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, 204 insertions, 0 deletions

diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h
new file mode 100644
index 000000000..79b6d70de
--- /dev/null
+++ b/drivers/net/wireguard/queueing.h
@@ -0,0 +1,204 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#ifndef _WG_QUEUEING_H
+#define _WG_QUEUEING_H
+
+#include "peer.h"
+#include <linux/types.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <net/ip_tunnels.h>
+
+struct wg_device;
+struct wg_peer;
+struct multicore_worker;
+struct crypt_queue;
+struct prev_queue;
+struct sk_buff;
+
+/* queueing.c APIs: */
+int wg_packet_queue_init(struct crypt_queue *queue, work_func_t function,
+			 unsigned int len);
+void wg_packet_queue_free(struct crypt_queue *queue, bool purge);
+struct multicore_worker __percpu *
+wg_packet_percpu_multicore_worker_alloc(work_func_t function, void *ptr);
+
+/* receive.c APIs: */
+void wg_packet_receive(struct wg_device *wg, struct sk_buff *skb);
+void wg_packet_handshake_receive_worker(struct work_struct *work);
+/* NAPI poll function: */
+int wg_packet_rx_poll(struct napi_struct *napi, int budget);
+/* Workqueue worker: */
+void wg_packet_decrypt_worker(struct work_struct *work);
+
+/* send.c APIs: */
+void wg_packet_send_queued_handshake_initiation(struct wg_peer *peer,
+						bool is_retry);
+void wg_packet_send_handshake_response(struct wg_peer *peer);
+void wg_packet_send_handshake_cookie(struct wg_device *wg,
+				     struct sk_buff *initiating_skb,
+				     __le32 sender_index);
+void wg_packet_send_keepalive(struct wg_peer *peer);
+void wg_packet_purge_staged_packets(struct wg_peer *peer);
+void wg_packet_send_staged_packets(struct wg_peer *peer);
+/* Workqueue workers: */
+void wg_packet_handshake_send_worker(struct work_struct *work);
+void wg_packet_tx_worker(struct work_struct *work);
+void wg_packet_encrypt_worker(struct work_struct *work);
+
+enum packet_state {
+	PACKET_STATE_UNCRYPTED,
+	PACKET_STATE_CRYPTED,
+	PACKET_STATE_DEAD
+};
+
+struct packet_cb {
+	u64 nonce;
+	struct noise_keypair *keypair;
+	atomic_t state;
+	u32 mtu;
+	u8 ds;
+};
+
+#define PACKET_CB(skb) ((struct packet_cb *)((skb)->cb))
+#define PACKET_PEER(skb) (PACKET_CB(skb)->keypair->entry.peer)
+
+static inline bool wg_check_packet_protocol(struct sk_buff *skb)
+{
+	__be16 real_protocol = ip_tunnel_parse_protocol(skb);
+	return real_protocol && skb->protocol == real_protocol;
+}
+
+static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating)
+{
+	u8 l4_hash = skb->l4_hash;
+	u8 sw_hash = skb->sw_hash;
+	u32 hash = skb->hash;
+	skb_scrub_packet(skb, true);
+	memset(&skb->headers, 0, sizeof(skb->headers));
+	if (encapsulating) {
+		skb->l4_hash = l4_hash;
+		skb->sw_hash = sw_hash;
+		skb->hash = hash;
+	}
+	skb->queue_mapping = 0;
+	skb->nohdr = 0;
+	skb->peeked = 0;
+	skb->mac_len = 0;
+	skb->dev = NULL;
+#ifdef CONFIG_NET_SCHED
+	skb->tc_index = 0;
+#endif
+	skb_reset_redirect(skb);
+	skb->hdr_len = skb_headroom(skb);
+	skb_reset_mac_header(skb);
+	skb_reset_network_header(skb);
+	skb_reset_transport_header(skb);
+	skb_probe_transport_header(skb);
+	skb_reset_inner_headers(skb);
+}
+
+static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id)
+{
+	unsigned int cpu = *stored_cpu;
+
+	while (unlikely(cpu >= nr_cpu_ids || !cpu_online(cpu)))
+		cpu = *stored_cpu = cpumask_nth(id % num_online_cpus(), cpu_online_mask);
+
+	return cpu;
+}
+
+/* This function is racy, in the sense that it's called while last_cpu is
+ * unlocked, so it could return the same CPU twice. Adding locking or using
+ * atomic sequence numbers is slower though, and the consequences of racing are
+ * harmless, so live with it.
