Add mutex lock for TDX quote generation

The TDX driver does not support concurrent access. Add global mutex
locks at both tdx-attest and dstack-attest layers to prevent race
conditions:

- tdx-attest: Lock in get_quote() to protect low-level TDX driver calls
- dstack-attest: Lock in quote_with_app_id() for future TEE environments

Author: kvinwang

dstack-attest/src/attestation.rs

@@ -28,6 +28,10 @@ const DSTACK_NITRO_ENCLAVE: &str = "dstack-nitro-enclave";
 #[cfg(feature = "quote")]
 const SYS_CONFIG_PATH: &str = "/dstack/.host-shared/.sys-config.json";
 
+/// Global lock for quote generation. The underlying TDX driver does not support concurrent access.
+#[cfg(feature = "quote")]
+static QUOTE_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());
+
 /// Read vm_config from sys-config.json
 #[cfg(feature = "quote")]
 fn read_vm_config() -> Result<String> {
@@ -574,6 +578,11 @@ impl Attestation {
     }
 
     pub fn quote_with_app_id(report_data: &[u8; 64], app_id: Option<[u8; 20]>) -> Result<Self> {
+        // Lock to prevent concurrent quote generation (TDX driver doesn't support it)
+        let _guard = QUOTE_LOCK
+            .lock()
+            .map_err(|_| anyhow!("Quote lock poisoned"))?;
+
         let mode = AttestationMode::detect()?;
         let runtime_events = if mode.is_composable() {
             RuntimeEvent::read_all().context("Failed to read runtime events")?

tdx-attest/src/linux.rs

@@ -6,9 +6,13 @@ use tdx_attest_sys as sys;
 
 use std::ptr;
 use std::slice;
+use std::sync::Mutex;
 
 use sys::*;
 
+/// Global lock for TDX attestation operations. The TDX driver does not support concurrent access.
+static TDX_LOCK: Mutex<()> = Mutex::new(());
+
 use num_enum::FromPrimitive;
 use thiserror::Error;
 
@@ -49,6 +53,9 @@ pub enum TdxAttestError {
 }
 
 pub fn get_quote(report_data: &TdxReportData) -> Result<Vec<u8>> {
+    // Lock to prevent concurrent access - TDX driver doesn't support it
+    let _guard = TDX_LOCK.lock().map_err(|_| TdxAttestError::Busy)?;
+
     let mut att_key_id = TdxUuid([0; TDX_UUID_SIZE as usize]);
     let mut quote_ptr = ptr::null_mut();
     let mut quote_size = 0;