tdx-attester: update TD platform detection

The attester crate pulls in DCAP 1.20 which only supports
/dev/tdx_guest ioctls so the two other (legacy) character devices
can be dropped.

However, this triggers another issue: we can have /dev/tdx_guest
ioctls (e.g., the RTMR extend) that are not part of Linux upstream
so the recently added runtime_measurement_extend_available() won't
work anymore. This change tries to mitigate that (for the time being)
by making the simplification that "if TSM reports, no RTMRs".

Signed-off-by: Mikko Ylinen <[email protected]>

attestation-agent/attester/src/tdx/mod.rs

@@ -23,13 +23,7 @@ const CCEL_PATH: &str = "/sys/firmware/acpi/tables/data/CCEL";
 const RUNTIME_MEASUREMENT_RTMR_INDEX: u64 = 2;
 
 pub fn detect_platform() -> bool {
-    TsmReportPath::new(TsmReportProvider::Tdx).is_ok() || tdx_getquote_ioctl_is_available()
-}
-
-fn tdx_getquote_ioctl_is_available() -> bool {
-    Path::new("/dev/tdx-attest").exists()
-        || Path::new("/dev/tdx-guest").exists()
-        || Path::new("/dev/tdx_guest").exists()
+    TsmReportPath::new(TsmReportProvider::Tdx).is_ok() || Path::new("/dev/tdx_guest").exists()
 }
 
 fn get_quote_ioctl(report_data: &Vec<u8>) -> Result<Vec<u8>> {
@@ -49,9 +43,11 @@ fn get_quote_ioctl(report_data: &Vec<u8>) -> Result<Vec<u8>> {
 }
 
 // Return true if the TD environment can extend runtime measurement,
-// else false.
+// else false. The best guess at the moment is that if "TSM reports"
+// is available, the TD runs Linux upstream kernel and is _currently_
+// not able to do it.
 fn runtime_measurement_extend_available() -> bool {
-    if Path::new("/dev/tdx_guest").exists() || Path::new("/sys/kernel/config/tsm/report").exists() {
+    if Path::new("/sys/kernel/config/tsm/report").exists() {
         return false;
     }