19 files changed, 825 insertions, 1234 deletions

diff --git a/arch/um/os-Linux/Makefile b/arch/um/os-Linux/Makefile
index 049dfa5bc9c6..fae836713487 100644
--- a/arch/um/os-Linux/Makefile
+++ b/arch/um/os-Linux/Makefile
@@ -8,7 +8,7 @@ KCOV_INSTRUMENT                := n
 
 obj-y = execvp.o file.o helper.o irq.o main.o mem.o process.o \
 	registers.o sigio.o signal.o start_up.o time.o tty.o \
-	umid.o user_syms.o util.o drivers/ skas/
+	umid.o user_syms.o util.o skas/
 
 CFLAGS_signal.o += -Wframe-larger-than=4096
 
diff --git a/arch/um/os-Linux/drivers/Makefile b/arch/um/os-Linux/drivers/Makefile
deleted file mode 100644
index cf2d75bb1884..000000000000
--- a/arch/um/os-Linux/drivers/Makefile
+++ /dev/null
@@ -1,13 +0,0 @@
-# SPDX-License-Identifier: GPL-2.0
-# 
-# Copyright (C) 2000, 2002 Jeff Dike (jdike@karaya.com)
-#
-
-ethertap-objs := ethertap_kern.o ethertap_user.o
-tuntap-objs := tuntap_kern.o tuntap_user.o
-
-obj-y = 
-obj-$(CONFIG_UML_NET_ETHERTAP) += ethertap.o
-obj-$(CONFIG_UML_NET_TUNTAP) += tuntap.o
-
-include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/arch/um/os-Linux/drivers/etap.h b/arch/um/os-Linux/drivers/etap.h
deleted file mode 100644
index a475259f90e1..000000000000
--- a/arch/um/os-Linux/drivers/etap.h
+++ /dev/null
@@ -1,21 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/* 
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- */
-
-#ifndef __DRIVERS_ETAP_H
-#define __DRIVERS_ETAP_H
-
-#include <net_user.h>
-
-struct ethertap_data {
-	char *dev_name;
-	char *gate_addr;
-	int data_fd;
-	int control_fd;
-	void *dev;
-};
-
-extern const struct net_user_info ethertap_user_info;
-
-#endif
diff --git a/arch/um/os-Linux/drivers/ethertap_kern.c b/arch/um/os-Linux/drivers/ethertap_kern.c
deleted file mode 100644
index 5e5ee40680ce..000000000000
--- a/arch/um/os-Linux/drivers/ethertap_kern.c
+++ /dev/null
@@ -1,100 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
- * James Leu (jleu@mindspring.net).
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Copyright (C) 2001 by various other people who didn't put their name here.
- */
-
-#include <linux/init.h>
-#include <linux/netdevice.h>
-#include "etap.h"
-#include <net_kern.h>
-
-struct ethertap_init {
-	char *dev_name;
-	char *gate_addr;
-};
-
-static void etap_init(struct net_device *dev, void *data)
-{
-	struct uml_net_private *pri;
-	struct ethertap_data *epri;
-	struct ethertap_init *init = data;
-
-	pri = netdev_priv(dev);
-	epri = (struct ethertap_data *) pri->user;
-	epri->dev_name = init->dev_name;
-	epri->gate_addr = init->gate_addr;
-	epri->data_fd = -1;
-	epri->control_fd = -1;
-	epri->dev = dev;
-
-	printk(KERN_INFO "ethertap backend - %s", epri->dev_name);
-	if (epri->gate_addr != NULL)
-		printk(KERN_CONT ", IP = %s", epri->gate_addr);
-	printk(KERN_CONT "\n");
-}
-
-static int etap_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
-{
-	int len;
-
-	len = net_recvfrom(fd, skb_mac_header(skb),
-			   skb->dev->mtu + 2 + ETH_HEADER_ETHERTAP);
-	if (len <= 0)
-		return(len);
-
-	skb_pull(skb, 2);
-	len -= 2;
-	return len;
-}
-
-static int etap_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
-{
-	skb_push(skb, 2);
-	return net_send(fd, skb->data, skb->len);
-}
-
-const struct net_kern_info ethertap_kern_info = {
-	.init			= etap_init,
-	.protocol		= eth_protocol,
-	.read			= etap_read,
-	.write 			= etap_write,
-};
-
-static int ethertap_setup(char *str, char **mac_out, void *data)
-{
-	struct ethertap_init *init = data;
-
-	*init = ((struct ethertap_init)
-		{ .dev_name 	= NULL,
-		  .gate_addr 	= NULL });
-	if (tap_setup_common(str, "ethertap", &init->dev_name, mac_out,
-			    &init->gate_addr))
-		return 0;
-	if (init->dev_name == NULL) {
-		printk(KERN_ERR "ethertap_setup : Missing tap device name\n");
-		return 0;
-	}
-
-	return 1;
-}
-
-static struct transport ethertap_transport = {
-	.list 		= LIST_HEAD_INIT(ethertap_transport.list),
-	.name 		= "ethertap",
-	.setup  	= ethertap_setup,
-	.user 		= &ethertap_user_info,
-	.kern 		= &ethertap_kern_info,
-	.private_size 	= sizeof(struct ethertap_data),
-	.setup_size 	= sizeof(struct ethertap_init),
-};
-
-static int register_ethertap(void)
-{
-	register_transport(&ethertap_transport);
-	return 0;
-}
-
-late_initcall(register_ethertap);
diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
deleted file mode 100644
index bdf215c0eca7..000000000000
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ /dev/null
@@ -1,248 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
- * James Leu (jleu@mindspring.net).
- * Copyright (C) 2001 by various other people who didn't put their name here.
- */
-
-#include <stdio.h>
-#include <unistd.h>
-#include <errno.h>
-#include <string.h>
-#include <sys/socket.h>
-#include <sys/wait.h>
-#include "etap.h"
-#include <os.h>
-#include <net_user.h>
-#include <um_malloc.h>
-
-#define MAX_PACKET ETH_MAX_PACKET
-
-static int etap_user_init(void *data, void *dev)
-{
-	struct ethertap_data *pri = data;
-
-	pri->dev = dev;
-	return 0;
-}
-
-struct addr_change {
-	enum { ADD_ADDR, DEL_ADDR } what;
-	unsigned char addr[4];
-	unsigned char netmask[4];
-};
-
-static void etap_change(int op, unsigned char *addr, unsigned char *netmask,
-			int fd)
-{
-	struct addr_change change;
-	char *output;
-	int n;
-
-	change.what = op;
-	memcpy(change.addr, addr, sizeof(change.addr));
-	memcpy(change.netmask, netmask, sizeof(change.netmask));
-	CATCH_EINTR(n = write(fd, &change, sizeof(change)));
-	if (n != sizeof(change)) {
-		printk(UM_KERN_ERR "etap_change - request failed, err = %d\n",
-		       errno);
-		return;
-	}
-
-	output = uml_kmalloc(UM_KERN_PAGE_SIZE, UM_GFP_KERNEL);
-	if (output == NULL)
-		printk(UM_KERN_ERR "etap_change : Failed to allocate output "
-		       "buffer\n");
-	read_output(fd, output, UM_KERN_PAGE_SIZE);
-	if (output != NULL) {
-		printk("%s", output);
-		kfree(output);
-	}
-}
-
-static void etap_open_addr(unsigned char *addr, unsigned char *netmask,
-			   void *arg)
-{
-	etap_change(ADD_ADDR, addr, netmask, *((int *) arg));
-}
-
-static void etap_close_addr(unsigned char *addr, unsigned char *netmask,
-			    void *arg)
-{
-	etap_change(DEL_ADDR, addr, netmask, *((int *) arg));
-}
-
-struct etap_pre_exec_data {
-	int control_remote;
-	int control_me;
-	int data_me;
-};
-
-static void etap_pre_exec(void *arg)
-{
-	struct etap_pre_exec_data *data = arg;
-
-	dup2(data->control_remote, 1);
-	close(data->data_me);
-	close(data->control_me);
-}
-
-static int etap_tramp(char *dev, char *gate, int control_me,
-		      int control_remote, int data_me, int data_remote)
-{
-	struct etap_pre_exec_data pe_data;
-	int pid, err, n;
-	char version_buf[sizeof("nnnnn\0")];
-	char data_fd_buf[sizeof("nnnnnn\0")];
-	char gate_buf[sizeof("nnn.nnn.nnn.nnn\0")];
-	char *setup_args[] = { "uml_net", version_buf, "ethertap", dev,
-			       data_fd_buf, gate_buf, NULL };
-	char *nosetup_args[] = { "uml_net", version_buf, "ethertap",
-				 dev, data_fd_buf, NULL };
-	char **args, c;
-
-	sprintf(data_fd_buf, "%d", data_remote);
-	sprintf(version_buf, "%d", UML_NET_VERSION);
-	if (gate != NULL) {
-		strscpy(gate_buf, gate);
-		args = setup_args;
-	}
-	else args = nosetup_args;
-
-	err = 0;
-	pe_data.control_remote = control_remote;
-	pe_data.control_me = control_me;
-	pe_data.data_me = data_me;
-	pid = run_helper(etap_pre_exec, &pe_data, args);
-
-	if (pid < 0)
-		err = pid;
-	close(data_remote);
-	close(control_remote);
-	CATCH_EINTR(n = read(control_me, &c, sizeof(c)));
-	if (n != sizeof(c)) {
-		err = -errno;
-		printk(UM_KERN_ERR "etap_tramp : read of status failed, "
-		       "err = %d\n", -err);
-		return err;
-	}
-	if (c != 1) {
-		printk(UM_KERN_ERR "etap_tramp : uml_net failed\n");
-		err = helper_wait(pid);
-	}
-	return err;
-}
-
-static int etap_open(void *data)
-{
-	struct ethertap_data *pri = data;
-	char *output;
-	int data_fds[2], control_fds[2], err, output_len;
-
-	err = tap_open_common(pri->dev, pri->gate_addr);
-	if (err)
-		return err;
-
-	err = socketpair(AF_UNIX, SOCK_DGRAM, 0, data_fds);
-	if (err) {
-		err = -errno;
-		printk(UM_KERN_ERR "etap_open - data socketpair failed - "
-		       "err = %d\n", errno);
-		return err;
-	}
-
-	err = socketpair(AF_UNIX, SOCK_STREAM, 0, control_fds);
-	if (err) {
-		err = -errno;
-		printk(UM_KERN_ERR "etap_open - control socketpair failed - "
-		       "err = %d\n", errno);
-		goto out_close_data;
-	}
-
-	err = etap_tramp(pri->dev_name, pri->gate_addr, control_fds[0],
-			 control_fds[1], data_fds[0], data_fds[1]);
-	output_len = UM_KERN_PAGE_SIZE;
-	output = uml_kmalloc(output_len, UM_GFP_KERNEL);
-	read_output(control_fds[0], output, output_len);
-
-	if (output == NULL)
-		printk(UM_KERN_ERR "etap_open : failed to allocate output "
-		       "buffer\n");
-	else {
-		printk("%s", output);
-		kfree(output);
-	}
-
-	if (err < 0) {
-		printk(UM_KERN_ERR "etap_tramp failed - err = %d\n", -err);
-		goto out_close_control;
-	}
-
-	pri->data_fd = data_fds[0];
-	pri->control_fd = control_fds[0];
-	iter_addresses(pri->dev, etap_open_addr, &pri->control_fd);
-	return data_fds[0];
-
-out_close_control:
-	close(control_fds[0]);
-	close(control_fds[1]);
-out_close_data:
-	close(data_fds[0]);
-	close(data_fds[1]);
-	return err;
-}
-
-static void etap_close(int fd, void *data)
-{
-	struct ethertap_data *pri = data;
-
-	iter_addresses(pri->dev, etap_close_addr, &pri->control_fd);
