Comment 0 for bug 1811722

On some firmware, attempting SecureBoot on arm64 will result in a crash. This is reproducible with a build EDK2 for the ArmVirtQemu target, but not with the older version we have packaged (edk2 0~20181115.85588389-2ubuntu1). The reason appears to be that our older version of edk2 had the firmware flash mapped at 0x0, which allowed NULL pointer dereferences to silently succeed. Latest upstream has changed that, so now such accesses result in a Synchronous Exception.

With SecureBoot disabled, we can boot successfully with the old firmware. However, I've found that this results in a corrupted firmware image, making subsequent boots fail. It maybe that the memory access that leads to the Synchronous Exception on newer firmware is a write to the firmware region that is causing the corruption, and therefore the same underlying root cause.

Note that I can also reproduce this with latest upstream GRUB. I looked for possible fixes for this in shim upstream, in case it is a problem with how shim invokes GRUB - or an issue with the Protocols shim registers. The only change I see that might be relevant that we don't already have is "6df7a8f Fix for "Section 0 has negative size" error when loading fbaa64.efi", but I could still reproduce after applying that.