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, 297 insertions, 0 deletions

diff --git a/net/sched/em_ipt.c b/net/sched/em_ipt.c
new file mode 100644
index 000000000..3650117da
--- /dev/null
+++ b/net/sched/em_ipt.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/em_ipt.c IPtables matches Ematch
+ *
+ * (c) 2018 Eyal Birger <eyal.birger@gmail.com>
+ */
+
+#include <linux/gfp.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/skbuff.h>
+#include <linux/tc_ematch/tc_em_ipt.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <net/pkt_cls.h>
+
+struct em_ipt_match {
+	const struct xt_match *match;
+	u32 hook;
+	u8 nfproto;
+	u8 match_data[] __aligned(8);
+};
+
+struct em_ipt_xt_match {
+	char *match_name;
+	int (*validate_match_data)(struct nlattr **tb, u8 mrev);
+};
+
+static const struct nla_policy em_ipt_policy[TCA_EM_IPT_MAX + 1] = {
+	[TCA_EM_IPT_MATCH_NAME]		= { .type = NLA_STRING,
+					    .len = XT_EXTENSION_MAXNAMELEN },
+	[TCA_EM_IPT_MATCH_REVISION]	= { .type = NLA_U8 },
+	[TCA_EM_IPT_HOOK]		= { .type = NLA_U32 },
+	[TCA_EM_IPT_NFPROTO]		= { .type = NLA_U8 },
+	[TCA_EM_IPT_MATCH_DATA]		= { .type = NLA_UNSPEC },
+};
+
+static int check_match(struct net *net, struct em_ipt_match *im, int mdata_len)
+{
+	struct xt_mtchk_param mtpar = {};
+	union {
+		struct ipt_entry e4;
+		struct ip6t_entry e6;
+	} e = {};
+
+	mtpar.net	= net;
+	mtpar.table	= "filter";
+	mtpar.hook_mask	= 1 << im->hook;
+	mtpar.family	= im->match->family;
+	mtpar.match	= im->match;
+	mtpar.entryinfo = &e;
+	mtpar.matchinfo	= (void *)im->match_data;
+	return xt_check_match(&mtpar, mdata_len, 0, 0);
+}
+
+static int policy_validate_match_data(struct nlattr **tb, u8 mrev)
+{
+	if (mrev != 0) {
+		pr_err("only policy match revision 0 supported");
+		return -EINVAL;
+	}
+
+	if (nla_get_u32(tb[TCA_EM_IPT_HOOK]) != NF_INET_PRE_ROUTING) {
+		pr_err("policy can only be matched on NF_INET_PRE_ROUTING");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int addrtype_validate_match_data(struct nlattr **tb, u8 mrev)
+{
+	if (mrev != 1) {
+		pr_err("only addrtype match revision 1 supported");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct em_ipt_xt_match em_ipt_xt_matches[] = {
+	{
+		.match_name = "policy",
+		.validate_match_data = policy_validate_match_data
+	},
+	{
+		.match_name = "addrtype",
+		.validate_match_data = addrtype_validate_match_data
+	},
+	{}
+};
+
+static struct xt_match *get_xt_match(struct nlattr **tb)
+{
+	const struct em_ipt_xt_match *m;
+	struct nlattr *mname_attr;
+	u8 nfproto, mrev = 0;
+	int ret;
+
+	mname_attr = tb[TCA_EM_IPT_MATCH_NAME];
+	for (m = em_ipt_xt_matches; m->match_name; m++) {
+		if (!nla_strcmp(mname_attr, m->match_name))
+			break;
+	}
+
+	if (!m->match_name) {
+		pr_err("Unsupported xt match");
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (tb[TCA_EM_IPT_MATCH_REVISION])
+		mrev = nla_get_u8(tb[TCA_EM_IPT_MATCH_REVISION]);
+
+	ret = m->validate_match_data(tb, mrev);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	nfproto = nla_get_u8(tb[TCA_EM_IPT_NFPROTO]);
+	return xt_request_find_match(nfproto, m->match_name, mrev);
+}
+
+static int em_ipt_change(struct net *net, void *data, int data_len,
+			 struct tcf_ematch *em)
+{
+	struct nlattr *tb[TCA_EM_IPT_MAX + 1];
+	struct em_ipt_match *im = NULL;
+	struct xt_match *match;
+	int mdata_len, ret;
+	u8 nfproto;
+
+	ret = nla_parse_deprecated(tb, TCA_EM_IPT_MAX, data, data_len,
+				   em_ipt_policy, NULL);
+	if (ret < 0)
+		return ret;
+
+	if (!tb[TCA_EM_IPT_HOOK] || !tb[TCA_EM_IPT_MATCH_NAME] ||
+	    !tb[TCA_EM_IPT_MATCH_DATA] || !tb[TCA_EM_IPT_NFPROTO])
+		return -EINVAL;
