host: add --port flag for inbound listen-port allowlist

.github/workflows/test-examples.yml

@@ -237,6 +237,10 @@ jobs:
             memory: "512Mi"
             args: "--net -- /urllib_get.py"
             expect: "SUCCESS: urllib GET worked!"
+          - example: networking-py
+            memory: "512Mi"
+            args: "--port 8080 -- /echo_server_test.py"
+            expect: "SUCCESS: bind\\+listen on port 8080 allowed"
     steps:
       - uses: actions/checkout@v4
 
@@ -569,6 +573,10 @@ jobs:
             memory: "512Mi"
             args: "--net -- /urllib_get.py"
             expect: "SUCCESS: urllib GET worked!"
+          - example: networking-py
+            memory: "512Mi"
+            args: "--port 8080 -- /echo_server_test.py"
+            expect: "SUCCESS: bind\\+listen on port 8080 allowed"
     steps:
       - uses: actions/checkout@v4
 

examples/networking-py/Dockerfile

@@ -9,6 +9,7 @@ COPY http_get.py /http_get.py
 COPY echo_server.py /echo_server.py
 COPY urllib_get.py /urllib_get.py
 COPY https_test.py /https_test.py
+COPY echo_server_test.py /echo_server_test.py
 
 # --- CPIO rootfs builder ---
 FROM alpine:3.20 AS cpio

examples/networking-py/Justfile

@@ -26,9 +26,9 @@ run-urllib:
 run-https:
     hyperlight-unikraft {{kernel}} --initrd {{initrd}} --memory {{memory}} --net -- /https_test.py
 
-# Run echo server
+# Run echo server (--port implies --net)
 run-echo:
-    hyperlight-unikraft {{kernel}} --initrd {{initrd}} --memory {{memory}} --net -- /echo_server.py
+    hyperlight-unikraft {{kernel}} --initrd {{initrd}} --memory {{memory}} --port 8080 -- /echo_server.py
 
 # Build rootfs via Docker (cross-platform)
 rootfs:

examples/networking-py/echo_server_test.py

@@ -0,0 +1,17 @@
+"""Test that --port allows bind+listen and no --port would reject it.
+
+This is a run-to-completion test for CI: it binds, listens, then exits.
+The fact that bind+listen succeed (instead of raising OSError) proves
+the --port allowlist is working.
+"""
+import socket
+
+HOST = "0.0.0.0"
+PORT = 8080
+
+srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+srv.bind((HOST, PORT))
+srv.listen(1)
+srv.close()
+print("SUCCESS: bind+listen on port 8080 allowed")

host/examples/pyhl_as_library.rs

@@ -22,7 +22,7 @@ fn main() -> anyhow::Result<()> {
     // expose host directories via the guest's hostfs.
     let mounts: &[Preopen] = &[];
 
-    let mut rt = pyhl::Runtime::new(&home, mounts, None)?;
+    let mut rt = pyhl::Runtime::new(&home, mounts, None, None)?;
 
     eprintln!("-- first run (hermetic from loaded snapshot) --");
     let t1 = rt.run_code(&code)?;

host/src/bin/pyhl.rs

@@ -26,7 +26,7 @@ use hyperlight_unikraft::pyhl::{
     copy_replace, discover_source_artifacts, extract_from_ghcr, GHCR_INITRD_IMAGE,
     GHCR_KERNEL_IMAGE,
 };
-use hyperlight_unikraft::{AllowList, BlockList, NetworkPolicy, Preopen, Sandbox};
+use hyperlight_unikraft::{AllowList, BlockList, ListenPorts, NetworkPolicy, Preopen, Sandbox};
 use std::fs;
 use std::path::{Path, PathBuf};
 use std::time::Instant;
@@ -41,6 +41,7 @@ fn build_network_policy(
     net: bool,
     net_allow: &[String],
     net_block: &[String],
+    has_ports: bool,
 ) -> Result<Option<NetworkPolicy>> {
     if !net_allow.is_empty() {
         Ok(Some(NetworkPolicy::AllowList(AllowList::from_hosts(
@@ -50,13 +51,21 @@ fn build_network_policy(
         Ok(Some(NetworkPolicy::BlockList(BlockList::from_hosts(
             net_block,
         )?)))
-    } else if net {
+    } else if net || has_ports {
         Ok(Some(NetworkPolicy::AllowAll))
     } else {
         Ok(None)
     }
 }
 
