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, 276 insertions, 0 deletions

diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
new file mode 100644
index 000000000..1b6388d50
--- /dev/null
+++ b/net/sched/sch_fifo.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/sch_fifo.c	The simplest FIFO queue.
+ *
+ * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+
+/* 1 band FIFO pseudo-"scheduler" */
+
+static int bfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+			 struct sk_buff **to_free)
+{
+	if (likely((u64)sch->qstats.backlog + qdisc_pkt_len(skb) <=
+		   READ_ONCE(sch->limit)))
+		return qdisc_enqueue_tail(skb, sch);
+
+	return qdisc_drop(skb, sch, to_free);
+}
+
+static int pfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+			 struct sk_buff **to_free)
+{
+	if (likely(sch->q.qlen < READ_ONCE(sch->limit)))
+		return qdisc_enqueue_tail(skb, sch);
+
+	return qdisc_drop(skb, sch, to_free);
+}
+
+static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+			      struct sk_buff **to_free)
+{
+	unsigned int prev_backlog;
+
+	if (unlikely(READ_ONCE(sch->limit) == 0))
+		return qdisc_drop(skb, sch, to_free);
+
+	if (likely(sch->q.qlen < READ_ONCE(sch->limit)))
+		return qdisc_enqueue_tail(skb, sch);
+
+	prev_backlog = sch->qstats.backlog;
+	/* queue full, remove one skb to fulfill the limit */
+	__qdisc_queue_drop_head(sch, &sch->q, to_free);
+	qdisc_qstats_drop(sch);
+	qdisc_enqueue_tail(skb, sch);
+
+	qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);
+	return NET_XMIT_CN;
+}
+
+static void fifo_offload_init(struct Qdisc *sch)
+{
+	struct net_device *dev = qdisc_dev(sch);
+	struct tc_fifo_qopt_offload qopt;
+
+	if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
+		return;
+
+	qopt.command = TC_FIFO_REPLACE;
+	qopt.handle = sch->handle;
+	qopt.parent = sch->parent;
+	dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_FIFO, &qopt);
+}
+
+static void fifo_offload_destroy(struct Qdisc *sch)
+{
+	struct net_device *dev = qdisc_dev(sch);
+	struct tc_fifo_qopt_offload qopt;
+
+	if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
+		return;
+
+	qopt.command = TC_FIFO_DESTROY;
+	qopt.handle = sch->handle;
+	qopt.parent = sch->parent;
+	dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_FIFO, &qopt);
+}
+
+static int fifo_offload_dump(struct Qdisc *sch)
+{
+	struct tc_fifo_qopt_offload qopt;
+
+	qopt.command = TC_FIFO_STATS;
+	qopt.handle = sch->handle;
+	qopt.parent = sch->parent;
+	qopt.stats.bstats = &sch->bstats;
+	qopt.stats.qstats = &sch->qstats;
+
+	return qdisc_offload_dump_helper(sch, TC_SETUP_QDISC_FIFO, &qopt);
+}
+
+static int __fifo_init(struct Qdisc *sch, struct nlattr *opt,
+		       struct netlink_ext_ack *extack)
+{
+	bool bypass;
+	bool is_bfifo = sch->ops == &bfifo_qdisc_ops;
+
+	if (opt == NULL) {
+		u32 limit = qdisc_dev(sch)->tx_queue_len;
+
+		if (is_bfifo)
+			limit *= psched_mtu(qdisc_dev(sch));
+
+		WRITE_ONCE(sch->limit, limit);
+	} else {
+		struct tc_fifo_qopt *ctl = nla_data(opt);
+
+		if (nla_len(opt) < sizeof(*ctl))
+			return -EINVAL;
+
+		WRITE_ONCE(sch->limit, ctl->limit);
+	}
+
+	if (is_bfifo)
+		bypass = sch->limit >= psched_mtu(qdisc_dev(sch));
+	else
+		bypass = sch->limit >= 1;
+
+	if (bypass)
+		sch->flags |= TCQ_F_CAN_BYPASS;
+	else
+		sch->flags &= ~TCQ_F_CAN_BYPASS;
+
+	return 0;
+}
+
