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

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Message-ID: <5wfozb7rrh7snccab6dxckrd3umk7u34bixwjfqveta76237um@l23sftnckeep>
Date: Mon, 15 Dec 2025 10:29:03 +1100
From: Alistair Popple <apopple@...dia.com>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: Alexandre Courbot <acourbot@...dia.com>, 
	Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	John Hubbard <jhubbard@...dia.com>, Timur Tabi <ttabi@...dia.com>, Edwin Peer <epeer@...dia.com>, 
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH 2/4] gpu: nova-core: gsp: Fix length of received messages

On 2025-12-12 at 18:59 +1100, Joel Fernandes <joelagnelf@...dia.com> wrote...
> Hi Alex,
> 
> > On Nov 22, 2025, at 12:00 AM, Alexandre Courbot <acourbot@...dia.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@...dia.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>();

Wouldn't it be better to add a new method to GspMsgElement to get the size of
the associated message rather than open coding it here?

 - Alistair

> 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
> >