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, 414 insertions, 0 deletions

diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c
new file mode 100644
index 000000000..abd77162f
--- /dev/null
+++ b/net/ipv4/esp4_offload.c
@@ -0,0 +1,414 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * IPV4 GSO/GRO offload support
+ * Linux INET implementation
+ *
+ * Copyright (C) 2016 secunet Security Networks AG
+ * Author: Steffen Klassert <steffen.klassert@secunet.com>
+ *
+ * ESP GRO support
+ */
+
+#include <linux/skbuff.h>
+#include <linux/init.h>
+#include <net/protocol.h>
+#include <crypto/aead.h>
+#include <crypto/authenc.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <net/gro.h>
+#include <net/gso.h>
+#include <net/ip.h>
+#include <net/xfrm.h>
+#include <net/esp.h>
+#include <linux/scatterlist.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <net/udp.h>
+
+static struct sk_buff *esp4_gro_receive(struct list_head *head,
+					struct sk_buff *skb)
+{
+	int offset = skb_gro_offset(skb);
+	struct xfrm_offload *xo;
+	struct xfrm_state *x;
+	int encap_type = 0;
+	__be32 seq;
+	__be32 spi;
+
+	if (!pskb_pull(skb, offset))
+		return NULL;
+
+	if (xfrm_parse_spi(skb, IPPROTO_ESP, &spi, &seq) != 0)
+		goto out;
+
+	xo = xfrm_offload(skb);
+	if (!xo || !(xo->flags & CRYPTO_DONE)) {
+		struct sec_path *sp = secpath_set(skb);
+
+		if (!sp)
+			goto out;
+
+		if (sp->len == XFRM_MAX_DEPTH)
+			goto out_reset;
+
+		x = xfrm_input_state_lookup(dev_net(skb->dev), skb->mark,
+					    (xfrm_address_t *)&ip_hdr(skb)->daddr,
+					    spi, IPPROTO_ESP, AF_INET);
+
+		if (unlikely(x && x->dir && x->dir != XFRM_SA_DIR_IN)) {
+			/* non-offload path will record the error and audit log */
+			xfrm_state_put(x);
+			x = NULL;
+		}
+
+		if (!x)
+			goto out_reset;
+
+		skb->mark = xfrm_smark_get(skb->mark, x);
+
+		sp->xvec[sp->len++] = x;
+		sp->olen++;
+
+		xo = xfrm_offload(skb);
+		if (!xo)
+			goto out_reset;
+	}
+
+	xo->flags |= XFRM_GRO;
+
+	if (NAPI_GRO_CB(skb)->proto == IPPROTO_UDP)
+		encap_type = UDP_ENCAP_ESPINUDP;
+
+	XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4 = NULL;
+	XFRM_SPI_SKB_CB(skb)->family = AF_INET;
+	XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct iphdr, daddr);
+	XFRM_SPI_SKB_CB(skb)->seq = seq;
+
+	/* We don't need to handle errors from xfrm_input, it does all
+	 * the error handling and frees the resources on error. */
+	xfrm_input(skb, IPPROTO_ESP, spi, encap_type);
+
+	return ERR_PTR(-EINPROGRESS);
+out_reset:
+	secpath_reset(skb);
+out:
+	skb_push(skb, offset);
+	NAPI_GRO_CB(skb)->same_flow = 0;
+	NAPI_GRO_CB(skb)->flush = 1;
+
+	return NULL;
+}
+
+static void esp4_gso_encap(struct xfrm_state *x, struct sk_buff *skb)
+{
+	struct ip_esp_hdr *esph;
+	struct iphdr *iph = ip_hdr(skb);
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	int proto = iph->protocol;
+
+	skb_push(skb, -skb_network_offset(skb));
+	esph = ip_esp_hdr(skb);
+	*skb_mac_header(skb) = IPPROTO_ESP;
+
+	esph->spi = x->id.spi;
+	esph->seq_no = htonl(XFRM_SKB_CB(skb)->seq.output.low);
+
+	xo->proto = proto;
+}
+
+static struct sk_buff *xfrm4_tunnel_gso_segment(struct xfrm_state *x,
+						struct sk_buff *skb,
+						netdev_features_t features)
+{
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	const struct xfrm_mode *inner_mode = xfrm_ip2inner_mode(x, xo->proto);
+	__be16 type = inner_mode->family == AF_INET6 ? htons(ETH_P_IPV6)
+						     : htons(ETH_P_IP);
+
+	return skb_eth_gso_segment(skb, features, type);
+}
+
+static struct sk_buff *xfrm4_transport_gso_segment(struct xfrm_state *x,
+						   struct sk_buff *skb,
+						   netdev_features_t features)
