[Bug 1811722] Re: arm64: shim crashes in SecureBoot mode w/ some firmware

[Julian Andres Klode]

** Changed in: shim-signed (Ubuntu)
       Status: Fix Committed => Fix Released

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Title:
  arm64: shim crashes in SecureBoot mode w/ some firmware

Status in shim package in Ubuntu:
  Fix Released
Status in shim-signed package in Ubuntu:
  Fix Released

Bug description:
  On some firmware, attempting SecureBoot on arm64 will result in a
  crash. This is reproducible with a build of latest upstream 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.

  Even though we can boot in SecureBoot mode successfully with the old
  firmware, I've found that doing so 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.

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