vmm: reset to the original termios

Previously, we used two different functions for configuring ttys.
vmm_sys_util::terminal::Terminal::set_raw_mode() was used to configure
stdio ttys, and cfmakeraw() was used to configure ptys created by
cloud-hypervisor.  When I centralized the stdio tty cleanup, I also
switched to using cfmakeraw() everywhere, to avoid duplication.

cfmakeraw sets the OPOST flag, but when we later reset the ttys, we
used vmm_sys_util::terminal::Terminal::set_canon_mode(), which does
not unset this flag.  This meant that the terminal was getting mostly,
but not fully, reset.

To fix this without depending on the implementation of cfmakeraw(),
let's just store the original termios for stdio terminals, and restore
them to exactly the state we found them in when cloud-hypervisor exits.

Fixes: b6feae0a ("vmm: only touch the tty flags if it's being used")
Signed-off-by: Alyssa Ross <hi@alyssa.is>

vmm/src/device_manager.rs

@@ -70,7 +70,6 @@ use std::os::unix::fs::OpenOptionsExt;
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::path::PathBuf;
 use std::result;
-use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
 use std::time::Instant;
 use tracer::trace_scoped;
@@ -101,7 +100,6 @@ use vm_migration::{
 use vm_virtio::AccessPlatform;
 use vm_virtio::VirtioDeviceType;
 use vmm_sys_util::eventfd::EventFd;
-use vmm_sys_util::terminal::Terminal;
 
 #[cfg(target_arch = "aarch64")]
 const MMIO_LEN: u64 = 0x1000;
@@ -833,8 +831,8 @@ pub struct DeviceManager {
     // pty foreground status,
     console_resize_pipe: Option<Arc<File>>,
 
-    // Are any devices using the tty?
-    on_tty: Option<Arc<AtomicBool>>,
+    // To restore on exit.
+    original_termios_opt: Arc<Mutex<Option<termios>>>,
 
     // Interrupt controller
     #[cfg(target_arch = "x86_64")]
@@ -1120,7 +1118,7 @@ impl DeviceManager {
             serial_manager: None,
             console_pty: None,
             console_resize_pipe: None,
-            on_tty: None,
+            original_termios_opt: Arc::new(Mutex::new(None)),
             virtio_mem_devices: Vec::new(),
             #[cfg(target_arch = "aarch64")]
             gpio_device: None,
@@ -1168,7 +1166,7 @@ impl DeviceManager {
         serial_pty: Option<PtyPair>,
         console_pty: Option<PtyPair>,
         console_resize_pipe: Option<File>,
-        on_tty: Arc<AtomicBool>,
+        original_termios_opt: Arc<Mutex<Option<termios>>>,
     ) -> DeviceManagerResult<()> {
         trace_scoped!("create_devices");
 
@@ -1224,15 +1222,15 @@ impl DeviceManager {
             )?;
         }
 
+        self.original_termios_opt = original_termios_opt;
+
         self.console = self.add_console_device(
             &legacy_interrupt_manager,
             &mut virtio_devices,
             serial_pty,
             console_pty,
             console_resize_pipe,
-            &on_tty,
         )?;
-        self.on_tty = Some(on_tty);
 
         if let Some(tpm) = self.config.clone().lock().unwrap().tpm.as_ref() {
             let tpm_dev = self.add_tpm_device(tpm.socket.clone())?;
@@ -1845,7 +1843,7 @@ impl DeviceManager {
     }
 
     fn modify_mode<F: FnOnce(&mut termios)>(
-        &self,
+        &mut self,
         fd: RawFd,
         f: F,
     ) -> vmm_sys_util::errno::Result<()> {
@@ -1862,6 +1860,10 @@ impl DeviceManager {
         if ret < 0 {
             return vmm_sys_util::errno::errno_result();
         }
+        let mut original_termios_opt = self.original_termios_opt.lock().unwrap();
+        if original_termios_opt.is_none() {
+            *original_termios_opt = Some(termios);
+        }
         f(&mut termios);
         // SAFETY: Safe because the syscall will only read the extent of termios and we check
         // the return result.
@@ -1873,7 +1875,7 @@ impl DeviceManager {
         Ok(())
     }
 
-    fn set_raw_mode(&self, f: &mut dyn AsRawFd) -> vmm_sys_util::errno::Result<()> {
+    fn set_raw_mode(&mut self, f: &mut dyn AsRawFd) -> vmm_sys_util::errno::Result<()> {
         // SAFETY: FFI call. Variable t is guaranteed to be a valid termios from modify_mode.
         self.modify_mode(f.as_raw_fd(), |t| unsafe { cfmakeraw(t) })
     }
@@ -1897,7 +1899,6 @@ impl DeviceManager {
         virtio_devices: &mut Vec<MetaVirtioDevice>,
         console_pty: Option<PtyPair>,
         resize_pipe: Option<File>,
-        on_tty: &Arc<AtomicBool>,
     ) -> DeviceManagerResult<Option<Arc<virtio_devices::ConsoleResizer>>> {
         let console_config = self.config.lock().unwrap().console.clone();
         let endpoint = match console_config.mode {
@@ -1938,8 +1939,6 @@ impl DeviceManager {
                 // SAFETY: stdout is valid and owned solely by us.
                 let mut stdout = unsafe { File::from_raw_fd(stdout) };
 
-                on_tty.store(true, Ordering::SeqCst);
-
                 // Make sure stdout is in raw mode, if it's a terminal.
                 let _ = self.set_raw_mode(&mut stdout);
 
@@ -2019,7 +2018,6 @@ impl DeviceManager {
         serial_pty: Option<PtyPair>,
         console_pty: Option<PtyPair>,
         console_resize_pipe: Option<File>,
-        on_tty: &Arc<AtomicBool>,
     ) -> DeviceManagerResult<Arc<Console>> {
         let serial_config = self.config.lock().unwrap().serial.clone();
         let serial_writer: Option<Box<dyn io::Write + Send>> = match serial_config.mode {
@@ -2043,7 +2041,6 @@ impl DeviceManager {
             }
             ConsoleOutputMode::Tty => {
                 let mut out = stdout();
-                on_tty.store(true, Ordering::SeqCst);
                 let _ = self.set_raw_mode(&mut out);
                 Some(Box::new(out))
             }
@@ -2073,12 +2070,8 @@ impl DeviceManager {
             };
         }
 
-        let console_resizer = self.add_virtio_console_device(
-            virtio_devices,
-            console_pty,
-            console_resize_pipe,
-            on_tty,
-        )?;
+        let console_resizer =
+            self.add_virtio_console_device(virtio_devices, console_pty, console_resize_pipe)?;
 
         Ok(Arc::new(Console { console_resizer }))
     }
@@ -4662,10 +4655,9 @@ impl Drop for DeviceManager {
             handle.virtio_device.lock().unwrap().shutdown();
         }
 
-        if let Some(ref on_tty) = self.on_tty {
-            if on_tty.load(Ordering::SeqCst) {
-                let _ = std::io::stdin().lock().set_canon_mode();
-            }
+        if let Some(termios) = *self.original_termios_opt.lock().unwrap() {
+            // SAFETY: FFI call
+            let _ = unsafe { tcsetattr(stdout().lock().as_raw_fd(), TCSANOW, &termios) };
         }
     }
 }