feat(initrd): support chaining multiple initrds (#101)

Add linux-initrd-chain to the chainload action and initrd-chain to the
edera action. Each file in the list is read in order and concatenated
into a single initrd. The chain can't be combined with the single
initrd option on the same action.

BLS entries with multiple initrds, either as repeated initrd lines or
as multiple paths on one line, previously only loaded the last one.
Parse all of them and set them in the initrd-0 through initrd-7 slots,
which the autoconfigured BLS action now chains. Unused slots stamp to
the filesystem root and are skipped. Entries with more than 8 initrds
are skipped with a warning.

crates/boot/src/actions/edera.rs

@@ -2,7 +2,7 @@ use crate::{actions, context::SproutContext};
 use alloc::rc::Rc;
 use alloc::vec::Vec;
 use alloc::{format, vec};
-use anyhow::{Context, Result};
+use anyhow::{Context, Result, bail};
 use edera_sprout_config::actions::chainload::ChainloadConfiguration;
 use edera_sprout_config::actions::edera::EderaConfiguration;
 use edera_sprout_parsing::{build_xen_config, combine_options, empty_is_none};
@@ -40,6 +40,11 @@ fn read_loader_payload(context: &Rc<SproutContext>, what: &str, path: &str) -> R
 /// Executes the edera action which will boot the Edera hypervisor with the specified
 /// `configuration` and `context`. This action uses Edera-specific Xen EFI stub functionality.
 pub fn edera(context: Rc<SproutContext>, configuration: &EderaConfiguration) -> Result<()> {
+    // The initrd can be provided as either a single initrd or a chain, but not both.
+    if configuration.initrd.is_some() && !configuration.initrd_chain.is_empty() {
+        bail!("initrd and initrd-chain cannot be used together");
+    }
+
     // Only register the initrd media loader if the user actually configured one.
     let xen_opts = combine_options(context.stamp_iter(configuration.xen_options.iter()));
     let dom0_args = combine_options(context.stamp_iter(configuration.kernel_options.iter()));
@@ -80,12 +85,18 @@ pub fn edera(context: Rc<SproutContext>, configuration: &EderaConfiguration) ->
         register_media_loader_bytes(XEN_EFI_KERNEL_MEDIA_GUID, "kernel", kernel_bytes)
             .context("unable to register kernel media loader")?;
 
-    // Extend PCR 9 with the initrd bytes (empty when no initrd is
-    // configured).
-    let initrd_bytes = match empty_is_none(configuration.initrd.as_ref()) {
-        Some(p) => read_loader_payload(&context, "initrd", p)?,
-        None => Vec::new(),
-    };
+    // Read the initrd, or each initrd in the chain concatenated in order, then
+    // extend PCR 9 with the combined bytes (empty when no initrd is configured).
+    let mut initrd_bytes = Vec::new();
+    for p in configuration
+        .initrd
+        .iter()
+        .chain(configuration.initrd_chain.iter())
+    {
+        if let Some(p) = empty_is_none(Some(p)) {
+            initrd_bytes.extend(read_loader_payload(&context, "initrd", p)?);
+        }
+    }
     PlatformTpm::log_event(
         PlatformTpm::PCR_INITRD,
         &initrd_bytes,
@@ -111,6 +122,7 @@ pub fn edera(context: Rc<SproutContext>, configuration: &EderaConfiguration) ->
             path: configuration.xen.clone(),
             options: vec![],
             linux_initrd: None,
+            linux_initrd_chain: vec![],
         },
     )
     .context("unable to chainload to xen");