use bounce buffers for loading kernel if secret freedom is enabled

If secret freedom is enabled, the guest kernel and potential initrd
needs to be loaded via bounce buffer, as we cannot directly do `read`
syscalls that target guest memory.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/vmm/src/arch/aarch64/mod.rs

@@ -18,11 +18,11 @@ pub mod vm;
 
 use std::cmp::min;
 use std::fmt::Debug;
-use std::fs::File;
+use std::io::{Read, Seek};
 
 use linux_loader::loader::pe::PE as Loader;
 use linux_loader::loader::{Cmdline, KernelLoader};
-use vm_memory::GuestMemoryError;
+use vm_memory::{GuestMemoryError, ReadVolatile};
 
 use crate::arch::{BootProtocol, EntryPoint};
 use crate::cpu_config::aarch64::{CpuConfiguration, CpuConfigurationError};
@@ -187,16 +187,10 @@ fn get_fdt_addr(mem: &GuestMemoryMmap) -> u64 {
 }
 
 /// Load linux kernel into guest memory.
-pub fn load_kernel(
-    kernel: &File,
+pub fn load_kernel<R: ReadVolatile + Read + Seek>(
+    mut kernel_file: R,
     guest_memory: &GuestMemoryMmap,
 ) -> Result<EntryPoint, ConfigurationError> {
-    // Need to clone the File because reading from it
-    // mutates it.
-    let mut kernel_file = kernel
-        .try_clone()
-        .map_err(|_| ConfigurationError::KernelFile)?;
-
     let entry_addr = Loader::load(
         guest_memory,
         Some(GuestAddress(get_kernel_start())),

src/vmm/src/arch/x86_64/mod.rs

@@ -31,7 +31,7 @@ pub mod xstate;
 #[allow(missing_docs)]
 pub mod generated;
 
-use std::fs::File;
+use std::io::{Read, Seek};
 
 use layout::CMDLINE_START;
 use linux_loader::configurator::linux::LinuxBootConfigurator;
@@ -44,6 +44,7 @@ use linux_loader::loader::elf::start_info::{
 };
 use linux_loader::loader::{Cmdline, KernelLoader, PvhBootCapability, load_cmdline};
 use log::debug;
+use vm_memory::ReadVolatile;
 
 use super::EntryPoint;
 use crate::acpi::create_acpi_tables;
@@ -438,20 +439,14 @@ fn add_e820_entry(
 }
 
 /// Load linux kernel into guest memory.
-pub fn load_kernel(
-    kernel: &File,
+pub fn load_kernel<R: Read + ReadVolatile + Seek>(
+    mut kernel: R,
     guest_memory: &GuestMemoryMmap,
 ) -> Result<EntryPoint, ConfigurationError> {
-    // Need to clone the File because reading from it
-    // mutates it.
-    let mut kernel_file = kernel
-        .try_clone()
-        .map_err(|_| ConfigurationError::KernelFile)?;
-
     let entry_addr = Loader::load(
         guest_memory,
         None,
-        &mut kernel_file,
+        &mut kernel,
         Some(GuestAddress(get_kernel_start())),
     )
     .map_err(ConfigurationError::KernelLoader)?;

src/vmm/src/builder.rs

@@ -5,6 +5,8 @@
 
 use std::fmt::Debug;
 use std::io;
+use std::os::fd::AsFd;
+use std::os::unix::fs::MetadataExt;
 #[cfg(feature = "gdb")]
 use std::sync::mpsc;
 use std::sync::{Arc, Mutex};
@@ -56,10 +58,11 @@ use crate::persist::{MicrovmState, MicrovmStateError};
 use crate::resources::VmResources;
 use crate::seccomp::BpfThreadMap;
 use crate::snapshot::Persist;
+use crate::utils::u64_to_usize;
 use crate::vmm_config::instance_info::InstanceInfo;
 use crate::vmm_config::machine_config::MachineConfigError;
 use crate::vstate::kvm::Kvm;
-use crate::vstate::memory::GuestRegionMmap;
+use crate::vstate::memory::{GuestRegionMmap, MaybeBounce};
 use crate::vstate::vcpu::{Vcpu, VcpuError};
 use crate::vstate::vm::Vm;
 use crate::{EventManager, Vmm, VmmError, device_manager};
@@ -242,8 +245,28 @@ pub fn build_microvm_for_boot(
         .register_memory_regions(guest_memory)
         .map_err(VmmError::Vm)?;
 
