gpu: nova-core: gsp: fix length of received messages

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 by introducing a method returning the payload size
and using it.

Fixes: 75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and handling")
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20251216-nova-fixes-v3-2-c7469a71f7c4@nvidia.com
[acourbot@nvidia.com: update `PANIC:` comments as pointed out by Joel.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

2 files changed, 17 insertions, 10 deletions

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index 6f946d14868a..3991ccc0c10f 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -588,21 +588,23 @@ impl Cmdq {
             header.length(),
         );
 
+        let payload_length = header.payload_length();
+
         // 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() < payload_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() {
-            // 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])
+        let (slice_1, slice_2) = if slice_1.len() > payload_length {
+            // PANIC: we checked above that `slice_1` is at least as long as `payload_length`.
+            (slice_1.split_at(payload_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,
+                // large as `payload_length`.
+                slice_2.split_at(payload_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..7b8e710b33e7 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -853,11 +853,16 @@ impl GspMsgElement {
         self.inner.checkSum = checksum;
     }
 
-    /// Returns the total length of the message.
+    /// Returns the length of the message's payload.
+    pub(crate) fn payload_length(&self) -> usize {
+        // `rpc.length` includes the length of the RPC message header.
+        num::u32_as_usize(self.inner.rpc.length)
+            .saturating_sub(size_of::<bindings::rpc_message_header_v>())
+    }
+
+    /// 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>()
-            + num::u32_as_usize(self.inner.rpc.length)
+        size_of::<Self>() + self.payload_length()
     }
 
     // Returns the sequence number of the message.