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, 328 insertions, 0 deletions

diff --git a/net/sched/act_skbmod.c b/net/sched/act_skbmod.c
new file mode 100644
index 000000000..7579cf1e0
--- /dev/null
+++ b/net/sched/act_skbmod.c
@@ -0,0 +1,328 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/act_skbmod.c  skb data modifier
+ *
+ * Copyright (c) 2016 Jamal Hadi Salim <jhs@mojatatu.com>
+*/
+
+#include <linux/module.h>
+#include <linux/if_arp.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/rtnetlink.h>
+#include <net/inet_ecn.h>
+#include <net/netlink.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+#include <net/tc_wrapper.h>
+
+#include <linux/tc_act/tc_skbmod.h>
+#include <net/tc_act/tc_skbmod.h>
+
+static struct tc_action_ops act_skbmod_ops;
+
+TC_INDIRECT_SCOPE int tcf_skbmod_act(struct sk_buff *skb,
+				     const struct tc_action *a,
+				     struct tcf_result *res)
+{
+	struct tcf_skbmod *d = to_skbmod(a);
+	struct tcf_skbmod_params *p;
+	int max_edit_len, err;
+	u64 flags;
+
+	tcf_lastuse_update(&d->tcf_tm);
+	bstats_update(this_cpu_ptr(d->common.cpu_bstats), skb);
+
+	p = rcu_dereference_bh(d->skbmod_p);
+	if (unlikely(p->action == TC_ACT_SHOT))
+		goto drop;
+
+	flags = p->flags;
+
+	/* tcf_skbmod_init() guarantees "flags" to be one of the following:
+	 *	1. a combination of SKBMOD_F_{DMAC,SMAC,ETYPE}
+	 *	2. SKBMOD_F_SWAPMAC
+	 *	3. SKBMOD_F_ECN
+	 * SKBMOD_F_ECN only works with IP packets; all other flags only work with Ethernet
+	 * packets.
+	 */
+	if (flags == SKBMOD_F_ECN) {
+		switch (skb_protocol(skb, true)) {
+		case cpu_to_be16(ETH_P_IP):
+			max_edit_len = sizeof(struct iphdr);
+			break;
+		case cpu_to_be16(ETH_P_IPV6):
+			max_edit_len = sizeof(struct ipv6hdr);
+			break;
+		default:
+			goto out;
+		}
+		max_edit_len += skb_network_offset(skb);
+	} else {
+		if (!skb->dev || skb->dev->type != ARPHRD_ETHER)
+			goto out;
+		max_edit_len = ETH_HLEN;
+	}
+
+	err = skb_ensure_writable(skb, max_edit_len);
+	if (unlikely(err)) /* best policy is to drop on the floor */
+		goto drop;
+
+	if (flags & SKBMOD_F_DMAC)
+		ether_addr_copy(eth_hdr(skb)->h_dest, p->eth_dst);
+	if (flags & SKBMOD_F_SMAC)
+		ether_addr_copy(eth_hdr(skb)->h_source, p->eth_src);
+	if (flags & SKBMOD_F_ETYPE)
+		eth_hdr(skb)->h_proto = p->eth_type;
+
+	if (flags & SKBMOD_F_SWAPMAC) {
+		u16 tmpaddr[ETH_ALEN / 2]; /* ether_addr_copy() requirement */
+		/*XXX: I am sure we can come up with more efficient swapping*/
+		ether_addr_copy((u8 *)tmpaddr, eth_hdr(skb)->h_dest);
+		ether_addr_copy(eth_hdr(skb)->h_dest, eth_hdr(skb)->h_source);
+		ether_addr_copy(eth_hdr(skb)->h_source, (u8 *)tmpaddr);
+	}
+
+	if (flags & SKBMOD_F_ECN)
+		INET_ECN_set_ce(skb);
+
+out:
+	return p->action;
+
+drop:
+	qstats_cpu_overlimit_inc(d->common.cpu_qstats);
+	return TC_ACT_SHOT;
+}
+
+static const struct nla_policy skbmod_policy[TCA_SKBMOD_MAX + 1] = {