-	close(fd);
-
-	if (shutdown(pri->data_fd, SHUT_RDWR) < 0)
-		printk(UM_KERN_ERR "etap_close - shutdown data socket failed, "
-		       "errno = %d\n", errno);
-
-	if (shutdown(pri->control_fd, SHUT_RDWR) < 0)
-		printk(UM_KERN_ERR "etap_close - shutdown control socket "
-		       "failed, errno = %d\n", errno);
-
-	close(pri->data_fd);
-	pri->data_fd = -1;
-	close(pri->control_fd);
-	pri->control_fd = -1;
-}
-
-static void etap_add_addr(unsigned char *addr, unsigned char *netmask,
-			  void *data)
-{
-	struct ethertap_data *pri = data;
-
-	tap_check_ips(pri->gate_addr, addr);
-	if (pri->control_fd == -1)
-		return;
-	etap_open_addr(addr, netmask, &pri->control_fd);
-}
-
-static void etap_del_addr(unsigned char *addr, unsigned char *netmask,
-			  void *data)
-{
-	struct ethertap_data *pri = data;
-
-	if (pri->control_fd == -1)
-		return;
-
-	etap_close_addr(addr, netmask, &pri->control_fd);
-}
-
-const struct net_user_info ethertap_user_info = {
-	.init		= etap_user_init,
-	.open		= etap_open,
-	.close	 	= etap_close,
-	.remove	 	= NULL,
-	.add_address	= etap_add_addr,
-	.delete_address = etap_del_addr,
-	.mtu		= ETH_MAX_PACKET,
-	.max_packet	= ETH_MAX_PACKET + ETH_HEADER_ETHERTAP,
-};
diff --git a/arch/um/os-Linux/drivers/tuntap.h b/arch/um/os-Linux/drivers/tuntap.h
deleted file mode 100644
index e364e42abfc5..000000000000
--- a/arch/um/os-Linux/drivers/tuntap.h
+++ /dev/null
@@ -1,21 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/* 
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- */
-
-#ifndef __UM_TUNTAP_H
-#define __UM_TUNTAP_H
-
-#include <net_user.h>
-
-struct tuntap_data {
-	char *dev_name;
-	int fixed_config;
-	char *gate_addr;
-	int fd;
-	void *dev;
-};
-
-extern const struct net_user_info tuntap_user_info;
-
-#endif
diff --git a/arch/um/os-Linux/drivers/tuntap_kern.c b/arch/um/os-Linux/drivers/tuntap_kern.c
deleted file mode 100644
index ff022d9cf0dd..000000000000
--- a/arch/um/os-Linux/drivers/tuntap_kern.c
+++ /dev/null
@@ -1,86 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- */
-
-#include <linux/netdevice.h>
-#include <linux/init.h>
-#include <linux/skbuff.h>
-#include <asm/errno.h>
-#include <net_kern.h>
-#include "tuntap.h"
-
-struct tuntap_init {
-	char *dev_name;
-	char *gate_addr;
-};
-
-static void tuntap_init(struct net_device *dev, void *data)
-{
-	struct uml_net_private *pri;
-	struct tuntap_data *tpri;
-	struct tuntap_init *init = data;
-
-	pri = netdev_priv(dev);
-	tpri = (struct tuntap_data *) pri->user;
-	tpri->dev_name = init->dev_name;
-	tpri->fixed_config = (init->dev_name != NULL);
-	tpri->gate_addr = init->gate_addr;
-	tpri->fd = -1;
-	tpri->dev = dev;
-
-	printk(KERN_INFO "TUN/TAP backend - ");
-	if (tpri->gate_addr != NULL)
-		printk(KERN_CONT "IP = %s", tpri->gate_addr);
-	printk(KERN_CONT "\n");
-}
-
-static int tuntap_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
-{
-	return net_read(fd, skb_mac_header(skb),
-			skb->dev->mtu + ETH_HEADER_OTHER);
-}
-
-static int tuntap_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
-{
-	return net_write(fd, skb->data, skb->len);
-}
-
-const struct net_kern_info tuntap_kern_info = {
-	.init			= tuntap_init,
-	.protocol		= eth_protocol,
-	.read			= tuntap_read,
-	.write 			= tuntap_write,
-};
-
-static int tuntap_setup(char *str, char **mac_out, void *data)
-{
-	struct tuntap_init *init = data;
-
-	*init = ((struct tuntap_init)
-		{ .dev_name 	= NULL,
-		  .gate_addr 	= NULL });
-	if (tap_setup_common(str, "tuntap", &init->dev_name, mac_out,
-			    &init->gate_addr))
-		return 0;
-
-	return 1;
-}
-
-static struct transport tuntap_transport = {
-	.list 		= LIST_HEAD_INIT(tuntap_transport.list),
-	.name 		= "tuntap",
-	.setup  	= tuntap_setup,
-	.user 		= &tuntap_user_info,
-	.kern 		= &tuntap_kern_info,
-	.private_size 	= sizeof(struct tuntap_data),
-	.setup_size 	= sizeof(struct tuntap_init),
-};
-
-static int register_tuntap(void)
-{
-	register_transport(&tuntap_transport);
-	return 0;
-}
-
-late_initcall(register_tuntap);
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
deleted file mode 100644
index 91f0e27ca3a6..000000000000
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ /dev/null
@@ -1,215 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/* 
- * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- */
-
-#include <stdio.h>
-#include <unistd.h>
-#include <errno.h>
-#include <string.h>
-#include <linux/if_tun.h>
-#include <net/if.h>
-#include <sys/ioctl.h>
-#include <sys/socket.h>
-#include <sys/wait.h>
-#include <sys/uio.h>
-#include <kern_util.h>
-#include <os.h>
-#include "tuntap.h"
-
-static int tuntap_user_init(void *data, void *dev)
-{
-	struct tuntap_data *pri = data;
-
-	pri->dev = dev;
-	return 0;
-}
-
-static void tuntap_add_addr(unsigned char *addr, unsigned char *netmask,
-			    void *data)
-{
-	struct tuntap_data *pri = data;
-
-	tap_check_ips(pri->gate_addr, addr);
-	if ((pri->fd == -1) || pri->fixed_config)
-		return;
-	open_addr(addr, netmask, pri->dev_name);
-}
-
-static void tuntap_del_addr(unsigned char *addr, unsigned char *netmask,
-			    void *data)
-{
-	struct tuntap_data *pri = data;
-
-	if ((pri->fd == -1) || pri->fixed_config)
-		return;
-	close_addr(addr, netmask, pri->dev_name);
-}
-
-struct tuntap_pre_exec_data {
-	int stdout_fd;
-	int close_me;
-};
-
-static void tuntap_pre_exec(void *arg)
-{
-	struct tuntap_pre_exec_data *data = arg;
-
-	dup2(data->stdout_fd, 1);
-	close(data->close_me);
-}
-
-static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
-			     char *buffer, int buffer_len, int *used_out)
-{
-	struct tuntap_pre_exec_data data;
-	char version_buf[sizeof("nnnnn\0")];
-	char *argv[] = { "uml_net", version_buf, "tuntap", "up", gate,
-			 NULL };
-	char buf[CMSG_SPACE(sizeof(*fd_out))];
-	struct msghdr msg;
-	struct cmsghdr *cmsg;
-	struct iovec iov;
-	int pid, n, err;
-
-	sprintf(version_buf, "%d", UML_NET_VERSION);
-
-	data.stdout_fd = remote;
-	data.close_me = me;
-
-	pid = run_helper(tuntap_pre_exec, &data, argv);
-
-	if (pid < 0)
-		return pid;
-
-	close(remote);
-
-	msg.msg_name = NULL;
-	msg.msg_namelen = 0;
-	if (buffer != NULL) {
-		iov = ((struct iovec) { buffer, buffer_len });
-		msg.msg_iov = &iov;
-		msg.msg_iovlen = 1;
-	}
-	else {
-		msg.msg_iov = NULL;
-		msg.msg_iovlen = 0;
-	}
-	msg.msg_control = buf;
-	msg.msg_controllen = sizeof(buf);
-	msg.msg_flags = 0;
-	n = recvmsg(me, &msg, 0);
-	*used_out = n;
-	if (n < 0) {
-		err = -errno;
-		printk(UM_KERN_ERR "tuntap_open_tramp : recvmsg failed - "
-		       "errno = %d\n", errno);
-		return err;
-	}
-	helper_wait(pid);
-
-	cmsg = CMSG_FIRSTHDR(&msg);
-	if (cmsg == NULL) {
-		printk(UM_KERN_ERR "tuntap_open_tramp : didn't receive a "
-		       "message\n");
-		return -EINVAL;
-	}
-	if ((cmsg->cmsg_level != SOL_SOCKET) ||
-	   (cmsg->cmsg_type != SCM_RIGHTS)) {
-		printk(UM_KERN_ERR "tuntap_open_tramp : didn't receive a "
-		       "descriptor\n");
-		return -EINVAL;
-	}
-	*fd_out = ((int *) CMSG_DATA(cmsg))[0];
-	os_set_exec_close(*fd_out);
-	return 0;
-}
-
-static int tuntap_open(void *data)
-{
-	struct ifreq ifr;
-	struct tuntap_data *pri = data;
-	char *output, *buffer;
-	int err, fds[2], len, used;
-
-	err = tap_open_common(pri->dev, pri->gate_addr);
-	if (err < 0)
-		return err;
-
-	if (pri->fixed_config) {
-		pri->fd = os_open_file("/dev/net/tun",
-				       of_cloexec(of_rdwr(OPENFLAGS())), 0);
-		if (pri->fd < 0) {
-			printk(UM_KERN_ERR "Failed to open /dev/net/tun, "
-			       "err = %d\n", -pri->fd);
-			return pri->fd;
-		}
-		memset(&ifr, 0, sizeof(ifr));
-		ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
-		strscpy(ifr.ifr_name, pri->dev_name);
-		if (ioctl(pri->fd, TUNSETIFF, &ifr) < 0) {
-			err = -errno;
-			printk(UM_KERN_ERR "TUNSETIFF failed, errno = %d\n",
-			       errno);
-			close(pri->fd);
-			return err;
-		}
-	}
-	else {
-		err = socketpair(AF_UNIX, SOCK_DGRAM, 0, fds);
-		if (err) {
-			err = -errno;
-			printk(UM_KERN_ERR "tuntap_open : socketpair failed - "
-			       "errno = %d\n", errno);
-			return err;
-		}
-
-		buffer = get_output_buffer(&len);
-		if (buffer != NULL)
-			len--;
-		used = 0;
-
-		err = tuntap_open_tramp(pri->gate_addr, &pri->fd, fds[0],
-					fds[1], buffer, len, &used);
-
-		output = buffer;
-		if (err < 0) {
-			printk("%s", output);
-			free_output_buffer(buffer);
-			printk(UM_KERN_ERR "tuntap_open_tramp failed - "
-			       "err = %d\n", -err);
-			return err;
-		}
-
-		pri->dev_name = uml_strdup(buffer);
-		output += IFNAMSIZ;
-		printk("%s", output);
-		free_output_buffer(buffer);
-
-		close(fds[0]);
-		iter_addresses(pri->dev, open_addr, pri->dev_name);
-	}
-
-	return pri->fd;
-}
-
-static void tuntap_close(int fd, void *data)
-{
-	struct tuntap_data *pri = data;
-
-	if (!pri->fixed_config)
-		iter_addresses(pri->dev, close_addr, pri->dev_name);
-	close(fd);
-	pri->fd = -1;
-}
-
-const struct net_user_info tuntap_user_info = {
-	.init		= tuntap_user_init,
-	.open		= tuntap_open,
-	.close	 	= tuntap_close,
-	.remove	 	= NULL,
-	.add_address	= tuntap_add_addr,
-	.delete_address = tuntap_del_addr,
-	.mtu		= ETH_MAX_PACKET,
-	.max_packet	= ETH_MAX_PACKET + ETH_HEADER_OTHER,
-};
diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
index a0d01c68ce3e..617886d1fb1e 100644
--- a/arch/um/os-Linux/file.c
+++ b/arch/um/os-Linux/file.c
@@ -106,21 +106,6 @@ int os_get_ifname(int fd, char* namebuf)
 	return 0;
 }
 
