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, 414 insertions, 0 deletions

diff --git a/net/sched/sch_multiq.c b/net/sched/sch_multiq.c
new file mode 100644
index 000000000..66df30939
--- /dev/null
+++ b/net/sched/sch_multiq.c
@@ -0,0 +1,414 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2008, Intel Corporation.
+ *
+ * Author: Alexander Duyck <alexander.h.duyck@intel.com>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <net/netlink.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+
+struct multiq_sched_data {
+	u16 bands;
+	u16 max_bands;
+	u16 curband;
+	struct tcf_proto __rcu *filter_list;
+	struct tcf_block *block;
+	struct Qdisc **queues;
+};
+
+
+static struct Qdisc *
+multiq_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	u32 band;
+	struct tcf_result res;
+	struct tcf_proto *fl = rcu_dereference_bh(q->filter_list);
+	int err;
+
+	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+	err = tcf_classify_qdisc(skb, fl, &res, false);
+#ifdef CONFIG_NET_CLS_ACT
+	switch (err) {
+	case TC_ACT_STOLEN:
+	case TC_ACT_QUEUED:
+	case TC_ACT_TRAP:
+		*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
+		fallthrough;
+	case TC_ACT_SHOT:
+		return NULL;
+	}
+#endif
+	band = skb_get_queue_mapping(skb);
+
+	if (band >= q->bands)
+		return q->queues[0];
+
+	return q->queues[band];
+}
+
+static int
+multiq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+	       struct sk_buff **to_free)
+{
+	struct Qdisc *qdisc;
+	int ret;
+
+	qdisc = multiq_classify(skb, sch, &ret);
+#ifdef CONFIG_NET_CLS_ACT
+	if (qdisc == NULL) {
+
+		if (ret & __NET_XMIT_BYPASS)
+			qdisc_qstats_drop(sch);
+		__qdisc_drop(skb, to_free);
+		return ret;
+	}
+#endif
+
+	ret = qdisc_enqueue(skb, qdisc, to_free);
+	if (ret == NET_XMIT_SUCCESS) {
+		qdisc_qlen_inc(sch);
+		return NET_XMIT_SUCCESS;
+	}
+	if (net_xmit_drop_count(ret))
+		qdisc_qstats_drop(sch);
+	return ret;
+}
+
+static struct sk_buff *multiq_dequeue(struct Qdisc *sch)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	struct Qdisc *qdisc;
+	struct sk_buff *skb;
+	int band;
+
+	for (band = 0; band < q->bands; band++) {
+		/* cycle through bands to ensure fairness */
+		q->curband++;
+		if (q->curband >= q->bands)
+			q->curband = 0;
+
+		/* Check that target subqueue is available before
+		 * pulling an skb to avoid head-of-line blocking.
+		 */
+		if (!netif_xmit_stopped(
+		    netdev_get_tx_queue(qdisc_dev(sch), q->curband))) {
+			qdisc = q->queues[q->curband];
+			skb = qdisc_dequeue_peeked(qdisc);
+			if (skb) {
+				qdisc_bstats_update(sch, skb);
+				qdisc_qlen_dec(sch);
+				return skb;
+			}
+		}
+	}
+	return NULL;
+
+}
+
+static struct sk_buff *multiq_peek(struct Qdisc *sch)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	unsigned int curband = q->curband;
+	struct Qdisc *qdisc;
+	struct sk_buff *skb;
+	int band;
+
+	for (band = 0; band < q->bands; band++) {
+		/* cycle through bands to ensure fairness */
+		curband++;
+		if (curband >= q->bands)
+			curband = 0;
+
+		/* Check that target subqueue is available before
+		 * pulling an skb to avoid head-of-line blocking.
