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, 547 insertions, 0 deletions

diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c
new file mode 100644
index 000000000..62a7eb779
--- /dev/null
+++ b/net/ipv6/seg6.c
@@ -0,0 +1,547 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  SR-IPv6 implementation
+ *
+ *  Author:
+ *  David Lebrun <david.lebrun@uclouvain.be>
+ */
+
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/net.h>
+#include <linux/in6.h>
+#include <linux/slab.h>
+#include <linux/rhashtable.h>
+
+#include <net/ipv6.h>
+#include <net/protocol.h>
+
+#include <net/seg6.h>
+#include <net/genetlink.h>
+#include <linux/seg6.h>
+#include <linux/seg6_genl.h>
+#include <net/seg6_hmac.h>
+
+bool seg6_validate_srh(struct ipv6_sr_hdr *srh, int len, bool reduced)
+{
+	unsigned int tlv_offset;
+	int max_last_entry;
+	int trailing;
+
+	if (len < sizeof(*srh))
+		return false;
+
+	if (srh->type != IPV6_SRCRT_TYPE_4)
+		return false;
+
+	if (((srh->hdrlen + 1) << 3) != len)
+		return false;
+
+	if (!reduced && srh->segments_left > srh->first_segment) {
+		return false;
+	} else {
+		max_last_entry = (srh->hdrlen / 2) - 1;
+
+		if (srh->first_segment > max_last_entry)
+			return false;
+
+		if (srh->segments_left > srh->first_segment + 1)
+			return false;
+	}
+
+	tlv_offset = sizeof(*srh) + ((srh->first_segment + 1) << 4);
+
+	trailing = len - tlv_offset;
+	if (trailing < 0)
+		return false;
+
+	while (trailing) {
+		struct sr6_tlv *tlv;
+		unsigned int tlv_len;
+
+		if (trailing < sizeof(*tlv))
+			return false;
+
+		tlv = (struct sr6_tlv *)((unsigned char *)srh + tlv_offset);
+		tlv_len = sizeof(*tlv) + tlv->len;
+
+		trailing -= tlv_len;
+		if (trailing < 0)
+			return false;
+
+		tlv_offset += tlv_len;
+	}
+
+	return true;
+}
+
+struct ipv6_sr_hdr *seg6_get_srh(struct sk_buff *skb, int flags)
+{
+	struct ipv6_sr_hdr *srh;
+	int len, srhoff = 0;
+
+	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, &flags) < 0)
+		return NULL;
+
+	if (!pskb_may_pull(skb, srhoff + sizeof(*srh)))
+		return NULL;
+
+	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
+
+	len = (srh->hdrlen + 1) << 3;
+
+	if (!pskb_may_pull(skb, srhoff + len))
+		return NULL;
+
+	/* note that pskb_may_pull may change pointers in header;
+	 * for this reason it is necessary to reload them when needed.
+	 */
+	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
+
+	if (!seg6_validate_srh(srh, len, true))
+		return NULL;
+
+	return srh;
+}
+
+/* Determine if an ICMP invoking packet contains a segment routing
+ * header.  If it does, extract the offset to the true destination
+ * address, which is in the first segment address.
+ */
+void seg6_icmp_srh(struct sk_buff *skb, struct inet6_skb_parm *opt)
+{
+	__u16 network_header = skb->network_header;
+	struct ipv6_sr_hdr *srh;
+
+	/* Update network header to point to the invoking packet
+	 * inside the ICMP packet, so we can use the seg6_get_srh()
+	 * helper.
