lib: add krun_set_init_binary, backcompat via new krun_init crate

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

Author: ggoodman

Cargo.lock

@@ -1,5 +1,5 @@
 [workspace]
-members = ["src/libkrun", "src/krun_input"]
+members = ["src/libkrun", "src/krun_input", "src/krun_init"]
 exclude = ["examples/gtk_display"]
 resolver = "2"
 

Cargo.toml

@@ -109,6 +109,24 @@ int32_t krun_set_vm_config(uint32_t ctx_id, uint8_t num_vcpus, uint32_t ram_mib)
  */
 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.
+ *
+ * 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.
+ *  "init_binary"     - pointer to init binary bytes.
+ *  "init_binary_len" - number of bytes at init_binary.
+ *
+ * Returns:
+ *  Zero on success or a negative error number on failure.
+ */
+int32_t krun_set_init(uint32_t ctx_id, const uint8_t *init_binary, size_t init_binary_len);
+
 /**
  * DEPRECATED. Use krun_add_disk instead.
  *

include/libkrun.h

@@ -3,7 +3,6 @@ name = "devices"
 version = "0.1.0"
 authors = ["The Chromium OS Authors"]
 edition = "2021"
-build = "build.rs"
 
 [features]
 tee = []

src/devices/Cargo.toml

@@ -59,6 +59,7 @@ impl Fs {
         shared_dir: String,
         exit_code: Arc<AtomicI32>,
         allow_root_dir_delete: bool,
+        init_payload: Option<&'static [u8]>,
     ) -> super::Result<Fs> {
         let avail_features = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_RING_F_EVENT_IDX);
 
@@ -70,6 +71,7 @@ impl Fs {
         let fs_cfg = passthrough::Config {
             root_dir: shared_dir,
             allow_root_dir_delete,
+            init_payload,
             ..Default::default()
         };
 

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

@@ -33,8 +33,6 @@ const EMPTY_CSTR: &[u8] = b"\0";
 const PROC_CSTR: &[u8] = b"/proc/self/fd\0";
 const INIT_CSTR: &[u8] = b"init.krun\0";
 
-static INIT_BINARY: &[u8] = include_bytes!(env!("KRUN_INIT_BINARY_PATH"));
-
 type Inode = u64;
 type Handle = u64;
 
@@ -328,6 +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<&'static [u8]>,
 }
 
 impl Default for Config {
@@ -343,6 +342,7 @@ impl Default for Config {
             export_fsid: 0,
             export_table: None,
             allow_root_dir_delete: false,
+            init_payload: None,
         }
     }
 }
@@ -439,7 +439,11 @@ impl PassthroughFs {
         Ok(PassthroughFs {
             inodes: RwLock::new(MultikeyBTreeMap::new()),
             next_inode: AtomicU64::new(fuse::ROOT_ID + 2),
-            init_inode: fuse::ROOT_ID + 1,
+            init_inode: if cfg.init_payload.is_some() {
+                fuse::ROOT_ID + 1
+            } else {
+                0
+            },
 
             handles: RwLock::new(BTreeMap::new()),
             next_handle: AtomicU64::new(1),
@@ -456,6 +460,10 @@ impl PassthroughFs {
         })
     }
 
+    fn init_payload(&self) -> io::Result<&[u8]> {
+        self.cfg.init_payload.ok_or_else(ebadf)
+    }
+
     fn open_inode(&self, inode: Inode, mut flags: i32) -> io::Result<File> {
         let data = self
             .inodes
@@ -996,7 +1004,7 @@ impl FileSystem for PassthroughFs {
 
         if self.init_inode != 0 && name == init_name {
             let mut st: libc::stat64 = unsafe { mem::zeroed() };
-            st.st_size = INIT_BINARY.len() as i64;
+            st.st_size = self.init_payload()?.len() as i64;
             st.st_ino = self.init_inode;
             st.st_mode = 0o100_755;
 
@@ -1235,13 +1243,16 @@ impl FileSystem for PassthroughFs {
     ) -> io::Result<usize> {
         debug!("read: {inode:?}");
         if inode == self.init_inode {
+            let init_payload = self.init_payload()?;
             let off: usize = offset.try_into().map_err(|_| einval())?;
-            let len = if off + (size as usize) < INIT_BINARY.len() {
-                size as usize
-            } else {
-                INIT_BINARY.len() - off
-            };
-            return w.write(&INIT_BINARY[off..(off + len)]);
+            if off >= init_payload.len() {
+                // Read past EOF should return 0 bytes.
+                return Ok(0);
+            }
+
+            let remaining = init_payload.len() - off;
+            let len = remaining.min(size as usize);
+            return w.write(&init_payload[off..(off + len)]);
         }
 
         let data = self
@@ -2088,6 +2099,7 @@ impl FileSystem for PassthroughFs {
         debug!("setupmapping: ino {inode:?} addr={addr:x} len={len}");
 
         if inode == self.init_inode {
+            let init_payload = self.init_payload()?;
             let ret = unsafe {
                 libc::mmap(
                     addr as *mut libc::c_void,
@@ -2102,15 +2114,15 @@ impl FileSystem for PassthroughFs {
                 return Err(io::Error::last_os_error());
             }
 
-            let to_copy = if len as usize > INIT_BINARY.len() {
-                INIT_BINARY.len()
+            let to_copy = if len as usize > init_payload.len() {
+                init_payload.len()
             } else {
                 len as usize
             };
             unsafe {
                 libc::memcpy(
                     addr as *mut libc::c_void,
-                    INIT_BINARY.as_ptr() as *const _,
+                    init_payload.as_ptr() as *const _,
                     to_copy,
                 )
             };

