From 60cdfbe265fe2a55fb35d695662e2b23fe8cef57 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20L=C3=B3pez?= <carlos.lopez@suse.com>
Date: Thu, 23 Nov 2023 00:34:54 +0100
Subject: [PATCH] greq: sanity check struct sizes at compile time
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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        | 28 ++++++++--------------------
 src/greq/pld_report.rs | 11 +++--------
 2 files changed, 11 insertions(+), 28 deletions(-)

diff --git a/src/greq/msg.rs b/src/greq/msg.rs
index e165bab7c..b2ae4c7f6 100644
--- a/src/greq/msg.rs
+++ b/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();
diff --git a/src/greq/pld_report.rs b/src/greq/pld_report.rs
index ac7699a11..1d7d7b59a 100644
--- a/src/greq/pld_report.rs
+++ b/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::*;