+	 */
+	skb_reset_network_header(skb);
+
+	srh = seg6_get_srh(skb, 0);
+	if (!srh)
+		goto out;
+
+	if (srh->type != IPV6_SRCRT_TYPE_4)
+		goto out;
+
+	opt->flags |= IP6SKB_SEG6;
+	opt->srhoff = (unsigned char *)srh - skb->data;
+
+out:
+	/* Restore the network header back to the ICMP packet */
+	skb->network_header = network_header;
+}
+
+static struct genl_family seg6_genl_family;
+
+static const struct nla_policy seg6_genl_policy[SEG6_ATTR_MAX + 1] = {
+	[SEG6_ATTR_DST]				= { .type = NLA_BINARY,
+		.len = sizeof(struct in6_addr) },
+	[SEG6_ATTR_DSTLEN]			= { .type = NLA_S32, },
+	[SEG6_ATTR_HMACKEYID]		= { .type = NLA_U32, },
+	[SEG6_ATTR_SECRET]			= { .type = NLA_BINARY, },
+	[SEG6_ATTR_SECRETLEN]		= { .type = NLA_U8, },
+	[SEG6_ATTR_ALGID]			= { .type = NLA_U8, },
+	[SEG6_ATTR_HMACINFO]		= { .type = NLA_NESTED, },
+};
+
+#ifdef CONFIG_IPV6_SEG6_HMAC
+
+static int seg6_genl_sethmac(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net *net = genl_info_net(info);
+	struct seg6_pernet_data *sdata;
+	struct seg6_hmac_info *hinfo;
+	u32 hmackeyid;
+	char *secret;
+	int err = 0;
+	u8 algid;
+	u8 slen;
+
+	sdata = seg6_pernet(net);
+
+	if (!info->attrs[SEG6_ATTR_HMACKEYID] ||
+	    !info->attrs[SEG6_ATTR_SECRETLEN] ||
+	    !info->attrs[SEG6_ATTR_ALGID])
+		return -EINVAL;
+
+	hmackeyid = nla_get_u32(info->attrs[SEG6_ATTR_HMACKEYID]);
+	slen = nla_get_u8(info->attrs[SEG6_ATTR_SECRETLEN]);
+	algid = nla_get_u8(info->attrs[SEG6_ATTR_ALGID]);
+
+	if (hmackeyid == 0)
+		return -EINVAL;
+
+	if (slen > SEG6_HMAC_SECRET_LEN)
+		return -EINVAL;
+
+	mutex_lock(&sdata->lock);
+	hinfo = seg6_hmac_info_lookup(net, hmackeyid);
+
+	if (!slen) {
+		err = seg6_hmac_info_del(net, hmackeyid);
+
+		goto out_unlock;
+	}
+
+	if (!info->attrs[SEG6_ATTR_SECRET]) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	if (slen > nla_len(info->attrs[SEG6_ATTR_SECRET])) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	if (hinfo) {
+		err = seg6_hmac_info_del(net, hmackeyid);
+		if (err)
+			goto out_unlock;
+	}
+
+	secret = (char *)nla_data(info->attrs[SEG6_ATTR_SECRET]);
+
+	hinfo = kzalloc_obj(*hinfo);
+	if (!hinfo) {
+		err = -ENOMEM;
+		goto out_unlock;
+	}
+
+	memcpy(hinfo->secret, secret, slen);
+	hinfo->slen = slen;
+	hinfo->alg_id = algid;
+	hinfo->hmackeyid = hmackeyid;
+
+	err = seg6_hmac_info_add(net, hmackeyid, hinfo);
+	if (err)
+		kfree(hinfo);
+
+out_unlock:
+	mutex_unlock(&sdata->lock);
+	return err;
+}
+
+#else
+
+static int seg6_genl_sethmac(struct sk_buff *skb, struct genl_info *info)
+{
+	return -ENOTSUPP;
+}
+
+#endif
+
+static int seg6_genl_set_tunsrc(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net *net = genl_info_net(info);
+	struct in6_addr *val, *t_old, *t_new;
+	struct seg6_pernet_data *sdata;
+
+	sdata = seg6_pernet(net);
+
+	if (!info->attrs[SEG6_ATTR_DST])
+		return -EINVAL;
+
+	val = nla_data(info->attrs[SEG6_ATTR_DST]);
+	t_new = kmemdup(val, sizeof(*val), GFP_KERNEL);
+	if (!t_new)
+		return -ENOMEM;
+
+	mutex_lock(&sdata->lock);
+
