Linux kernel (drivers/gpu/drm/nouveau): When the device-to-host copy behind a page fault silently fails, the fault

Impact

When the device-to-host copy behind a page fault silently fails, the fault handler still hands the process a HIGH_USER page that was never written. The tenant reads whatever was previously in that page - residual data from other workloads on the node. This is the cross-tenant information-disclosure case, and the upstream fix calls it a security vulnerability in those words.

Who can reach it

Tenant holding /dev/dri/renderD* on nouveau using SVM/HMM device memory: fault a migrated page back to host RAM while the copy engine fails (a hung or erroring GPU, itself tenant-inducible). No capabilities required. nouveau device-memory (dmem) path only.

What to do

Update to a kernel carrying the fix (stable commits below; no fixed_in published). Interim: disable SVM/HMM device memory on nouveau nodes, or do not share nouveau GPUs across tenants.

References