+		 */
+		if (!netif_xmit_stopped(
+		    netdev_get_tx_queue(qdisc_dev(sch), curband))) {
+			qdisc = q->queues[curband];
+			skb = qdisc->ops->peek(qdisc);
+			if (skb)
+				return skb;
+		}
+	}
+	return NULL;
+
+}
+
+static void
+multiq_reset(struct Qdisc *sch)
+{
+	u16 band;
+	struct multiq_sched_data *q = qdisc_priv(sch);
+
+	for (band = 0; band < q->bands; band++)
+		qdisc_reset(q->queues[band]);
+	q->curband = 0;
+}
+
+static void
+multiq_destroy(struct Qdisc *sch)
+{
+	int band;
+	struct multiq_sched_data *q = qdisc_priv(sch);
+
+	tcf_block_put(q->block);
+	for (band = 0; band < q->bands; band++)
+		qdisc_put(q->queues[band]);
+
+	kfree(q->queues);
+}
+
+static int multiq_tune(struct Qdisc *sch, struct nlattr *opt,
+		       struct netlink_ext_ack *extack)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	struct tc_multiq_qopt *qopt;
+	struct Qdisc **removed;
+	int i, n_removed = 0;
+
+	if (!netif_is_multiqueue(qdisc_dev(sch)))
+		return -EOPNOTSUPP;
+	if (nla_len(opt) < sizeof(*qopt))
+		return -EINVAL;
+
+	qopt = nla_data(opt);
+
+	qopt->bands = qdisc_dev(sch)->real_num_tx_queues;
+
+	removed = kmalloc(sizeof(*removed) * (q->max_bands - qopt->bands),
+			  GFP_KERNEL);
+	if (!removed)
+		return -ENOMEM;
+
+	sch_tree_lock(sch);
+	q->bands = qopt->bands;
+	for (i = q->bands; i < q->max_bands; i++) {
+		if (q->queues[i] != &noop_qdisc) {
+			struct Qdisc *child = q->queues[i];
+
+			q->queues[i] = &noop_qdisc;
+			qdisc_purge_queue(child);
+			removed[n_removed++] = child;
+		}
+	}
+
+	sch_tree_unlock(sch);
+
+	for (i = 0; i < n_removed; i++)
+		qdisc_put(removed[i]);
+	kfree(removed);
+
+	for (i = 0; i < q->bands; i++) {
+		if (q->queues[i] == &noop_qdisc) {
+			struct Qdisc *child, *old;
+			child = qdisc_create_dflt(sch->dev_queue,
+						  &pfifo_qdisc_ops,
+						  TC_H_MAKE(sch->handle,
+							    i + 1), extack);
+			if (child) {
+				sch_tree_lock(sch);
+				old = q->queues[i];
+				q->queues[i] = child;
+				if (child != &noop_qdisc)
+					qdisc_hash_add(child, true);
+
+				if (old != &noop_qdisc)
+					qdisc_purge_queue(old);
+				sch_tree_unlock(sch);
+				qdisc_put(old);
+			}
+		}
+	}
+	return 0;
+}
+
+static int multiq_init(struct Qdisc *sch, struct nlattr *opt,
+		       struct netlink_ext_ack *extack)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	int i, err;
+
+	q->queues = NULL;
+
+	if (!opt)
+		return -EINVAL;
+
+	err = tcf_block_get(&q->block, &q->filter_list, sch, extack);
+	if (err)
+		return err;
+
+	q->max_bands = qdisc_dev(sch)->num_tx_queues;
+
+	q->queues = kzalloc_objs(struct Qdisc *, q->max_bands);
+	if (!q->queues)
+		return -ENOBUFS;
+	for (i = 0; i < q->max_bands; i++)
+		q->queues[i] = &noop_qdisc;
+
+	return multiq_tune(sch, opt, extack);
+}
+
+static int multiq_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	unsigned char *b = skb_tail_pointer(skb);
+	struct tc_multiq_qopt opt;
+
+	opt.bands = q->bands;
+	opt.max_bands = q->max_bands;
+
+	if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
+		goto nla_put_failure;
+
+	return skb->len;
+
+nla_put_failure:
+	nlmsg_trim(skb, b);
+	return -1;
+}
+
