Re: [PATCH 3/3] drm/nouveau/gsp: Fix NULL dereference in nvkm_gsp_gcx_ready()

[lyude]

Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>

Will push to drm-misc-fixes in a moment, thanks!

On Fri, 2026-10-02 at 12:09 -0600, Jim Cromie via B4 Relay wrote:
> From: Jim Cromie <jim.cromie@xxxxxxxxx>
> 
> Commit cb4c7603678c ("drm/nouveau/gsp/r570: Add support for
> INTERNAL_GCX_ENTRY_PREREQUISITE") hooked nvif_device_gcx_ready() into
> nouveau_pmops_runtime_suspend() to consult GSP before runtime
> suspend.
> 
> On GPUs running without GSP-RM (e.g. Volta GV100, NvGspRm=0, or
> missing
> GSP firmware blobs), device->gsp is instantiated but gsp->rm remains
> NULL. nvkm_udevice_gcx_ready() checked "!gsp" instead of verifying
> nvkm_gsp_rm(gsp), allowing non-RM instances to invoke
> nvkm_gsp_gcx_ready(). nvkm_gsp_gcx_ready() then unconditionally
> dereferenced gsp->rm->api, causing a kernel oops:
> 
>   RIP: 0010:nvkm_gsp_gcx_ready+0x10/0x30 [nouveau]
>   Code: ... 48 8b 87 70 0e 00 00 <48> 8b 40 18 ...
>   RAX: 0000000000000000 RDI: ffff8c9555fca000
>   Call Trace:
>    nvkm_udevice_mthd+0xa5/0x150 [nouveau]
>    nvkm_ioctl+0xcc/0x1d0 [nouveau]
>    nvif_object_mthd+0x110/0x1e0 [nouveau]
>    nvif_device_gcx_ready+0x36/0x60 [nouveau]
>    nouveau_pmops_runtime_suspend+0x39/0x140 [nouveau]
> 
> Instruction decode shows `mov rax, [rdi+0xe70]` loads gsp->rm (0x0),
> and `<48> 8b 40 18` (`mov rax, [rax+0x18]`) faults accessing rm->api.
> 
> Fix by:
> 0. Checking !nvkm_gsp_rm(gsp) in nvkm_udevice_gcx_ready() so non-RM
>    devices report GC6/GcOff ready and bypass the GSP call entirely.
> 1. Guarding gsp and gsp->rm in nvkm_gsp_gcx_ready() before inspecting
>    gsp->rm->api->gsp->gcx_ready.
> 
> Fixes: cb4c7603678c ("drm/nouveau/gsp/r570: Add support for
> INTERNAL_GCX_ENTRY_PREREQUISITE")
> Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/device/user.c | 2 +-
>  drivers/gpu/drm/nouveau/nvkm/subdev/gsp/base.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> index f78e6b9b4292..d469437eb991 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/user.c
> @@ -201,7 +201,7 @@ nvkm_udevice_gcx_ready(struct nvkm_udevice *udev,
> void *data, u32 size)
>  	} *args = data;
>  	int ret = -ENOSYS;
>  
> -	if (!gsp) {
> +	if (!nvkm_gsp_rm(gsp)) {
>  		args->v0.ready = NV_DEVICE_GC6_READY |
> NV_DEVICE_GCOFF_READY;
>  		return 0;
>  	}
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/base.c
> b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/base.c
> index e475d0e8fa7b..9e07d67dcb0f 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/base.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/base.c
> @@ -51,7 +51,7 @@ nvkm_gsp_intr_stall(struct nvkm_gsp *gsp, enum
> nvkm_subdev_type type, int inst)
>  int
>  nvkm_gsp_gcx_ready(struct nvkm_gsp *gsp)
>  {
> -	if (!gsp->rm->api->gsp->gcx_ready)
> +	if (!gsp || !gsp->rm || !gsp->rm->api->gsp->gcx_ready)
>  		return NV_DEVICE_GC6_READY | NV_DEVICE_GCOFF_READY;
>  
>  	return gsp->rm->api->gsp->gcx_ready(gsp);