+	t_old = sdata->tun_src;
+	rcu_assign_pointer(sdata->tun_src, t_new);
+
+	mutex_unlock(&sdata->lock);
+
+	synchronize_net();
+	kfree(t_old);
+
+	return 0;
+}
+
+static int seg6_genl_get_tunsrc(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net *net = genl_info_net(info);
+	struct in6_addr *tun_src;
+	struct sk_buff *msg;
+	void *hdr;
+
+	msg = genlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq,
+			  &seg6_genl_family, 0, SEG6_CMD_GET_TUNSRC);
+	if (!hdr)
+		goto free_msg;
+
+	rcu_read_lock();
+	tun_src = rcu_dereference(seg6_pernet(net)->tun_src);
+
+	if (nla_put(msg, SEG6_ATTR_DST, sizeof(struct in6_addr), tun_src))
+		goto nla_put_failure;
+
+	rcu_read_unlock();
+
+	genlmsg_end(msg, hdr);
+	return genlmsg_reply(msg, info);
+
+nla_put_failure:
+	rcu_read_unlock();
+free_msg:
+	nlmsg_free(msg);
+	return -ENOMEM;
+}
+
+#ifdef CONFIG_IPV6_SEG6_HMAC
+
+static int __seg6_hmac_fill_info(struct seg6_hmac_info *hinfo,
+				 struct sk_buff *msg)
+{
+	if (nla_put_u32(msg, SEG6_ATTR_HMACKEYID, hinfo->hmackeyid) ||
+	    nla_put_u8(msg, SEG6_ATTR_SECRETLEN, hinfo->slen) ||
+	    nla_put(msg, SEG6_ATTR_SECRET, hinfo->slen, hinfo->secret) ||
+	    nla_put_u8(msg, SEG6_ATTR_ALGID, hinfo->alg_id))
+		return -1;
+
+	return 0;
+}
+
+static int __seg6_genl_dumphmac_element(struct seg6_hmac_info *hinfo,
+					u32 portid, u32 seq, u32 flags,
+					struct sk_buff *skb, u8 cmd)
+{
+	void *hdr;
+
+	hdr = genlmsg_put(skb, portid, seq, &seg6_genl_family, flags, cmd);
+	if (!hdr)
+		return -ENOMEM;
+
+	if (__seg6_hmac_fill_info(hinfo, skb) < 0)
+		goto nla_put_failure;
+
+	genlmsg_end(skb, hdr);
+	return 0;
+
+nla_put_failure:
+	genlmsg_cancel(skb, hdr);
+	return -EMSGSIZE;
+}
+
+static int seg6_genl_dumphmac_start(struct netlink_callback *cb)
+{
+	struct net *net = sock_net(cb->skb->sk);
+	struct seg6_pernet_data *sdata;
+	struct rhashtable_iter *iter;
+
+	sdata = seg6_pernet(net);
+	iter = (struct rhashtable_iter *)cb->args[0];
+
+	if (!iter) {
+		iter = kmalloc_obj(*iter);
+		if (!iter)
+			return -ENOMEM;
+
+		cb->args[0] = (long)iter;
+	}
+
+	rhashtable_walk_enter(&sdata->hmac_infos, iter);
+
+	return 0;
+}
+
+static int seg6_genl_dumphmac_done(struct netlink_callback *cb)
+{
+	struct rhashtable_iter *iter = (struct rhashtable_iter *)cb->args[0];
+
+	rhashtable_walk_exit(iter);
+
+	kfree(iter);
+
+	return 0;
+}
+
+static int seg6_genl_dumphmac(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct rhashtable_iter *iter = (struct rhashtable_iter *)cb->args[0];
+	struct seg6_hmac_info *hinfo;
+	int ret;
+
+	rhashtable_walk_start(iter);
+
+	for (;;) {
+		hinfo = rhashtable_walk_next(iter);
+
+		if (IS_ERR(hinfo)) {
+			if (PTR_ERR(hinfo) == -EAGAIN)
+				continue;
+			ret = PTR_ERR(hinfo);
+			goto done;
+		} else if (!hinfo) {
+			break;
+		}
+
+		ret = __seg6_genl_dumphmac_element(hinfo,
+						   NETLINK_CB(cb->skb).portid,
+						   cb->nlh->nlmsg_seq,
+						   NLM_F_MULTI,
+						   skb, SEG6_CMD_DUMPHMAC);
+		if (ret)
+			goto done;
+	}
+
+	ret = skb->len;
+
+done:
