x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 578 insertions, 0 deletions

diff --git a/net/sched/sch_teql.c b/net/sched/sch_teql.c
new file mode 100644
index 000000000..9e52afc2d
--- /dev/null
+++ b/net/sched/sch_teql.c
@@ -0,0 +1,578 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* net/sched/sch_teql.c	"True" (or "trivial") link equalizer.
+ *
+ * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/if_arp.h>
+#include <linux/netdevice.h>
+#include <linux/init.h>
+#include <linux/skbuff.h>
+#include <linux/moduleparam.h>
+#include <net/dst.h>
+#include <net/neighbour.h>
+#include <net/pkt_sched.h>
+
+/*
+   How to setup it.
+   ----------------
+
+   After loading this module you will find a new device teqlN
+   and new qdisc with the same name. To join a slave to the equalizer
+   you should just set this qdisc on a device f.e.
+
+   # tc qdisc add dev eth0 root teql0
+   # tc qdisc add dev eth1 root teql0
+
+   That's all. Full PnP 8)
+
+   Applicability.
+   --------------
+
+   1. Slave devices MUST be active devices, i.e., they must raise the tbusy
+      signal and generate EOI events. If you want to equalize virtual devices
+      like tunnels, use a normal eql device.
+   2. This device puts no limitations on physical slave characteristics
+      f.e. it will equalize 9600baud line and 100Mb ethernet perfectly :-)
+      Certainly, large difference in link speeds will make the resulting
+      eqalized link unusable, because of huge packet reordering.
+      I estimate an upper useful difference as ~10 times.
+   3. If the slave requires address resolution, only protocols using
+      neighbour cache (IPv4/IPv6) will work over the equalized link.
+      Other protocols are still allowed to use the slave device directly,
+      which will not break load balancing, though native slave
+      traffic will have the highest priority.  */
+
+struct teql_master {
+	struct Qdisc_ops qops;
+	struct net_device *dev;
+	struct Qdisc __rcu	*slaves;
+	spinlock_t		slaves_lock; /* serializes writes to ->slaves */
+	struct list_head master_list;
+	unsigned long	tx_bytes;
+	unsigned long	tx_packets;
+	unsigned long	tx_errors;
+	unsigned long	tx_dropped;
+};
+
+struct teql_sched_data {
+	struct Qdisc __rcu	*next;
+	struct teql_master *m;
+	struct sk_buff_head q;
+};
+
+#define NEXT_SLAVE(q) (((struct teql_sched_data *)qdisc_priv(q))->next)
+
+#define FMASK (IFF_BROADCAST | IFF_POINTOPOINT)
+
+/* "teql*" qdisc routines */
+
+static int
+teql_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
+{
+	struct net_device *dev = qdisc_dev(sch);
+	struct teql_sched_data *q = qdisc_priv(sch);
+
+	if (q->q.qlen < READ_ONCE(dev->tx_queue_len)) {
+		__skb_queue_tail(&q->q, skb);
+		return NET_XMIT_SUCCESS;
+	}
+
+	return qdisc_drop(skb, sch, to_free);
+}
+
+static struct sk_buff *
+teql_dequeue(struct Qdisc *sch)
