greq: sanity check struct sizes at compile time

The size of SnpGuestRequestMsg, SnpGuestRequestMsgType, and
AttestationReport can be asserted at compile time. This allows us to
remove asserts within several functions and to remove a corresponding
redundant test, since the SVSM will not build at all if one of these
assertions fails.

Signed-off-by: Carlos López <carlos.lopez@suse.com>

src/greq/msg.rs

@@ -102,15 +102,11 @@ pub struct SnpGuestRequestMsgHdr {
     rsvd3: [u8; 35],
 }
 
+const _: () = assert!(size_of::<SnpGuestRequestMsgHdr>() <= u16::MAX as usize);
+
 impl SnpGuestRequestMsgHdr {
     /// Allocate a new [`SnpGuestRequestMsgHdr`] and initialize it
-    ///
-    /// # Panic
-    ///
-    /// * [`SnpGuestRequestMsgHdr`] size does not fit in a u16.
     pub fn new(msg_sz: u16, msg_type: SnpGuestRequestMsgType, msg_seqno: u64) -> Self {
-        assert!(u16::try_from(MSG_HDR_SIZE).is_ok());
-
         Self {
             msg_seqno,
             algo: SnpGuestRequestAead::Aes256Gcm as u8,
@@ -139,10 +135,8 @@ impl SnpGuestRequestMsgHdr {
         msg_type: SnpGuestRequestMsgType,
         msg_seqno: u64,
     ) -> Result<(), SvsmReqError> {
-        let header_size =
-            u16::try_from(MSG_HDR_SIZE).map_err(|_| SvsmReqError::invalid_format())?;
         if self.hdr_version != HDR_VERSION
-            || self.hdr_sz != header_size
+            || self.hdr_sz != MSG_HDR_SIZE as u16
             || self.algo != SnpGuestRequestAead::Aes256Gcm as u8
             || self.msg_type != msg_type as u8
             || self.msg_vmpck != 0
@@ -209,20 +203,19 @@ pub struct SnpGuestRequestMsg {
     pld: [u8; MSG_PAYLOAD_SIZE],
 }
 
+// The GHCB spec says it has to fit in one page and be page aligned
+const _: () = assert!(size_of::<SnpGuestRequestMsg>() <= PAGE_SIZE);
+
 impl SnpGuestRequestMsg {
     /// Allocate the object in the heap without going through stack as
     /// this is a large object
     ///
-    /// # Panic
+    /// # Panics
     ///
-    /// * Memory allocated is not page aligned or Self does not
-    ///   fit into a page
+    /// Panics if the new allocation is not page aligned.
     pub fn boxed_new() -> Result<Box<Self>, SvsmReqError> {
         let layout = Layout::new::<Self>();
 
-        // The GHCB spec says it has to fit in one page and be page aligned
-        assert!(layout.size() <= PAGE_SIZE);
-
         unsafe {
             let addr = alloc_zeroed(layout);
             if addr.is_null() {
@@ -590,11 +583,6 @@ mod tests {
         assert!(data.data.iter().all(|c| *c == 0));
     }
 
-    #[test]
-    fn u16_from_guest_msg_hdr_size() {
-        assert!(u16::try_from(MSG_HDR_SIZE).is_ok());
-    }
-
     #[test]
     fn aad_size() {
         let hdr = SnpGuestRequestMsgHdr::default();

src/greq/pld_report.rs

@@ -102,19 +102,12 @@ impl SnpReportResponse {
     }
 
     /// Validate the [SnpReportResponse] fields
-    ///
-    /// # Panic
-    ///
-    /// * The size of the struct [`AttestationReport`] must fit in a u32
     pub fn validate(&self) -> Result<(), SvsmReqError> {
         if self.status != SnpReportResponseStatus::Success as u32 {
             return Err(SvsmReqError::invalid_request());
         }
 
-        const REPORT_SIZE: usize = size_of::<AttestationReport>();
-        assert!(u32::try_from(REPORT_SIZE).is_ok());
-
-        if self.report_size != REPORT_SIZE as u32 {
+        if self.report_size != size_of::<AttestationReport>() as u32 {
             return Err(SvsmReqError::invalid_format());
         }
 
@@ -199,6 +192,8 @@ pub struct AttestationReport {
     signature: Signature,
 }
 
+const _: () = assert!(size_of::<AttestationReport>() <= u32::MAX as usize);
+
 #[cfg(test)]
 mod tests {
     use super::*;