initrd: normalize root filesystem boot paths

Signed-off-by: Sean Rhodes <sean@starlabs.systems>

Author: Sean-StarLabs

initrd/bin/kexec-parse-boot.sh

@@ -68,14 +68,28 @@ fix_path() {
 # GRUB kernel lines (linux/multiboot) can include a command line.  Check whether
 # the file path exists in $bootdir.
 check_path() {
-	local checkpath firstval
+	local checkpath firstval relative relative_firstval
 	checkpath="$1"
 	firstval="$(echo "$checkpath" | cut -d\  -f1)"
-	if ! [ -r "$bootdir$firstval" ]; then
-		DEBUG "parse-boot: check_path $bootdir$firstval not found"
-		return 1
+	if [ -r "$bootdir$firstval" ]; then
+		return 0
 	fi
-	return 0
+
+	# A GRUB configuration on a root filesystem can use /boot-prefixed
+	# paths even though that directory is exposed directly at $bootdir.
+	case "$firstval" in
+	/boot/*)
+		relative="${checkpath#/boot}"
+		relative_firstval="$(echo "$relative" | cut -d\  -f1)"
+		if [ -r "$bootdir$relative_firstval" ]; then
+			path="$relative"
+			return 0
+		fi
+		;;
+	esac
+
+	DEBUG "parse-boot: check_path $bootdir$firstval not found"
+	return 1
 }
 
 echo_entry() {
@@ -160,6 +174,7 @@ grub_entry() {
 				--nounzip*) val=$(echo $val | cut -d\  -f2-) ;;
 			esac
 			fix_path $val
+			check_path "$path" 2>/dev/null || :
 			modules="$modules|module $path"
 			;;
 		linux*)

tests/starlabs/test_root_boot_paths.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set -euo pipefail
+
+repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)
+tmpdir=$(mktemp -d)
+trap 'rm -rf "$tmpdir"' EXIT
+
+mkdir -p "$tmpdir/boot/grub"
+touch "$tmpdir/boot/vmlinuz" "$tmpdir/boot/initrd" \
+	"$tmpdir/boot/xen.gz" "$tmpdir/boot/dom0-vmlinuz" \
+	"$tmpdir/boot/dom0-initrd"
+
+printf '%s\n' \
+	'menuentry "root boot" {' \
+	' linux /boot/vmlinuz root=/dev/test' \
+	' initrd /boot/initrd' \
+	'}' \
+	'menuentry "root xen" {' \
+	' multiboot /boot/xen.gz placeholder' \
+	' module /boot/dom0-vmlinuz root=/dev/test' \
+	' module --nounzip /boot/dom0-initrd' \
+	'}' >"$tmpdir/boot/grub/grub.cfg"
+
+printf '%s\n' \
+	'DEBUG() { :; }' \
+	'DIE() { echo "$*" >&2; exit 1; }' >"$tmpdir/functions.sh"
+
+sed "s|^\. /etc/functions.sh$|. $tmpdir/functions.sh|" \
+	"$repo_root/initrd/bin/kexec-parse-boot.sh" >"$tmpdir/kexec-parse-boot.sh"
+chmod +x "$tmpdir/kexec-parse-boot.sh"
+
+entry=$("$tmpdir/kexec-parse-boot.sh" "$tmpdir/boot" \
+	"$tmpdir/boot/grub/grub.cfg")
+
+case "$entry" in
+*'|kernel /vmlinuz|initrd /initrd|append root=/dev/test'*) ;;
+*)
+	echo "Unexpected parsed entry: $entry" >&2
+	exit 1
+	;;
+esac
+
+case "$entry" in
+*'|kernel /xen.gz placeholder|module /dom0-vmlinuz root=/dev/test|module /dom0-initrd'*) ;;
+*)
+	echo "Unexpected parsed Xen entry: $entry" >&2
+	exit 1
+	;;
+esac
+
+echo "Root-filesystem /boot path tests passed"