+{
+	struct teql_sched_data *dat = qdisc_priv(sch);
+	struct netdev_queue *dat_queue;
+	struct sk_buff *skb;
+	struct Qdisc *q;
+
+	skb = __skb_dequeue(&dat->q);
+	dat_queue = netdev_get_tx_queue(dat->m->dev, 0);
+	q = rcu_dereference_bh(dat_queue->qdisc);
+
+	if (skb == NULL) {
+		struct net_device *m = qdisc_dev(q);
+		if (m) {
+			spin_lock_bh(&dat->m->slaves_lock);
+			rcu_assign_pointer(dat->m->slaves, sch);
+			spin_unlock_bh(&dat->m->slaves_lock);
+			netif_wake_queue(m);
+		}
+	} else {
+		qdisc_bstats_update(sch, skb);
+	}
+	WRITE_ONCE(sch->q.qlen, dat->q.qlen + READ_ONCE(q->q.qlen));
+	return skb;
+}
+
+static struct sk_buff *
+teql_peek(struct Qdisc *sch)
+{
+	/* teql is meant to be used as root qdisc */
+	return NULL;
+}
+
+static void
+teql_reset(struct Qdisc *sch)
+{
+	struct teql_sched_data *dat = qdisc_priv(sch);
+
+	skb_queue_purge(&dat->q);
+}
+
+static void
+teql_destroy(struct Qdisc *sch)
+{
+	struct Qdisc *q, *prev;
+	struct teql_sched_data *dat = qdisc_priv(sch);
+	struct teql_master *master = dat->m;
+	struct netdev_queue *txq = NULL;
+	bool reset_master_queue = false;
+
+	if (!master)
+		return;
+
+	spin_lock_bh(&master->slaves_lock);
+	prev = rcu_dereference_protected(master->slaves,
+					 lockdep_is_held(&master->slaves_lock));
+	if (prev) {
+		do {
+			struct Qdisc *head, *next;
+
+			q = rcu_dereference_protected(NEXT_SLAVE(prev),
+						      lockdep_is_held(&master->slaves_lock));
+			if (q != sch) {
+				prev = q;
+				continue;
+			}
+
+			next = rcu_dereference_protected(NEXT_SLAVE(q),
+							 lockdep_is_held(&master->slaves_lock));
+			rcu_assign_pointer(NEXT_SLAVE(prev), next);
+
+			head = rcu_dereference_protected(master->slaves,
+							 lockdep_is_held(&master->slaves_lock));
+			if (q == head) {
+				rcu_assign_pointer(master->slaves, next);
+				if (q == next) {
+					txq = netdev_get_tx_queue(master->dev, 0);
+					rcu_assign_pointer(master->slaves, NULL);
+					reset_master_queue = true;
+				}
+			}
+			skb_queue_purge(&dat->q);
+			break;
+		} while (prev != rcu_dereference_protected(master->slaves,
+							   lockdep_is_held(&master->slaves_lock)));
+	}
+	spin_unlock_bh(&master->slaves_lock);
+
+	if (reset_master_queue)
+		dev_reset_queue(master->dev, txq, NULL);
+}
+
+static int teql_qdisc_init(struct Qdisc *sch, struct nlattr *opt,
+			   struct netlink_ext_ack *extack)
+{
+	struct net_device *dev = qdisc_dev(sch);
+	struct teql_master *m = (struct teql_master *)sch->ops;
+	struct teql_sched_data *q = qdisc_priv(sch);
+	struct Qdisc *first;
+
+	if (dev->hard_header_len > m->dev->hard_header_len)
+		return -EINVAL;
+
+	if (m->dev == dev)
+		return -ELOOP;
+
+	if (sch->parent != TC_H_ROOT) {
+		NL_SET_ERR_MSG_MOD(extack, "teql can only be used as root");
+		return -EOPNOTSUPP;
+	}
+
+	q->m = m;
+
+	skb_queue_head_init(&q->q);
+
+	spin_lock_bh(&m->slaves_lock);
