Linux kernel Tegra241 CMDQV: oversized guest vSID truncates and aliases the wrong Stream ID

Impact

On NVIDIA Grace (Tegra241) hosts, the CMDQV virtual interface programs a guest-supplied virtual Stream ID into the SID_MATCH register, whose VIRT_SID field is only 20 bits wide. The bound check rejected only values above UINT_MAX, so a wider vSID silently truncates - the record gives 0x80000000 landing as a match on vSID 0 - and the command-queue entry then matches a Stream ID the guest was never assigned. Because virt_id is guest-controlled through the VMM, a tenant VM on a Grace node can make the host's SMMU virtualization alias another device's Stream ID, which is exactly the isolation boundary that makes accelerator passthrough safe on these systems. This matters more than a typical IOMMU hardening fix because Grace platforms are datacenter GPU nodes, not incidental hardware.

Who can reach it

A guest VM (through its VMM) on a Grace/Tegra241 host that is using CMDQV virtual interfaces for passthrough. Requires the ability to run a VM on the node; no host credentials needed.

What to do

Take a stable kernel with the FIELD_MAX/FIELD_PREP validation fix and reboot the Grace hosts - drain tenants first. Until patched, treat CMDQV-backed passthrough on shared Grace nodes as a tenant-isolation risk. The record names no fixed release numbers beyond the linked stable commits.

References

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