+	[TCA_SKBMOD_PARMS]		= { .len = sizeof(struct tc_skbmod) },
+	[TCA_SKBMOD_DMAC]		= { .len = ETH_ALEN },
+	[TCA_SKBMOD_SMAC]		= { .len = ETH_ALEN },
+	[TCA_SKBMOD_ETYPE]		= { .type = NLA_U16 },
+};
+
+static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
+			   struct nlattr *est, struct tc_action **a,
+			   struct tcf_proto *tp, u32 flags,
+			   struct netlink_ext_ack *extack)
+{
+	struct tc_action_net *tn = net_generic(net, act_skbmod_ops.net_id);
+	bool ovr = flags & TCA_ACT_FLAGS_REPLACE;
+	bool bind = flags & TCA_ACT_FLAGS_BIND;
+	struct nlattr *tb[TCA_SKBMOD_MAX + 1];
+	struct tcf_skbmod_params *p, *p_old;
+	struct tcf_chain *goto_ch = NULL;
+	struct tc_skbmod *parm;
+	u32 lflags = 0, index;
+	struct tcf_skbmod *d;
+	bool exists = false;
+	u8 *daddr = NULL;
+	u8 *saddr = NULL;
+	u16 eth_type = 0;
+	int ret = 0, err;
+
+	if (!nla)
+		return -EINVAL;
+
+	err = nla_parse_nested_deprecated(tb, TCA_SKBMOD_MAX, nla,
+					  skbmod_policy, NULL);
+	if (err < 0)
+		return err;
+
+	if (!tb[TCA_SKBMOD_PARMS])
+		return -EINVAL;
+
+	if (tb[TCA_SKBMOD_DMAC]) {
+		daddr = nla_data(tb[TCA_SKBMOD_DMAC]);
+		lflags |= SKBMOD_F_DMAC;
+	}
+
+	if (tb[TCA_SKBMOD_SMAC]) {
+		saddr = nla_data(tb[TCA_SKBMOD_SMAC]);
+		lflags |= SKBMOD_F_SMAC;
+	}
+
+	if (tb[TCA_SKBMOD_ETYPE]) {
+		eth_type = nla_get_u16(tb[TCA_SKBMOD_ETYPE]);
+		lflags |= SKBMOD_F_ETYPE;
+	}
+
+	parm = nla_data(tb[TCA_SKBMOD_PARMS]);
+	index = parm->index;
+	if (parm->flags & SKBMOD_F_SWAPMAC)
+		lflags = SKBMOD_F_SWAPMAC;
+	if (parm->flags & SKBMOD_F_ECN)
+		lflags = SKBMOD_F_ECN;
+
+	err = tcf_idr_check_alloc(tn, &index, a, bind);
+	if (err < 0)
+		return err;
+	exists = err;
+	if (exists && bind)
+		return ACT_P_BOUND;
+
+	if (!lflags) {
+		if (exists)
+			tcf_idr_release(*a, bind);
+		else
+			tcf_idr_cleanup(tn, index);
+		return -EINVAL;
+	}
+
+	if (!exists) {
+		ret = tcf_idr_create(tn, index, est, a,
+				     &act_skbmod_ops, bind, true, flags);
+		if (ret) {
+			tcf_idr_cleanup(tn, index);
+			return ret;
+		}
+
+		ret = ACT_P_CREATED;
+	} else if (!ovr) {
+		tcf_idr_release(*a, bind);
+		return -EEXIST;
+	}
+	err = tcf_action_check_ctrlact(parm->action, tp, &goto_ch, extack);
+	if (err < 0)
+		goto release_idr;
+
+	d = to_skbmod(*a);
+
+	p = kzalloc_obj(struct tcf_skbmod_params);
+	if (unlikely(!p)) {
+		err = -ENOMEM;
+		goto put_chain;
+	}
+
+	p->flags = lflags;
+	p->action = parm->action;
+	if (ovr)
+		spin_lock_bh(&d->tcf_lock);
+	/* Protected by tcf_lock if overwriting existing action. */
+	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);
+	p_old = rcu_dereference_protected(d->skbmod_p, 1);
+
+	if (lflags & SKBMOD_F_DMAC)
+		ether_addr_copy(p->eth_dst, daddr);
+	if (lflags & SKBMOD_F_SMAC)
+		ether_addr_copy(p->eth_src, saddr);
+	if (lflags & SKBMOD_F_ETYPE)
+		p->eth_type = htons(eth_type);
+
+	rcu_assign_pointer(d->skbmod_p, p);
+	if (ovr)
+		spin_unlock_bh(&d->tcf_lock);
+
+	if (p_old)
