Insyde InsydeH2O (FvbServicesRuntimeDxe shared buffer, DMA TOCTOU): Firmware Volume Block services again, this time

Impact

Firmware Volume Block services again, this time via the shared SMM/non-SMM buffer. Same consequence as its 2022 twin: an attacker influencing SPI flash writes, which is the difference between a node you can clean by reimaging and a node you have to physically reflash before it goes back in the pool.

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. Verify SPI write protection is set. 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