Insyde InsydeH2O (IdeBusDxe shared buffer, DMA TOCTOU): Racy shared buffer in the legacy IDE/ATA driver leading

Impact

Racy shared buffer in the legacy IDE/ATA driver leading to SMRAM corruption. As with its 2022 counterpart, this driver is generally only active where CSM/legacy storage compatibility is enabled, so a UEFI-only server profile may not expose it at all.

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. Insyde lists kernel 5.0 through 5.5 affected; take the per-kernel fixed version from the advisory. Disable CSM / legacy storage on UEFI-only nodes to remove the driver rather than patch it. 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. This is Insyde's second pass at the same defect class in a different set of buffers - a fleet that took the 2022 BIOS release is NOT covered for this batch, and OEM release notes rarely make that distinction clear. Verify by kernel version, not by 'we patched the Insyde DMA bugs'.

References