api: krun_set_init takes static binary only

Signed-off-by: Geoffrey Goodman <geoff@goodman.dev>

Author: ggoodman

include/libkrun.h

@@ -112,8 +112,10 @@ int32_t krun_set_root(uint32_t ctx_id, const char *root_path);
 /**
  * Sets the init binary payload that will be exposed as /init.krun inside the guest.
  *
- * The payload is copied when this API is called. It will be used for /dev/root
- * virtio-fs devices configured in this context.
+ * IMPORTANT LIFETIME CONTRACT:
+ * The memory range [init_binary, init_binary + init_binary_len) is NOT copied.
+ * The caller MUST keep that memory valid and unchanged for the full VM lifetime
+ * in this context (until krun_start_enter() returns and the VM is torn down).
  *
  * Arguments:
  *  "ctx_id"          - the configuration context ID.

src/devices/src/virtio/fs/device.rs

@@ -17,8 +17,8 @@ use super::super::{
 };
 use super::passthrough;
 use super::worker::FsWorker;
+use super::ExportTable;
 use super::{defs, defs::uapi};
-use super::{ExportTable, InitPayload};
 use crate::virtio::InterruptTransport;
 
 #[derive(Copy, Clone)]
@@ -59,7 +59,7 @@ impl Fs {
         shared_dir: String,
         exit_code: Arc<AtomicI32>,
         allow_root_dir_delete: bool,
-        init_payload: Option<InitPayload>,
+        init_payload: Option<&'static [u8]>,
     ) -> super::Result<Fs> {
         let avail_features = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_RING_F_EVENT_IDX);
 

src/devices/src/virtio/fs/linux/passthrough.rs

@@ -26,7 +26,6 @@ use super::super::filesystem::{
 };
 use super::super::fuse;
 use super::super::multikey::MultikeyBTreeMap;
-use super::super::InitPayload;
 
 const CURRENT_DIR_CSTR: &[u8] = b".\0";
 const PARENT_DIR_CSTR: &[u8] = b"..\0";
@@ -327,7 +326,7 @@ pub struct Config {
     /// Table of exported FDs to share with other subsystems.
     pub export_table: Option<ExportTable>,
     pub allow_root_dir_delete: bool,
-    pub init_payload: Option<InitPayload>,
+    pub init_payload: Option<&'static [u8]>,
 }
 
 impl Default for Config {
@@ -462,11 +461,7 @@ impl PassthroughFs {
     }
 
     fn init_payload(&self) -> io::Result<&[u8]> {
-        self.cfg
-            .init_payload
-            .as_ref()
-            .map(InitPayload::as_slice)
-            .ok_or_else(ebadf)
+        self.cfg.init_payload.ok_or_else(ebadf)
     }
 
     fn open_inode(&self, inode: Inode, mut flags: i32) -> io::Result<File> {

src/devices/src/virtio/fs/macos/passthrough.rs

@@ -30,7 +30,6 @@ use super::super::filesystem::{
 };
 use super::super::fuse;
 use super::super::multikey::MultikeyBTreeMap;
-use super::super::InitPayload;
 
 const INIT_CSTR: &[u8] = b"init.krun\0";
 const XATTR_KEY: &[u8] = b"user.containers.override_stat\0";
@@ -516,7 +515,7 @@ pub struct Config {
     /// Table of exported FDs to share with other subsystems. Not supported for macos.
     pub export_table: Option<ExportTable>,
     pub allow_root_dir_delete: bool,
-    pub init_payload: Option<InitPayload>,
+    pub init_payload: Option<&'static [u8]>,
 }
 
 impl Default for Config {
@@ -600,11 +599,7 @@ impl PassthroughFs {
     }
 
     fn init_payload(&self) -> io::Result<&[u8]> {
-        self.cfg
-            .init_payload
-            .as_ref()
-            .map(InitPayload::as_slice)
-            .ok_or_else(ebadf)
+        self.cfg.init_payload.ok_or_else(ebadf)
     }
 
     fn inode_to_handle(&self, inode: Inode, supports_fd: bool) -> io::Result<InodeHandle> {

src/devices/src/virtio/fs/mod.rs

@@ -27,35 +27,6 @@ pub use self::defs::uapi::VIRTIO_ID_FS as TYPE_FS;
 pub use self::device::Fs;
 pub use self::filesystem::ExportTable;
 
