Re: [PATCH v3 5/5] nouveau/gsp: Cleanup IS_ERR_OR_NULL in nvkm_gsp_rpc_rd()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] The commit message explains that `nvkm_gsp_rpc_push()` should not return `NULL` for RECV policies, but this assumption is incorrect, leaving callers vulnerable to NULL pointer dereferences.
- [Medium] Memory leak of large RPC payloads in `r535_gsp_rpc_push()` on error paths.
--

commit 1659548cc5b32b66b3c5a9f4367151960bb1562d
Author: Hongling Zeng <zenghongling@kylinos.cn>

nouveau/gsp: Cleanup IS_ERR_OR_NULL in nvkm_gsp_rpc_rd()

nvkm_gsp_rpc_rd() calls nvkm_gsp_rpc_get() which never returns NULL,
only valid pointers or error pointers. Clean up by using IS_ERR()
instead, matching the actual return value contract.

> Note: nvkm_gsp_rpc_push() can return NULL when policy is NOWAIT or
> NOSEQ, but nvkm_gsp_rpc_rd() uses RECV policy which expects a reply.
> If the RPC fails to get a reply, it should return an error pointer,
> not NULL.

[Severity: High]
This isn't a bug introduced by this patch, but is this description accurate?

If the RPC reply has an invalid length, r535_gsp_msgq_recv() returns NULL:

drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c:r535_gsp_msgq_recv() {
...
	if (WARN_ON(rpc->length > max_rpc_size))
		return NULL;
...
}

This NULL propagates up through r535_gsp_msg_recv() and
r535_gsp_rpc_handle_reply(), causing nvkm_gsp_rpc_push() to return NULL even
with the RECV policy.

Since callers like r535_gsp_get_static_info() only check IS_ERR(), won't they
dereference the NULL pointer?

drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/gsp.c:r535_gsp_get_static_info() {
...
	rpc = nvkm_gsp_rpc_rd(gsp, NV_VGPU_MSG_FUNCTION_GET_STATIC_INFO, 0);
	if (IS_ERR(rpc))
		return PTR_ERR(rpc);

	gsp->internal.client.object.client = &gsp->internal.client;
	gsp->internal.client.object.parent = NULL;
	gsp->internal.client.object.handle = rpc->hInternalClient;
...
}


> diff --git a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> index 64fed208e4cf8..a061779e0107b 100644
> --- a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> +++ b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> @@ -293,7 +293,7 @@ nvkm_gsp_rpc_rd(struct nvkm_gsp *gsp, u32 fn, u32 argc)
>  {
>  	void *argv = nvkm_gsp_rpc_get(gsp, fn, argc);
>  
> -	if (IS_ERR_OR_NULL(argv))
> +	if (IS_ERR(argv))
>  		return argv;
>  
>  	return nvkm_gsp_rpc_push(gsp, argv, NVKM_GSP_RPC_REPLY_RECV, argc);

[Severity: Medium]
This is a pre-existing issue, but does r535_gsp_rpc_push() leak memory on
error paths for large payloads?

If a large RPC payload fails to send, the kvfree(msg) call is skipped:

drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c:r535_gsp_rpc_push() {
...
		/* Wait for reply. */
		repv = r535_gsp_rpc_handle_reply(gsp, fn, policy, payload_size +
						 sizeof(*rpc));
		if (!IS_ERR(repv))
			kvfree(msg);
	} else {
		repv = r535_gsp_rpc_send(gsp, payload, policy, gsp_rpc_len);
	}
...
}

Since small RPCs unconditionally free msg via r535_gsp_cmdq_push(), callers
assume the RPC layer consumes the buffer. Will this leak the large staging
buffer if r535_gsp_rpc_get(), r535_gsp_rpc_send(), or
r535_gsp_rpc_handle_reply() fails and returns an error pointer?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260622021207.14764-1-zenghongling@kylinos.cn?part=5