-int os_set_slip(int fd)
-{
-	int disc, sencap;
-
-	disc = N_SLIP;
-	if (ioctl(fd, TIOCSETD, &disc) < 0)
-		return -errno;
-
-	sencap = 0;
-	if (ioctl(fd, SIOCSIFENCAP, &sencap) < 0)
-		return -errno;
-
-	return 0;
-}
-
 int os_mode_fd(int fd, int mode)
 {
 	int err;
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index 3cb8ac63be6e..89c2ad2a4e3a 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <sched.h>
+#include <pthread.h>
 #include <linux/limits.h>
 #include <sys/socket.h>
 #include <sys/wait.h>
@@ -121,6 +122,10 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 	unsigned long stack, sp;
 	int pid, status, err;
 
+	/* To share memory space, use os_run_helper_thread() instead. */
+	if (flags & CLONE_VM)
+		return -EINVAL;
+
 	stack = alloc_stack(0, __uml_cant_sleep());
 	if (stack == 0)
 		return -ENOMEM;
@@ -167,3 +172,65 @@ int helper_wait(int pid)
 	} else
 		return 0;
 }
+
+struct os_helper_thread {
+	pthread_t handle;
+};
+
+int os_run_helper_thread(struct os_helper_thread **td_out,
+			 void *(*routine)(void *), void *arg)
+{
+	struct os_helper_thread *td;
+	sigset_t sigset, oset;
+	int err, flags;
+
+	flags = __uml_cant_sleep() ? UM_GFP_ATOMIC : UM_GFP_KERNEL;
+	td = uml_kmalloc(sizeof(*td), flags);
+	if (!td)
+		return -ENOMEM;
+
+	sigfillset(&sigset);
+	if (sigprocmask(SIG_SETMASK, &sigset, &oset) < 0) {
+		err = -errno;
+		kfree(td);
+		return err;
+	}
+
+	err = pthread_create(&td->handle, NULL, routine, arg);
+
+	if (sigprocmask(SIG_SETMASK, &oset, NULL) < 0)
+		panic("Failed to restore the signal mask: %d", errno);
+
+	if (err != 0)
+		kfree(td);
+	else
+		*td_out = td;
+
+	return -err;
+}
+
+void os_kill_helper_thread(struct os_helper_thread *td)
+{
+	pthread_cancel(td->handle);
+	pthread_join(td->handle, NULL);
+	kfree(td);
+}
+
+void os_fix_helper_thread_signals(void)
+{
+	sigset_t sigset;
+
+	sigemptyset(&sigset);
+
+	sigaddset(&sigset, SIGWINCH);
+	sigaddset(&sigset, SIGPIPE);
+	sigaddset(&sigset, SIGPROF);
+	sigaddset(&sigset, SIGINT);
+	sigaddset(&sigset, SIGTERM);
+	sigaddset(&sigset, SIGCHLD);
+	sigaddset(&sigset, SIGALRM);
+	sigaddset(&sigset, SIGIO);
+	sigaddset(&sigset, SIGUSR1);
+
+	pthread_sigmask(SIG_SETMASK, &sigset, NULL);
+}
diff --git a/arch/um/os-Linux/internal.h b/arch/um/os-Linux/internal.h
index 317fca190c2b..5d8d3b0817a9 100644
--- a/arch/um/os-Linux/internal.h
+++ b/arch/um/os-Linux/internal.h
@@ -2,6 +2,9 @@
 #ifndef __UM_OS_LINUX_INTERNAL_H
 #define __UM_OS_LINUX_INTERNAL_H
 
+#include <mm_id.h>
+#include <stub-data.h>
+
 /*
  * elf_aux.c
  */
@@ -16,5 +19,5 @@ void check_tmpexec(void);
  * skas/process.c
  */
 void wait_stub_done(int pid);
-
+void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys);
 #endif /* __UM_OS_LINUX_INTERNAL_H */
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index 0afcdeb8995b..3c63ce19e3bf 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -19,13 +19,11 @@
 #include <um_malloc.h>
 #include "internal.h"
 
-#define PGD_BOUND (4 * 1024 * 1024)
 #define STACKSIZE (8 * 1024 * 1024)
-#define THREAD_NAME_LEN (256)
 
 long elf_aux_hwcap;
 
-static void set_stklim(void)
+static void __init set_stklim(void)
 {
 	struct rlimit lim;
 
@@ -48,7 +46,7 @@ static void last_ditch_exit(int sig)
 	exit(1);
 }
 
-static void install_fatal_handler(int sig)
+static void __init install_fatal_handler(int sig)
 {
 	struct sigaction action;
 
@@ -73,7 +71,7 @@ static void install_fatal_handler(int sig)
 
 #define UML_LIB_PATH	":" OS_LIB_PATH "/uml"
 
-static void setup_env_path(void)
+static void __init setup_env_path(void)
 {
 	char *new_path = NULL;
 	char *old_path = NULL;
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index 9f086f939420..00b49e90d05f 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -18,17 +18,29 @@
 #include <init.h>
 #include <longjmp.h>
 #include <os.h>
+#include <skas/skas.h>
 
 void os_alarm_process(int pid)
 {
+	if (pid <= 0)
+		return;
+
 	kill(pid, SIGALRM);
 }
 
 void os_kill_process(int pid, int reap_child)
 {
+	if (pid <= 0)
+		return;
+
+	/* Block signals until child is reaped */
+	block_signals();
+
 	kill(pid, SIGKILL);
 	if (reap_child)
 		CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+	unblock_signals();
 }
 