+{
+	const struct net_offload *ops;
+	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	struct xfrm_offload *xo = xfrm_offload(skb);
+
+	skb->transport_header += x->props.header_len;
+	ops = rcu_dereference(inet_offloads[xo->proto]);
+	if (likely(ops && ops->callbacks.gso_segment))
+		segs = ops->callbacks.gso_segment(skb, features);
+
+	return segs;
+}
+
+static struct sk_buff *xfrm4_beet_gso_segment(struct xfrm_state *x,
+					      struct sk_buff *skb,
+					      netdev_features_t features)
+{
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	const struct net_offload *ops;
+	u8 proto = xo->proto;
+
+	skb->transport_header += x->props.header_len;
+
+	if (x->sel.family != AF_INET6) {
+		if (proto == IPPROTO_BEETPH) {
+			struct ip_beet_phdr *ph =
+				(struct ip_beet_phdr *)skb->data;
+
+			skb->transport_header += ph->hdrlen * 8;
+			proto = ph->nexthdr;
+		} else {
+			skb->transport_header -= IPV4_BEET_PHMAXLEN;
+		}
+	} else {
+		__be16 frag;
+
+		skb->transport_header +=
+			ipv6_skip_exthdr(skb, 0, &proto, &frag);
+		if (proto == IPPROTO_TCP)
+			skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4;
+	}
+
+	if (proto == IPPROTO_IPV6)
+		skb_shinfo(skb)->gso_type |= SKB_GSO_IPXIP4;
+
+	__skb_pull(skb, skb_transport_offset(skb));
+	ops = rcu_dereference(inet_offloads[proto]);
+	if (likely(ops && ops->callbacks.gso_segment))
+		segs = ops->callbacks.gso_segment(skb, features);
+
+	return segs;
+}
+
+static struct sk_buff *xfrm4_outer_mode_gso_segment(struct xfrm_state *x,
+						    struct sk_buff *skb,
+						    netdev_features_t features)
+{
+	switch (x->outer_mode.encap) {
+	case XFRM_MODE_TUNNEL:
+		return xfrm4_tunnel_gso_segment(x, skb, features);
+	case XFRM_MODE_TRANSPORT:
+		return xfrm4_transport_gso_segment(x, skb, features);
+	case XFRM_MODE_BEET:
+		return xfrm4_beet_gso_segment(x, skb, features);
+	}
+
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static struct sk_buff *esp4_gso_segment(struct sk_buff *skb,
+				        netdev_features_t features)
+{
+	struct xfrm_state *x;
+	struct ip_esp_hdr *esph;
+	struct crypto_aead *aead;
+	netdev_features_t esp_features = features;
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	struct sec_path *sp;
+
+	if (!xo)
+		return ERR_PTR(-EINVAL);
+
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
+		return ERR_PTR(-EINVAL);
+
+	sp = skb_sec_path(skb);
+	x = sp->xvec[sp->len - 1];
+	aead = x->data;
+	esph = ip_esp_hdr(skb);
+
+	if (esph->spi != x->id.spi)
+		return ERR_PTR(-EINVAL);
+
+	if (!pskb_may_pull(skb, sizeof(*esph) + crypto_aead_ivsize(aead)))
+		return ERR_PTR(-EINVAL);
+
+	__skb_pull(skb, sizeof(*esph) + crypto_aead_ivsize(aead));
+
+	skb->encap_hdr_csum = 1;
+
+	if ((!(skb->dev->gso_partial_features & NETIF_F_HW_ESP) &&
+	     !(features & NETIF_F_HW_ESP)) || x->xso.dev != skb->dev)
+		esp_features = features & ~(NETIF_F_SG | NETIF_F_CSUM_MASK |
+					    NETIF_F_SCTP_CRC);
+	else if (!(features & NETIF_F_HW_ESP_TX_CSUM) &&
+		 !(skb->dev->gso_partial_features & NETIF_F_HW_ESP_TX_CSUM))
+		esp_features = features & ~(NETIF_F_CSUM_MASK |
+					    NETIF_F_SCTP_CRC);
+
+	xo->flags |= XFRM_GSO_SEGMENT;
+
+	return xfrm4_outer_mode_gso_segment(x, skb, esp_features);
+}
+
+static int esp_input_tail(struct xfrm_state *x, struct sk_buff *skb)
+{
+	struct crypto_aead *aead = x->data;
+	struct xfrm_offload *xo = xfrm_offload(skb);
+
+	if (!pskb_may_pull(skb, sizeof(struct ip_esp_hdr) + crypto_aead_ivsize(aead)))
+		return -EINVAL;
+
+	if (!(xo->flags & CRYPTO_DONE))
+		skb->ip_summed = CHECKSUM_NONE;
+
+	return esp_input_done2(skb, 0);
+}
+
