[PATCH v2 2/4] gpu: nova-core: gsp: Fix length of received messages

[Alexandre Courbot <acourbot@nvidia.com>]

The size of messages' payload is miscalculated, leading to extra data
passed to the message handler. While this is not a problem with our
current set of commands, others with a variable-length payload may
misbehave. Fix this.

Fixes: 75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and handling")
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 drivers/gpu/nova-core/gsp/cmdq.rs | 11 +++++++----
 drivers/gpu/nova-core/gsp/fw.rs   |  2 +-
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index 6f946d14868a..dab73377c526 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -588,21 +588,24 @@ fn wait_for_msg(&self, timeout: Delta) -> Result<GspMessage<'_>> {
             header.length(),
         );
 
+        // The length of the message that follows the header.
+        let msg_length = header.length() - size_of::<GspMsgElement>();
+
         // Check that the driver read area is large enough for the message.
-        if slice_1.len() + slice_2.len() < header.length() {
+        if slice_1.len() + slice_2.len() < msg_length {
             return Err(EIO);
         }
 
         // Cut the message slices down to the actual length of the message.
-        let (slice_1, slice_2) = if slice_1.len() > header.length() {
+        let (slice_1, slice_2) = if slice_1.len() > msg_length {
             // PANIC: we checked above that `slice_1` is at least as long as `msg_header.length()`.
-            (slice_1.split_at(header.length()).0, &slice_2[0..0])
+            (slice_1.split_at(msg_length).0, &slice_2[0..0])
         } else {
             (
                 slice_1,
                 // PANIC: we checked above that `slice_1.len() + slice_2.len()` is at least as
                 // large as `msg_header.length()`.
-                slice_2.split_at(header.length() - slice_1.len()).0,
+                slice_2.split_at(msg_length - slice_1.len()).0,
             )
         };
 
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index abffd6beec65..7fcba5afb0a3 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -853,7 +853,7 @@ pub(crate) fn set_checksum(&mut self, checksum: u32) {
         self.inner.checkSum = checksum;
     }
 
-    /// Returns the total length of the message.
+    /// Returns the total length of the message, message and RPC headers included.
     pub(crate) fn length(&self) -> usize {
         // `rpc.length` includes the length of the GspRpcHeader but not the message header.
         size_of::<Self>() - size_of::<bindings::rpc_message_header_v>()

-- 
2.51.2