-/// Payload backing for the synthetic `/init.krun` file exposed by virtio-fs.
-///
-/// We support two storage modes:
-/// - `Static` for any compile-time embedded payload (for example via
-///   `include_bytes!`), including but not limited to libkrun's default init.
-///   This keeps the common embedded case zero-copy.
-/// - `Owned` for runtime-provided bytes (for example from the C API), where we
-///   must not borrow caller memory.
-///
-/// This keeps read paths uniform via `as_slice()` while preserving zero-copy for
-/// embedded payloads and safe ownership for dynamic payload injection.
-#[derive(Clone, Debug)]
-pub enum InitPayload {
-    /// Compile-time embedded payload (`&'static [u8]`) with zero-copy use.
-    Static(&'static [u8]),
-    /// Runtime-provided payload with owned, reference-counted backing storage.
-    Owned(Arc<[u8]>),
-}
-
-impl InitPayload {
-    /// View the payload as a byte slice regardless of backing representation.
-    pub fn as_slice(&self) -> &[u8] {
-        match self {
-            InitPayload::Static(bytes) => bytes,
-            InitPayload::Owned(bytes) => bytes,
-        }
-    }
-}
-
 mod defs {
     use super::super::QueueConfig;
 
@@ -75,7 +46,6 @@ mod defs {
 
 use std::ffi::{FromBytesWithNulError, FromVecWithNulError};
 use std::io;
-use std::sync::Arc;
 
 use descriptor_utils::Error as DescriptorError;
 

src/libkrun/src/lib.rs

@@ -14,8 +14,6 @@ use env_logger::{Env, Target};
 #[cfg(feature = "gpu")]
 use krun_display::DisplayBackend;
 
-#[cfg(not(feature = "tee"))]
-use devices::virtio::fs::InitPayload;
 use libc::{c_char, c_int, size_t};
 use once_cell::sync::Lazy;
 use polly::event_manager::EventManager;
@@ -36,8 +34,6 @@ use std::os::fd::{BorrowedFd, FromRawFd, RawFd};
 use std::path::PathBuf;
 use std::slice;
 use std::sync::atomic::{AtomicI32, Ordering};
-#[cfg(not(any(feature = "tee", feature = "aws-nitro")))]
-use std::sync::Arc;
 use std::sync::{LazyLock, Mutex};
 use utils::eventfd::EventFd;
 use vmm::resources::{
@@ -94,7 +90,7 @@ static KRUNFW: LazyLock<Option<libloading::Library>> =
     LazyLock::new(|| unsafe { libloading::Library::new(KRUNFW_NAME).ok() });
 
 #[cfg(not(any(feature = "tee", feature = "aws-nitro")))]
-const DEFAULT_INIT_PAYLOAD: InitPayload = InitPayload::Static(krun_init::DEFAULT_INIT);
+const DEFAULT_INIT_PAYLOAD: &[u8] = krun_init::DEFAULT_INIT;
 
 pub struct KrunfwBindings {
     get_kernel: libloading::Symbol<
@@ -171,7 +167,7 @@ struct ContextConfig {
     vmm_uid: Option<libc::uid_t>,
     vmm_gid: Option<libc::gid_t>,
     #[cfg(not(feature = "tee"))]
-    init_payload: Option<InitPayload>,
+    init_payload: Option<&'static [u8]>,
 }
 
 impl ContextConfig {
@@ -241,13 +237,13 @@ impl ContextConfig {
     }
 
     #[cfg(not(feature = "tee"))]
-    fn set_init_payload(&mut self, init_payload: InitPayload) {
-        self.init_payload = Some(init_payload);
+    fn set_init_binary(&mut self, init_binary: &'static [u8]) {
+        self.init_payload = Some(init_binary);
     }
 