+fn build_listen_ports(ports: &[u16]) -> Option<ListenPorts> {
+    if ports.is_empty() {
+        None
+    } else {
+        Some(ListenPorts::from_ports(ports.iter().copied()))
+    }
+}
+
 /// Keep in sync with `py_initialize_once` in examples/python-agent-driver/
 /// hl_pydriver.c. These modules are imported during `pyhl setup`'s warmup
 /// so they're already in `sys.modules` in every `pyhl run` invocation —
@@ -187,6 +196,12 @@ struct SetupArgs {
         conflicts_with = "net_allow"
     )]
     net_block: Vec<String>,
+
+    /// Allow the guest to bind (listen) on the given port. Implies --net.
+    /// Without this flag, `net_bind` is rejected (outbound-only).
+    /// Repeatable: `--port 8080 --port 3000`.
+    #[arg(long, value_name = "PORT")]
+    port: Vec<u16>,
 }
 
 #[derive(Args)]
@@ -236,6 +251,12 @@ struct RunArgs {
     )]
     net_block: Vec<String>,
 
+    /// Allow the guest to bind (listen) on the given port. Implies --net.
+    /// Without this flag, `net_bind` is rejected (outbound-only).
+    /// Repeatable: `--port 8080 --port 3000`.
+    #[arg(long, value_name = "PORT")]
+    port: Vec<u16>,
+
     /// Print evolve/warmup/per-run timing to stderr. Off by default so the
     /// user's script output is clean.
     #[arg(short = 'v', long = "verbose")]
@@ -393,7 +414,13 @@ fn cmd_setup(args: SetupArgs) -> Result<()> {
         .iter()
         .map(|m| parse_mount(m))
         .collect::<Result<_>>()?;
-    let network = build_network_policy(args.net, &args.net_allow, &args.net_block)?;
+    let listen_ports = build_listen_ports(&args.port);
+    let network = build_network_policy(
+        args.net,
+        &args.net_allow,
+        &args.net_block,
+        listen_ports.is_some(),
+    )?;
 
     eprintln!("pyhl: warming up Python and persisting snapshot…");
     let t_warm = Instant::now();
@@ -407,6 +434,9 @@ fn cmd_setup(args: SetupArgs) -> Result<()> {
         if let Some(ref policy) = network {
             builder = builder.network(policy.clone());
         }
+        if let Some(ref lp) = listen_ports {
+            builder = builder.listen_ports(lp.clone());
+        }
         let mut sbox = builder.build()?;
         sbox.restore()?;
         let _: () = sbox.call_named("run", "pass".to_string())?;
@@ -531,7 +561,13 @@ fn cmd_run(args: RunArgs) -> Result<()> {
         .iter()
         .map(|m| parse_mount(m))
         .collect::<Result<_>>()?;
-    let network = build_network_policy(args.net, &args.net_allow, &args.net_block)?;
+    let listen_ports = build_listen_ports(&args.port);
+    let network = build_network_policy(
+        args.net,
+        &args.net_allow,
+        &args.net_block,
+        listen_ports.is_some(),
+    )?;
 
     let initrd = home.join(INITRD_FILE);
 
@@ -546,6 +582,7 @@ fn cmd_run(args: RunArgs) -> Result<()> {
         &run_preopens,
         initrd_ref,
         network.as_ref(),
+        listen_ports.as_ref(),
     )?;
     if args.verbose {
         eprintln!(