[PATCH 02/10] gpu: nova-core: gsp: cmdq: validate checksum earlier on receive

[Alexandre Courbot]

The checksum validation error message of `wait_for_msg` prints the
message's sequence number before validating the checksum.

But the checksum is part of the transport layer, and it not validating
indicates a corruption that could very well be in the RPC message
header, meaning the value of this field cannot be trusted.

Furthermore, the transport layer is not supposed to know the kind of
message it transports, and it accessing the RPC header is a layering
violation.

Thus, move the checksum validation before we start looking at the
message header, and drop that information from the error message.

Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
---
 drivers/gpu/nova-core/gsp/cmdq.rs | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index 9285fd796f9d..08a49450bca0 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -768,6 +768,17 @@ fn wait_for_msg(&self, timeout: Delta) -> Result<GspMessage<'_>> {
         // Extract the `GspMsgElement`.
         let (header, slice_1) = GspMsgElement::from_bytes_prefix(slice_1).ok_or(EIO)?;
 
+        // Validate checksum.
+        if Cmdq::calculate_checksum(SBufferIter::new_reader([
+            header.as_bytes(),
+            slice_1,
+            slice_2,
+        ])) != 0
+        {
+            dev_err!(&self.dev, "GSP receive: bad checksum\n");
+            return Err(EIO);
+        }
+
         dev_dbg!(
             &self.dev,
             "GSP RPC: receive: seq# {}, function={:?}, length=0x{:x}\n",
@@ -796,21 +807,6 @@ fn wait_for_msg(&self, timeout: Delta) -> Result<GspMessage<'_>> {
             )
         };
 
-        // Validate checksum.
-        if Cmdq::calculate_checksum(SBufferIter::new_reader([
-            header.as_bytes(),
-            slice_1,
-            slice_2,
-        ])) != 0
-        {
-            dev_err!(
-                &self.dev,
-                "GSP RPC: receive: Call {} - bad checksum\n",
-                header.sequence()
-            );
-            return Err(EIO);
-        }
-
         Ok(GspMessage {
             header,
             contents: (slice_1, slice_2),

-- 
2.55.0