vmm: Add support for booting raw binary (e.g. firmware) on x86-64

If the provided binary isn't an ELF binary assume that it is a firmware
to be loaded in directly. In this case we shouldn't program any of the
registers as KVM starts in that state.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

arch/src/x86_64/mod.rs

@@ -57,7 +57,7 @@ const KVM_FEATURE_STEAL_TIME_BIT: u8 = 5;
 /// is to be used to configure the guest initial state.
 pub struct EntryPoint {
     /// Address in guest memory where the guest must start execution
-    pub entry_addr: GuestAddress,
+    pub entry_addr: Option<GuestAddress>,
 }
 
 const E820_RAM: u32 = 1;
@@ -741,11 +741,12 @@ pub fn configure_vcpu(
 
     regs::setup_msrs(fd).map_err(Error::MsrsConfiguration)?;
     if let Some(kernel_entry_point) = kernel_entry_point {
-        // Safe to unwrap because this method is called after the VM is configured
-        regs::setup_regs(fd, kernel_entry_point.entry_addr.raw_value())
-            .map_err(Error::RegsConfiguration)?;
-        regs::setup_fpu(fd).map_err(Error::FpuConfiguration)?;
-        regs::setup_sregs(&vm_memory.memory(), fd).map_err(Error::SregsConfiguration)?;
+        if let Some(entry_addr) = kernel_entry_point.entry_addr {
+            // Safe to unwrap because this method is called after the VM is configured
+            regs::setup_regs(fd, entry_addr.raw_value()).map_err(Error::RegsConfiguration)?;
+            regs::setup_fpu(fd).map_err(Error::FpuConfiguration)?;
+            regs::setup_sregs(&vm_memory.memory(), fd).map_err(Error::SregsConfiguration)?;
+        }
     }
     interrupts::set_lint(fd).map_err(|e| Error::LocalIntConfiguration(e.into()))?;
     Ok(())

vmm/src/vm.rs

@@ -70,9 +70,7 @@ use std::{result, str, thread};
 use vm_device::Bus;
 #[cfg(target_arch = "x86_64")]
 use vm_device::BusDevice;
-#[cfg(any(target_arch = "aarch64", feature = "tdx"))]
-use vm_memory::Address;
-use vm_memory::{Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic};
+use vm_memory::{Address, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic};
 #[cfg(feature = "tdx")]
 use vm_memory::{GuestMemory, GuestMemoryRegion};
 use vm_migration::{
@@ -238,6 +236,18 @@ pub enum Error {
     /// Kernel lacks PVH header
     KernelMissingPvhHeader,
 
+    /// Failed to allocate firmware RAM
+    AllocateFirmwareMemory(MemoryManagerError),
+
+    /// Error manipulating firmware file
+    FirmwareFile(std::io::Error),
+
+    /// Firmware too big
+    FirmwareTooLarge,
+
+    // Failed to copy to memory
+    FirmwareLoad(vm_memory::GuestMemoryError),
+
     /// Error doing I/O on TDX firmware file
     #[cfg(feature = "tdx")]
     LoadTdvf(std::io::Error),
@@ -961,6 +971,7 @@ impl Vm {
 
     #[cfg(target_arch = "x86_64")]
     fn load_kernel(&mut self) -> Result<EntryPoint> {
+        use linux_loader::loader::{elf::Error::InvalidElfMagicNumber, Error::Elf};
         info!("Loading kernel");
         let cmdline = self.get_cmdline()?;
         let guest_memory = self.memory_manager.lock().as_ref().unwrap().guest_memory();
@@ -973,9 +984,41 @@ impl Vm {
             Some(arch::layout::HIGH_RAM_START),
         ) {
             Ok(entry_addr) => entry_addr,
-            Err(e) => {
-                return Err(Error::KernelLoad(e));
-            }
+            Err(e) => match e {
+                Elf(InvalidElfMagicNumber) => {
+                    // Not an ELF header - assume raw binary data / firmware
+                    let size = kernel.seek(SeekFrom::End(0)).map_err(Error::FirmwareFile)?;
+
+                    // The OVMF firmware is as big as you might expect and it's 4MiB so limit to that
+                    if size > 4 << 20 {
+                        return Err(Error::FirmwareTooLarge);
+                    }
+
+                    // Loaded at the end of the 4GiB
+                    let load_address = GuestAddress(4 << 30)
+                        .checked_sub(size)
+                        .ok_or(Error::FirmwareTooLarge)?;
+
+                    self.memory_manager
+                        .lock()
+                        .unwrap()
+                        .add_ram_region(load_address, size as usize)
+                        .map_err(Error::AllocateFirmwareMemory)?;
+
+                    kernel
+                        .seek(SeekFrom::Start(0))
+                        .map_err(Error::FirmwareFile)?;
+                    guest_memory
+                        .memory()
+                        .read_exact_from(load_address, &mut kernel, size as usize)
+                        .map_err(Error::FirmwareLoad)?;
+
+                    return Ok(EntryPoint { entry_addr: None });
+                }
+                _ => {
+                    return Err(Error::KernelLoad(e));
+                }
+            },
         };
 
         linux_loader::loader::load_cmdline(mem.deref(), arch::layout::CMDLINE_START, &cmdline)
@@ -984,7 +1027,9 @@ impl Vm {
         if let PvhEntryPresent(entry_addr) = entry_addr.pvh_boot_cap {
             // Use the PVH kernel entry point to boot the guest
             info!("Kernel loaded: entry_addr = 0x{:x}", entry_addr.0);
-            Ok(EntryPoint { entry_addr })
+            Ok(EntryPoint {
+                entry_addr: Some(entry_addr),
+            })
         } else {
             Err(Error::KernelMissingPvhHeader)
         }