HOOKS)
	struct proc *p = curlwp->l_proc;
#endif

#ifdef KDTRACE_HOOKS
	if (sy->sy_return) {
		(*p->p_emul->e_dtrace_syscall)(sy->sy_return, code, sy, args,
		    rval, error);
	}
#endif

#ifdef SYSCALL_DEBUG
	scdebug_ret(code, error, rval);
#endif /* SYSCALL_DEBUG */

	ktrsysret(code, error, rval);
	
#ifdef PTRACE
	if ((p->p_slflag & (PSL_SYSCALL|PSL_TRACED|PSL_SYSCALLEMU)) ==
	    (PSL_SYSCALL|PSL_TRACED)) {
		proc_stoptrace(TRAP_SCX);
	}
	CLR(p->p_slflag, PSL_SYSCALLEMU);
#endif
}