Insyde InsydeH2O (PcdSmmDxe parameter buffer, DMA TOCTOU): A DMA race against the Platform Configuration Database SMI

Impact

A DMA race against the Platform Configuration Database SMI handler corrupts ACPI fields and adjacent memory. ACPI tables are consumed by the OS after boot, so this driver is the one that reaches OS-visible platform description - an attacker can corrupt what the kernel believes about the hardware, not just SMRAM. Insyde notes exploitation needs detailed knowledge of the PCD contents on the specific platform, which raises the bar but does not close the race.

Who can reach it

An attacker able to drive DMA at host memory while the SMI handler is mid-flight - a malicious PCIe device, a peripheral running attacker-flashed firmware (NIC, GPU, NVMe), or a tenant with a passed-through device that is not behind a correctly configured IOMMU. Notably does NOT require host root, which is what separates this family from the ordinary SMM callout bugs.

What to do

Firmware flash from the server OEM, not from Insyde - the fixed Insyde kernel has to be rebased by Dell/HPE/Lenovo/Supermicro and re-qualified before it reaches you, which for this batch ran months behind Insyde's own release. One reboot per node, so schedule it against a GPU drain. Fixed in the kernel releases named in the advisory (Insyde does not enumerate per-kernel versions for this one). The compensating control that actually works here is the IOMMU, and Insyde says so in the advisory: enable VT-d/AMD-Vi with pre-boot DMA protection so the ACPI runtime buffer the handler reads is not reachable by an untrusted device. That is a BIOS setting, deployable fleet-wide without a flash, and it should be on already on any node that passes devices through to tenants. Patch the batch, not the CVE - Insyde filed one advisory per driver for the same defect, so fixing this one leaves every sibling handler reachable.

References