-    let entry_point = load_kernel(&boot_config.kernel_file, vmm.vm.guest_memory())?;
-    let initrd = InitrdConfig::from_config(boot_config, vmm.vm.guest_memory())?;
+    let entry_point = load_kernel(
+        MaybeBounce::new(
+            boot_config.kernel_file.try_clone().unwrap(),
+            vm_resources.machine_config.secret_free,
+        ),
+        vmm.vm.guest_memory(),
+    )?;
+    let initrd = match &boot_config.initrd_file {
+        Some(initrd_file) => {
+            let size = initrd_file
+                .metadata()
+                .map_err(InitrdError::Metadata)?
+                .size();
+
+            Some(InitrdConfig::from_reader(
+                vmm.vm.guest_memory(),
+                MaybeBounce::new(initrd_file.as_fd(), vm_resources.machine_config.secret_free),
+                u64_to_usize(size),
+            )?)
+        }
+        None => None,
+    };
 
     #[cfg(feature = "gdb")]
     let (gdb_tx, gdb_rx) = mpsc::channel();

src/vmm/src/initrd.rs

@@ -1,14 +1,9 @@
 // Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::fs::File;
-use std::os::unix::fs::MetadataExt;
-
 use vm_memory::{GuestAddress, GuestMemory, ReadVolatile, VolatileMemoryError};
 
 use crate::arch::initrd_load_addr;
-use crate::utils::u64_to_usize;
-use crate::vmm_config::boot_source::BootConfig;
 use crate::vstate::memory::GuestMemoryMmap;
 
 /// Errors associated with initrd loading.
@@ -20,8 +15,6 @@ pub enum InitrdError {
     Load,
     /// Cannot image metadata: {0}
     Metadata(std::io::Error),
-    /// Cannot copy initrd file fd: {0}
-    CloneFd(std::io::Error),
     /// Cannot load initrd due to an invalid image: {0}
     Read(VolatileMemoryError),
 }
@@ -36,31 +29,20 @@ pub struct InitrdConfig {
 }
 
 impl InitrdConfig {
-    /// Load initrd into guest memory based on the boot config.
-    pub fn from_config(
-        boot_cfg: &BootConfig,
-        vm_memory: &GuestMemoryMmap,
-    ) -> Result<Option<Self>, InitrdError> {
-        Ok(match &boot_cfg.initrd_file {
-            Some(f) => {
-                let f = f.try_clone().map_err(InitrdError::CloneFd)?;
-                Some(Self::from_file(vm_memory, f)?)
-            }
-            None => None,
-        })
-    }
-
     /// Loads the initrd from a file into guest memory.
-    pub fn from_file(vm_memory: &GuestMemoryMmap, mut file: File) -> Result<Self, InitrdError> {
-        let size = file.metadata().map_err(InitrdError::Metadata)?.size();
-        let size = u64_to_usize(size);
+    pub fn from_reader<R: ReadVolatile>(
+        vm_memory: &GuestMemoryMmap,
+        mut reader: R,
+        size: usize,
+    ) -> Result<Self, InitrdError> {
         let Some(address) = initrd_load_addr(vm_memory, size) else {
             return Err(InitrdError::Address);
         };
         let mut slice = vm_memory
             .get_slice(GuestAddress(address), size)
             .map_err(|_| InitrdError::Load)?;
-        file.read_exact_volatile(&mut slice)
+        reader
+            .read_exact_volatile(&mut slice)
             .map_err(InitrdError::Read)?;
 
         Ok(InitrdConfig {
@@ -105,7 +87,7 @@ mod tests {
 
         // Need to reset the cursor to read initrd properly.
         tempfile.seek(SeekFrom::Start(0)).unwrap();
-        let initrd = InitrdConfig::from_file(&gm, tempfile).unwrap();
+        let initrd = InitrdConfig::from_reader(&gm, tempfile, image.len()).unwrap();
         assert!(gm.address_in_range(initrd.address));
         assert_eq!(initrd.size, image.len());
     }
@@ -120,7 +102,7 @@ mod tests {
 
         // Need to reset the cursor to read initrd properly.
         tempfile.seek(SeekFrom::Start(0)).unwrap();
-        let res = InitrdConfig::from_file(&gm, tempfile);
+        let res = InitrdConfig::from_reader(&gm, tempfile, image.len());
         assert!(matches!(res, Err(InitrdError::Address)), "{:?}", res);
     }
 
@@ -134,7 +116,7 @@ mod tests {
 
         // Need to reset the cursor to read initrd properly.
         tempfile.seek(SeekFrom::Start(0)).unwrap();
-        let res = InitrdConfig::from_file(&gm, tempfile);
+        let res = InitrdConfig::from_reader(&gm, tempfile, image.len());
         assert!(matches!(res, Err(InitrdError::Address)), "{:?}", res);
     }
 }