+	rhashtable_walk_stop(iter);
+	return ret;
+}
+
+#else
+
+static int seg6_genl_dumphmac_start(struct netlink_callback *cb)
+{
+	return 0;
+}
+
+static int seg6_genl_dumphmac_done(struct netlink_callback *cb)
+{
+	return 0;
+}
+
+static int seg6_genl_dumphmac(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	return -ENOTSUPP;
+}
+
+#endif
+
+static int __net_init seg6_net_init(struct net *net)
+{
+	struct seg6_pernet_data *sdata;
+
+	sdata = kzalloc_obj(*sdata);
+	if (!sdata)
+		return -ENOMEM;
+
+	mutex_init(&sdata->lock);
+
+	sdata->tun_src = kzalloc_obj(*sdata->tun_src);
+	if (!sdata->tun_src) {
+		kfree(sdata);
+		return -ENOMEM;
+	}
+
+	net->ipv6.seg6_data = sdata;
+
+	if (seg6_hmac_net_init(net)) {
+		kfree(rcu_dereference_raw(sdata->tun_src));
+		kfree(sdata);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void __net_exit seg6_net_exit(struct net *net)
+{
+	struct seg6_pernet_data *sdata = seg6_pernet(net);
+
+	seg6_hmac_net_exit(net);
+
+	kfree(rcu_dereference_raw(sdata->tun_src));
+	kfree(sdata);
+}
+
+static struct pernet_operations ip6_segments_ops = {
+	.init = seg6_net_init,
+	.exit = seg6_net_exit,
+};
+
+static const struct genl_ops seg6_genl_ops[] = {
+	{
+		.cmd	= SEG6_CMD_SETHMAC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= seg6_genl_sethmac,
+		.flags	= GENL_ADMIN_PERM,
+	},
+	{
+		.cmd	= SEG6_CMD_DUMPHMAC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.start	= seg6_genl_dumphmac_start,
+		.dumpit	= seg6_genl_dumphmac,
+		.done	= seg6_genl_dumphmac_done,
+		.flags	= GENL_ADMIN_PERM,
+	},
+	{
+		.cmd	= SEG6_CMD_SET_TUNSRC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= seg6_genl_set_tunsrc,
+		.flags	= GENL_ADMIN_PERM,
+	},
+	{
+		.cmd	= SEG6_CMD_GET_TUNSRC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= seg6_genl_get_tunsrc,
+		.flags	= GENL_ADMIN_PERM,
+	},
+};
+
+static struct genl_family seg6_genl_family __ro_after_init = {
+	.hdrsize	= 0,
+	.name		= SEG6_GENL_NAME,
+	.version	= SEG6_GENL_VERSION,
+	.maxattr	= SEG6_ATTR_MAX,
+	.policy = seg6_genl_policy,
+	.netnsok	= true,
+	.parallel_ops	= true,
+	.ops		= seg6_genl_ops,
+	.n_ops		= ARRAY_SIZE(seg6_genl_ops),
+	.resv_start_op	= SEG6_CMD_GET_TUNSRC + 1,
+	.module		= THIS_MODULE,
+};
+
+int __init seg6_init(void)
+{
+	int err;
+
+	err = register_pernet_subsys(&ip6_segments_ops);
+	if (err)
+		goto out;
+
+	err = genl_register_family(&seg6_genl_family);
+	if (err)
+		goto out_unregister_pernet;
+
+	err = seg6_iptunnel_init();
+	if (err)
+		goto out_unregister_genl;
+
+	err = seg6_local_init();
+	if (err)
+		goto out_unregister_iptun;
+
+	pr_info("Segment Routing with IPv6\n");
+
+out:
+	return err;
+out_unregister_iptun:
+	seg6_iptunnel_exit();
+out_unregister_genl:
+	genl_unregister_family(&seg6_genl_family);
+out_unregister_pernet:
+	unregister_pernet_subsys(&ip6_segments_ops);
+	goto out;
+}
+
+void seg6_exit(void)
+{
+	seg6_local_exit();
+	seg6_iptunnel_exit();
+	genl_unregister_family(&seg6_genl_family);
+	unregister_pernet_subsys(&ip6_segments_ops);
+}