nix-community · jbgi · Mar 11, 2025
diff --git a/nix/modules/lanzaboote.nix b/nix/modules/lanzaboote.nix
@@ -60,6 +60,8 @@ in
       '';
     };
 
+    keepCurrentBootedConfiguration = lib.mkEnableOption "keeping the current booted configuration (labeled 'SAFE' in boot menu)";
+
     pkiBundle = lib.mkOption {
       type = lib.types.nullOr lib.types.externalPath;
       description = "PKI bundle containing db, PK, KEK";
@@ -170,15 +172,15 @@ in
           --systemd-boot-loader-config ${loaderConfigFile} \
           --configuration-limit ${toString configurationLimit} \
           --allow-unsigned ${lib.boolToString cfg.allowUnsigned} \
-          --bootcounting-initial-tries ${toString cfg.bootCounting.initialTries}'';
+          --bootcounting-initial-tries ${toString cfg.bootCounting.initialTries}${lib.optionalString cfg.keepCurrentBootedConfiguration " \\\n  --safe-generation /run/booted-system"}'';
       defaultText = lib.literalExpression ''
         ''${lib.getExe config.boot.lanzaboote.package} install \
           --system ''${config.boot.kernelPackages.stdenv.hostPlatform.system} \
           --systemd ''${config.systemd.package} \
           --systemd-boot-loader-config ''${loaderConfigFile} \
           --configuration-limit ''${toString configurationLimit} \
           --allow-unsigned ''${lib.boolToString config.boot.lanzaboote.allowUnsigned} \
-          --bootcounting-initial-tries ''${toString config.boot.lanzaboote.bootCounting.initialTries}'';
+          --bootcounting-initial-tries ''${toString config.boot.lanzaboote.bootCounting.initialTries}''${lib.optionalString config.boot.lanzaboote.keepCurrentBootedConfiguration " \\\n --safe-generation /run/booted-system"}'';
     };
 
     extraEfiSysMountPoints = lib.mkOption {

diff --git a/rust/tool/shared/src/generation.rs b/rust/tool/shared/src/generation.rs
@@ -64,6 +64,8 @@ impl From<bootspec::BootJson> for LanzabooteExtension {
 pub struct Generation {
     /// Profile symlink index
     pub version: u64,
+    // Custom label, replacing version if present
+    pub label: Option<String>,
     /// Build time
     pub build_time: Option<Date>,
     /// Top-level specialisation name
@@ -93,6 +95,7 @@ impl Generation {
     ) -> Result<Self> {
         Ok(Self {
             version: link.version,
+            label: link.label.clone(),
             build_time: link.build_time,
             specialisation_name: Some(specialisation_name),
             spec: ExtendedBootJson {
@@ -128,6 +131,7 @@ impl Generation {
 
         Ok(Self {
             version: link.version,
+            label: link.label.clone(),
             build_time: link.build_time,
             specialisation_name,
             spec: ExtendedBootJson {
@@ -160,23 +164,30 @@ impl Generation {
             .map(|x| x.to_string())
             .unwrap_or_else(|| String::from("Unknown"));
 
-        format!(
-            "Generation {}{}, {}",
-            self.version,
-            self.describe_specialisation(),
-            build_time
-        )
+        format!("Generation {}, {}", self.version_tag(), build_time)
     }
 
     /// A unique short identifier.
     pub fn version_tag(&self) -> String {
-        format!("{}{}", self.version, self.describe_specialisation(),)
+        format!(
+            "{}{}",
+            self.label
+                .clone()
+                .unwrap_or_else(|| self.version.to_string()),
+            self.describe_specialisation(),
+        )
     }
 }
 
 impl fmt::Display for Generation {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self.version)
+        write!(
+            f,
+            "{}",
+            self.label
+                .clone()
+                .unwrap_or_else(|| self.version.to_string())
+        )
     }
 }
 