+		kfree_rcu(p_old, rcu);
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+
+	return ret;
+put_chain:
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+release_idr:
+	tcf_idr_release(*a, bind);
+	return err;
+}
+
+static void tcf_skbmod_cleanup(struct tc_action *a)
+{
+	struct tcf_skbmod *d = to_skbmod(a);
+	struct tcf_skbmod_params  *p;
+
+	p = rcu_dereference_protected(d->skbmod_p, 1);
+	if (p)
+		kfree_rcu(p, rcu);
+}
+
+static int tcf_skbmod_dump(struct sk_buff *skb, struct tc_action *a,
+			   int bind, int ref)
+{
+	struct tcf_skbmod *d = to_skbmod(a);
+	unsigned char *b = skb_tail_pointer(skb);
+	struct tcf_skbmod_params  *p;
+	struct tc_skbmod opt;
+	struct tcf_t t;
+
+	memset(&opt, 0, sizeof(opt));
+	opt.index   = d->tcf_index;
+	opt.refcnt  = refcount_read(&d->tcf_refcnt) - ref;
+	opt.bindcnt = atomic_read(&d->tcf_bindcnt) - bind;
+	rcu_read_lock();
+	p = rcu_dereference(d->skbmod_p);
+	opt.action = p->action;
+	opt.flags  = p->flags;
+	if (nla_put(skb, TCA_SKBMOD_PARMS, sizeof(opt), &opt))
+		goto nla_put_failure;
+	if ((p->flags & SKBMOD_F_DMAC) &&
+	    nla_put(skb, TCA_SKBMOD_DMAC, ETH_ALEN, p->eth_dst))
+		goto nla_put_failure;
+	if ((p->flags & SKBMOD_F_SMAC) &&
+	    nla_put(skb, TCA_SKBMOD_SMAC, ETH_ALEN, p->eth_src))
+		goto nla_put_failure;
+	if ((p->flags & SKBMOD_F_ETYPE) &&
+	    nla_put_u16(skb, TCA_SKBMOD_ETYPE, ntohs(p->eth_type)))
+		goto nla_put_failure;
+
+	tcf_tm_dump(&t, &d->tcf_tm);
+	if (nla_put_64bit(skb, TCA_SKBMOD_TM, sizeof(t), &t, TCA_SKBMOD_PAD))
+		goto nla_put_failure;
+
+	rcu_read_unlock();
+	return skb->len;
+nla_put_failure:
+	rcu_read_unlock();
+	nlmsg_trim(skb, b);
+	return -1;
+}
+
+static struct tc_action_ops act_skbmod_ops = {
+	.kind		=	"skbmod",
+	.id		=	TCA_ACT_SKBMOD,
+	.owner		=	THIS_MODULE,
+	.act		=	tcf_skbmod_act,
+	.dump		=	tcf_skbmod_dump,
+	.init		=	tcf_skbmod_init,
+	.cleanup	=	tcf_skbmod_cleanup,
+	.size		=	sizeof(struct tcf_skbmod),
+};
+MODULE_ALIAS_NET_ACT("skbmod");
+
+static __net_init int skbmod_init_net(struct net *net)
+{
+	struct tc_action_net *tn = net_generic(net, act_skbmod_ops.net_id);
+
+	return tc_action_net_init(net, tn, &act_skbmod_ops);
+}
+
+static void __net_exit skbmod_exit_net(struct list_head *net_list)
+{
+	tc_action_net_exit(net_list, act_skbmod_ops.net_id);
+}
+
+static struct pernet_operations skbmod_net_ops = {
+	.init = skbmod_init_net,
+	.exit_batch = skbmod_exit_net,
+	.id   = &act_skbmod_ops.net_id,
+	.size = sizeof(struct tc_action_net),
+};
+
+MODULE_AUTHOR("Jamal Hadi Salim, <jhs@mojatatu.com>");
+MODULE_DESCRIPTION("SKB data mod-ing");
+MODULE_LICENSE("GPL");
+
+static int __init skbmod_init_module(void)
+{
+	return tcf_register_action(&act_skbmod_ops, &skbmod_net_ops);
+}
+
+static void __exit skbmod_cleanup_module(void)
+{
+	tcf_unregister_action(&act_skbmod_ops, &skbmod_net_ops);
+}
+
+module_init(skbmod_init_module);
+module_exit(skbmod_cleanup_module);