+	first = rcu_dereference_protected(m->slaves, lockdep_is_held(&m->slaves_lock));
+	if (first) {
+		if (m->dev->flags & IFF_UP) {
+			if ((m->dev->flags & IFF_POINTOPOINT &&
+			     !(dev->flags & IFF_POINTOPOINT)) ||
+			    (m->dev->flags & IFF_BROADCAST &&
+			     !(dev->flags & IFF_BROADCAST)) ||
+			    (m->dev->flags & IFF_MULTICAST &&
+			     !(dev->flags & IFF_MULTICAST)) ||
+			    dev->mtu < m->dev->mtu) {
+				spin_unlock_bh(&m->slaves_lock);
+				return -EINVAL;
+			}
+		} else {
+			if (!(dev->flags&IFF_POINTOPOINT))
+				m->dev->flags &= ~IFF_POINTOPOINT;
+			if (!(dev->flags&IFF_BROADCAST))
+				m->dev->flags &= ~IFF_BROADCAST;
+			if (!(dev->flags&IFF_MULTICAST))
+				m->dev->flags &= ~IFF_MULTICAST;
+			if (dev->mtu < m->dev->mtu)
+				m->dev->mtu = dev->mtu;
+		}
+		rcu_assign_pointer(q->next,
+				   rcu_dereference_protected(NEXT_SLAVE(first),
+							     lockdep_is_held(&m->slaves_lock)));
+		rcu_assign_pointer(NEXT_SLAVE(first), sch);
+	} else {
+		rcu_assign_pointer(q->next, sch);
+		rcu_assign_pointer(m->slaves, sch);
+		m->dev->mtu = dev->mtu;
+		m->dev->flags = (m->dev->flags&~FMASK)|(dev->flags&FMASK);
+	}
+	spin_unlock_bh(&m->slaves_lock);
+	return 0;
+}
+
+
+static int
+__teql_resolve(struct sk_buff *skb, struct sk_buff *skb_res,
+	       struct net_device *dev, struct netdev_queue *txq,
+	       struct dst_entry *dst)
+{
+	struct neighbour *n;
+	int err = 0;
+
+	n = dst_neigh_lookup_skb(dst, skb);
+	if (!n)
+		return -ENOENT;
+
+	if (dst->dev != dev) {
+		struct neighbour *mn;
+
+		mn = __neigh_lookup_errno(n->tbl, n->primary_key, dev);
+		neigh_release(n);
+		if (IS_ERR(mn))
+			return PTR_ERR(mn);
+		n = mn;
+	}
+
+	if (neigh_event_send(n, skb_res) == 0) {
+		int err;
+		char haddr[MAX_ADDR_LEN];
+
+		neigh_ha_snapshot(haddr, n, dev);
+		err = dev_hard_header(skb, dev, ntohs(skb_protocol(skb, false)),
+				      haddr, NULL, skb->len);
+
+		if (err < 0)
+			err = -EINVAL;
+	} else {
+		err = (skb_res == NULL) ? -EAGAIN : 1;
+	}
+	neigh_release(n);
+	return err;
+}
+
+static inline int teql_resolve(struct sk_buff *skb,
+			       struct sk_buff *skb_res,
+			       struct net_device *dev,
+			       struct netdev_queue *txq)
+{
+	struct dst_entry *dst = skb_dst(skb);
+	int res;
+
+	if (rcu_access_pointer(txq->qdisc) == &noop_qdisc)
+		return -ENODEV;
+
+	if (!dev->header_ops || !dst)
+		return 0;
+
+	rcu_read_lock();
+	res = __teql_resolve(skb, skb_res, dev, txq, dst);
+	rcu_read_unlock();
+
+	return res;
+}
+
+static netdev_tx_t teql_master_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct teql_master *master = netdev_priv(dev);
+	struct Qdisc *start, *q;
+	int busy;
+	int nores;
+	int subq = skb_get_queue_mapping(skb);
+	struct sk_buff *skb_res = NULL;
+
+restart:
+	nores = 0;
+	busy = 0;
+
+	rcu_read_lock();
+
+	start = rcu_dereference(master->slaves);
+
+	q = start;
