NVIDIA DGX A100 - SBIOS / SMM firmware: The SmiFlash SMM handler lets a privileged local user read, write and erase

Impact

The SmiFlash SMM handler lets a privileged local user read, write and erase the SPI flash directly - a direct write primitive to the platform firmware, with scope extending to other components. This is firmware-level persistence: it survives OS reinstall, image re-flash and tenant handoff, and it is invisible to anything running above it. On a bare-metal GPU rental business it is the difference between wiping a node between tenants and not actually being able to.

Who can reach it

Local and already privileged - host root, or code that has reached the platform firmware/SMM path. It is not a first foothold; it is what turns a one-time root compromise into something you cannot remediate by reimaging.

What to do

Flash the fixed SBIOS from bulletin 5435. Cost: not live-patchable. Full node drain, host power cycle, and on DGX the SBIOS ships inside a firmware bundle alongside BMC and CPLD components, so budget 30-60 minutes of node downtime plus a post-flash health check. Firmware rollback protection means you cannot cleanly revert - stage on one node before the fleet.

References