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, 259 insertions, 0 deletions

diff --git a/net/ipv4/raw_diag.c b/net/ipv4/raw_diag.c
new file mode 100644
index 000000000..943e5998e
--- /dev/null
+++ b/net/ipv4/raw_diag.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+
+#include <linux/inet_diag.h>
+#include <linux/sock_diag.h>
+
+#include <net/inet_sock.h>
+#include <net/raw.h>
+#include <net/rawv6.h>
+
+#ifdef pr_fmt
+# undef pr_fmt
+#endif
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+static struct raw_hashinfo *
+raw_get_hashinfo(const struct inet_diag_req_v2 *r)
+{
+	if (r->sdiag_family == AF_INET) {
+		return &raw_v4_hashinfo;
+#if IS_ENABLED(CONFIG_IPV6)
+	} else if (r->sdiag_family == AF_INET6) {
+		return &raw_v6_hashinfo;
+#endif
+	} else {
+		return ERR_PTR(-EINVAL);
+	}
+}
+
+/*
+ * Due to requirement of not breaking user API we can't simply
+ * rename @pad field in inet_diag_req_v2 structure, instead
+ * use helper to figure it out.
+ */
+
+static bool raw_lookup(struct net *net, const struct sock *sk,
+		       const struct inet_diag_req_v2 *req)
+{
+	struct inet_diag_req_raw *r = (void *)req;
+
+	if (r->sdiag_family == AF_INET)
+		return raw_v4_match(net, sk, r->sdiag_raw_protocol,
+				    r->id.idiag_dst[0],
+				    r->id.idiag_src[0],
+				    r->id.idiag_if, 0);
+#if IS_ENABLED(CONFIG_IPV6)
+	else
+		return raw_v6_match(net, sk, r->sdiag_raw_protocol,
+				    (const struct in6_addr *)r->id.idiag_src,
+				    (const struct in6_addr *)r->id.idiag_dst,
+				    r->id.idiag_if, 0);
+#endif
+	return false;
+}
+
+static struct sock *raw_sock_get(struct net *net, const struct inet_diag_req_v2 *r)
+{
+	struct raw_hashinfo *hashinfo = raw_get_hashinfo(r);
+	struct hlist_head *hlist;
+	struct sock *sk;
+	int slot;
+
+	if (IS_ERR(hashinfo))
+		return ERR_CAST(hashinfo);
+
+	rcu_read_lock();
+	for (slot = 0; slot < RAW_HTABLE_SIZE; slot++) {
+		hlist = &hashinfo->ht[slot];
+		sk_for_each_rcu(sk, hlist) {
+			if (raw_lookup(net, sk, r)) {
+				/*
+				 * Grab it and keep until we fill
+				 * diag message to be reported, so
+				 * caller should call sock_put then.
+				 */
+				if (refcount_inc_not_zero(&sk->sk_refcnt))
+					goto out_unlock;
+			}
+		}
+	}
+	sk = ERR_PTR(-ENOENT);
+out_unlock:
+	rcu_read_unlock();
+
+	return sk;
+}
+
+static int raw_diag_dump_one(struct netlink_callback *cb,
+			     const struct inet_diag_req_v2 *r)
+{
+	struct sk_buff *in_skb = cb->skb;
+	struct sk_buff *rep;
+	struct sock *sk;
+	struct net *net;
+	int err;
+
+	net = sock_net(in_skb->sk);
+	sk = raw_sock_get(net, r);
+	if (IS_ERR(sk))
+		return PTR_ERR(sk);
+
+	rep = nlmsg_new(nla_total_size(sizeof(struct inet_diag_msg)) +
+			inet_diag_msg_attrs_size() +
+			nla_total_size(sizeof(struct inet_diag_meminfo)) + 64,
+			GFP_KERNEL);
+	if (!rep) {
+		sock_put(sk);
+		return -ENOMEM;
+	}
+
+	err = inet_sk_diag_fill(sk, NULL, rep, cb, r, 0,
+				netlink_net_capable(in_skb, CAP_NET_ADMIN));
+	sock_put(sk);
+
+	if (err < 0) {
+		kfree_skb(rep);
+		return err;
+	}
+
+	err = nlmsg_unicast(net->diag_nlsk, rep, NETLINK_CB(in_skb).portid);
+
+	return err;
+}
+
+static int sk_diag_dump(struct sock *sk, struct sk_buff *skb,
+			struct netlink_callback *cb,
+			const struct inet_diag_req_v2 *r,
+			bool net_admin)
+{
+	if (!inet_diag_bc_sk(cb->data, sk))
+		return 0;
+
+	return inet_sk_diag_fill(sk, NULL, skb, cb, r, NLM_F_MULTI, net_admin);
