Boot configurator: trait (and associated objects) that write boot params in guest memory

coverage_config_aarch64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 75.7,
+  "coverage_score": 80.3,
   "exclude_path": "",
   "crate_features": ""
 }

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 74.8,
+  "coverage_score": 78.5,
   "exclude_path": "",
   "crate_features": ""
 }

src/configurator/aarch64/fdt.rs

@@ -0,0 +1,125 @@
+// Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
+
+//! Traits and structs for loading the device tree.
+
+use vm_memory::{Bytes, GuestMemory};
+
+use std::error::Error as StdError;
+use std::fmt;
+
+use crate::configurator::{BootConfigurator, BootParams, Error as BootConfiguratorError, Result};
+
+/// 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,
+}
+
+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.",
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Device Tree Boot Configurator Error: {}",
+            StdError::description(self)
+        )
+    }
+}
+
+impl From<Error> for BootConfiguratorError {
+    fn from(err: Error) -> Self {
+        BootConfiguratorError::Fdt(err)
+    }
+}
+
+/// Boot configurator for device tree.
+pub struct FdtBootConfigurator {}
+
+impl BootConfigurator for FdtBootConfigurator {
+    /// Writes the boot parameters (configured elsewhere) into guest memory.
+    ///
+    /// # Arguments
+    ///
+    /// * `params` - boot parameters containing the FDT.
+    /// * `guest_memory` - guest's physical memory.
+    fn write_bootparams<M>(params: BootParams, guest_memory: &M) -> Result<()>
+    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)
+            .map_err(|_| Error::WriteFDTToMemory.into())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use vm_memory::{Address, ByteValued, GuestAddress, GuestMemoryMmap};
+
+    const FDT_MAX_SIZE: usize = 0x20;
+    const MEM_SIZE: u64 = 0x100_0000;
+
+    fn create_guest_mem() -> GuestMemoryMmap {
+        GuestMemoryMmap::from_ranges(&[(GuestAddress(0x0), (MEM_SIZE as usize))]).unwrap()
+    }
+
+    #[derive(Clone, Copy, Default)]
+    struct FdtPlaceholder([u8; FDT_MAX_SIZE]);
+    unsafe impl ByteValued for FdtPlaceholder {}
+
+    #[test]
+    fn test_configure_fdt_boot() {
+        let fdt = FdtPlaceholder([0u8; FDT_MAX_SIZE]);
+        let guest_memory = create_guest_mem();
+
+        // Error case: FDT doesn't fit in guest memory.
+        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::FDTPastRamEnd.into())
+        );
+
+        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,
+        )
+        .is_ok());
+    }
+
+    #[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."
+        );
+    }
+}

src/configurator/aarch64/mod.rs

@@ -0,0 +1,9 @@
+// Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
+
+//! Traits and structs for configuring and loading boot parameters on `aarch64`.
+
+#![cfg(target_arch = "aarch64")]
+
+pub mod fdt;