 /* Kill off a ptraced child by all means available.  kill it normally first,
@@ -38,11 +50,27 @@ void os_kill_process(int pid, int reap_child)
 
 void os_kill_ptraced_process(int pid, int reap_child)
 {
+	if (pid <= 0)
+		return;
+
+	/* Block signals until child is reaped */
+	block_signals();
+
 	kill(pid, SIGKILL);
 	ptrace(PTRACE_KILL, pid);
 	ptrace(PTRACE_CONT, pid);
 	if (reap_child)
 		CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+	unblock_signals();
+}
+
+pid_t os_reap_child(void)
+{
+	int status;
+
+	/* Try to reap a child */
+	return waitpid(-1, &status, WNOHANG);
 }
 
 /* Don't use the glibc version, which caches the result in TLS. It misses some
@@ -142,57 +170,6 @@ out:
 	return ok;
 }
 
-static int os_page_mincore(void *addr)
-{
-	char vec[2];
-	int ret;
-
-	ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
-	if (ret < 0) {
-		if (errno == ENOMEM || errno == EINVAL)
-			return 0;
-		else
-			return -errno;
-	}
-
-	return vec[0] & 1;
-}
-
-int os_mincore(void *addr, unsigned long len)
-{
-	char *vec;
-	int ret, i;
-
-	if (len <= UM_KERN_PAGE_SIZE)
-		return os_page_mincore(addr);
-
-	vec = calloc(1, (len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE);
-	if (!vec)
-		return -ENOMEM;
-
-	ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
-	if (ret < 0) {
-		if (errno == ENOMEM || errno == EINVAL)
-			ret = 0;
-		else
-			ret = -errno;
-
-		goto out;
-	}
-
-	for (i = 0; i < ((len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE); i++) {
-		if (!(vec[i] & 1)) {
-			ret = 0;
-			goto out;
-		}
-	}
-
-	ret = 1;
-out:
-	free(vec);
-	return ret;
-}
-
 void init_new_thread_signals(void)
 {
 	set_handler(SIGSEGV);
@@ -202,6 +179,9 @@ void init_new_thread_signals(void)
 	set_handler(SIGBUS);
 	signal(SIGHUP, SIG_IGN);
 	set_handler(SIGIO);
+	/* We (currently) only use the child reaper IRQ in seccomp mode */
+	if (using_seccomp)
+		set_handler(SIGCHLD);
 	signal(SIGWINCH, SIG_IGN);
 }
 
diff --git a/arch/um/os-Linux/registers.c b/arch/um/os-Linux/registers.c
index d7ca148807b2..bfba2cbc9478 100644
--- a/arch/um/os-Linux/registers.c
+++ b/arch/um/os-Linux/registers.c
@@ -14,8 +14,8 @@
 
 /* This is set once at boot time and not changed thereafter */
 
-static unsigned long exec_regs[MAX_REG_NR];
-static unsigned long *exec_fp_regs;
+unsigned long exec_regs[MAX_REG_NR];
+unsigned long *exec_fp_regs;
 
 int init_pid_registers(int pid)
 {
diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
index 9aac8def4d63..6de145f8fe3d 100644
--- a/arch/um/os-Linux/sigio.c
+++ b/arch/um/os-Linux/sigio.c
@@ -11,6 +11,8 @@
 #include <sched.h>
 #include <signal.h>
 #include <string.h>
+#include <sys/epoll.h>
+#include <asm/unistd.h>
 #include <kern_util.h>
 #include <init.h>
 #include <os.h>
@@ -21,184 +23,51 @@
  * Protected by sigio_lock(), also used by sigio_cleanup, which is an
  * exitcall.
  */
-static int write_sigio_pid = -1;
-static unsigned long write_sigio_stack;
+static struct os_helper_thread *write_sigio_td;
 
-/*
- * These arrays are initialized before the sigio thread is started, and
- * the descriptors closed after it is killed.  So, it can't see them change.
- * On the UML side, they are changed under the sigio_lock.
- */
-#define SIGIO_FDS_INIT {-1, -1}
-
-static int write_sigio_fds[2] = SIGIO_FDS_INIT;
-static int sigio_private[2] = SIGIO_FDS_INIT;
+static int epollfd = -1;
 
-struct pollfds {
-	struct pollfd *poll;
-	int size;
-	int used;
-};
+#define MAX_EPOLL_EVENTS 64
 
-/*
- * Protected by sigio_lock().  Used by the sigio thread, but the UML thread
- * synchronizes with it.
- */
-static struct pollfds current_poll;
-static struct pollfds next_poll;
-static struct pollfds all_sigio_fds;
+static struct epoll_event epoll_events[MAX_EPOLL_EVENTS];
 
-static int write_sigio_thread(void *unused)
+static void *write_sigio_thread(void *unused)
 {
-	struct pollfds *fds, tmp;
-	struct pollfd *p;
-	int i, n, respond_fd;
-	char c;
-
-	os_set_pdeathsig();
-	os_fix_helper_signals();
-	fds = &current_poll;
+	int pid = getpid();
+	int r;
+
+	os_fix_helper_thread_signals();
+
 	while (1) {
-		n = poll(fds->poll, fds->used, -1);
-		if (n < 0) {
+		r = epoll_wait(epollfd, epoll_events, MAX_EPOLL_EVENTS, -1);
+		if (r < 0) {
 			if (errno == EINTR)
 				continue;
-			printk(UM_KERN_ERR "write_sigio_thread : poll returned "
-			       "%d, errno = %d\n", n, errno);
+			printk(UM_KERN_ERR "%s: epoll_wait failed, errno = %d\n",
+			       __func__, errno);
 		}
-		for (i = 0; i < fds->used; i++) {
-			p = &fds->poll[i];
-			if (p->revents == 0)
-				continue;
-			if (p->fd == sigio_private[1]) {
-				CATCH_EINTR(n = read(sigio_private[1], &c,
-						     sizeof(c)));
-				if (n != sizeof(c))
-					printk(UM_KERN_ERR
-					       "write_sigio_thread : "
-					       "read on socket failed, "
-					       "err = %d\n", errno);
-				tmp = current_poll;
-				current_poll = next_poll;
-				next_poll = tmp;
-				respond_fd = sigio_private[1];
-			}
-			else {
-				respond_fd = write_sigio_fds[1];
-				fds->used--;
-				memmove(&fds->poll[i], &fds->poll[i + 1],
-					(fds->used - i) * sizeof(*fds->poll));
-			}
-
-			CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
-			if (n != sizeof(c))
-				printk(UM_KERN_ERR "write_sigio_thread : "
-				       "write on socket failed, err = %d\n",
-				       errno);
-		}
-	}
 
-	return 0;
-}
-
-static int need_poll(struct pollfds *polls, int n)
-{
-	struct pollfd *new;
-
-	if (n <= polls->size)
-		return 0;
-
-	new = uml_kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
-	if (new == NULL) {
-		printk(UM_KERN_ERR "need_poll : failed to allocate new "
-		       "pollfds\n");
-		return -ENOMEM;
+		CATCH_EINTR(r = syscall(__NR_tgkill, pid, pid, SIGIO));
+		if (r < 0)
+			printk(UM_KERN_ERR "%s: tgkill failed, errno = %d\n",
+			       __func__, errno);
 	}
 
-	memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
-	kfree(polls->poll);
-
-	polls->poll = new;
-	polls->size = n;
-	return 0;
-}
-
-/*
- * Must be called with sigio_lock held, because it's needed by the marked
- * critical section.
- */
-static void update_thread(void)
-{
-	unsigned long flags;
-	int n;
-	char c;
-
-	flags = um_set_signals_trace(0);
-	CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
-	if (n != sizeof(c)) {
-		printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
-		       errno);
-		goto fail;
-	}
-
-	CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
-	if (n != sizeof(c)) {
-		printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
-		       errno);
-		goto fail;
-	}
-
-	um_set_signals_trace(flags);
-	return;
- fail:
-	/* Critical section start */
-	if (write_sigio_pid != -1) {
-		os_kill_process(write_sigio_pid, 1);
-		free_stack(write_sigio_stack, 0);
-	}
-	write_sigio_pid = -1;
-	close(sigio_private[0]);
-	close(sigio_private[1]);
-	close(write_sigio_fds[0]);
-	close(write_sigio_fds[1]);
-	/* Critical section end */
-	um_set_signals_trace(flags);
+	return NULL;
 }
 
 int __add_sigio_fd(int fd)
 {
-	struct pollfd *p;
-	int err, i, n;
-
-	for (i = 0; i < all_sigio_fds.used; i++) {
-		if (all_sigio_fds.poll[i].fd == fd)
-			break;
-	}
-	if (i == all_sigio_fds.used)
-		return -ENOSPC;
-
-	p = &all_sigio_fds.poll[i];
-
-	for (i = 0; i < current_poll.used; i++) {
-		if (current_poll.poll[i].fd == fd)
-			return 0;
-	}
-
-	n = current_poll.used;
-	err = need_poll(&next_poll, n + 1);
-	if (err)
-		return err;
-
-	memcpy(next_poll.poll, current_poll.poll,
-	       current_poll.used * sizeof(struct pollfd));
-	next_poll.poll[n] = *p;
-	next_poll.used = n + 1;
-	update_thread();
-
-	return 0;
+	struct epoll_event event = {
+		.data.fd = fd,
+		.events = EPOLLIN | EPOLLET,
+	};
+	int r;
+
+	CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event));
+	return r < 0 ? -errno : 0;
 }
 
-
 int add_sigio_fd(int fd)
 {
 	int err;
@@ -212,38 +81,11 @@ int add_sigio_fd(int fd)
 
 int __ignore_sigio_fd(int fd)
 {
-	struct pollfd *p;
-	int err, i, n = 0;
-
-	/*
-	 * This is called from exitcalls elsewhere in UML - if
-	 * sigio_cleanup has already run, then update_thread will hang
-	 * or fail because the thread is no longer running.
-	 */
-	if (write_sigio_pid == -1)
-		return -EIO;
-
-	for (i = 0; i < current_poll.used; i++) {
-		if (current_poll.poll[i].fd == fd)
-			break;
-	}
-	if (i == current_poll.used)
-		return -ENOENT;
-
-	err = need_poll(&next_poll, current_poll.used - 1);
-	if (err)
-		return err;
-
-	for (i = 0; i < current_poll.used; i++) {
-		p = &current_poll.poll[i];
-		if (p->fd != fd)
-			next_poll.poll[n++] = *p;
-	}
-	next_poll.used = current_poll.used - 1;
-
-	update_thread();
+	struct epoll_event event;
+	int r;
 
