fix: sanitize kernel cmdline to prevent InvalidAscii panic on macOS

Add insert_str_safe() that replaces non-printable ASCII characters
with '?' before inserting into kernel cmdline. This prevents
InvalidAscii errors when macOS system info contains emoji.

Author: RoyLin

src/kernel/src/cmdline/mod.rs

@@ -154,6 +154,26 @@ impl Cmdline {
         Ok(())
     }
 
+    /// Inserts a string, replacing non-printable ASCII characters with '?'.
+    /// This is safe for use with strings that may contain emoji or special characters
+    /// (e.g., from macOS system info) that would otherwise cause InvalidAscii errors.
+    pub fn insert_str_safe<T: AsRef<str>>(&mut self, slug: T) -> Result<()> {
+        let s = slug.as_ref();
+        let sanitized: String = s.chars().map(|c| if valid_char(c) { c } else { '?' }).collect();
+        let trimmed = sanitized.trim();
+        if trimmed.is_empty() {
+            return Ok(());
+        }
+
+        self.has_capacity(trimmed.len())?;
+
+        self.start_push();
+        self.line.push_str(trimmed);
+        self.end_push();
+
+        Ok(())
+    }
+
     /// Returns the cmdline in progress without nul termination.
     pub fn as_str(&self) -> &str {
         self.line.as_str()

src/vmm/src/builder.rs

@@ -1948,9 +1948,9 @@ pub fn build_microvm(
     #[allow(unused_mut)]
     let mut kernel_cmdline = Cmdline::new(arch::CMDLINE_MAX_SIZE);
     if let Some(cmdline) = payload_config.kernel_cmdline {
-        kernel_cmdline.insert_str(cmdline.as_str()).unwrap();
+        kernel_cmdline.insert_str_safe(cmdline.as_str()).unwrap();
     } else if let Some(cmdline) = &vm_resources.kernel_cmdline.prolog {
-        kernel_cmdline.insert_str(cmdline).unwrap();
+        kernel_cmdline.insert_str_safe(cmdline).unwrap();
     } else {
         kernel_cmdline.insert_str(DEFAULT_KERNEL_CMDLINE).unwrap();
     }
@@ -1978,7 +1978,7 @@ pub fn build_microvm(
             format!("console={kernel_console}").as_str(),
         );
         kernel_cmdline = Cmdline::new(arch::CMDLINE_MAX_SIZE);
-        kernel_cmdline.insert_str(cmdline).unwrap();
+        kernel_cmdline.insert_str_safe(cmdline).unwrap();
     }
 
     #[cfg(target_os = "windows")]
@@ -2547,7 +2547,7 @@ pub fn build_microvm(
     }
 
     if let Some(s) = &vm_resources.kernel_cmdline.epilog {
-        vmm.kernel_cmdline.insert_str(s).unwrap();
+        vmm.kernel_cmdline.insert_str_safe(s).unwrap();
     };
 
     #[cfg(all(target_arch = "x86_64", target_os = "windows"))]