@@ -193,6 +204,7 @@ fn read_build_time(path: &Path) -> Result<Date> {
 #[derive(Debug)]
 pub struct GenerationLink {
     pub version: u64,
+    pub label: Option<String>,
     pub path: PathBuf,
     pub build_time: Option<Date>,
 }
@@ -201,6 +213,15 @@ impl GenerationLink {
     pub fn from_path(path: impl AsRef<Path>) -> Result<Self> {
         Ok(Self {
             version: parse_version(&path).context("Failed to parse version")?,
+            label: None,
+            path: PathBuf::from(path.as_ref()),
+            build_time: read_build_time(path.as_ref()).ok(),
+        })
+    }
+    pub fn from_path_with_label(path: impl AsRef<Path>, label: String) -> Result<Self> {
+        Ok(Self {
+            version: 0,
+            label: Some(label),
             path: PathBuf::from(path.as_ref()),
             build_time: read_build_time(path.as_ref()).ok(),
         })

diff --git a/rust/tool/systemd/src/cli.rs b/rust/tool/systemd/src/cli.rs
@@ -70,6 +70,10 @@ struct InstallCommand {
 
     /// List of generation links (e.g. /nix/var/nix/profiles/system-*-link)
     generations: Vec<PathBuf>,
+
+    /// A safe generation (usually /run/booted-system) that should always be kept, ignored from --configuration-limit if used
+    #[arg(long)]
+    safe_generation: Option<PathBuf>,
 }
 
 impl Cli {
@@ -113,6 +117,7 @@ fn install(args: InstallCommand) -> Result<()> {
         args.bootcounting_initial_tries,
         args.esp,
         args.generations,
+        args.safe_generation,
     );
 
     if args.allow_unsigned

diff --git a/rust/tool/systemd/src/install.rs b/rust/tool/systemd/src/install.rs
@@ -33,6 +33,7 @@ pub struct InstallerBuilder {
     bootcounting_initial_tries: u32,
     esp: PathBuf,
     generation_links: Vec<PathBuf>,
+    safe_generation: Option<PathBuf>,
 }
 
 impl InstallerBuilder {
@@ -46,6 +47,7 @@ impl InstallerBuilder {
         bootcounting_initial_tries: u32,
         esp: PathBuf,
         generation_links: Vec<PathBuf>,
+        safe_generation: Option<PathBuf>,
     ) -> Self {
         Self {
             lanzaboote_stub: lanzaboote_stub.as_ref().to_path_buf(),
@@ -56,6 +58,7 @@ impl InstallerBuilder {
             bootcounting_initial_tries,
             esp,
             generation_links,
+            safe_generation,
         }
     }
 
@@ -75,6 +78,7 @@ impl InstallerBuilder {
             bootcounting_initial_tries: self.bootcounting_initial_tries,
             esp_paths,
             generation_links: self.generation_links,
+            safe_generation : self.safe_generation,
             arch: self.arch,
         }
     }
@@ -91,6 +95,7 @@ pub struct Installer<S: Signer> {
     bootcounting_initial_tries: u32,
     esp_paths: SystemdEspPaths,
     generation_links: Vec<PathBuf>,
+    safe_generation: Option<PathBuf>,
     arch: Architecture,
 }
 
@@ -104,6 +109,12 @@ impl<S: Signer> Installer<S> {
             .map(GenerationLink::from_path)
             .collect::<Result<Vec<GenerationLink>>>()?;
 
+        let mut all_links = self
+            .safe_generation
+            .iter()
+            .map(|p| GenerationLink::from_path_with_label(p, "SAFE".to_string()))
+            .collect::<Result<Vec<GenerationLink>>>()?;
+
         // Sort the links by version, so that the limit actually skips the oldest generations.
         links.sort_by_key(|l| l.version);
 
@@ -118,9 +129,11 @@ impl<S: Signer> Installer<S> {
                 .rev()
                 .take(self.configuration_limit)
                 .rev()
-                .collect()
+                .collect();
         };
-        self.install_generations_from_links(&links)?;
+        all_links.append(&mut links);
+
+        self.install_generations_from_links(&all_links)?;
 
         self.install_systemd_boot()?;