+	if (!q)
+		goto drop;
+
+	do {
+		struct net_device *slave = qdisc_dev(q);
+		struct netdev_queue *slave_txq = netdev_get_tx_queue(slave, 0);
+
+		if (rcu_access_pointer(slave_txq->qdisc_sleeping) != q)
+			continue;
+		if (netif_xmit_stopped(netdev_get_tx_queue(slave, subq)) ||
+		    !netif_running(slave)) {
+			busy = 1;
+			continue;
+		}
+
+		switch (teql_resolve(skb, skb_res, slave, slave_txq)) {
+		case 0:
+			if (__netif_tx_trylock(slave_txq)) {
+				unsigned int length = qdisc_pkt_len(skb);
+
+				skb->dev = slave;
+				if (!netif_xmit_frozen_or_stopped(slave_txq) &&
+				    netdev_start_xmit(skb, slave, slave_txq, false) ==
+				    NETDEV_TX_OK) {
+					__netif_tx_unlock(slave_txq);
+					spin_lock(&master->slaves_lock);
+					if (rcu_dereference_protected(master->slaves,
+								      lockdep_is_held(&master->slaves_lock)) == q)
+						rcu_assign_pointer(master->slaves,
+								   rcu_dereference_protected(NEXT_SLAVE(q),
+											     lockdep_is_held(&master->slaves_lock)));
+					spin_unlock(&master->slaves_lock);
+					netif_wake_queue(dev);
+					master->tx_packets++;
+					master->tx_bytes += length;
+					rcu_read_unlock();
+					return NETDEV_TX_OK;
+				}
+				__netif_tx_unlock(slave_txq);
+			}
+			if (netif_xmit_stopped(netdev_get_tx_queue(dev, 0)))
+				busy = 1;
+			break;
+		case 1:
+			spin_lock(&master->slaves_lock);
+			if (rcu_dereference_protected(master->slaves,
+						      lockdep_is_held(&master->slaves_lock)) == q)
+				rcu_assign_pointer(master->slaves,
+						   rcu_dereference_protected(NEXT_SLAVE(q),
+									     lockdep_is_held(&master->slaves_lock)));
+			spin_unlock(&master->slaves_lock);
+			rcu_read_unlock();
+			return NETDEV_TX_OK;
+		default:
+			nores = 1;
+			break;
+		}
+		skb->dev = dev;
+		__skb_pull(skb, skb_network_offset(skb));
+	} while ((q = rcu_dereference(NEXT_SLAVE(q))) != start);
+
+	if (nores && skb_res == NULL) {
+		skb_res = skb;
+		rcu_read_unlock();
+		goto restart;
+	}
+
+	if (busy) {
+		netif_stop_queue(dev);
+		rcu_read_unlock();
+		return NETDEV_TX_BUSY;
+	}
+	master->tx_errors++;
+
+drop:
+	master->tx_dropped++;
+	rcu_read_unlock();
+	dev_kfree_skb(skb);
+	return NETDEV_TX_OK;
+}
+
+static int teql_master_open(struct net_device *dev)
+{
+	struct Qdisc *q, *first;
+	struct teql_master *m = netdev_priv(dev);
+	int mtu = 0xFFFE;
+	unsigned int flags = IFF_NOARP | IFF_MULTICAST;
+
+	first = rtnl_dereference(m->slaves);
+	if (!first)
+		return -EUNATCH;
+
+	flags = FMASK;
+
+	q = first;
+	do {
+		struct net_device *slave = qdisc_dev(q);
+
+		if (slave == NULL)
+			return -EUNATCH;
+
+		if (slave->mtu < mtu)
+			mtu = slave->mtu;
+		if (slave->hard_header_len > LL_MAX_HEADER)
+			return -EINVAL;
+
+		/* If all the slaves are BROADCAST, master is BROADCAST
+		   If all the slaves are PtP, master is PtP
+		   Otherwise, master is NBMA.
