From 64fe4e744574c8e0273dd1e5d54ceae9714748a0 Mon Sep 17 00:00:00 2001
From: Wei <wei@0g.ai>
Date: Wed, 24 Jun 2026 19:42:45 +0800
Subject: [PATCH] fix(fde): fall back to default GRUB menuentry when grubenv
 has no saved_entry

show-reference-value (load_kernel_artifacts) aborted with
"saved_entry not found in GRUB environment" on freshly built / never-booted
images, whose GRUB environment block is empty.

GRUB's default selection order is next_entry > saved_entry > `set default`.
On such images GRUB boots the default entry (`set default="0"`, i.e. the first
menuentry), so fall back to resolving the first menuentry id from grub.cfg
instead of failing. This lets reference values be computed for images that
have not been booted yet, without mutating the image to fabricate a saved_entry.
---
 cryptpilot-fde/src/disk/grub.rs | 52 +++++++++++++++++++++++++++++----
 1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/cryptpilot-fde/src/disk/grub.rs b/cryptpilot-fde/src/disk/grub.rs
index a1bdc1ff..bfb8b44b 100644
--- a/cryptpilot-fde/src/disk/grub.rs
+++ b/cryptpilot-fde/src/disk/grub.rs
@@ -131,6 +131,30 @@ impl BootArtifacts for GrubBootArtifacts {
     }
 }
 
+/// Resolve the id of GRUB's default menuentry from a `grub.cfg`.
+///
+/// Used when the GRUB environment block has no `saved_entry` (e.g. an image that
+/// has never been booted). The default selection on such images is
+/// `set default="0"`, i.e. the first menuentry, so its id is returned. The id is
+/// the quoted token right before the entry's opening brace, e.g.
+/// `menuentry 'Ubuntu' --class os $menuentry_id_option 'gnulinux-simple-<uuid>' {`.
+fn default_menuentry_id(grub_cfg: &str) -> Option<String> {
+    for line in grub_cfg.lines() {
+        let line = line.trim();
+        // Match an actual menuentry definition (not e.g. `menuentry_id_option=...`).
+        if !line.starts_with("menuentry ") || !line.contains('{') {
+            continue;
+        }
+        let head = line.split('{').next().unwrap_or(line).trim_end();
+        if let Some(end) = head.rfind('\'') {
+            if let Some(start) = head[..end].rfind('\'') {
+                return Some(head[start + 1..end].to_string());
+            }
+        }
+    }
+    None
+}
+
 fn parse_pe(bytes: &[u8]) -> Result<Box<dyn PeTrait + '_>, object::read::Error> {
     if let Ok(pe) = PeFile64::parse(bytes) {
         Ok(Box::new(pe))
@@ -382,12 +406,30 @@ pub(super) trait FdeDiskGrubExt: Disk {
         grub_vars: &HashMap<String, String>,
         grub_cfg: &str,
     ) -> Result<KernelArtifacts> {
-        let saved_entry = grub_vars
-            .get("saved_entry")
-            .ok_or_else(|| anyhow::anyhow!("saved_entry not found in GRUB environment"))?;
+        // GRUB's default selection order is: next_entry > saved_entry > `set default`.
+        // Freshly built / never-booted images have an empty GRUB environment block
+        // (no `saved_entry`); GRUB then boots the default entry (`set default="0"`,
+        // i.e. the first menuentry). Fall back to that instead of failing, so that
+        // reference values can be computed for images that have never been booted.
+        let saved_entry = match grub_vars.get("saved_entry") {
+            Some(entry) => entry.clone(),
+            None => {
+                let entry = default_menuentry_id(grub_cfg).ok_or_else(|| {
+                    anyhow::anyhow!(
+                        "saved_entry not found in GRUB environment and no menuentry found in grub.cfg"
+                    )
+                })?;
+                tracing::warn!(
+                    %entry,
+                    "saved_entry not set in GRUB environment (image likely never booted); \
+                     falling back to the default grub.cfg menuentry"
+                );
+                entry
+            }
+        };
 
         let (mut kernel_path, mut initrd_path, cmdline) = match self
-            .load_from_loader_entry_file(saved_entry, grub_vars)
+            .load_from_loader_entry_file(&saved_entry, grub_vars)
             .await
         {
             Ok(v) => v,
@@ -397,7 +439,7 @@ pub(super) trait FdeDiskGrubExt: Disk {
                     "Failed to parse kernel artifacts info from loader entry file, fallback to parse from grub.cfg"
                 );
 
-                self.load_from_grub_cfg(saved_entry, grub_cfg).await?
+                self.load_from_grub_cfg(&saved_entry, grub_cfg).await?
             }
         };