+
+	nfproto = nla_get_u8(tb[TCA_EM_IPT_NFPROTO]);
+	switch (nfproto) {
+	case NFPROTO_IPV4:
+	case NFPROTO_IPV6:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	match = get_xt_match(tb);
+	if (IS_ERR(match)) {
+		pr_err("unable to load match\n");
+		return PTR_ERR(match);
+	}
+
+	mdata_len = XT_ALIGN(nla_len(tb[TCA_EM_IPT_MATCH_DATA]));
+	im = kzalloc(sizeof(*im) + mdata_len, GFP_KERNEL);
+	if (!im) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	im->match = match;
+	im->hook = nla_get_u32(tb[TCA_EM_IPT_HOOK]);
+	im->nfproto = nfproto;
+	nla_memcpy(im->match_data, tb[TCA_EM_IPT_MATCH_DATA], mdata_len);
+
+	ret = check_match(net, im, mdata_len);
+	if (ret)
+		goto err;
+
+	em->datalen = sizeof(*im) + mdata_len;
+	em->data = (unsigned long)im;
+	return 0;
+
+err:
+	kfree(im);
+	module_put(match->me);
+	return ret;
+}
+
+static void em_ipt_destroy(struct tcf_ematch *em)
+{
+	struct em_ipt_match *im = (void *)em->data;
+
+	if (!im)
+		return;
+
+	if (im->match->destroy) {
+		struct xt_mtdtor_param par = {
+			.net = em->net,
+			.match = im->match,
+			.matchinfo = im->match_data,
+			.family = im->match->family
+		};
+		im->match->destroy(&par);
+	}
+	module_put(im->match->me);
+	kfree(im);
+}
+
+static int em_ipt_match(struct sk_buff *skb, struct tcf_ematch *em,
+			struct tcf_pkt_info *info)
+{
+	const struct em_ipt_match *im = (const void *)em->data;
+	struct xt_action_param acpar = {};
+	struct net_device *indev = NULL;
+	u8 nfproto = im->match->family;
+	struct nf_hook_state state;
+	int ret;
+
+	switch (skb_protocol(skb, true)) {
+	case htons(ETH_P_IP):
+		if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
+			return 0;
+		if (nfproto == NFPROTO_UNSPEC)
+			nfproto = NFPROTO_IPV4;
+		break;
+	case htons(ETH_P_IPV6):
+		if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
+			return 0;
+		if (nfproto == NFPROTO_UNSPEC)
+			nfproto = NFPROTO_IPV6;
+		break;
+	default:
+		return 0;
+	}
+
+	rcu_read_lock();
+
+	if (skb->skb_iif)
+		indev = dev_get_by_index_rcu(em->net, skb->skb_iif);
+
+	nf_hook_state_init(&state, im->hook, nfproto,
+			   indev ?: skb->dev, skb->dev, NULL, em->net, NULL);
+
+	acpar.match = im->match;
+	acpar.matchinfo = im->match_data;
+	acpar.state = &state;
+
+	ret = im->match->match(skb, &acpar);
+
+	rcu_read_unlock();
+	return ret;
+}
+
+static int em_ipt_dump(struct sk_buff *skb, struct tcf_ematch *em)
+{
+	struct em_ipt_match *im = (void *)em->data;
+
+	if (nla_put_string(skb, TCA_EM_IPT_MATCH_NAME, im->match->name) < 0)
+		return -EMSGSIZE;
+	if (nla_put_u32(skb, TCA_EM_IPT_HOOK, im->hook) < 0)
+		return -EMSGSIZE;
+	if (nla_put_u8(skb, TCA_EM_IPT_MATCH_REVISION, im->match->revision) < 0)
+		return -EMSGSIZE;
+	if (nla_put_u8(skb, TCA_EM_IPT_NFPROTO, im->nfproto) < 0)
+		return -EMSGSIZE;
+	if (nla_put(skb, TCA_EM_IPT_MATCH_DATA,
+		    im->match->usersize ?: im->match->matchsize,
+		    im->match_data) < 0)
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+static struct tcf_ematch_ops em_ipt_ops = {
+	.kind	  = TCF_EM_IPT,
+	.change	  = em_ipt_change,
+	.destroy  = em_ipt_destroy,
+	.match	  = em_ipt_match,
+	.dump	  = em_ipt_dump,
+	.owner	  = THIS_MODULE,
+	.link	  = LIST_HEAD_INIT(em_ipt_ops.link)
+};
+
+static int __init init_em_ipt(void)
+{
+	return tcf_em_register(&em_ipt_ops);
+}
+
+static void __exit exit_em_ipt(void)
+{
+	tcf_em_unregister(&em_ipt_ops);
+}
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Eyal Birger <eyal.birger@gmail.com>");
+MODULE_DESCRIPTION("TC extended match for IPtables matches");
+
+module_init(init_em_ipt);
+module_exit(exit_em_ipt);
+
+MODULE_ALIAS_TCF_EMATCH(TCF_EM_IPT);