psp: provide encapsulation helper for drivers

Create a new function psp_encapsulate(), which takes a TCP packet and
PSP encapsulates it according to the "Transport Mode Packet Format"
section of the PSP Architecture Specification.

psp_encapsulate() does not push a PSP trailer onto the skb. Both IPv6
and IPv4 are supported. Virtualization cookie is not included.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Co-developed-by: Daniel Zahka <daniel.zahka@gmail.com>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250917000954.859376-14-daniel.zahka@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 69 insertions, 0 deletions

diff --git a/include/net/psp/functions.h b/include/net/psp/functions.h
index 183a3c9216b7..0a539e1b39f4 100644
--- a/include/net/psp/functions.h
+++ b/include/net/psp/functions.h
@@ -17,6 +17,8 @@ struct psp_dev *
 psp_dev_create(struct net_device *netdev, struct psp_dev_ops *psd_ops,
 	       struct psp_dev_caps *psd_caps, void *priv_ptr);
 void psp_dev_unregister(struct psp_dev *psd);
+bool psp_dev_encapsulate(struct net *net, struct sk_buff *skb, __be32 spi,
+			 u8 ver, __be16 sport);
 
 /* Kernel-facing API */
 void psp_assoc_put(struct psp_assoc *pas);
diff --git a/include/net/psp/types.h b/include/net/psp/types.h
index ec218747ced0..d9688e66cf09 100644
--- a/include/net/psp/types.h
+++ b/include/net/psp/types.h
@@ -20,6 +20,8 @@ struct psphdr {
 	__be64	vc[]; /* optional */
 };
 
+#define PSP_ENCAP_HLEN (sizeof(struct udphdr) + sizeof(struct psphdr))
+
 #define PSP_SPI_KEY_ID		GENMASK(30, 0)
 #define PSP_SPI_KEY_PHASE	BIT(31)
 
diff --git a/net/psp/psp_main.c b/net/psp/psp_main.c
index 98ad8c85b58e..e026880fa1a2 100644
--- a/net/psp/psp_main.c
+++ b/net/psp/psp_main.c
@@ -1,10 +1,12 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
+#include <linux/bitfield.h>
 #include <linux/list.h>
 #include <linux/netdevice.h>
 #include <linux/xarray.h>
 #include <net/net_namespace.h>
 #include <net/psp.h>
+#include <net/udp.h>
 
 #include "psp.h"
 #include "psp-nl-gen.h"
@@ -158,6 +160,69 @@ unsigned int psp_key_size(u32 version)
 }
 EXPORT_SYMBOL(psp_key_size);
 
+static void psp_write_headers(struct net *net, struct sk_buff *skb, __be32 spi,
+			      u8 ver, unsigned int udp_len, __be16 sport)
+{
+	struct udphdr *uh = udp_hdr(skb);
+	struct psphdr *psph = (struct psphdr *)(uh + 1);
+
+	uh->dest = htons(PSP_DEFAULT_UDP_PORT);
+	uh->source = udp_flow_src_port(net, skb, 0, 0, false);
+	uh->check = 0;
+	uh->len = htons(udp_len);
+
+	psph->nexthdr = IPPROTO_TCP;
+	psph->hdrlen = PSP_HDRLEN_NOOPT;
+	psph->crypt_offset = 0;
+	psph->verfl = FIELD_PREP(PSPHDR_VERFL_VERSION, ver) |
+		      FIELD_PREP(PSPHDR_VERFL_ONE, 1);
+	psph->spi = spi;
+	memset(&psph->iv, 0, sizeof(psph->iv));
+}
+
+/* Encapsulate a TCP packet with PSP by adding the UDP+PSP headers and filling
+ * them in.
+ */
+bool psp_dev_encapsulate(struct net *net, struct sk_buff *skb, __be32 spi,
+			 u8 ver, __be16 sport)
+{
+	u32 network_len = skb_network_header_len(skb);
+	u32 ethr_len = skb_mac_header_len(skb);
+	u32 bufflen = ethr_len + network_len;
+
+	if (skb_cow_head(skb, PSP_ENCAP_HLEN))
+		return false;
+
+	skb_push(skb, PSP_ENCAP_HLEN);
+	skb->mac_header		-= PSP_ENCAP_HLEN;
+	skb->network_header	-= PSP_ENCAP_HLEN;
+	skb->transport_header	-= PSP_ENCAP_HLEN;
+	memmove(skb->data, skb->data + PSP_ENCAP_HLEN, bufflen);
+
+	if (skb->protocol == htons(ETH_P_IP)) {
+		ip_hdr(skb)->protocol = IPPROTO_UDP;
+		be16_add_cpu(&ip_hdr(skb)->tot_len, PSP_ENCAP_HLEN);
+		ip_hdr(skb)->check = 0;
+		ip_hdr(skb)->check =
+			ip_fast_csum((u8 *)ip_hdr(skb), ip_hdr(skb)->ihl);
+	} else if (skb->protocol == htons(ETH_P_IPV6)) {
+		ipv6_hdr(skb)->nexthdr = IPPROTO_UDP;
+		be16_add_cpu(&ipv6_hdr(skb)->payload_len, PSP_ENCAP_HLEN);
+	} else {
+		return false;
+	}
+
+	skb_set_inner_ipproto(skb, IPPROTO_TCP);
+	skb_set_inner_transport_header(skb, skb_transport_offset(skb) +
+						    PSP_ENCAP_HLEN);
+	skb->encapsulation = 1;
+	psp_write_headers(net, skb, spi, ver,
+			  skb->len - skb_transport_offset(skb), sport);
+
+	return true;
+}
+EXPORT_SYMBOL(psp_dev_encapsulate);
+
 static int __init psp_init(void)
 {
 	mutex_init(&psp_devs_lock);