kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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);
+}