-	return 0;
+	CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &event));
+	return r < 0 ? -errno : 0;
 }
 
 int ignore_sigio_fd(int fd)
@@ -257,125 +99,37 @@ int ignore_sigio_fd(int fd)
 	return err;
 }
 
-static struct pollfd *setup_initial_poll(int fd)
-{
-	struct pollfd *p;
-
-	p = uml_kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
-	if (p == NULL) {
-		printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
-		       "poll\n");
-		return NULL;
-	}
-	*p = ((struct pollfd) { .fd		= fd,
-				.events 	= POLLIN,
-				.revents 	= 0 });
-	return p;
-}
-
 static void write_sigio_workaround(void)
 {
-	struct pollfd *p;
 	int err;
-	int l_write_sigio_fds[2];
-	int l_sigio_private[2];
-	int l_write_sigio_pid;
 
-	/* We call this *tons* of times - and most ones we must just fail. */
 	sigio_lock();
-	l_write_sigio_pid = write_sigio_pid;
-	sigio_unlock();
-
-	if (l_write_sigio_pid != -1)
-		return;
+	if (write_sigio_td)
+		goto out;
 
-	err = os_pipe(l_write_sigio_fds, 1, 1);
-	if (err < 0) {
-		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
-		       "err = %d\n", -err);
-		return;
+	epollfd = epoll_create(MAX_EPOLL_EVENTS);
+	if (epollfd < 0) {
+		printk(UM_KERN_ERR "%s: epoll_create failed, errno = %d\n",
+		       __func__, errno);
+		goto out;
 	}
-	err = os_pipe(l_sigio_private, 1, 1);
+
+	err = os_run_helper_thread(&write_sigio_td, write_sigio_thread, NULL);
 	if (err < 0) {
-		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
-		       "err = %d\n", -err);
-		goto out_close1;
+		printk(UM_KERN_ERR "%s: os_run_helper_thread failed, errno = %d\n",
+		       __func__, -err);
+		close(epollfd);
+		epollfd = -1;
+		goto out;
 	}
 
-	p = setup_initial_poll(l_sigio_private[1]);
-	if (!p)
-		goto out_close2;
-
-	sigio_lock();
-
-	/*
-	 * Did we race? Don't try to optimize this, please, it's not so likely
-	 * to happen, and no more than once at the boot.
-	 */
-	if (write_sigio_pid != -1)
-		goto out_free;
-
-	current_poll = ((struct pollfds) { .poll 	= p,
-					   .used 	= 1,
-					   .size 	= 1 });
-
-	if (write_sigio_irq(l_write_sigio_fds[0]))
-		goto out_clear_poll;
-
-	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
-	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
-
-	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
-					    CLONE_FILES | CLONE_VM,
-					    &write_sigio_stack);
-
-	if (write_sigio_pid < 0)
-		goto out_clear;
-
-	sigio_unlock();
-	return;
-
-out_clear:
-	write_sigio_pid = -1;
-	write_sigio_fds[0] = -1;
-	write_sigio_fds[1] = -1;
-	sigio_private[0] = -1;
-	sigio_private[1] = -1;
-out_clear_poll:
-	current_poll = ((struct pollfds) { .poll	= NULL,
-					   .size	= 0,
-					   .used	= 0 });
-out_free:
+out:
 	sigio_unlock();
-	kfree(p);
-out_close2:
-	close(l_sigio_private[0]);
-	close(l_sigio_private[1]);
-out_close1:
-	close(l_write_sigio_fds[0]);
-	close(l_write_sigio_fds[1]);
 }
 
-void sigio_broken(int fd)
+void sigio_broken(void)
 {
-	int err;
-
 	write_sigio_workaround();
-
-	sigio_lock();
-	err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
-	if (err) {
-		printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
-		       "for descriptor %d\n", fd);
-		goto out;
-	}
-
-	all_sigio_fds.poll[all_sigio_fds.used++] =
-		((struct pollfd) { .fd  	= fd,
-				   .events 	= POLLIN,
-				   .revents 	= 0 });
-out:
-	sigio_unlock();
 }
 
 /* Changed during early boot */
@@ -389,17 +143,16 @@ void maybe_sigio_broken(int fd)
 	if (pty_output_sigio)
 		return;
 
-	sigio_broken(fd);
+	sigio_broken();
 }
 
 static void sigio_cleanup(void)
 {
-	if (write_sigio_pid == -1)
+	if (!write_sigio_td)
 		return;
 
-	os_kill_process(write_sigio_pid, 1);
-	free_stack(write_sigio_stack, 0);
-	write_sigio_pid = -1;
+	os_kill_helper_thread(write_sigio_td);
+	write_sigio_td = NULL;
 }
 
 __uml_exitcall(sigio_cleanup);
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 9ea7269ffb77..11f07f498270 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -21,7 +21,7 @@
 #include <sys/ucontext.h>
 #include <timetravel.h>
 
-void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
+void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) = {
 	[SIGTRAP]	= relay_signal,
 	[SIGFPE]	= relay_signal,
 	[SIGILL]	= relay_signal,
@@ -29,6 +29,7 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 	[SIGBUS]	= relay_signal,
 	[SIGSEGV]	= segv_handler,
 	[SIGIO]		= sigio_handler,
+	[SIGCHLD]	= sigchld_handler,
 };
 
 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
@@ -44,10 +45,10 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 	}
 
 	/* enable signals if sig isn't IRQ signal */
-	if ((sig != SIGIO) && (sig != SIGWINCH))
+	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGCHLD))
 		unblock_signals_trace();
 
-	(*sig_info[sig])(sig, si, &r);
+	(*sig_info[sig])(sig, si, &r, mc);
 
 	errno = save_errno;
 }
@@ -64,6 +65,9 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 #define SIGALRM_BIT 1
 #define SIGALRM_MASK (1 << SIGALRM_BIT)
 
+#define SIGCHLD_BIT 2
+#define SIGCHLD_MASK (1 << SIGCHLD_BIT)
+
 int signals_enabled;
 #if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
 static int signals_blocked, signals_blocked_pending;
@@ -102,6 +106,11 @@ static void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
 		return;
 	}
 
+	if (!enabled && (sig == SIGCHLD)) {
+		signals_pending |= SIGCHLD_MASK;
+		return;
+	}
+
 	block_signals_trace();
 
 	sig_handler_common(sig, si, mc);
@@ -181,6 +190,8 @@ static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 
 	[SIGIO] = sig_handler,
 	[SIGWINCH] = sig_handler,
+	/* SIGCHLD is only actually registered in seccomp mode. */
+	[SIGCHLD] = sig_handler,
 	[SIGALRM] = timer_alarm_handler,
 
 	[SIGUSR1] = sigusr1_handler,
@@ -309,6 +320,12 @@ void unblock_signals(void)
 		if (save_pending & SIGIO_MASK)
 			sig_handler_common(SIGIO, NULL, NULL);
 
+		if (save_pending & SIGCHLD_MASK) {
+			struct uml_pt_regs regs = {};
+
+			sigchld_handler(SIGCHLD, NULL, &regs, NULL);
+		}
+
 		/* Do not reenter the handler */
 
 		if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index d7f1814b0e5a..8b9921ac3ef8 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -43,6 +43,16 @@ void syscall_stub_dump_error(struct mm_id *mm_idp)
 
 	print_hex_dump(UM_KERN_ERR, "    syscall data: ", 0,
 		       16, 4, sc, sizeof(*sc), 0);
+
+	if (using_seccomp) {
+		printk(UM_KERN_ERR "%s: FD map num: %d", __func__,
+		       mm_idp->syscall_fd_num);
+		print_hex_dump(UM_KERN_ERR,
+				"    FD map: ", 0, 16,
+				sizeof(mm_idp->syscall_fd_map[0]),
+				mm_idp->syscall_fd_map,
+				sizeof(mm_idp->syscall_fd_map), 0);
+	}
 }
 
 static inline unsigned long *check_init_stack(struct mm_id * mm_idp,
@@ -80,27 +90,32 @@ static inline long do_syscall_stub(struct mm_id *mm_idp)
 	int n, i;
 	int err, pid = mm_idp->pid;
 
-	n = ptrace_setregs(pid, syscall_regs);
-	if (n < 0) {
-		printk(UM_KERN_ERR "Registers - \n");
-		for (i = 0; i < MAX_REG_NR; i++)
-			printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
-		panic("%s : PTRACE_SETREGS failed, errno = %d\n",
-		      __func__, -n);
-	}
-
 	/* Inform process how much we have filled in. */
 	proc_data->syscall_data_len = mm_idp->syscall_data_len;
 
-	err = ptrace(PTRACE_CONT, pid, 0, 0);
-	if (err)
-		panic("Failed to continue stub, pid = %d, errno = %d\n", pid,
-		      errno);
-
-	wait_stub_done(pid);
+	if (using_seccomp) {
+		proc_data->restart_wait = 1;
+		wait_stub_done_seccomp(mm_idp, 0, 1);
+	} else {
+		n = ptrace_setregs(pid, syscall_regs);
+		if (n < 0) {
+			printk(UM_KERN_ERR "Registers -\n");
+			for (i = 0; i < MAX_REG_NR; i++)
+				printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
+			panic("%s : PTRACE_SETREGS failed, errno = %d\n",
+			      __func__, -n);
+		}
+
+		err = ptrace(PTRACE_CONT, pid, 0, 0);
+		if (err)
+			panic("Failed to continue stub, pid = %d, errno = %d\n",
+			      pid, errno);
+
+		wait_stub_done(pid);
+	}
 