+static int multiq_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
+			struct Qdisc **old, struct netlink_ext_ack *extack)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	unsigned long band = arg - 1;
+
+	if (new == NULL)
+		new = &noop_qdisc;
+
+	*old = qdisc_replace(sch, new, &q->queues[band]);
+	return 0;
+}
+
+static struct Qdisc *
+multiq_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	unsigned long band = arg - 1;
+
+	return q->queues[band];
+}
+
+static unsigned long multiq_find(struct Qdisc *sch, u32 classid)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	unsigned long band = TC_H_MIN(classid);
+
+	if (band - 1 >= q->bands)
+		return 0;
+	return band;
+}
+
+static unsigned long multiq_bind(struct Qdisc *sch, unsigned long parent,
+				 u32 classid)
+{
+	return multiq_find(sch, classid);
+}
+
+
+static void multiq_unbind(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static int multiq_dump_class(struct Qdisc *sch, unsigned long cl,
+			     struct sk_buff *skb, struct tcmsg *tcm)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+
+	tcm->tcm_handle |= TC_H_MIN(cl);
+	tcm->tcm_info = q->queues[cl - 1]->handle;
+	return 0;
+}
+
+static int multiq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
+				 struct gnet_dump *d)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	struct Qdisc *cl_q;
+
+	cl_q = q->queues[cl - 1];
+	if (gnet_stats_copy_basic(d, cl_q->cpu_bstats, &cl_q->bstats, true) < 0 ||
+	    qdisc_qstats_copy(d, cl_q) < 0)
+		return -1;
+
+	return 0;
+}
+
+static void multiq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+	int band;
+
+	if (arg->stop)
+		return;
+
+	for (band = 0; band < q->bands; band++) {
+		if (!tc_qdisc_stats_dump(sch, band + 1, arg))
+			break;
+	}
+}
+
+static struct tcf_block *multiq_tcf_block(struct Qdisc *sch, unsigned long cl,
+					  struct netlink_ext_ack *extack)
+{
+	struct multiq_sched_data *q = qdisc_priv(sch);
+
+	if (cl)
+		return NULL;
+	return q->block;
+}
+
+static const struct Qdisc_class_ops multiq_class_ops = {
+	.graft		=	multiq_graft,
+	.leaf		=	multiq_leaf,
+	.find		=	multiq_find,
+	.walk		=	multiq_walk,
+	.tcf_block	=	multiq_tcf_block,
+	.bind_tcf	=	multiq_bind,
+	.unbind_tcf	=	multiq_unbind,
+	.dump		=	multiq_dump_class,
+	.dump_stats	=	multiq_dump_class_stats,
+};
+
+static struct Qdisc_ops multiq_qdisc_ops __read_mostly = {
+	.next		=	NULL,
+	.cl_ops		=	&multiq_class_ops,
+	.id		=	"multiq",
+	.priv_size	=	sizeof(struct multiq_sched_data),
+	.enqueue	=	multiq_enqueue,
+	.dequeue	=	multiq_dequeue,
+	.peek		=	multiq_peek,
+	.init		=	multiq_init,
+	.reset		=	multiq_reset,
+	.destroy	=	multiq_destroy,
+	.change		=	multiq_tune,
+	.dump		=	multiq_dump,
+	.owner		=	THIS_MODULE,
+};
+MODULE_ALIAS_NET_SCH("multiq");
+
+static int __init multiq_module_init(void)
+{
+	return register_qdisc(&multiq_qdisc_ops);
+}
+
+static void __exit multiq_module_exit(void)
+{
+	unregister_qdisc(&multiq_qdisc_ops);
+}
+
+module_init(multiq_module_init)
+module_exit(multiq_module_exit)
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Multi queue to hardware queue mapping qdisc");