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

[Joel Fernandes <joelagnelf@nvidia.com>]

Hi Alex,

> On Nov 22, 2025, at 12:00 AM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> 
> 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.
> 
> 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>();

Is this immune to under flow without one of the checked subtraction wrappers? Either way, we should not tolerate the underflow I think. Which means it can panic when the rust overflow checks are enabled. Since the header length comes from firmware, this cannot be guaranteed to not underflow in the event of a malformed message.

thanks,

 - Joel



> +
>         // 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
>