 	/*
-	 * proc_data->err will be non-zero if there was an (unexpected) error.
+	 * proc_data->err will be negative if there was an (unexpected) error.
 	 * In that case, syscall_data_len points to the last executed syscall,
 	 * otherwise it will be zero (but we do not need to rely on that).
 	 */
@@ -113,6 +128,9 @@ static inline long do_syscall_stub(struct mm_id *mm_idp)
 		mm_idp->syscall_data_len = 0;
 	}
 
+	if (using_seccomp)
+		mm_idp->syscall_fd_num = 0;
+
 	return mm_idp->syscall_data_len;
 }
 
@@ -175,6 +193,44 @@ static struct stub_syscall *syscall_stub_get_previous(struct mm_id *mm_idp,
 	return NULL;
 }
 
+static int get_stub_fd(struct mm_id *mm_idp, int fd)
+{
+	int i;
+
+	/* Find an FD slot (or flush and use first) */
+	if (!using_seccomp)
+		return fd;
+
+	/* Already crashed, value does not matter */
+	if (mm_idp->syscall_data_len < 0)
+		return 0;
+
+	/* Find existing FD in map if we can allocate another syscall */
+	if (mm_idp->syscall_data_len <
+	    ARRAY_SIZE(((struct stub_data *)NULL)->syscall_data)) {
+		for (i = 0; i < mm_idp->syscall_fd_num; i++) {
+			if (mm_idp->syscall_fd_map[i] == fd)
+				return i;
+		}
+
+		if (mm_idp->syscall_fd_num < STUB_MAX_FDS) {
+			i = mm_idp->syscall_fd_num;
+			mm_idp->syscall_fd_map[i] = fd;
+
+			mm_idp->syscall_fd_num++;
+
+			return i;
+		}
+	}
+
+	/* FD map full or no syscall space available, continue after flush */
+	do_syscall_stub(mm_idp);
+	mm_idp->syscall_fd_map[0] = fd;
+	mm_idp->syscall_fd_num = 1;
+
+	return 0;
+}
+
 int map(struct mm_id *mm_idp, unsigned long virt, unsigned long len, int prot,
 	int phys_fd, unsigned long long offset)
 {
@@ -182,12 +238,21 @@ int map(struct mm_id *mm_idp, unsigned long virt, unsigned long len, int prot,
 
 	/* Compress with previous syscall if that is possible */
 	sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MMAP, virt);
-	if (sc && sc->mem.prot == prot && sc->mem.fd == phys_fd &&
+	if (sc && sc->mem.prot == prot &&
 	    sc->mem.offset == MMAP_OFFSET(offset - sc->mem.length)) {
-		sc->mem.length += len;
-		return 0;
+		int prev_fd = sc->mem.fd;
+
+		if (using_seccomp)
+			prev_fd = mm_idp->syscall_fd_map[sc->mem.fd];
+
+		if (phys_fd == prev_fd) {
+			sc->mem.length += len;
+			return 0;
+		}
 	}
 
+	phys_fd = get_stub_fd(mm_idp, phys_fd);
+
 	sc = syscall_stub_alloc(mm_idp);
 	sc->syscall = STUB_SYSCALL_MMAP;
 	sc->mem.addr = virt;
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index f683cfc9e51a..e42ffac23e3c 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  */
@@ -15,6 +16,7 @@
 #include <sys/mman.h>
 #include <sys/wait.h>
 #include <sys/stat.h>
+#include <sys/socket.h>
 #include <asm/unistd.h>
 #include <as-layout.h>
 #include <init.h>
@@ -25,8 +27,11 @@
 #include <registers.h>
 #include <skas.h>
 #include <sysdep/stub.h>
+#include <sysdep/mcontext.h>
+#include <linux/futex.h>
 #include <linux/threads.h>
 #include <timetravel.h>
+#include <asm-generic/rwonce.h>
 #include "../internal.h"
 
 int is_skas_winch(int pid, int fd, void *data)
@@ -142,6 +147,105 @@ bad_wait:
 	fatal_sigsegv();
 }
 
+void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys)
+{
+	struct stub_data *data = (void *)mm_idp->stack;
+	int ret;
+
+	do {
+		const char byte = 0;
+		struct iovec iov = {
+			.iov_base = (void *)&byte,
+			.iov_len = sizeof(byte),
+		};
+		union {
+			char data[CMSG_SPACE(sizeof(mm_idp->syscall_fd_map))];
+			struct cmsghdr align;
+		} ctrl;
+		struct msghdr msgh = {
+			.msg_iov = &iov,
+			.msg_iovlen = 1,
+		};
+
+		if (!running) {
+			if (mm_idp->syscall_fd_num) {
+				unsigned int fds_size =
+					sizeof(int) * mm_idp->syscall_fd_num;
+				struct cmsghdr *cmsg;
+
+				msgh.msg_control = ctrl.data;
+				msgh.msg_controllen = CMSG_SPACE(fds_size);
+				cmsg = CMSG_FIRSTHDR(&msgh);
+				cmsg->cmsg_level = SOL_SOCKET;
+				cmsg->cmsg_type = SCM_RIGHTS;
+				cmsg->cmsg_len = CMSG_LEN(fds_size);
+				memcpy(CMSG_DATA(cmsg), mm_idp->syscall_fd_map,
+				       fds_size);
+
+				CATCH_EINTR(syscall(__NR_sendmsg, mm_idp->sock,
+						&msgh, 0));
+			}
+
+			data->signal = 0;
+			data->futex = FUTEX_IN_CHILD;
+			CATCH_EINTR(syscall(__NR_futex, &data->futex,
+					    FUTEX_WAKE, 1, NULL, NULL, 0));
+		}
+
+		do {
+			/*
+			 * We need to check whether the child is still alive
+			 * before and after the FUTEX_WAIT call. Before, in
+			 * case it just died but we still updated data->futex
+			 * to FUTEX_IN_CHILD. And after, in case it died while
+			 * we were waiting (and SIGCHLD woke us up, see the
+			 * IRQ handler in mmu.c).
+			 *
+			 * Either way, if PID is negative, then we have no
+			 * choice but to kill the task.
+			 */
+			if (__READ_ONCE(mm_idp->pid) < 0)
+				goto out_kill;
+
+			ret = syscall(__NR_futex, &data->futex,
+				      FUTEX_WAIT, FUTEX_IN_CHILD,
+				      NULL, NULL, 0);
+			if (ret < 0 && errno != EINTR && errno != EAGAIN) {
+				printk(UM_KERN_ERR "%s : FUTEX_WAIT failed, errno = %d\n",
+				       __func__, errno);
+				goto out_kill;
+			}
+		} while (data->futex == FUTEX_IN_CHILD);
+
+		if (__READ_ONCE(mm_idp->pid) < 0)
+			goto out_kill;
+
+		running = 0;
+
+		/* We may receive a SIGALRM before SIGSYS, iterate again. */
+	} while (wait_sigsys && data->signal == SIGALRM);
+
+	if (data->mctx_offset > sizeof(data->sigstack) - sizeof(mcontext_t)) {
+		printk(UM_KERN_ERR "%s : invalid mcontext offset", __func__);
+		goto out_kill;
+	}
+
+	if (wait_sigsys && data->signal != SIGSYS) {
+		printk(UM_KERN_ERR "%s : expected SIGSYS but got %d",
+		       __func__, data->signal);
+		goto out_kill;
+	}
+
+	return;
+
+out_kill:
+	printk(UM_KERN_ERR "%s : failed to wait for stub, pid = %d, errno = %d\n",
+	       __func__, mm_idp->pid, errno);
+	/* This is not true inside start_userspace */
+	if (current_mm_id() == mm_idp)
+		fatal_sigsegv();
+}
+
 extern unsigned long current_stub_stack(void);
 
 static void get_skas_faultinfo(int pid, struct faultinfo *fi)
@@ -163,12 +267,6 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
 	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 }
 
-static void handle_segv(int pid, struct uml_pt_regs *regs)
-{
-	get_skas_faultinfo(pid, &regs->faultinfo);
-	segv(regs->faultinfo, 0, 1, NULL);
-}
-
 static void handle_trap(int pid, struct uml_pt_regs *regs)
 {
 	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
@@ -181,50 +279,80 @@ extern char __syscall_stub_start[];
 
 static int stub_exe_fd;
 
-static int userspace_tramp(void *stack)
+struct tramp_data {
+	struct stub_data *stub_data;
+	/* 0 is inherited, 1 is the kernel side */
+	int sockpair[2];
+};
+
+#ifndef CLOSE_RANGE_CLOEXEC
+#define CLOSE_RANGE_CLOEXEC	(1U << 2)
+#endif
+
+static int userspace_tramp(void *data)
 {
+	struct tramp_data *tramp_data = data;
 	char *const argv[] = { "uml-userspace", NULL };
-	int pipe_fds[2];
 	unsigned long long offset;
 	struct stub_init_data init_data = {
+		.seccomp = using_seccomp,
 		.stub_start = STUB_START,
-		.segv_handler = STUB_CODE +
-				(unsigned long) stub_segv_handler -
-				(unsigned long) __syscall_stub_start,
 	};
 	struct iomem_region *iomem;
 	int ret;
 
+	if (using_seccomp) {
+		init_data.signal_handler = STUB_CODE +
+					   (unsigned long) stub_signal_interrupt -
+					   (unsigned long) __syscall_stub_start;
+		init_data.signal_restorer = STUB_CODE +
+					   (unsigned long) stub_signal_restorer -
+					   (unsigned long) __syscall_stub_start;
+	} else {
+		init_data.signal_handler = STUB_CODE +
+					   (unsigned long) stub_segv_handler -
+					   (unsigned long) __syscall_stub_start;
+		init_data.signal_restorer = 0;
+	}
+
 	init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
 					      &offset);
 	init_data.stub_code_offset = MMAP_OFFSET(offset);
 