+ */
+static inline int wg_cpumask_next_online(int *last_cpu)
+{
+	int cpu = cpumask_next(READ_ONCE(*last_cpu), cpu_online_mask);
+	if (cpu >= nr_cpu_ids)
+		cpu = cpumask_first(cpu_online_mask);
+	WRITE_ONCE(*last_cpu, cpu);
+	return cpu;
+}
+
+void wg_prev_queue_init(struct prev_queue *queue);
+
+/* Multi producer */
+bool wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb);
+
+/* Single consumer */
+struct sk_buff *wg_prev_queue_dequeue(struct prev_queue *queue);
+
+/* Single consumer */
+static inline struct sk_buff *wg_prev_queue_peek(struct prev_queue *queue)
+{
+	if (queue->peeked)
+		return queue->peeked;
+	queue->peeked = wg_prev_queue_dequeue(queue);
+	return queue->peeked;
+}
+
+/* Single consumer */
+static inline void wg_prev_queue_drop_peeked(struct prev_queue *queue)
+{
+	queue->peeked = NULL;
+}
+
+static inline int wg_queue_enqueue_per_device_and_peer(
+	struct crypt_queue *device_queue, struct prev_queue *peer_queue,
+	struct sk_buff *skb, struct workqueue_struct *wq)
+{
+	int cpu;
+
+	atomic_set_release(&PACKET_CB(skb)->state, PACKET_STATE_UNCRYPTED);
+	/* We first queue this up for the peer ingestion, but the consumer
+	 * will wait for the state to change to CRYPTED or DEAD before.
+	 */
+	if (unlikely(!wg_prev_queue_enqueue(peer_queue, skb)))
+		return -ENOSPC;
+
+	/* Then we queue it up in the device queue, which consumes the
+	 * packet as soon as it can.
+	 */
+	cpu = wg_cpumask_next_online(&device_queue->last_cpu);
+	if (unlikely(ptr_ring_produce_bh(&device_queue->ring, skb)))
+		return -EPIPE;
+	queue_work_on(cpu, wq, &per_cpu_ptr(device_queue->worker, cpu)->work);
+	return 0;
+}
+
+static inline void wg_queue_enqueue_per_peer_tx(struct sk_buff *skb, enum packet_state state)
+{
+	/* We take a reference, because as soon as we call atomic_set, the
+	 * peer can be freed from below us.
+	 */
+	struct wg_peer *peer = wg_peer_get(PACKET_PEER(skb));
+
+	atomic_set_release(&PACKET_CB(skb)->state, state);
+	queue_work_on(wg_cpumask_choose_online(&peer->serial_work_cpu, peer->internal_id),
+		      peer->device->packet_crypt_wq, &peer->transmit_packet_work);
+	wg_peer_put(peer);
+}
+
+static inline void wg_queue_enqueue_per_peer_rx(struct sk_buff *skb, enum packet_state state)
+{
+	/* We take a reference, because as soon as we call atomic_set, the
+	 * peer can be freed from below us.
+	 */
+	struct wg_peer *peer = wg_peer_get(PACKET_PEER(skb));
+
+	atomic_set_release(&PACKET_CB(skb)->state, state);
+	napi_schedule(&peer->napi);
+	wg_peer_put(peer);
+}
+
+#ifdef DEBUG
+bool wg_packet_counter_selftest(void);
+#endif
+
+#endif /* _WG_QUEUEING_H */