FDT configurator: specific FDT size check

Signed-off-by: Alexandra Iordache <aghecen@amazon.com>

coverage_config_aarch64.json

@@ -1,5 +1,5 @@
 {
- "coverage_score": 79.9,
+ "coverage_score": 80.3,
  "exclude_path": "",
  "crate_features": ""
 }

src/configurator/aarch64/fdt.rs

@@ -14,6 +14,8 @@ use crate::configurator::{BootConfigurator, BootParams, Error as BootConfigurato
 /// Errors specific to the device tree boot protocol configuration.
 #[derive(Debug, PartialEq)]
 pub enum Error {
+ /// FDT does not fit in guest memory.
+ FDTPastRamEnd,
  /// Error writing FDT in memory.
  WriteFDTToMemory,
 }
@@ -22,6 +24,7 @@ impl StdError for Error {
  fn description(&self) -> &str {
  use Error::*;
  match self {
+ FDTPastRamEnd => "FDT does not fit in guest memory.",
  WriteFDTToMemory => "Error writing FDT in guest memory.",
  }
  }
@@ -57,6 +60,10 @@ impl BootConfigurator for FdtBootConfigurator {
  where
  M: GuestMemory,
  {
+ guest_memory
+ .checked_offset(params.header_start, params.header.len())
+ .ok_or(Error::FDTPastRamEnd)?;
+
  // The VMM has filled an FDT and passed it as a `ByteValued` object.
  guest_memory
  .write_slice(params.header.as_slice(), params.header_start)
@@ -86,23 +93,17 @@ mod tests {
  let guest_memory = create_guest_mem();
 
  // Error case: FDT doesn't fit in guest memory.
- let fdt_addr = guest_memory
- .last_addr()
- .checked_sub(FDT_MAX_SIZE as u64 - 2)
- .unwrap();
+ let fdt_addr = GuestAddress(guest_memory.last_addr().raw_value() - FDT_MAX_SIZE as u64 + 1);
  assert_eq!(
  FdtBootConfigurator::write_bootparams::<GuestMemoryMmap>(
  BootParams::new::<FdtPlaceholder>(&fdt, fdt_addr),
  &guest_memory,
  )
  .err(),
- Some(Error::WriteFDTToMemory.into())
+ Some(Error::FDTPastRamEnd.into())
  );
 
- let fdt_addr = guest_memory
- .last_addr()
- .checked_sub(FDT_MAX_SIZE as u64 - 1)
- .unwrap();
+ let fdt_addr = GuestAddress(guest_memory.last_addr().raw_value() - FDT_MAX_SIZE as u64);
  assert!(FdtBootConfigurator::write_bootparams::<GuestMemoryMmap>(
  BootParams::new::<FdtPlaceholder>(&fdt, fdt_addr),
  &guest_memory,
@@ -112,9 +113,13 @@ mod tests {
 
  #[test]
  fn test_error_messages() {
+ assert_eq!(
+ format!("{}", Error::FDTPastRamEnd),
+ "Device Tree Boot Configurator Error: FDT does not fit in guest memory."
+ );
  assert_eq!(
  format!("{}", Error::WriteFDTToMemory),
  "Device Tree Boot Configurator Error: Error writing FDT in guest memory."
- )
+ );
  }
 }