pvmfw: apply_debug_policy: Backup DT before unpacking
As the DT needs to be backed-up before applying the overlay due to
fdt_apply_overlay corrupting its inputs on failure, do so before
unpacking it, reducing the amount of memory needed by the backup Vec
from the maximum size that the DT could occupy (here, 2MiB) to the
actual size that the DT has (here, a few KiB).
Note: This wasn't detected previously due to a bug in Fdt::header()
causing fdt.as_slice() == &[] but will be required once the bug is
fixed as pvmfw's HEAP can't hold a 2MiB slice.
Test: atest MicrodroidHostTests
Change-Id: Ic6e651a73c4fb97e4bf97c32edc0b327b6cd1def
diff --git a/pvmfw/src/fdt.rs b/pvmfw/src/fdt.rs
index b3ce483..c009971 100644
--- a/pvmfw/src/fdt.rs
+++ b/pvmfw/src/fdt.rs
@@ -722,21 +722,26 @@
debug_policy: Option<&mut [u8]>,
debuggable: bool,
) -> libfdt::Result<()> {
- fdt.unpack()?;
+ if let Some(debug_policy) = debug_policy {
+ let backup = Vec::from(fdt.as_slice());
+ fdt.unpack()?;
+ let backup_fdt = Fdt::from_slice(backup.as_slice()).unwrap();
+ if apply_debug_policy(fdt, backup_fdt, debug_policy)? {
+ info!("Debug policy applied.");
+ } else {
+ // apply_debug_policy restored fdt to backup_fdt so unpack it again.
+ fdt.unpack()?;
+ }
+ } else {
+ info!("No debug policy found.");
+ fdt.unpack()?;
+ }
patch_dice_node(fdt, bcc.as_ptr() as usize, bcc.len())?;
set_or_clear_chosen_flag(fdt, cstr!("avf,strict-boot"), strict_boot)?;
set_or_clear_chosen_flag(fdt, cstr!("avf,new-instance"), new_instance)?;
- if let Some(debug_policy) = debug_policy {
- if apply_debug_policy(fdt, debug_policy)? {
- info!("Debug policy applied.");
- }
- } else {
- info!("No debug policy found.");
- }
-
if debuggable {
if let Some(bootargs) = read_bootargs_from(fdt)? {
filter_out_dangerous_bootargs(fdt, &bootargs)?;
@@ -779,9 +784,11 @@
/// Apply the debug policy overlay to the guest DT.
///
/// Returns Ok(true) on success, Ok(false) on recovered failure and Err(_) on corruption of the DT.
-fn apply_debug_policy(fdt: &mut Fdt, debug_policy: &[u8]) -> libfdt::Result<bool> {
- let backup_fdt = Vec::from(fdt.as_slice());
-
+fn apply_debug_policy(
+ fdt: &mut Fdt,
+ backup_fdt: &Fdt,
+ debug_policy: &[u8],
+) -> libfdt::Result<bool> {
let mut debug_policy = Vec::from(debug_policy);
let overlay = match Fdt::from_mut_slice(debug_policy.as_mut_slice()) {
Ok(overlay) => overlay,