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-rw-r--r--Documentation/admin-guide/sysctl/net.rst28
-rw-r--r--drivers/vhost/vsock.c13
-rw-r--r--include/net/af_vsock.h9
-rw-r--r--include/net/netns/vsock.h2
-rw-r--r--net/vmw_vsock/af_vsock.c35
-rw-r--r--net/vmw_vsock/virtio_transport.c7
6 files changed, 89 insertions, 5 deletions
diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 3b2ad61995d4..0724a793798f 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -602,3 +602,31 @@ it does not modify the current namespace or any existing children.
A namespace with ``ns_mode`` set to ``local`` cannot change
``child_ns_mode`` to ``global`` (returns ``-EPERM``).
+
+g2h_fallback
+------------
+
+Controls whether connections to CIDs not owned by the host-to-guest (H2G)
+transport automatically fall back to the guest-to-host (G2H) transport.
+
+When enabled, if a connect targets a CID that the H2G transport (e.g.
+vhost-vsock) does not serve, or if no H2G transport is loaded at all, the
+connection is routed via the G2H transport (e.g. virtio-vsock) instead. This
+allows a host running both nested VMs (via vhost-vsock) and sibling VMs
+reachable through the hypervisor (e.g. Nitro Enclaves) to address both using
+a single CID space, without requiring applications to set
+``VMADDR_FLAG_TO_HOST``.
+
+When the fallback is taken, ``VMADDR_FLAG_TO_HOST`` is automatically set on
+the remote address so that userspace can determine the path via
+``getpeername()``.
+
+Note: With this sysctl enabled, user space that attempts to talk to a guest
+CID which is not implemented by the H2G transport will create host vsock
+traffic. Environments that rely on H2G-only isolation should set it to 0.
+
+Values:
+
+ - 0 - Connections to CIDs <= 2 or with VMADDR_FLAG_TO_HOST use G2H;
+ all others use H2G (or fail with ENODEV if H2G is not loaded).
+ - 1 - Connections to CIDs not owned by H2G fall back to G2H. (default)
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 054f7a718f50..1d8ec6bed53e 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -91,6 +91,18 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid, struct net *net)
return NULL;
}
+static bool vhost_transport_has_remote_cid(struct vsock_sock *vsk, u32 cid)
+{
+ struct sock *sk = sk_vsock(vsk);
+ struct net *net = sock_net(sk);
+ bool found;
+
+ rcu_read_lock();
+ found = !!vhost_vsock_get(cid, net);
+ rcu_read_unlock();
+ return found;
+}
+
static void
vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
struct vhost_virtqueue *vq)
@@ -424,6 +436,7 @@ static struct virtio_transport vhost_transport = {
.module = THIS_MODULE,
.get_local_cid = vhost_transport_get_local_cid,
+ .has_remote_cid = vhost_transport_has_remote_cid,
.init = virtio_transport_do_socket_init,
.destruct = virtio_transport_destruct,
diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 533d8e75f7bb..4e40063adab4 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -179,6 +179,15 @@ struct vsock_transport {
/* Addressing. */
u32 (*get_local_cid)(void);
+ /* Check if this transport serves a specific remote CID.
+ * For H2G transports: return true if the CID belongs to a registered
+ * guest. If not implemented, all CIDs > VMADDR_CID_HOST go to H2G.
+ * For G2H transports: return true if the transport can reach arbitrary
+ * CIDs via the hypervisor (i.e. supports the fallback overlay). VMCI
+ * does not implement this as it only serves CIDs 0 and 2.
