Re: [PATCH v3 3/5] nouveau/gsp/rm/alloc: Cleanup IS_ERR_OR_NULL usage

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Silently dropping oversized GSP RPC messages and reporting false success.
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commit c03df51ffa049e6fe56eec7d75137d404fe0855b
Author: Hongling Zeng <zenghongling@kylinos.cn>

nouveau/gsp/rm/alloc: Cleanup IS_ERR_OR_NULL usage
    
This commit cleans up error checking by using IS_ERR() instead of 
WARN_ON(IS_ERR_OR_NULL()) after nvkm_gsp_rpc_get() calls, matching 
the actual return value contract.

> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/alloc.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/alloc.c
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/alloc.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/alloc.c
> @@ -35,7 +35,7 @@ r535_gsp_rpc_rm_free(struct nvkm_gsp_object *object)
>  		   client->object.handle, object->handle);
>  
>  	rpc = nvkm_gsp_rpc_get(gsp, NV_VGPU_MSG_FUNCTION_FREE, sizeof(*rpc));
> -	if (WARN_ON(IS_ERR_OR_NULL(rpc)))
> +	if (WARN_ON(IS_ERR(rpc)))
>  		return -EIO;
>  
>  	rpc->params.hRoot = client->object.handle;
>  	rpc->params.hObjectParent = 0;
>  	rpc->params.hObjectOld = object->handle;
>  	return nvkm_gsp_rpc_wr(gsp, rpc, NVKM_GSP_RPC_REPLY_RECV);

[Severity: High]
This isn't a bug introduced by this patch, but since this commit is
cleaning up error handling around GSP RPC interactions, does
nvkm_gsp_rpc_wr() also have an error handling issue that hides critical
failures?

Looking at drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c, if the
GSP sends an RPC message where rpc->length > max_rpc_size,
r535_gsp_msgq_recv() returns NULL without advancing the message queue read
pointer:

r535_gsp_msgq_recv()
    ...
    if (WARN_ON(rpc->length > max_rpc_size))
        return NULL;

This NULL propagates to nvkm_gsp_rpc_wr() in
drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h, which translates it into
a false success:

nvkm_gsp_rpc_wr()
    ...
    if (IS_ERR(repv))
        return PTR_ERR(repv);
    return 0;

Since repv is NULL, IS_ERR(repv) evaluates to false, causing the function
to silently return 0.

Could this cause the caller to proceed assuming the RPC succeeded,
potentially leading to an invalid state or use-after-free, while the
unadvanced read pointer permanently wedges the message queue for all
subsequent reads?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260622021207.14764-1-zenghongling@kylinos.cn?part=3