[PATCH 1/2] drm/nouveau: Fix NULL pointer dereferences in GETPARAM ioctl

[Jim Cromie]

When hardware or firmware initialization fails, the graphics engine
(gr) or device functions may remain NULL. Attempting to access these
during the GETPARAM ioctl (e.g., NOUVEAU_GETPARAM_GRAPH_UNITS) results
in a kernel NULL pointer dereference, causing a crash when userspace
(GNOME/Mesa) attempts to probe the device.

Add safety checks for 'gr', 'gr->func', and 'nvkm_device->func' in the
ioctl handler. Return -ENODEV to signal the missing hardware state to
userspace, and use NV_ERROR_ONCE to provide diagnostic proof in the
kernel log without risking a console flood.

RFC:

These crashes may not be repeatable, they happened while I was trying
to build nouveau as a builtin module, with binary blobs in the kernel
image, on a laptop with an encrypted disk.  Gemini tells me this won't
work, so I punted.

Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
---
 drivers/gpu/drm/nouveau/nouveau_abi16.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_abi16.c b/drivers/gpu/drm/nouveau/nouveau_abi16.c
index 291203121f0c..c9270c5b0fac 100644
--- a/drivers/gpu/drm/nouveau/nouveau_abi16.c
+++ b/drivers/gpu/drm/nouveau/nouveau_abi16.c
@@ -306,7 +306,12 @@ nouveau_abi16_ioctl_getparam(ABI16_IOCTL_ARGS)
 		getparam->value = 1;
 		break;
 	case NOUVEAU_GETPARAM_GRAPH_UNITS:
-		getparam->value = nvkm_gr_units(gr);
+		if (gr && gr->func) {
+			getparam->value = nvkm_gr_units(gr);
+		} else {
+			NV_ERROR_ONCE(drm, "GETPARAM_GRAPH_UNITS: no gr engine or func\n");
+			return -ENODEV;
+		}
 		break;
 	case NOUVEAU_GETPARAM_EXEC_PUSH_MAX: {
 		int ib_max = getparam_dma_ib_max(device);
@@ -315,11 +320,23 @@ nouveau_abi16_ioctl_getparam(ABI16_IOCTL_ARGS)
 		break;
 	}
 	case NOUVEAU_GETPARAM_VRAM_BAR_SIZE:
-		getparam->value = nvkm_device->func->resource_size(nvkm_device, NVKM_BAR1_FB);
+		if (nvkm_device && nvkm_device->func && nvkm_device->func->resource_size) {
+			getparam->value =
+				nvkm_device->func->resource_size(nvkm_device, NVKM_BAR1_FB);
+		} else {
+			NV_ERROR_ONCE(drm, "GETPARAM_VRAM_BAR_SIZE: no device func\n");
+			return -ENODEV;
+		}
 		break;
 	case NOUVEAU_GETPARAM_VRAM_USED: {
-		struct ttm_resource_manager *vram_mgr = ttm_manager_type(&drm->ttm.bdev, TTM_PL_VRAM);
-		getparam->value = (u64)ttm_resource_manager_usage(vram_mgr);
+		struct ttm_resource_manager *vram_mgr =
+			ttm_manager_type(&drm->ttm.bdev, TTM_PL_VRAM);
+		if (vram_mgr) {
+			getparam->value = (u64)ttm_resource_manager_usage(vram_mgr);
+		} else {
+			NV_ERROR_ONCE(drm, "GETPARAM_VRAM_USED: no vram mgr\n");
+			return -ENODEV;
+		}
 		break;
 	}
 	case NOUVEAU_GETPARAM_HAS_VMA_TILEMODE:

-- 
2.55.0