-	init_data.stub_data_fd = phys_mapping(uml_to_phys(stack), &offset);
+	init_data.stub_data_fd = phys_mapping(uml_to_phys(tramp_data->stub_data),
+					      &offset);
 	init_data.stub_data_offset = MMAP_OFFSET(offset);
 
-	/* Set CLOEXEC on all FDs and then unset on all memory related FDs */
-	close_range(0, ~0U, CLOSE_RANGE_CLOEXEC);
+	/*
+	 * Avoid leaking unneeded FDs to the stub by setting CLOEXEC on all FDs
+	 * and then unsetting it on all memory related FDs.
+	 * This is not strictly necessary from a safety perspective.
+	 */
+	syscall(__NR_close_range, 0, ~0U, CLOSE_RANGE_CLOEXEC);
 
 	fcntl(init_data.stub_data_fd, F_SETFD, 0);
-	for (iomem = iomem_regions; iomem; iomem = iomem->next)
-		fcntl(iomem->fd, F_SETFD, 0);
 
-	/* Create a pipe for init_data (no CLOEXEC) and dup2 to STDIN */
-	if (pipe(pipe_fds))
-		exit(2);
+	/* In SECCOMP mode, these FDs are passed when needed */
+	if (!using_seccomp) {
+		for (iomem = iomem_regions; iomem; iomem = iomem->next)
+			fcntl(iomem->fd, F_SETFD, 0);
+	}
 
-	if (dup2(pipe_fds[0], 0) < 0)
+	/* dup2 signaling FD/socket to STDIN */
+	if (dup2(tramp_data->sockpair[0], 0) < 0)
 		exit(3);
-	close(pipe_fds[0]);
+	close(tramp_data->sockpair[0]);
 
 	/* Write init_data and close write side */
-	ret = write(pipe_fds[1], &init_data, sizeof(init_data));
-	close(pipe_fds[1]);
+	ret = write(tramp_data->sockpair[1], &init_data, sizeof(init_data));
+	close(tramp_data->sockpair[1]);
 
 	if (ret != sizeof(init_data))
 		exit(4);
 
-	execveat(stub_exe_fd, "", argv, NULL, AT_EMPTY_PATH);
+	/* Raw execveat for compatibility with older libc versions */
+	syscall(__NR_execveat, stub_exe_fd, (unsigned long)"",
+		(unsigned long)argv, NULL, AT_EMPTY_PATH);
 
 	exit(5);
 }
@@ -305,11 +433,12 @@ static int __init init_stub_exe_fd(void)
 }
 __initcall(init_stub_exe_fd);
 
+int using_seccomp;
 int userspace_pid[NR_CPUS];
 
 /**
  * start_userspace() - prepare a new userspace process
- * @stub_stack:	pointer to the stub stack.
+ * @mm_id: The corresponding struct mm_id
  *
  * 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.
@@ -318,11 +447,15 @@ int userspace_pid[NR_CPUS];
  *         when negative: an error number.
  * FIXME: can PIDs become negative?!
  */
-int start_userspace(unsigned long stub_stack)
+int start_userspace(struct mm_id *mm_id)
 {
+	struct stub_data *proc_data = (void *)mm_id->stack;
+	struct tramp_data tramp_data = {
+		.stub_data = proc_data,
+	};
 	void *stack;
 	unsigned long sp;
-	int pid, status, n, err;
+	int status, n, err;
 
 	/* setup a temporary stack page */
 	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
@@ -338,40 +471,55 @@ int start_userspace(unsigned long stub_stack)
 	/* set stack pointer to the end of the stack page, so it can grow downwards */
 	sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;
 
-	/* clone into new userspace process */
-	pid = clone(userspace_tramp, (void *) sp,
+	/* socket pair for init data and SECCOMP FD passing (no CLOEXEC here) */
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, tramp_data.sockpair)) {
+		err = -errno;
+		printk(UM_KERN_ERR "%s : socketpair failed, errno = %d\n",
+		       __func__, errno);
+		return err;
+	}
+
+	if (using_seccomp)
+		proc_data->futex = FUTEX_IN_CHILD;
+
+	mm_id->pid = clone(userspace_tramp, (void *) sp,
 		    CLONE_VFORK | CLONE_VM | SIGCHLD,
-		    (void *)stub_stack);
-	if (pid < 0) {
+		    (void *)&tramp_data);
+	if (mm_id->pid < 0) {
 		err = -errno;
 		printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
 		       __func__, errno);
-		return err;
+		goto out_close;
 	}
 
-	do {
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
-		if (n < 0) {
+	if (using_seccomp) {
+		wait_stub_done_seccomp(mm_id, 1, 1);
+	} else {
+		do {
+			CATCH_EINTR(n = waitpid(mm_id->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_SETOPTIONS, mm_id->pid, NULL,
+			   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
 			err = -errno;
-			printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
+			printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS 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_SETOPTIONS, pid, NULL,
-		   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
-		err = -errno;
-		printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
-		       __func__, errno);
-		goto out_kill;
 	}
 
 	if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
@@ -381,10 +529,22 @@ int start_userspace(unsigned long stub_stack)
 		goto out_kill;
 	}
 
-	return pid;
+	close(tramp_data.sockpair[0]);
+	if (using_seccomp)
+		mm_id->sock = tramp_data.sockpair[1];
+	else
+		close(tramp_data.sockpair[1]);
+
+	return 0;
+
+out_kill:
+	os_kill_ptraced_process(mm_id->pid, 1);
+out_close:
+	close(tramp_data.sockpair[0]);
+	close(tramp_data.sockpair[1]);
+
+	mm_id->pid = -1;
 
- out_kill:
-	os_kill_ptraced_process(pid, 1);
 	return err;
 }
 
@@ -394,7 +554,9 @@ extern unsigned long tt_extra_sched_jiffies;
 void userspace(struct uml_pt_regs *regs)
 {
 	int err, status, op, pid = userspace_pid[0];
-	siginfo_t si;
+	siginfo_t si_ptrace;
+	siginfo_t *si;
+	int sig;
 
 	/* Handle any immediate reschedules or signals */
 	interrupt_end();
@@ -427,103 +589,177 @@ void userspace(struct uml_pt_regs *regs)
 
 		current_mm_sync();
 
-		/* Flush out any pending syscalls */
-		err = syscall_stub_flush(current_mm_id());
-		if (err) {
-			if (err == -ENOMEM)
-				report_enomem();
+		if (using_seccomp) {
+			struct mm_id *mm_id = current_mm_id();
+			struct stub_data *proc_data = (void *) mm_id->stack;
+			int ret;
 
-			printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
-				__func__, -err);
-			fatal_sigsegv();
-		}
+			ret = set_stub_state(regs, proc_data, singlestepping());
+			if (ret) {
+				printk(UM_KERN_ERR "%s - failed to set regs: %d",
+				       __func__, ret);
+				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();
-		}
+			/* Must have been reset by the syscall caller */
+			if (proc_data->restart_wait != 0)
+				panic("Programming error: Flag to only run syscalls in child was not cleared!");
 
-		if (put_fp_registers(pid, regs->fp)) {
-			printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
-			       __func__, errno);
-			fatal_sigsegv();
-		}
+			/* Mark pending syscalls for flushing */
+			proc_data->syscall_data_len = mm_id->syscall_data_len;
 
-		if (singlestepping())
-			op = PTRACE_SYSEMU_SINGLESTEP;
-		else
-			op = PTRACE_SYSEMU;
+			wait_stub_done_seccomp(mm_id, 0, 0);
 
-		if (ptrace(op, pid, 0, 0)) {
-			printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
-			       __func__, op, errno);
-			fatal_sigsegv();
-		}
+			sig = proc_data->signal;
 
-		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();
-		}
+			if (sig == SIGTRAP && proc_data->err != 0) {
+				printk(UM_KERN_ERR "%s - Error flushing stub syscalls",
+				       __func__);
+				syscall_stub_dump_error(mm_id);
+				mm_id->syscall_data_len = proc_data->err;
+				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();
-		}
+			mm_id->syscall_data_len = 0;
+			mm_id->syscall_fd_num = 0;
 
-		if (get_fp_registers(pid, regs->fp)) {
-			printk(UM_KERN_ERR "%s -  get_fp_registers failed, errno = %d\n",
-			       __func__, errno);
-			fatal_sigsegv();
-		}
+			ret = get_stub_state(regs, proc_data, NULL);
+			if (ret) {
+				printk(UM_KERN_ERR "%s - failed to get regs: %d",
+				       __func__, ret);
+				fatal_sigsegv();
+			}
 
-		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
+			if (proc_data->si_offset > sizeof(proc_data->sigstack) - sizeof(*si))
+				panic("%s - Invalid siginfo offset from child",
+				      __func__);
+			si = (void *)&proc_data->sigstack[proc_data->si_offset];
 
-		if (WIFSTOPPED(status)) {
-			int sig = WSTOPSIG(status);
+			regs->is_user = 1;
 
-			/* These signal handlers need the si argument.
-			 * The SIGIO and SIGALARM handlers which constitute the
-			 * majority of invocations, do not use it.
+			/* Fill in ORIG_RAX and extract fault information */
+			PT_SYSCALL_NR(regs->gp) = si->si_syscall;
+			if (sig == SIGSEGV) {
+				mcontext_t *mcontext = (void *)&proc_data->sigstack[proc_data->mctx_offset];
+
+				GET_FAULTINFO_FROM_MC(regs->faultinfo, mcontext);
+			}
+		} else {
+			/* Flush out any pending syscalls */
+			err = syscall_stub_flush(current_mm_id());
+			if (err) {
+				if (err == -ENOMEM)
+					report_enomem();
+
+				printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
+					__func__, -err);
+				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.
 			 */
-			switch (sig) {
-			case SIGSEGV:
-			case SIGTRAP:
-			case SIGILL:
-			case SIGBUS:
-			case SIGFPE:
-			case SIGWINCH:
-				ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
-				break;
+			if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
+				printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
 			}
 