+ */
+ bool (*has_remote_cid)(struct vsock_sock *vsk, u32 remote_cid);
+
/* Read a single skb */
int (*read_skb)(struct vsock_sock *, skb_read_actor_t);
diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
index dc8cbe45f406..7f84aad92f57 100644
--- a/include/net/netns/vsock.h
+++ b/include/net/netns/vsock.h
@@ -20,5 +20,7 @@ struct netns_vsock {
/* 0 = unlocked, 1 = locked to global, 2 = locked to local */
int child_ns_mode_locked;
+
+ int g2h_fallback;
};
#endif /* __NET_NET_NAMESPACE_VSOCK_H */
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index f0ab2f13e9db..cc4b225250b9 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -545,9 +545,13 @@ static void vsock_deassign_transport(struct vsock_sock *vsk)
* The vsk->remote_addr is used to decide which transport to use:
* - remote CID == VMADDR_CID_LOCAL or g2h->local_cid or VMADDR_CID_HOST if
* g2h is not loaded, will use local transport;
- * - remote CID <= VMADDR_CID_HOST or h2g is not loaded or remote flags field
- * includes VMADDR_FLAG_TO_HOST flag value, will use guest->host transport;
- * - remote CID > VMADDR_CID_HOST will use host->guest transport;
+ * - remote CID <= VMADDR_CID_HOST or remote flags field includes
+ * VMADDR_FLAG_TO_HOST, will use guest->host transport;
+ * - remote CID > VMADDR_CID_HOST and h2g is loaded and h2g claims that CID,
+ * will use host->guest transport;
+ * - h2g not loaded or h2g does not claim that CID and g2h claims the CID via
+ * has_remote_cid, will use guest->host transport (when g2h_fallback=1)
+ * - anything else goes to h2g or returns -ENODEV if no h2g is available
*/
int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
{
@@ -581,11 +585,21 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
case SOCK_SEQPACKET:
if (vsock_use_local_transport(remote_cid))
new_transport = transport_local;
- else if (remote_cid <= VMADDR_CID_HOST || !transport_h2g ||
+ else if (remote_cid <= VMADDR_CID_HOST ||
(remote_flags & VMADDR_FLAG_TO_HOST))
new_transport = transport_g2h;
- else
+ else if (transport_h2g &&
+ (!transport_h2g->has_remote_cid ||
+ transport_h2g->has_remote_cid(vsk, remote_cid)))
+ new_transport = transport_h2g;
+ else if (sock_net(sk)->vsock.g2h_fallback &&
+ transport_g2h && transport_g2h->has_remote_cid &&
+ transport_g2h->has_remote_cid(vsk, remote_cid)) {
+ vsk->remote_addr.svm_flags |= VMADDR_FLAG_TO_HOST;
+ new_transport = transport_g2h;
+ } else {
new_transport = transport_h2g;
+ }
break;
default:
ret = -ESOCKTNOSUPPORT;
@@ -2879,6 +2893,15 @@ static struct ctl_table vsock_table[] = {
.mode = 0644,
.proc_handler = vsock_net_child_mode_string
},
+ {
+ .procname = "g2h_fallback",
+ .data = &init_net.vsock.g2h_fallback,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
+ },
};
static int __net_init vsock_sysctl_register(struct net *net)
@@ -2894,6 +2917,7 @@ static int __net_init vsock_sysctl_register(struct net *net)
table[0].data = &net->vsock.mode;
table[1].data = &net->vsock.child_ns_mode;
+ table[2].data = &net->vsock.g2h_fallback;
}
net->vsock.sysctl_hdr = register_net_sysctl_sz(net, "net/vsock", table,
@@ -2928,6 +2952,7 @@ static void vsock_net_init(struct net *net)
net->vsock.mode = vsock_net_child_mode(current->nsproxy->net_ns);
net->vsock.child_ns_mode = net->vsock.mode;
+ net->vsock.g2h_fallback = 1;
}
static __net_init int vsock_sysctl_init_net(struct net *net)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 77fe5b7b066c..57f2d6ec3ffc 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -547,11 +547,18 @@ bool virtio_transport_stream_allow(struct vsock_sock *vsk, u32 cid, u32 port)
static bool virtio_transport_seqpacket_allow(struct vsock_sock *vsk,
u32 remote_cid);
+static bool virtio_transport_has_remote_cid(struct vsock_sock *vsk, u32 cid)
+{
+ /* The CID could be implemented by the host. Always assume it is. */
+ return true;
+}
+
static struct virtio_transport virtio_transport = {
.transport = {
.module = THIS_MODULE,
.get_local_cid = virtio_transport_get_local_cid,
+ .has_remote_cid = virtio_transport_has_remote_cid,
.init = virtio_transport_do_socket_init,
.destruct = virtio_transport_destruct,
generated by cgit v1.2.3 (git 2.39.0) at 2026-05-13 16:40:50 +0300