+static int esp_xmit(struct xfrm_state *x, struct sk_buff *skb,  netdev_features_t features)
+{
+	int err;
+	int alen;
+	int blksize;
+	struct xfrm_offload *xo;
+	struct ip_esp_hdr *esph;
+	struct crypto_aead *aead;
+	struct esp_info esp;
+	bool hw_offload = true;
+	__u32 seq;
+	int encap_type = 0;
+
+	esp.inplace = true;
+
+	xo = xfrm_offload(skb);
+
+	if (!xo)
+		return -EINVAL;
+
+	if ((!(features & NETIF_F_HW_ESP) &&
+	     !(skb->dev->gso_partial_features & NETIF_F_HW_ESP)) ||
+	    x->xso.dev != skb->dev) {
+		xo->flags |= CRYPTO_FALLBACK;
+		hw_offload = false;
+	}
+
+	esp.proto = xo->proto;
+
+	/* skb is pure payload to encrypt */
+
+	aead = x->data;
+	alen = crypto_aead_authsize(aead);
+
+	esp.tfclen = 0;
+	/* XXX: Add support for tfc padding here. */
+
+	blksize = ALIGN(crypto_aead_blocksize(aead), 4);
+	esp.clen = ALIGN(skb->len + 2 + esp.tfclen, blksize);
+	esp.plen = esp.clen - skb->len - esp.tfclen;
+	esp.tailen = esp.tfclen + esp.plen + alen;
+
+	esp.esph = ip_esp_hdr(skb);
+
+	if (x->encap)
+		encap_type = x->encap->encap_type;
+
+	if (!hw_offload || !skb_is_gso(skb) || (hw_offload && encap_type == UDP_ENCAP_ESPINUDP)) {
+		esp.nfrags = esp_output_head(x, skb, &esp);
+		if (esp.nfrags < 0)
+			return esp.nfrags;
+	}
+
+	seq = xo->seq.low;
+
+	esph = esp.esph;
+	esph->spi = x->id.spi;
+
+	skb_push(skb, -skb_network_offset(skb));
+
+	if (xo->flags & XFRM_GSO_SEGMENT) {
+		esph->seq_no = htonl(seq);
+
+		if (!skb_is_gso(skb))
+			xo->seq.low++;
+		else
+			xo->seq.low += skb_shinfo(skb)->gso_segs;
+	}
+
+	if (xo->seq.low < seq)
+		xo->seq.hi++;
+
+	esp.seqno = cpu_to_be64(seq + ((u64)xo->seq.hi << 32));
+
+	if (hw_offload && encap_type == UDP_ENCAP_ESPINUDP) {
+		/* In the XFRM stack, the encapsulation protocol is set to iphdr->protocol by
+		 * setting *skb_mac_header(skb) (see esp_output_udp_encap()) where skb->mac_header
+		 * points to iphdr->protocol (see xfrm4_tunnel_encap_add()).
+		 * However, in esp_xmit(), skb->mac_header doesn't point to iphdr->protocol.
+		 * Therefore, the protocol field needs to be corrected.
+		 */
+		ip_hdr(skb)->protocol = IPPROTO_UDP;
+
+		esph->seq_no = htonl(seq);
+	}
+
+	ip_hdr(skb)->tot_len = htons(skb->len);
+	ip_send_check(ip_hdr(skb));
+
+	if (hw_offload) {
+		if (!skb_ext_add(skb, SKB_EXT_SEC_PATH))
+			return -ENOMEM;
+
+		xo = xfrm_offload(skb);
+		if (!xo)
+			return -EINVAL;
+
+		xo->flags |= XFRM_XMIT;
+		return 0;
+	}
+
+	err = esp_output_tail(x, skb, &esp);
+	if (err)
+		return err;
+
+	secpath_reset(skb);
+
+	if (skb_needs_linearize(skb, skb->dev->features) &&
+	    __skb_linearize(skb))
+		return -ENOMEM;
+	return 0;
+}
+
+static const struct net_offload esp4_offload = {
+	.callbacks = {
+		.gro_receive = esp4_gro_receive,
+		.gso_segment = esp4_gso_segment,
+	},
+};
+
+static const struct xfrm_type_offload esp_type_offload = {
+	.owner		= THIS_MODULE,
+	.proto	     	= IPPROTO_ESP,
+	.input_tail	= esp_input_tail,
+	.xmit		= esp_xmit,
+	.encap		= esp4_gso_encap,
+};
+
+static int __init esp4_offload_init(void)
+{
+	if (xfrm_register_type_offload(&esp_type_offload, AF_INET) < 0) {
+		pr_info("%s: can't add xfrm type offload\n", __func__);
+		return -EAGAIN;
+	}
+
+	return inet_add_offload(&esp4_offload, IPPROTO_ESP);
+}
+
+static void __exit esp4_offload_exit(void)
+{
+	xfrm_unregister_type_offload(&esp_type_offload, AF_INET);
+	inet_del_offload(&esp4_offload, IPPROTO_ESP);
+}
+
+module_init(esp4_offload_init);
+module_exit(esp4_offload_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Steffen Klassert <steffen.klassert@secunet.com>");
+MODULE_ALIAS_XFRM_OFFLOAD_TYPE(AF_INET, XFRM_PROTO_ESP);
+MODULE_DESCRIPTION("IPV4 GSO/GRO offload support");