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

@@ -37,8 +37,6 @@ const SECURITY_CAPABILITY: &[u8] = b"security.capability\0";
 
 const UID_MAX: u32 = u32::MAX - 1;
 
-static INIT_BINARY: &[u8] = include_bytes!(env!("KRUN_INIT_BINARY_PATH"));
-
 type Inode = u64;
 type Handle = u64;
 
@@ -517,6 +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<&'static [u8]>,
 }
 
 impl Default for Config {
@@ -532,6 +531,7 @@ impl Default for Config {
             export_fsid: 0,
             export_table: None,
             allow_root_dir_delete: false,
+            init_payload: None,
         }
     }
 }
@@ -580,7 +580,11 @@ impl PassthroughFs {
         Ok(PassthroughFs {
             inodes: RwLock::new(MultikeyBTreeMap::new()),
             next_inode: AtomicU64::new(fuse::ROOT_ID + 2),
-            init_inode: fuse::ROOT_ID + 1,
+            init_inode: if cfg.init_payload.is_some() {
+                fuse::ROOT_ID + 1
+            } else {
+                0
+            },
 
             handles: RwLock::new(BTreeMap::new()),
             next_handle: AtomicU64::new(1),
@@ -594,6 +598,10 @@ impl PassthroughFs {
         })
     }
 
+    fn init_payload(&self) -> io::Result<&[u8]> {
+        self.cfg.init_payload.ok_or_else(ebadf)
+    }
+
     fn inode_to_handle(&self, inode: Inode, supports_fd: bool) -> io::Result<InodeHandle> {
         debug!("inode_to_handle: inode={inode}");
         let data = self
@@ -1205,7 +1213,7 @@ impl FileSystem for PassthroughFs {
 
         if self.init_inode != 0 && name == _init_name {
             let mut st: bindings::stat64 = unsafe { mem::zeroed() };
-            st.st_size = INIT_BINARY.len() as i64;
+            st.st_size = self.init_payload()?.len() as i64;
             st.st_ino = self.init_inode;
             st.st_mode = 0o100_755;
 
@@ -1457,15 +1465,18 @@ impl FileSystem for PassthroughFs {
     ) -> io::Result<usize> {
         debug!("read: {inode:?}");
         if inode == self.init_inode {
+            let init_payload = self.init_payload()?;
             let off: usize = offset
                 .try_into()
                 .map_err(|_| io::Error::from_raw_os_error(libc::EINVAL))?;
-            let len = if off + (size as usize) < INIT_BINARY.len() {
-                size as usize
-            } else {
-                INIT_BINARY.len() - off
-            };
-            return w.write(&INIT_BINARY[off..(off + len)]);
+            if off >= init_payload.len() {
+                // Read past EOF should return 0 bytes.
+                return Ok(0);
+            }
+
+            let remaining = init_payload.len() - off;
+            let len = remaining.min(size as usize);
+            return w.write(&init_payload[off..(off + len)]);
         }
 
         let data = self

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

@@ -0,0 +1,8 @@
+[package]
+name = "krun_init"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+
+[lib]
+path = "src/lib.rs"

src/krun_init/Cargo.toml

@@ -2,7 +2,7 @@ use std::ffi::OsStr;
 use std::path::PathBuf;
 use std::process::Command;
 
-fn build_default_init() -> PathBuf {
+fn build_default_init() -> Option<PathBuf> {
     let manifest_dir = PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap());
     let libkrun_root = manifest_dir.join("../..");
     let init_src = libkrun_root.join("init/init.c");
@@ -39,20 +39,35 @@ fn build_default_init() -> PathBuf {
         .unwrap_or_else(|e| panic!("failed to execute {cc}: {e}"));
 
     if !status.success() {
-        panic!("failed to compile init/init.c: {status}");
+        return None;
     }
-    init_bin
+    Some(init_bin)
 }
 
 fn main() {
+    let manifest_dir = PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap());
+    let repo_init_bin = manifest_dir.join("../..").join("init/init");
+    println!("cargo:rerun-if-changed={}", repo_init_bin.display());
+
     let init_binary_path = std::env::var_os("KRUN_INIT_BINARY_PATH")
         .map(PathBuf::from)
+        .or_else(build_default_init)
+        .or_else(|| {
+            if repo_init_bin.exists() {
+                Some(repo_init_bin)
+            } else {
+                None
+            }
+        })
         .unwrap_or_else(|| {
-            let init_path = build_default_init();
-            // SAFETY: The build script is single threaded.
-            unsafe { std::env::set_var("KRUN_INIT_BINARY_PATH", &init_path) };
-            init_path
+            panic!(
+                "failed to produce an init binary: set KRUN_INIT_BINARY_PATH or ensure init/init exists"
+            )
         });
+
+    // SAFETY: The build script is single threaded.
+    unsafe { std::env::set_var("KRUN_INIT_BINARY_PATH", &init_binary_path) };
+
     println!(
         "cargo:rustc-env=KRUN_INIT_BINARY_PATH={}",
         init_binary_path.display()

src/devices/build.rs src/krun_init/build.rssrc/devices/build.rs renamed to src/krun_init/build.rs

@@ -0,0 +1 @@
+pub static DEFAULT_INIT: &[u8] = include_bytes!(env!("KRUN_INIT_BINARY_PATH"));