+static int fifo_init(struct Qdisc *sch, struct nlattr *opt,
+		     struct netlink_ext_ack *extack)
+{
+	int err;
+
+	err = __fifo_init(sch, opt, extack);
+	if (err)
+		return err;
+
+	fifo_offload_init(sch);
+	return 0;
+}
+
+static int fifo_hd_init(struct Qdisc *sch, struct nlattr *opt,
+			struct netlink_ext_ack *extack)
+{
+	return __fifo_init(sch, opt, extack);
+}
+
+static void fifo_destroy(struct Qdisc *sch)
+{
+	fifo_offload_destroy(sch);
+}
+
+static int __fifo_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct tc_fifo_qopt opt = { .limit = READ_ONCE(sch->limit) };
+
+	if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
+		goto nla_put_failure;
+	return skb->len;
+
+nla_put_failure:
+	return -1;
+}
+
+static int fifo_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	int err;
+
+	err = fifo_offload_dump(sch);
+	if (err)
+		return err;
+
+	return __fifo_dump(sch, skb);
+}
+
+static int fifo_hd_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	return __fifo_dump(sch, skb);
+}
+
+struct Qdisc_ops pfifo_qdisc_ops __read_mostly = {
+	.id		=	"pfifo",
+	.priv_size	=	0,
+	.enqueue	=	pfifo_enqueue,
+	.dequeue	=	qdisc_dequeue_head,
+	.peek		=	qdisc_peek_head,
+	.init		=	fifo_init,
+	.destroy	=	fifo_destroy,
+	.reset		=	qdisc_reset_queue,
+	.change		=	fifo_init,
+	.dump		=	fifo_dump,
+	.owner		=	THIS_MODULE,
+};
+EXPORT_SYMBOL(pfifo_qdisc_ops);
+
+struct Qdisc_ops bfifo_qdisc_ops __read_mostly = {
+	.id		=	"bfifo",
+	.priv_size	=	0,
+	.enqueue	=	bfifo_enqueue,
+	.dequeue	=	qdisc_dequeue_head,
+	.peek		=	qdisc_peek_head,
+	.init		=	fifo_init,
+	.destroy	=	fifo_destroy,
+	.reset		=	qdisc_reset_queue,
+	.change		=	fifo_init,
+	.dump		=	fifo_dump,
+	.owner		=	THIS_MODULE,
+};
+EXPORT_SYMBOL(bfifo_qdisc_ops);
+
+struct Qdisc_ops pfifo_head_drop_qdisc_ops __read_mostly = {
+	.id		=	"pfifo_head_drop",
+	.priv_size	=	0,
+	.enqueue	=	pfifo_tail_enqueue,
+	.dequeue	=	qdisc_dequeue_head,
+	.peek		=	qdisc_peek_head,
+	.init		=	fifo_hd_init,
+	.reset		=	qdisc_reset_queue,
+	.change		=	fifo_hd_init,
+	.dump		=	fifo_hd_dump,
+	.owner		=	THIS_MODULE,
+};
+
+/* Pass size change message down to embedded FIFO */
+int fifo_set_limit(struct Qdisc *q, unsigned int limit)
+{
+	struct nlattr *nla;
+	int ret = -ENOMEM;
+
+	/* Hack to avoid sending change message to non-FIFO */
+	if (strncmp(q->ops->id + 1, "fifo", 4) != 0)
+		return 0;
+
+	if (!q->ops->change)
+		return 0;
+
+	nla = kmalloc(nla_attr_size(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
+	if (nla) {
+		nla->nla_type = RTM_NEWQDISC;
+		nla->nla_len = nla_attr_size(sizeof(struct tc_fifo_qopt));
+		((struct tc_fifo_qopt *)nla_data(nla))->limit = limit;
+
+		ret = q->ops->change(q, nla, NULL);
+		kfree(nla);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(fifo_set_limit);
+
+struct Qdisc *fifo_create_dflt(struct Qdisc *sch, struct Qdisc_ops *ops,
+			       unsigned int limit,
+			       struct netlink_ext_ack *extack)
+{
+	struct Qdisc *q;
+	int err = -ENOMEM;
+
+	q = qdisc_create_dflt(sch->dev_queue, ops, TC_H_MAKE(sch->handle, 1),
+			      extack);
+	if (q) {
+		err = fifo_set_limit(q, limit);
+		if (err < 0) {
+			qdisc_put(q);
+			q = NULL;
+		}
+	}
+
+	return q ? : ERR_PTR(err);
+}
+EXPORT_SYMBOL(fifo_create_dflt);
+MODULE_DESCRIPTION("Single queue packet and byte based First In First Out(P/BFIFO) scheduler");