+		 */
+		if (!(slave->flags&IFF_POINTOPOINT))
+			flags &= ~IFF_POINTOPOINT;
+		if (!(slave->flags&IFF_BROADCAST))
+			flags &= ~IFF_BROADCAST;
+		if (!(slave->flags&IFF_MULTICAST))
+			flags &= ~IFF_MULTICAST;
+	} while ((q = rtnl_dereference(NEXT_SLAVE(q))) != first);
+
+	m->dev->mtu = mtu;
+	m->dev->flags = (m->dev->flags&~FMASK) | flags;
+	netif_start_queue(m->dev);
+	return 0;
+}
+
+static int teql_master_close(struct net_device *dev)
+{
+	netif_stop_queue(dev);
+	return 0;
+}
+
+static void teql_master_stats64(struct net_device *dev,
+				struct rtnl_link_stats64 *stats)
+{
+	struct teql_master *m = netdev_priv(dev);
+
+	stats->tx_packets	= m->tx_packets;
+	stats->tx_bytes		= m->tx_bytes;
+	stats->tx_errors	= m->tx_errors;
+	stats->tx_dropped	= m->tx_dropped;
+}
+
+static int teql_master_mtu(struct net_device *dev, int new_mtu)
+{
+	struct teql_master *m = netdev_priv(dev);
+	struct Qdisc *q, *first;
+
+	first = rtnl_dereference(m->slaves);
+	q = first;
+	if (q) {
+		do {
+			if (new_mtu > qdisc_dev(q)->mtu)
+				return -EINVAL;
+		} while ((q = rtnl_dereference(NEXT_SLAVE(q))) != first);
+	}
+
+	WRITE_ONCE(dev->mtu, new_mtu);
+	return 0;
+}
+
+static const struct net_device_ops teql_netdev_ops = {
+	.ndo_open	= teql_master_open,
+	.ndo_stop	= teql_master_close,
+	.ndo_start_xmit	= teql_master_xmit,
+	.ndo_get_stats64 = teql_master_stats64,
+	.ndo_change_mtu	= teql_master_mtu,
+};
+
+static __init void teql_master_setup(struct net_device *dev)
+{
+	struct teql_master *master = netdev_priv(dev);
+	struct Qdisc_ops *ops = &master->qops;
+
+	spin_lock_init(&master->slaves_lock);
+	master->dev	= dev;
+	ops->priv_size  = sizeof(struct teql_sched_data);
+
+	ops->enqueue	=	teql_enqueue;
+	ops->dequeue	=	teql_dequeue;
+	ops->peek	=	teql_peek;
+	ops->init	=	teql_qdisc_init;
+	ops->reset	=	teql_reset;
+	ops->destroy	=	teql_destroy;
+	ops->owner	=	THIS_MODULE;
+
+	dev->netdev_ops =       &teql_netdev_ops;
+	dev->type		= ARPHRD_VOID;
+	dev->mtu		= 1500;
+	dev->min_mtu		= 68;
+	dev->max_mtu		= 65535;
+	dev->tx_queue_len	= 100;
+	dev->flags		= IFF_NOARP;
+	dev->hard_header_len	= LL_MAX_HEADER;
+	netif_keep_dst(dev);
+}
+
+static LIST_HEAD(master_dev_list);
+static int max_equalizers = 1;
+module_param(max_equalizers, int, 0);
+MODULE_PARM_DESC(max_equalizers, "Max number of link equalizers");
+
+static int __init teql_init(void)
+{
+	int i;
+	int err = -ENODEV;
+
+	for (i = 0; i < max_equalizers; i++) {
+		struct net_device *dev;
+		struct teql_master *master;
+
+		dev = alloc_netdev(sizeof(struct teql_master), "teql%d",
+				   NET_NAME_UNKNOWN, teql_master_setup);
+		if (!dev) {
+			err = -ENOMEM;
+			break;
+		}
+
+		if ((err = register_netdev(dev))) {
+			free_netdev(dev);
+			break;
+		}
+
+		master = netdev_priv(dev);
+
+		strscpy(master->qops.id, dev->name, IFNAMSIZ);
+		err = register_qdisc(&master->qops);
+
+		if (err) {
+			unregister_netdev(dev);
+			free_netdev(dev);
+			break;
+		}
+
+		list_add_tail(&master->master_list, &master_dev_list);
+	}
+	return i ? 0 : err;
+}
+
+static void __exit teql_exit(void)
+{
+	struct teql_master *master, *nxt;
+
+	list_for_each_entry_safe(master, nxt, &master_dev_list, master_list) {
+
+		list_del(&master->master_list);
+
+		unregister_qdisc(&master->qops);
+		unregister_netdev(master->dev);
+		free_netdev(master->dev);
+	}
+}
+
+module_init(teql_init);
+module_exit(teql_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("True (or trivial) link equalizer qdisc");