-			switch (sig) {
-			case SIGSEGV:
-				if (PTRACE_FULL_FAULTINFO) {
+			if (put_fp_registers(pid, regs->fp)) {
+				printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			if (singlestepping())
+				op = PTRACE_SYSEMU_SINGLESTEP;
+			else
+				op = PTRACE_SYSEMU;
+
+			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();
+			}
+
+			if (WIFSTOPPED(status)) {
+				sig = WSTOPSIG(status);
+
+				/*
+				 * These signal handlers need the si argument
+				 * and SIGSEGV needs the faultinfo.
+				 * The SIGIO and SIGALARM handlers which constitute
+				 * the majority of invocations, do not use it.
+				 */
+				switch (sig) {
+				case SIGSEGV:
 					get_skas_faultinfo(pid,
 							   &regs->faultinfo);
-					(*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
-							     regs);
+					fallthrough;
+				case SIGTRAP:
+				case SIGILL:
+				case SIGBUS:
+				case SIGFPE:
+				case SIGWINCH:
+					ptrace(PTRACE_GETSIGINFO, pid, 0,
+					       (struct siginfo *)&si_ptrace);
+					si = &si_ptrace;
+					break;
+				default:
+					si = NULL;
+					break;
 				}
-				else handle_segv(pid, regs);
+			} else {
+				sig = 0;
+			}
+		}
+
+		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
+
+		if (sig) {
+			switch (sig) {
+			case SIGSEGV:
+				if (using_seccomp || PTRACE_FULL_FAULTINFO)
+					(*sig_info[SIGSEGV])(SIGSEGV,
+							     (struct siginfo *)si,
+							     regs, NULL);
+				else
+					segv(regs->faultinfo, 0, 1, NULL, NULL);
+
+				break;
+			case SIGSYS:
+				handle_syscall(regs);
 				break;
 			case SIGTRAP + 0x80:
 				handle_trap(pid, regs);
 				break;
 			case SIGTRAP:
-				relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
+				relay_signal(SIGTRAP, (struct siginfo *)si, regs, NULL);
 				break;
 			case SIGALRM:
 				break;
@@ -533,7 +769,7 @@ void userspace(struct uml_pt_regs *regs)
 			case SIGFPE:
 			case SIGWINCH:
 				block_signals_trace();
-				(*sig_info[sig])(sig, (struct siginfo *)&si, regs);
+				(*sig_info[sig])(sig, (struct siginfo *)si, regs, NULL);
 				unblock_signals_trace();
 				break;
 			default:
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 93fc82c01aba..a827c2e01aa5 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  */
 
@@ -24,6 +25,13 @@
 #include <kern_util.h>
 #include <mem_user.h>
 #include <ptrace_user.h>
+#include <stdbool.h>
+#include <stub-data.h>
+#include <sys/prctl.h>
+#include <linux/seccomp.h>
+#include <linux/filter.h>
+#include <sysdep/mcontext.h>
+#include <sysdep/stub.h>
 #include <registers.h>
 #include <skas.h>
 #include "internal.h"
@@ -224,6 +232,140 @@ static void __init check_ptrace(void)
 	check_sysemu();
 }
 
+extern unsigned long host_fp_size;
+extern unsigned long exec_regs[MAX_REG_NR];
+extern unsigned long *exec_fp_regs;
+
+__initdata static struct stub_data *seccomp_test_stub_data;
+
+static void __init sigsys_handler(int sig, siginfo_t *info, void *p)
+{
+	ucontext_t *uc = p;
+
+	/* Stow away the location of the mcontext in the stack */
+	seccomp_test_stub_data->mctx_offset = (unsigned long)&uc->uc_mcontext -
+					      (unsigned long)&seccomp_test_stub_data->sigstack[0];
+
+	/* Prevent libc from clearing memory (mctx_offset in particular) */
+	syscall(__NR_exit, 0);
+}
+
+static int __init seccomp_helper(void *data)
+{
+	static struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+			 offsetof(struct seccomp_data, nr)),
+		BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_clock_nanosleep, 1, 0),
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_TRAP),
+	};
+	static struct sock_fprog prog = {
+		.len = ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+	struct sigaction sa;
+
+	/* close_range is needed for the stub */
+	if (stub_syscall3(__NR_close_range, 1, ~0U, 0))
+		exit(1);
+
+	set_sigstack(seccomp_test_stub_data->sigstack,
+			sizeof(seccomp_test_stub_data->sigstack));
+
+	sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
+	sa.sa_sigaction = (void *) sigsys_handler;
+	sa.sa_restorer = NULL;
+	if (sigaction(SIGSYS, &sa, NULL) < 0)
+		exit(2);
+
+	prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+	if (syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER,
+			SECCOMP_FILTER_FLAG_TSYNC, &prog) != 0)
+		exit(3);
+
+	sleep(0);
+
+	/* Never reached. */
+	_exit(4);
+}
+
+static bool __init init_seccomp(void)
+{
+	int pid;
+	int status;
+	int n;
+	unsigned long sp;
+
+	/*
+	 * We check that we can install a seccomp filter and then exit(0)
+	 * from a trapped syscall.
+	 *
+	 * Note that we cannot verify that no seccomp filter already exists
+	 * for a syscall that results in the process/thread to be killed.
+	 */
+
+	os_info("Checking that seccomp filters can be installed...");
+
+	seccomp_test_stub_data = mmap(0, sizeof(*seccomp_test_stub_data),
+				      PROT_READ | PROT_WRITE,
+				      MAP_SHARED | MAP_ANON, 0, 0);
+
+	/* Use the syscall data area as stack, we just need something */
+	sp = (unsigned long)&seccomp_test_stub_data->syscall_data +
+	     sizeof(seccomp_test_stub_data->syscall_data) -
+	     sizeof(void *);
+	pid = clone(seccomp_helper, (void *)sp, CLONE_VFORK | CLONE_VM, NULL);
+
+	if (pid < 0)
+		fatal_perror("check_seccomp : clone failed");
+
+	CATCH_EINTR(n = waitpid(pid, &status, __WCLONE));
+	if (n < 0)
+		fatal_perror("check_seccomp : waitpid failed");
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+		struct uml_pt_regs *regs;
+		unsigned long fp_size;
+		int r;
+
+		/* Fill in the host_fp_size from the mcontext. */
+		regs = calloc(1, sizeof(struct uml_pt_regs));
+		get_stub_state(regs, seccomp_test_stub_data, &fp_size);
+		host_fp_size = fp_size;
+		free(regs);
+
+		/* Repeat with the correct size */
+		regs = calloc(1, sizeof(struct uml_pt_regs) + host_fp_size);
+		r = get_stub_state(regs, seccomp_test_stub_data, NULL);
+
+		/* Store as the default startup registers */
+		exec_fp_regs = malloc(host_fp_size);
+		memcpy(exec_regs, regs->gp, sizeof(exec_regs));
+		memcpy(exec_fp_regs, regs->fp, host_fp_size);
+
+		munmap(seccomp_test_stub_data, sizeof(*seccomp_test_stub_data));
+
+		free(regs);
+
+		if (r) {
+			os_info("failed to fetch registers: %d\n", r);
+			return false;
+		}
+
+		os_info("OK\n");
+		return true;
+	}
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 2)
+		os_info("missing\n");
+	else
+		os_info("error\n");
+
+	munmap(seccomp_test_stub_data, sizeof(*seccomp_test_stub_data));
+	return false;
+}
+
+
 static void __init check_coredump_limit(void)
 {
 	struct rlimit lim;
@@ -278,6 +420,44 @@ void  __init get_host_cpu_features(
 	}
 }
 
+static int seccomp_config __initdata;
+
+static int __init uml_seccomp_config(char *line, int *add)
+{
+	*add = 0;
+
+	if (strcmp(line, "off") == 0)
+		seccomp_config = 0;
+	else if (strcmp(line, "auto") == 0)
+		seccomp_config = 1;
+	else if (strcmp(line, "on") == 0)
+		seccomp_config = 2;
+	else
+		fatal("Invalid seccomp option '%s', expected on/auto/off\n",
+		      line);
+
+	return 0;
+}
+
+__uml_setup("seccomp=", uml_seccomp_config,
+"seccomp=<on/auto/off>\n"
+"    Configure whether or not SECCOMP is used. With SECCOMP, userspace\n"
+"    processes work collaboratively with the kernel instead of being\n"
+"    traced using ptrace. All syscalls from the application are caught and\n"
+"    redirected using a signal. This signal handler in turn is permitted to\n"
+"    do the selected set of syscalls to communicate with the UML kernel and\n"
+"    do the required memory management.\n"
+"\n"
+"    This method is overall faster than the ptrace based userspace, primarily\n"
+"    because it reduces the number of context switches for (minor) page faults.\n"
+"\n"
+"    However, the SECCOMP filter is not (yet) restrictive enough to prevent\n"
+"    userspace from reading and writing all physical memory. Userspace\n"
+"    processes could also trick the stub into disabling SIGALRM which\n"
+"    prevents it from being interrupted for scheduling purposes.\n"
+"\n"
+"    This is insecure and should only be used with a trusted userspace\n\n"
+);
 
 void __init os_early_checks(void)
 {
@@ -286,13 +466,24 @@ void __init os_early_checks(void)
 	/* Print out the core dump limits early */
 	check_coredump_limit();
 
-	check_ptrace();
-
 	/* Need to check this early because mmapping happens before the
 	 * kernel is running.
 	 */
 	check_tmpexec();
 
+	if (seccomp_config) {
+		if (init_seccomp()) {
+			using_seccomp = 1;
+			return;
+		}
+
+		if (seccomp_config == 2)
+			fatal("SECCOMP userspace requested but not functional!\n");
+	}
+
+	using_seccomp = 0;
+	check_ptrace();
+
 	pid = start_ptraced_child();
 	if (init_pid_registers(pid))
 		fatal("Failed to initialize default registers");