     #[cfg(not(feature = "tee"))]
-    fn get_init_payload(&self) -> InitPayload {
-        self.init_payload.clone().unwrap_or(DEFAULT_INIT_PAYLOAD)
+    fn get_init_binary(&self) -> &'static [u8] {
+        self.init_payload.unwrap_or(DEFAULT_INIT_PAYLOAD)
     }
 
     fn get_args(&self) -> String {
@@ -613,7 +609,7 @@ pub unsafe extern "C" fn krun_set_root(ctx_id: u32, c_root_path: *const c_char)
                 // Default to a conservative 512 MB window.
                 shm_size: Some(1 << 29),
                 allow_root_dir_delete: false,
-                init_payload: Some(cfg.get_init_payload()),
+                init_payload: Some(cfg.get_init_binary()),
             });
         }
         Entry::Vacant(_) => return -libc::ENOENT,
@@ -634,18 +630,18 @@ pub unsafe extern "C" fn krun_set_init(
         return -libc::EINVAL;
     }
 
-    let payload = InitPayload::Owned(Arc::<[u8]>::from(slice::from_raw_parts(
-        init_binary,
-        init_binary_len,
-    )));
+    // SAFETY CONTRACT: The caller guarantees that this memory range remains
+    // valid for the full VM lifetime (until krun_start_enter() returns and the
+    // context is dropped). We do not copy the bytes.
+    let payload: &'static [u8] = slice::from_raw_parts(init_binary, init_binary_len);
 
     match CTX_MAP.lock().unwrap().entry(ctx_id) {
         Entry::Occupied(mut ctx_cfg_entry) => {
             let ctx_cfg = ctx_cfg_entry.get_mut();
-            ctx_cfg.set_init_payload(payload.clone());
+            ctx_cfg.set_init_binary(payload);
 
             for fs_cfg in &mut ctx_cfg.vmr.fs {
-                fs_cfg.init_payload = Some(payload.clone());
+                fs_cfg.init_payload = Some(payload);
             }
         }
         Entry::Vacant(_) => return -libc::ENOENT,
@@ -679,7 +675,7 @@ pub unsafe extern "C" fn krun_add_virtiofs(
                 shared_dir: path.to_string(),
                 shm_size: None,
                 allow_root_dir_delete: false,
-                init_payload: Some(cfg.get_init_payload()),
+                init_payload: Some(cfg.get_init_binary()),
             });
         }
         Entry::Vacant(_) => return -libc::ENOENT,
@@ -714,7 +710,7 @@ pub unsafe extern "C" fn krun_add_virtiofs2(
                 shared_dir: path.to_string(),
                 shm_size: Some(shm_size.try_into().unwrap()),
                 allow_root_dir_delete: false,
-                init_payload: Some(cfg.get_init_payload()),
+                init_payload: Some(cfg.get_init_binary()),
             });
         }
         Entry::Vacant(_) => return -libc::ENOENT,
@@ -2347,7 +2343,7 @@ pub unsafe extern "C" fn krun_set_root_disk_remount(
                 // Default to a conservative 512 MB window.
                 shm_size: Some(1 << 29),
                 allow_root_dir_delete: true,
-                init_payload: Some(ctx_cfg.get_init_payload()),
+                init_payload: Some(ctx_cfg.get_init_binary()),
             });
 
             ctx_cfg.set_block_root(device, fstype, options);

src/vmm/src/builder.rs

@@ -1911,7 +1911,7 @@ fn attach_fs_devices(
                 config.shared_dir.clone(),
                 exit_code.clone(),
                 config.allow_root_dir_delete,
-                config.init_payload.clone(),
+                config.init_payload,
             )
             .unwrap(),
         ));

src/vmm/src/vmm_config/fs.rs

@@ -1,10 +1,8 @@
-use devices::virtio::fs::InitPayload;
-
 #[derive(Clone, Debug)]
 pub struct FsDeviceConfig {
     pub fs_id: String,
     pub shared_dir: String,
     pub shm_size: Option<usize>,
     pub allow_root_dir_delete: bool,
-    pub init_payload: Option<InitPayload>,
+    pub init_payload: Option<&'static [u8]>,
 }