+}
+
+static void raw_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
+			  const struct inet_diag_req_v2 *r)
+{
+	bool net_admin = netlink_net_capable(cb->skb, CAP_NET_ADMIN);
+	struct raw_hashinfo *hashinfo = raw_get_hashinfo(r);
+	struct net *net = sock_net(skb->sk);
+	int num, s_num, slot, s_slot;
+	struct hlist_head *hlist;
+	struct sock *sk = NULL;
+
+	if (IS_ERR(hashinfo))
+		return;
+
+	s_slot = cb->args[0];
+	num = s_num = cb->args[1];
+
+	rcu_read_lock();
+	for (slot = s_slot; slot < RAW_HTABLE_SIZE; s_num = 0, slot++) {
+		num = 0;
+
+		hlist = &hashinfo->ht[slot];
+		sk_for_each_rcu(sk, hlist) {
+			struct inet_sock *inet = inet_sk(sk);
+
+			if (!net_eq(sock_net(sk), net))
+				continue;
+			if (num < s_num)
+				goto next;
+			if (sk->sk_family != r->sdiag_family)
+				goto next;
+			if (r->id.idiag_sport != inet->inet_sport &&
+			    r->id.idiag_sport)
+				goto next;
+			if (r->id.idiag_dport != inet->inet_dport &&
+			    r->id.idiag_dport)
+				goto next;
+			if (sk_diag_dump(sk, skb, cb, r, net_admin) < 0)
+				goto out_unlock;
+next:
+			num++;
+		}
+	}
+
+out_unlock:
+	rcu_read_unlock();
+
+	cb->args[0] = slot;
+	cb->args[1] = num;
+}
+
+static void raw_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
+			      void *info)
+{
+	r->idiag_rqueue = sk_rmem_alloc_get(sk);
+	r->idiag_wqueue = sk_wmem_alloc_get(sk);
+}
+
+#ifdef CONFIG_INET_DIAG_DESTROY
+static int raw_diag_destroy(struct sk_buff *in_skb,
+			    const struct inet_diag_req_v2 *r)
+{
+	struct net *net = sock_net(in_skb->sk);
+	struct sock *sk;
+	int err;
+
+	sk = raw_sock_get(net, r);
+	if (IS_ERR(sk))
+		return PTR_ERR(sk);
+	err = sock_diag_destroy(sk, ECONNABORTED);
+	sock_put(sk);
+	return err;
+}
+#endif
+
+static const struct inet_diag_handler raw_diag_handler = {
+	.owner			= THIS_MODULE,
+	.dump			= raw_diag_dump,
+	.dump_one		= raw_diag_dump_one,
+	.idiag_get_info		= raw_diag_get_info,
+	.idiag_type		= IPPROTO_RAW,
+	.idiag_info_size	= 0,
+#ifdef CONFIG_INET_DIAG_DESTROY
+	.destroy		= raw_diag_destroy,
+#endif
+};
+
+static void __always_unused __check_inet_diag_req_raw(void)
+{
+	/*
+	 * Make sure the two structures are identical,
+	 * except the @pad field.
+	 */
+#define __offset_mismatch(m1, m2)			\
+	(offsetof(struct inet_diag_req_v2, m1) !=	\
+	 offsetof(struct inet_diag_req_raw, m2))
+
+	BUILD_BUG_ON(sizeof(struct inet_diag_req_v2) !=
+		     sizeof(struct inet_diag_req_raw));
+	BUILD_BUG_ON(__offset_mismatch(sdiag_family, sdiag_family));
+	BUILD_BUG_ON(__offset_mismatch(sdiag_protocol, sdiag_protocol));
+	BUILD_BUG_ON(__offset_mismatch(idiag_ext, idiag_ext));
+	BUILD_BUG_ON(__offset_mismatch(pad, sdiag_raw_protocol));
+	BUILD_BUG_ON(__offset_mismatch(idiag_states, idiag_states));
+	BUILD_BUG_ON(__offset_mismatch(id, id));
+#undef __offset_mismatch
+}
+
+static int __init raw_diag_init(void)
+{
+	return inet_diag_register(&raw_diag_handler);
+}
+
+static void __exit raw_diag_exit(void)
+{
+	inet_diag_unregister(&raw_diag_handler);
+}
+
+module_init(raw_diag_init);
+module_exit(raw_diag_exit);
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("RAW socket monitoring via SOCK_DIAG");
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_SOCK_DIAG, 2-255 /* AF_INET - IPPROTO_RAW */);
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_SOCK_DIAG, 10-255 /* AF_INET6 - IPPROTO_RAW */);